Patent Application
20240375975
This invention relates, generally, to media used to improve efficiencies of contaminant removal from fluids, such as water sources. More specifically, it relates to a synergistic zero-valent-iron and perlite based green sorption media composition that is used to remove color from fluid.
The increasing needs of drinking water due to population growth has spurred a need to find new tap water sources. However, these large-scale tap water sources are often discolored. Natural or synthetic color present in aquatic systems can occur from dyes from domestic or industrial wastewater (Tara et al., 2020), dissolved natural organic matter (hereinafter “NOM”) from plant species (Kutser et al., 2005), and algae (Shengguang et al., 1991). More specifically, NOM including humic, fulvic, and tannic acids (Darko et al., 2014) can result in a yellow, red, brown and/or gray color in aquatic system. Humic and fulvic acids are the final products from the natural decay of plants and animals while tannin acid mostly occurs from leaching of twigs and swelling of certain trees including chestnut and oak trees. While these organic acids are beneficial to soil for agricultural processes, they can cause color contamination in water bodies. Therefore, they can affect the ability of these water bodies to be used as drinking water sources as they are precursors to disinfectant by-products (hereinafter “DBPs”) after drinking water treatment (EPA, 2012; Ahamed et al., 2019). For this reason, the US Environmental Protection Agency (hereinafter “EPA”) has regulated color concentration in drinking water to 15 Pt—Co units (e.g., visual color on the Platinum-Cobalt Scale) under the secondary drinking water standards (Dietrich and Burlingame, 2015).
Disinfection byproducts (DBPs hereafter) are unintentional by-products resulting from the interaction of disinfectants like chlorine with NOM (Tak and Vellanki, 2018). Trihalomethanes, halo acetic acids, formaldehyde, and acetaldehyde are some of the commonly found DBPs (Krasner et al., 1989; Palmstrom et al., 1988). The occurrence of DBPs in drinking water can cause adverse effects on human health, (Fawell et al., 1997) including increasing risk of bladder cancer (Li and Mitch, 2018), and influencing reproduction, which can result in birth defects (Wigle, 1998). The removal of DBP precursors (e.g., NOMs) within drinking water treatment facilities typically requires coagulation, microfiltration (Bottino et al., 2001) or adsorption (Gora and Andrews, 2017; Sun et al., 2017). Given such complicated treatment processes, the removal of color from the natural aquatic sources utilized as drinking water is of importance as it can lower the treatment cost and minimize the emergence of DBPs.
Currently there are four different ways to remove tannic or humic acids (e.g., color) including 1) photocatalytic methods; 2) coagulation; 3) microfiltration; and 4) adsorption. The first three methods are relatively expensive and require sophisticated control schemes.
The removal of NOM (e.g., tannic and humic acid) and the degradation of dyes (e.g., color) by photocatalytic methods is an effective approach. In the photocatalytic process, heterogeneous photocatalysis involves the irradiation of semiconductor catalysts (e.g., TiO2, ZnO, WO3, Fe2O3, CdO, CdS, SnO2, etc.) with a light source (e.g., ultraviolet (UV), sunlight, or artificial light) to generate highly reactive oxygen species (ROS) (e.g., ·OH, O2·—) for the subsequent mineralization of long chain or short chain organic pollutants. An example is the degradation of dyes, detergents, and organic acids by TiO2 nanofilms (Albu et al., 2007).
As to the coagulation, the most common coagulates are aluminum and iron salts. Aluminum and iron salt when added to water dissolve negatively into particle trivalent forms (e.g., Al3+ and Fe3+) which allows the attachment to negative charged particles. Given the composition of NOM, its removal mechanism encompasses charge neutralization, entrapment, adsorption, and complexation with coagulant metal ions into the insoluble particles. Besides, the use of ferric salts has increased, with ferric chloride (i.e., FeCl3) and ferric sulphate (i.e., Fe(SO4)3) being the most common alternatives (Matilainen et al., 2010). Furthermore, membrane filtration is an alternative physical treatment that can be used to remove color from source water or wastewater. The use of a flat ceramic microfiltration membrane made of natural perlite as the base material showed turbidity removal above 96% from industrial wastewater (Saja et al., 2018).
Adsorption methods are relatively easier than the previous three methods. Activated Carbon (hereinafter “AC”) filter is the most common method to remove color from water and wastewater due to its simplicity and regeneration potential (Rao and Krishnaiah, 1994; Singh et al., 2003). This conventional treatment is designed to absorb particles and organic contaminants in drinking water that may result in bad tastes and odors. The utilization of AC in early stage has expanded to the innovated use of agricultural waste (Suba and Rathika, 2016). Sun and Xu (1997) revealed that sunflower stalks have a maximum adsorption potential of 105 and 317 mg·g−1 to remove basic dyes, Methylene Blue and Basic Red 9, respectively. Other innovated agricultural waste materials have been studied including mango peels (Jawad et al., 2017), rice husk (Vadivelan and Kumar, 2005), palm kernel shell (El-Sayed, 2011), coconut shell (Aljeboree et al., 2017), and banana and orange peels (Mane and Bhusari, 2012). The removal of humic acid by AC has been previously studied, where it showed a 98.9% removal of humic acid by a combined system of plasma and AC adsorption, after 90 minutes. Furthermore, it has been reported that AC had a maximum color removal efficiency of 90.72% with Fe0 synthesized nanoparticles of size 16.64 nm. (Prema et al., 2011) Moreover, a polysilicate aluminum magnesium and cationic polyacrylamide flocculant have been successfully designed and have been able to obtain turbidity and color removal above 98% at optimum in drinking water. (Ma et al., 2019)
Additionally, other materials have been implemented for color removal, including clay to remove tannic and humic acid (Chang and Juang, 2004), where the maximum adsorption capacity was reported to be 153 mg·g−1 and 28.3 mg·g−1 for tannic and humic acid correspondingly. Moreover, the adsorption of tannic and humic acid to activated clay follows pseudo-first order model and can be best model by intraparticle diffusion given that they are denser solids and have better mass transfer blockage in comparison with other absorbents (Chang and Juang, 2004).
The use of membranes to remove color and dyes have also been investigated. Rambabu et al. (2019) studied the dye rejection potential of a polyethersurfone nano-porous membrane modified with calcium chloride. A 95% rejection of Congo Red dye with the polyethersurfone nano-porous membrane was observed.
Perlite is a soil amendment derived from volcanic rock usually formed from siliceous lava or ash. Natural perlite is usually grey, but it can also be green, red, blue, or brown; yet after heating it usually takes on a white color. The chemical formula of perlite is Al2CaFe2K2MgNa2O12Si and the molecular weight is 574.29 g·mol−1; hence it is natural sodium-potassium-aluminum-silicate. The use of perlite and volcanic rock has also been studied for the removal of dyes from aqueous solutions (Rossatto et al., 2021). Dogan et al. (2000) examined the adsorption of methylene blue from aqueous solutions to unexpanded and expanded perlite samples activated by H2SO4 and NaCl solutions to remove cationic dyes. Their results indicated that perlite can be used for removal of methylene; a better removal efficacy was observed from unexpanded perlite. Meesuk and Seammai (2010) suggested that expanded perlite can be used to remove dark color from spent palm oil via physical mechanism and can also remove benzo (a) pyrene from the palm oil. Although the adsorption of tannic acid onto perlite has not been broadly explored, the adsorption efficiency of humic substances onto expanded perlite was investigated by Chassapis et al. (2010). Chassapis et al. (2010) indicated that the adsorption of humic substance stems involved Coulombic attraction forces related to the positively charged humic substances and negative sites of the perlite (i.e., alumino-silicate).
Accordingly, what is needed is an improved and cost-effective approach to removing color from water sources. However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.
The long-standing but heretofore unfulfilled need, stated above, is now met by a novel and non-obvious invention disclosed and claimed herein. In an aspect, the present disclosure pertains to a filtration media. In an embodiment the filtration media may comprise: (a) at least one silicon atom; (b) at least one aluminum atom; and (c) at least one zero-valence-iron (hereinafter “ZVI”) atom. In this embodiment, the at least one ZVI atom may be chemically bonded to at least one silicon atom of at least one grain of perlite, such that at least one ZVI-perlite structure may be formed. Additionally, the at least one ZVI-perlite structure may then be chemically bonded to at least one alternative silicon atom of at least one grain of sand, such that at least one quartz structure may be formed. In this embodiment, the at least one ZVI atom may be configured to be disposed about at least a portion of a surface of the at least one quartz structure. Moreover, in this embodiment, the at least one ZVI-coated quartz structure may be metallically bonded to at least one aluminum atom, such that an aluminum-doped ZVI-quartz construct may be formed. Furthermore, in this embodiment, the aluminum-doped ZVI-quartz construct may further comprise at least one potassium atom and/or at least one calcium atom, and/or the aluminum-doped ZVI-quartz construct may comprise a heterogenous morphological structure.
In some embodiments, the ratio of the at least one ZVI atom to the at least one grain of sand within the aluminum-doped ZVI-quartz construct may be at most 0.071 by percent volume. In addition, in these other embodiments, the aluminum-doped ZVI-quartz construct may comprise a composition ratio of at least 85% sand, at most 5% clay, at most 6% ZVI, and at most 4% perlite by percent volume.
In some embodiments, the aluminum-doped ZVI-quartz construct may comprise a surface area of at most 3.00 m2·g−1. In this manner, the aluminum-doped ZVI-quartz construct may be configured to be hydraulicly conductive and/or highly porous. As such, in these other embodiments, the aluminum-doped ZVI-quartz construct may comprise a porosity of at least 29.0% of percent surface area.
In some embodiments, the aluminum-doped ZVI-quartz construct may comprise a density of at least 2.50 g·cm−3. In addition, the aluminum-doped ZVI-quartz construct may be electrochemically stable and/or hydrophobic.
Another aspect of the present disclosure pertains to a method of optimizing a color removal reaction within a water sample. In an embodiment, the method may comprise: (a) incorporating a filtration media into the water sample, the filtration media comprising: (i) at least one silicon atom; (ii) at least one aluminum atom; and (iii) at least one zero-valence-iron (hereinafter “ZVI”) atom. In this embodiment, the at least one ZVI atom may be chemically bonded to at least one silicon atom of at least one grain of perlite, such that at least one ZVI-perlite structure may be formed. Additionally, the at least one ZVI-perlite structure may then be chemically bonded to at least one alternative silicon atom of at least one grain of sand, such that at least one quartz structure may be formed. In this embodiment, the at least one ZVI atom may be configured to be disposed about at least a portion of a surface of the at least one quartz structure. Moreover, in this embodiment, the at least one ZVI-coated quartz structure may be metallically bonded to at least one aluminum atom, such that an aluminum-doped ZVI-quartz construct may be formed. As such, in this embodiment, the incorporation of the filtration media to the water sample thereof may optimize the color removal reaction within the water sample.
In some embodiments, the aluminum-doped ZVI-quartz construct may be configured to maintain an effluent concentration below at least 40 color units of Pt—Co. In this manner, in these other embodiments, the aluminum-doped ZVI-quartz construct may be configured to operate continuously in the water sample for at least 14,000 minutes.
As such, in some embodiments, the aluminum-doped ZVI-quartz construct may be configured to inhibit ponding and/or clogging within at least one pour of the aluminum-doped ZVI-quartz construct for at least 40,000 minutes. In addition, the aluminum-doped ZVI-quartz construct may be configured to maintain an adsorption capacity of at least 25.0 mg of Pt—Co·g−1 during the color removal reaction.
Furthermore, an additional aspect of the present disclosure pertains to a method of synthesizing a filtration media. In an embodiment, the method may comprise: (a) pretreating at least one iron atom, such that the at least one iron atom may comprise zero-valence (hereinafter “ZVI”); (b) chemically bonding at least one silicon atom of at least one grain of perlite to the at least one ZVI atom to form a ZVI-perlite structure; (c) chemically bonding at least one alternative silicon atom of at least one grain of sand to the ZVI-perlite structure to a quartz structure, such that the at least one ZVI atom may be disposed about at least a portion of a surface of the quartz structure; and (d) metallically bonding at least one aluminum atom to the ZVI-coated quartz structure to form the filtration media which is an aluminum-doped ZVI-quartz construct.
In some embodiments, heat treatment may be used to chemically bond the at least one grain of perlite to the at least one grain of sand. Additionally, the heat treatment may be used to chemically bond the at least one ZVI atom to the at least one grain of perlite, and furthermore, in these other embodiments the heat treatment may be used to chemically bond the at least one aluminum atom to the at least one ZVI-coated quartz structure.
Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only illustrative embodiments of the present disclosure are shown and described. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the disclosure set forth hereinafter and the scope of the invention will be indicated in the claims.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part thereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that one skilled in the art will recognize that other embodiments may be utilized, and it will be apparent to one skilled in the art that structural changes may be made without departing from the scope of the invention. Elements/components shown in diagrams are illustrative of exemplary embodiments of the disclosure and are meant to avoid obscuring the disclosure. Any headings, used herein, are for organizational purposes only and shall not be used to limit the scope of the description or the claims. Furthermore, the use of certain terms in various places in the specification, described herein, are for illustration and should not be construed as limiting.
Reference in the specification to “one embodiment,” “preferred embodiment,” “an embodiment,” or “embodiments” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the disclosure and may be in more than one embodiment. The appearances of the phrases “in one embodiment,” “in an embodiment,” “in embodiments,” “in alternative embodiments,” “in an alternative embodiment,” or “in some embodiments” in various places in the specification are not necessarily all referring to the same embodiment or embodiments. The terms “include,” “including,” “comprise,” and “comprising” shall be understood to be open terms and any lists that follow are examples and not meant to be limited to the listed items.
As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the context clearly dictates otherwise.
As used herein, the term “about” or “roughly” means approximately or nearly and in the context of a numerical value or range set forth means±15% of the numerical.
All numerical designations, including ranges, are approximations which are varied up or down by increments of 1.0, 0.1, 0.01 or 0.001 as appropriate. It is to be understood, even if it is not always explicitly stated, that all numerical designations are preceded by the term “about”. It is also to be understood, even if it is not always explicitly stated, that the compounds and structures described herein are merely exemplary and that equivalents of such are known in the art and can be substituted for the compounds and structures explicitly stated herein.
Wherever the term “at least,” “greater than,” or “greater than or equal to” precedes the first numerical value in a series of two or more numerical values, the term “at least,” “greater than” or “greater than or equal to” applies to each of the numerical values in that series of numerical values. For example, greater than or equal to 1, 2, or 3 is equivalent to greater than or equal to 1, greater than or equal to 2, or greater than or equal to 3.
Wherever the term “no more than,” “less than,” or “less than or equal to” precedes the first numerical value in a series of two or more numerical values, the term “no more than,” “less than” or “less than or equal to” applies to each of the numerical values in that series of numerical values. For example, less than or equal to 1, 2, or 3 is equivalent to less than or equal to 1, less than or equal to 2, or less than or equal to 3.
The present disclosure pertains to an optimum, low maintenance, and low-cost filtration media (i.e., ZIPGEM) that may be implemented near a source water location as a pretreatment to remove tannic acid or humic acid (i.e., color) from dissolved natural organic matter (hereinafter “NOM”) (i.e., tannic acid, humic acid) to impede the prompt production of disinfection by-products collectively termed trihalomethanes and are abbreviated as either THM or TTHM (for total trihalomethanes) in drinking water treatment processes.
The unit cost per color removal is about 10+ times lower than that of photocatalytic, coagulation, and/or microfiltration methods. As such, the filtration media may be used as soil amendment in forest land and/or in landfill as at least one daily cover material. In an embodiment, the filtration media may be configured to remove color by maintaining the effluent concentration below at least forty (40) color units of Pt—Co for at least 10,000 minutes (e.g., 14,080 minutes) given the quantity of at least 500 ml (e.g., 900 ml) media volume and/or the hydraulic loading rate of at least 30 gallon·day−1·ft−2 (e.g., 31.02 gallon·day−1·ft−2), which may be very competitive with respect to other existing options known in the art. Additionally, in this embodiment, the filtration media may not only be used to remove tannic acid and/or humic acid in natural water, but also filtration media may be applied to remove at least one dye in at least one of a plurality of industrial wastewater effluents, with a fairly broad application spectrum. The filtration media may also comprise one of the green sorption media, such that at least one recycled material may be used as at least one ingredient in the mix in a circular economy that meet the sustainable development goals of the United Nations.
The deficiencies of prior art such as lower than photocatalytic, coagulation, and/or microfiltration methods have at least 10 times a higher price, and/or photocatalytic, coagulation, and/or microfiltration methods require sophisticated control schemes with operational complexity. In contrast, as shown in
The following list provides at least one possible usage of the filtration media for cost-effective and/or large-scale color removal that can be applied either for ex situ or in situ facilities. Possible applications may include, but are not limited to, springs protection facilities, stormwater utilities, wastewater treatment plants, water treatment plants, integrated water resources management facilities at the watershed scale, environmental remediation facilities for soil and water remediation, forest runoff, the mining industry (e.g., tailing water for treatment), the textile industry, the dyeing industry, the food industry, the beverage industry, the drug industry, and/or the paper mill industry.
In an embodiment, the filtration media (i.e., ZIPGEM) may comprise a surface area having a range of at least 2.00 m2·g−1 to at most 3.00 m2·g−1. For example, in some embodiments the surface area of the filtration media may be 2.55 m2·g−1, which comprises the largest surface area as compared to the sorption media known in the art (e.g., CTS, IFGEM-1, IFGEM-4, and/or CPS). As such, as known in the art, larger surface area may lead to better adsorption potential. In terms of porosity, the filtration media may be at least 15%. For example, in some embodiments, the filtration media may have a porosity of 29.04%. Additionally, in an embodiment, the filtration media may comprise a saturated hydraulic conductivity within the typical range for sand (at least 10−3 to at most 10−5 m·sec−1), indicating that the filtration media may be appropriate for field implementation. Finally, in this embodiment, the inclusion of ZVI in the filtration media may be associated with the resultant higher density and/or larger surface area within the filtration media, such that the filtration media may optimize color removal facilitation. In this manner, in an embodiment, the filtration media may comprise a density having a range of at least 1.50 g·cm−3. As such, in some embodiments, for example, the filtration media may comprise a density of 2.80 g·cm−3. Furthermore, in an embodiment, the filtration media may have a chemical composition comprising at least one Al atom, at least one Si atom, at least one P atom, at least one K atom, at least one Ca atom, and/or at least one Fe atom.
In this manner, in an embodiment, the filtration media may comprise at least one Si atom (e.g., silica) within its chemical composition, such that the at least one Si atom comprises the main chemical element of the filtration media. As known in the art, amino-functionalized magnetic mesoporous silica may remove tannic acid from aqueous solution, via adsorption. Next, in this embodiment, the second most abundant chemical component within the chemical composition of the filtration media may be Al (i.e., aluminum). Accordingly, the presence of at least one Al atom within chemical composition of the filtration media may be explained by the inclusion of clay as at least one ingredient of the filtration media. As such, the at least one Al atom may be utilized for removal of diverse contaminants including but not limited to nutrients, metals, and/or contaminants of emerging concern. In addition, in this embodiment, the filtration media may also comprise at least one ZVI atom and/or at least one recycled ZVI (e.g., 95.6% Fc) atom within the chemical composition of the filtration media, such that a removal of contaminants may be substantially improved given the reactivity, large surface area, lower cost, and/or environmentally friendly nature of the at least one ZVI atom and/or the at least one recycled ZVI. Furthermore, in this embodiment, the filtration media may also comprise at least one K (i.e., potassium) atom and/or Ca (i.e., calcium) atom (e.g., 1-2.5% and/or 0.7-1%, respectively) within the filtration media's chemical composition, and thus, to some extent their presence may aid in a synergistic effect that can be helpful for the removal of contaminants.
In this manner, as known in the art, the clogging and/or ponding may be associated with the ZVI particles undergoing oxidization resulting in iron oxide clogging the pore space in the media mix and affecting the infiltration negatively. Given that some Al and Fe can be dissolved in water the major tannic acid removal mechanism could be chemical precipitation driven by the formation of solid organometallic complexes, the emergence of Al-tannate can also contribute to clogging issues. The higher the content of ZVI, the larger the chance to have a ponding effect due to accumulation of aluminum and iron salts on the surface of Si (found in sand). As such, in an embodiment, the filtration media may comprise a ZVI and Sand ratio of at most 0.090 (ZVI/Sand percent by volume). In some embodiments, for example, the ZVI and Sand ratio may be at least 0.071 (ZVI/Sand percent by volume). Additionally, in an embodiment, since the filtration media comprises a larger surface area and/or hydraulic conductivity, high porosity, and/or a high-grade heterogenous morphological structure as compared to the sorption media known in the art (e.g., CTS, IFGEM-1, IFGEM-4, and/or CPS), in addition to comprising stronger ionic interactions, van der Walls forces, and/or hydrogen bonding effects as compared to the sorption media known in the art, the removal of color from a water sample may be optimized.
As known in the art, tannic acid tends to spontaneously adsorb to different surfaces to yield a hydrophilic coating. In this manner, it has been suggested the interactions between soil minerals and tannins result in adsorption. It was discovered that the adsorption mechanism is heterogeneous, and dependent on pH and ionic strength. Moreover, prior studies have indicated that the adsorption of tannic acid to silicate is completed after about 15 minutes revealing that it produces a thin layer on SiO2. The removal of tannic acids with clay is also related to adsorption. However, as noted in the prior art, attapulgite clay coated with chitosan was found to adsorb 95.3 mg g−1 of tannic acid driven by electrostatic interactions, hydrogen bonding, and Van der Waals forces. In addition, since the anionic functional groups of tannic acid include hydroxyl and carboxyl groups, it has been noted that it can adsorb on oxide surfaces. Furthermore, as stated in the prior art, tannic acid is negatively charged, hence Ca2+ can aid to bind negatively charged surfaces such as species of tannic acid.
Besides, as known in the art, an Al ion has the possibility of interacting with multiple tannic acid molecules and the formation of insoluble complexes resulting from aluminum compounds such as Al—OH at low and/or high pH. While at pH between 5-6, when Al(OH)3 is the predominant form, complex formation is replaced by adsorption onto Al(OH)3 surface. As such, the coprecipitation of tannic acid with Al(OH)3 occurs in the presence of hydrous aluminum oxide (e.g., Al(OH)3) leading to soluble colloidal hydroxy-Al-tannate complexes. In the case of humic substances, prior studies have noted that when Al-humic complexes are formed, charge neutralization occurs. Similarly, since tannic acid is a polymeric molecule, it can chelate with Fe3+ ions, producing an insoluble complex where the structure is contingent on the solution.
As known in the art, given the composition of NOM present in natural water, the color removal mechanism encompasses the process of precipitation, charge neutralization, entrapment, adsorption, and complexation with coagulant metal ions into insoluble particles. The reduction in tannic acid in water can also be attained by precipitation leading to the formation of solid complexes which can be separated in processes like coagulation and sedimentation. As known in the art, the effect of tannic acid on phosphate and organism matter removal during wastewater treatment: inorganic salts of aluminum or iron are primary coagulants in natural or engineered systems that can hydrolyze to generate insoluble precipitates and entrap particles, neutralizing the charge on the particles. As mentioned in prior studies, accumulation of positively charged aluminum and iron salts (i.e., coagulating metal ions) on the surface of Si given the suitable pH values in water, could also attract negatively charged particles. In this manner, the NOM removal with ferric salts has been reported in a range for 29-70%, and NOM may also react with polyvalent metal cations producing soluble metal-NOM complexes.
Adsorption is still one of the most cost-effective treatment methods for the removal of color for drinking water treatment. Given the influent condition of 175±10 Pt—Co units, the adsorption capacity can be ranked in terms of how long the proposed media sustained the color removal of greater than or equal to 77%. As such, in an embodiment, the filtration media is configured to optimize the color removal efficiency during drinking water treatment. In this manner, in this embodiment, the filtration media may be configured to maintain the effluent below 40 Pt—Co units for at least 14,000 minutes, such that the filtration media may comprise a composition mix of at least 1000 ml by volume (e.g., 1200 ml by volume) and/or the prescribed adsorption capacity. As such, the performance of the filtration media may be attributed to the inclusion of at least one the following, including but not limited to perlite and/or ZVI and/or synergetic effects between clay and sand. Moreover, as compared to the sorption media known in the art (e.g., CTS, IFGEM-1, IFGEM-4, and/or CPS), the adsorption capacity of the filtration media (e.g., at least 25.0 mg of Pt—Co·g−1) may be superior to the adsorption capacity of the rest the sorption media known in the art. Moreover, observed morphology of ZIPGEM shown by SEM indicated a heterogenous surface further supporting the longer duration of color removal observed. Additionally, in this embodiment, the filtration media may comprise at least one synergistic interactions among at least two compounds with unique morphological structure within the composition mix of the filtration media, such that the filtration media may be configured to promote color removal by improving physicochemical interactions via better dispersion and/or diffusion, optimizing color removal efficiency within drinking water treatment.
In an embodiment, the ZIPGEM-based filtration system may achieve an average percent removal of about 97.9% to about 78.9%, encompassing every value in between, from the initial about 60 minute to about 300-minute range. For example, in some embodiments, ZIPGEM may comprise an approximately 52.8% removal at roughly the 5,480 minutes mark.
In an embodiment, the optimum removal of ZIPGEM may be the result of a synergetic effect among the different ingredients of recycled materials of ZVI, clay, and/or perlite in the filtration media. As such, in this embodiment, the different specialty ingredients (i.e., media components) may contribute to the overall physicochemical characteristics of each media mix in a synergistic way. Each specialty ingredient may be carefully selected to obtain a sorption media mix capable of excelling in the removal of one or more contaminants (i.e., phosphate vs. nitrate) from different water matrices with cost-effective, scalable, and/or sustainable nature. For example, in some embodiments, silicate sand may have a low cost and/or may maintain an appropriated flow rate (Table 1). Silicate sand may also be plentiful while providing an appropriate environment for microbial ecology to thrive, and it is simple to maintain and operate (Valencia et al., 2020). The adsorption of phosphorus to sand is mainly dependent on the Ca+2 content of the sand (Brix et al., 2001), as the negatively charged phosphorus is attracted to the positively charged Ca+2 (Equation 12) (Deng et al., 2018, Lei et al., 2018). In addition, the percent content of CA+2 of ZIPGEM may comprise about 1.0, and/or about 1.1% of the media in terms of element composition, respectively, suggesting that only some phosphorus removal can be associated with the electrochemical interaction of Ca+2 and/or phosphorus.
Moreover, in an embodiment, the percentage of Fe in ZIPGEM may be much higher than compositions known in the art, owing to the inclusion of recycled ZVI as specialty ingredient of the green sorption media matrices. ZVI can be oxidized by oxygen in the presence of water to form ferrous iron, which may be further be oxidized to ferric iron with oxygen. Subsequently, in this embodiment, phosphate may precipitate with ferrous [Fe(II)] and/or ferric [Fe(III)] iron, further contributing to phosphate removal.
Additionally, in an embodiment, the effect that different pH values have on the adsorption capacity ZIPGEM may be realized via a series of isotherm experiments, as shown in
The following examples are provided for the purpose of exemplification and are not intended to be limiting.
Experimental Comparison of ZIPGEM (i.e., filtration media) and Sorption Media Known in the Art (e.g., CTS, IFGEM-1, IFGEM-4, and CPS)
Within the five tested sorption media, a media recipe of Zero-valent-Iron and Perlite Based Green Sorption Media (hereinafter “filtration media” and/or “ZIPGEM) comprising a composition ratio of 85% sand, 5% clay, 6% zero-valent-iron (ZVI) and 4% perlite by volume stood out as the best option for color removal. Findings showed that ZIPGEM (i.e., filtration media) can maintain a color removal of ˜77% for about 14,080 minutes, maintaining the effluent concentration below 40 Pt—Co units given the influent condition of 175±10 Pt—Co units. A recovery on the adsorption capacity of ZIPGEM was observed around 40,000 minutes due to synergetic effects among several different components of recycled ZVI, clay, sand, and perlites. ZIPGEM can be applied to industrial wastewater treatment for dye removal as well.
Five sorption media, including Clay-Tire crumb and Sand sorption media (denoted CTS, hereafter), Iron-Filing Green Environmental media 1 and 4 (denoted IFGEM-1 and IFGEM-4, hereafter, respectively), Clay-Perlite and Sand sorption media (denoted CPS, hereafter) and Zero-valent Iron and Perlite Green Environmental Media (denoted as ZIPGEM), were tested to evaluate their effectiveness to remove color from a source water collected from a water canal polluted with tannic acid.
The tannic acid in this canal is high given the abundant in cypress forests within the water sample area. Among these sorption media, CTS and IFGEM-1 were previously studied for nutrient and metal removal (Chang et al., 2019a; Chang et al., 2019b; Valencia et al., 2019; Wen et al., 2018; Chang et al., 2020). IFGEM-4, CPS and ZIPGEM were developed, due to the potential contribution of coupled perlite and zero-valent iron (hereinafter “ZVI”) on the top of traditional sand and clay to the removal of color. The research objective and novelty associated with exploring and comparing the effectiveness of five sorption media (made from recycled materials) which are cheaper than activated carbon to treat water with high concentration of color and to examine whether they can meet the regulatory requirement (i.e., 40 Pt—Co color unit) in the St. Johns River Water Management District for source water pretreatment (SJRWMD, 2021). The questions to be answered were: (1) Is there any incremental effect on color removal from the sequential use of recycled iron filings and perlite? (2) What is the removal mechanism of color the proposed sorption media composition comprising components of recycled iron filings, clay, and perlite? (3) Which media mix of the five used can achieve the best color removal efficiency?
Lake Brooklyn near Keystone Heights in Clay County, Florida, the United States (US) is facing a problem with low water level which is affecting recreational use and nearby shallow aquifer drinking water wells. Some wells have gone dry due to aquifer overuse, and hence the Lake Brooklyn is in acute need of replenishment. A state project to pump water from the Black Creek South Prong, a tributary of the St. Johns River, to Lake Brooklyn to recharge the semi-confined Upper Floridian aquifer at Keystone Heights has moved forward with the recent land acquisition needed for the about 27-km pipeline through southwest Clay County. The Floridan aquifer is one of the main sources of groundwater in the US and it is mainly composed of limestone and dolomite beds. The Floridan aquifer has confined, unconfined, and semiconfined areas, where the areas in the St. Johns River Management District are mostly semiconfined (Kat B. G., 1992). This is the first attempt in Northeast Florida for a project of this magnitude and will take up to 37,000 metric tons per day (e.g., 10 million gallons per day) from Black Creek, as shown in
Before water can be transferred to the Upper Floridan aquifer, the water from Black Creek needs to be treated for color removal in situ. Current concentrations in this region range from 170 to 325 Pt—Co color units. However, the St. John River Management District standard for drinking source water is less than 40 color units Pt—Co (SJRWMD, 2021) before the interbasin transfer is allowed. Given the low cost associated with adsorption processes, and low maintenance requirements for filtration facilities, column studies to compare the application of sorption media were conducted to find the most appropriate design. Water collected from Black Creek was used as the influent for the column studies and was collected in 18.9×10−3 m3 plastic buckets and stored at the University of Central Florida (UCF) in a walk-in refrigerator set at a temperature of −17.8° C.
The five sorption media compositions were tested systematically for their potential to remove color from Black Creek water. The composition and matrix of the sorption media studied are summarized in TABLE 1. To further explore the effect on zero valent iron (ZVI) (e.g., iron filings) as component of the media, new iron-sand based sorption media mixes, known as IFGEM-1 and IFGEM-4, were developed. Furthermore, the utilization of perlite for the removal of contaminant (i.e., metals, dyes, and nutrients) is a novel development (Alakan and Dogan, 2001; Hosseini and Toghroli, 2021; Moussavi and Bagheri, 2012). It has been suggested in the prior studies that perlite has considerable potential to remove methyl violet dye from aquatic solutions, and its efficiency improves with increasing temperature and pH. (Dogan and Alkan, 2003) Such studies substantiate the inclusion of perlite in two newly developed sorption media denoted as Clay-Perlite and Sand media (denoted as CPS, hereafter) and Zero-valent Iron and Perlite Green Environmental Media (denoted as “ZIPGEM”, hereafter (i.e., the filtration media)). The media compositions followed previous ones. (Valencia et al., 2021). Presently, as shown in TABLE 1, the CTS media mix was used as control to compare against iron-based media mixes, including IFGEM-1 and IFGEM-4, as well as perlite-based media mixes, including CPS and ZIPGEM.
These five sorption media were characterized by hydraulic conductivity (m·sec−1), BET surface area (m2·g−1), porosity (%), bulk density (g·cm−3), and chemical composition (% per element). Media samples were delivered to the laboratories of EMSL Analytical, Inc. in Orange City, Florida for the measurement of grain size distribution, bulk density and BET surface area. The methods ASTM D422, ASTM D854 and ASTM B922 for particle size analysis for soils, specific gravity of soils and standard test methods for metal powder specific surface area by physical adsorption, respectively, were followed.
The hydraulic conductivity (or intrinsic permeability) was determined in a standard permeameter following the protocol for Constant Head Permeability test in the Geotechnical Laboratory at UCF. The porosity and the hydraulic retention time (HRT) of the sorption media were measured at UCF. The porosity was determined by measuring the volume of water needed to fill the pores of a dry media sample. The HRT was determined via a tracer examination with Rhodamine dye (CAS Number 37299-86-8). Rhodamine dye was selected due to low cost, easy operation and detection via a fluorometer, low natural background, limited toxicity level, and nonreactivity (Richard et al., 2004). For the tracer examination, about 1 ml of Rhodamine dye was injected at the top of the column, subsequently effluent samples were collected at 5-10 min intervals and measured by an Aquaflour™ (Turner Designs 998-0851) handheld fluorometer until the rhodamine dye breakthrough was observed and completed.
The chemical compositions of the different media were analyzed via an X-Ray Fluorescence Spectrophotometer (XRF) PANalytical Epsilion at the Materials Characterization Facility (MCF) at UCF (Dewi et al., 2018). Textural characterization of the media was obtained at the MCF at UCF with a Scanning Electron Microscopy (SEM) Jeol JSM-6480 SEM instrument. The Jeol SEM allows a variable pressure mode of operation allowing microscopy of non-conductive, oily, and damp samples.
As shown in
A series of experiments with fixed bed columns was performed for the purpose of exploring the color removal efficiency and life expectancy of these selected sorption media. Columns 30.48 cm (12 in) in depth and 7.62 cm (3 in) diameter were filled with 1200 ml of the selected sorption media (i.e., CTS, IFGEM-1, CPS, IFGEM-4 and ZIPGEM) and a 5.08 cm (2-in) free space was left above the media in case of overflow. Each column set-up included a filter and a layer of pebbles at the bottom to prevent clogging, while a layer of pebbles was placed at the top of each column to aid in water distribution.
All column experiments were operated with a downward flow, simulating the planned implementation at field scale. Before the experiment, each column was flushed with de-ionized water (DI) at a flowrate of 8 ml·min−1 for approximately 3 bed volumes and left to drain for >10 hours to remove any pre-existing contaminants in the sorption media. Subsequently, water collected from the Black Creek tributary of the St. Johns River (denoted as influent, hereafter) was supplied to each column via a peristaltic pump at a fixed flowrate of 4 ml . . . . The color concentration of the influent was modified to 175±10 Pt—Co units by adding DI water if necessary to maintain the same influent color concentration for all the column experiments. T for the column studies the hydraulic loading rate maintained was 1.26 (m3·day−1·m−2).
Water samples from the influent and effluent at distinct time intervals were collected, analyzed, and catalogued to obtain information on color removal. All water samples were analyzed for color within 24 hours of collection to prevent any biological and chemical processes from altering color concentrations. All water sample analysis were performed at the Environmental Engineering Laboratories at UCF. true color of each water sample was measured using a Hach Method 8025 spectrophotometer. First, water samples were filtered through a Millipore Sigma MF-Millipore Cellulose Ester membrane with 0.45-μm pore size. Subsequently, 10 ml of filter samples were used to fill a 465 nm cell and placed in the DR-5000 Hach Spectrophotometer meter to measure and catalogue true color concentrations.
Dynamic modeling of the breakthrough curves allows the understanding of the sorption behavior of color to the sorption media. Thomas, Modified Dose Response (hereinafter “MDR”), and Yoon-Nelson models were selected to characterize the dynamic sorption mechanism. The Thomas model is derived from the Langmuir adsorption isotherm to describe the equilibrium between adsorbate and adsorbent where diffusion is neglected (Ghasemi et al., 2011; Mustafa and Ebrahim, 2010). The MDR model is an empirical model, appropriate for applications in breakthrough curves that have an asymmetric behavior (Chang et al., 2016). The Yoon-Nelson model is the simplest dynamic adsorption model as it does not require information on the adsorbent, adsorbate, or the physical characteristics of the sorption bed (Ghribi and Chlendi, 2011). The linear forms of these dynamic adsorption models with the definitions of parameters are shown in TABLE 2.
To improve the goodness of fit of the dynamic adsorption models, a method for outlier detection and removal was performed. Detection of outliers from the data sets was accomplished by drawing 95% confidence intervals (CI) around the scatter plots of the effluent concentration (in color units) vs. time (minutes). Outliers outside of the 95% CI were removed from the data sets. Moreover, these steps were performed multiple times after the removal of outliers until all data points were within the 95% CI (Uusipaikka, 2008).
For field implementation, it is important to determine the frequency of media replacement after treatment capacity has been exhausted. This can be achieved by formulating life expectancy curves for a range of removal efficiencies (e.g., 40-90%) to treat a volume of color impacted water. To estimate the media's replacement frequency, first the media usage rate (i.e., Eq. 3) is determined according to the target removal efficiency (R). The usage rate (g·L−1) specifies the mass of media in grams that can treat 1 L of water based on the desired effluent concentration. As a result, each removal efficiency will have its corresponding usage rate and thus corresponding life expectancy curve. The determination of usage rate employs the influent concentration C0 (mg·L−1), the average target effluent concentration C1 (mg·L−1) (where C1=C0 (1−R)), and the maximum adsorption capacity q0 (mg·g−1) selected from the appropriate dynamic adsorption model that can best describe the experimental data collected from column studies. The modeled R is dependent on the reasonable range of color removal obtained from the column exam. To produce the life expectancy curves, a range of volume of treated water Vwater treated (L) is selected to calculate the corresponding range of mass of media required for treatment massmedia (g) according to Eq. 4.
Additionally, since the determination of the media's replacement frequency is dependent on the flow rate specified, the design flow rate (Q in L·h−1) needs to be first selected by taking into account the maximum flow rate (Qthreshold in L·h−1) considered as the design threshold and it is preferred for Q to be less than Qthreshold. Having an understanding of the Qthreshold is crucial to prevent possible ponding effect. In this case, gravity is assumed to dominate the flow path contributing to vertical flow as the filter depth is small (i.e., 0.3-0.6 m). Hence the laboratory HRT determined from the column tracer exam is utilized to determine the Qthreshold (i.e., Eq.6) to be representative when scaling from a laboratory examination up to a filed application. To estimate the life expectancy, the void volume or pore space (Vvoid in m3) corresponding to the available water retention capacity in the media is first determined from Eq.5, using the media mass, media porosity Ø, and density (ρmedia in kg·m−3). Once the design flow rate (Q) is selected, the surface area of the filter cell is determined from the hydraulic loading rate (HLR in m3/m2 d−1) based on the experimental column-exam conditions following Eq. 7. The volume of the cell Vcell (m3) representing the volume occupied by the media is determined according to the area areadesign (m2) and the depth of cell depthfilter (m) (i.e., Eq.8). Hence, the massmedia design corresponding to the filter cell dimensions and the density of media, can be calculated according to Eq. 9. Lastly, the life expectancy is calculated from Eq. 10, for a specified media mass (massmedia design) corresponding to filter design and the design flow rate (Q). A design chart can be generated accordingly with a few turning lines to link the target removal efficiency curve with the treated water in volume and the selected mass of media.
The physical characteristics of the five selected sorption media (i.e., CTS, IFGEM-1, IFGEM-4, CPS, and ZIPGEM) are provided below in TABLE 3. Among the selected sorption media, ZIPGEM has the largest surface area (2.55 m2·g−1) followed by IFGEM-4, CPS, CTS, and IFGEM-1. Larger surface area can lead to have better adsorption potential (Wang et al., 2014). In terms of porosity CTS has the highest porosity (40.10%) followed by IFGEM-1, ZIPGEM, CPS, and finally IFGEM-4. The saturated hydraulic conductivity for all media is within the typical range for sand (10−3 to 10−5 m·sec−1) (Reddi and Inyang, 2000), indicating appropriateness for field implementation. Finally, the inclusion of ZVI in the sorption media can be associated with the resultant higher density and larger surface area in ZIPGEM contributing to better color removal.
The gradation curves or particle size distribution curves of each sorption media are presented in
In addition to physical characterization of the media mixes, samples were evaluated via an XRF analysis to describe the chemical composition of the media mixes, as provided below in TABLE 4. The main chemical element in all mixes was silica (Si), as shown in TABLE 4, provided below. As known in the prior art, amino-functionalized magnetic mesoporous silica can remove tannic acid from aqueous solution by adsorption. (Wang et al., 2010) The second most abundant chemical components for all sorption media mixes, excluding IFGEM-1 is aluminum (Al). The presence of Al as a chemical component in the sorption media mixes can be explained by the inclusion of clay as key ingredient of the mixes (Nayak et al., 2007). Al is utilized for removal of diverse contaminants including nutrients, metals, and contaminants of emerging concern (Nouri et al., 2010; Ordonez et al., 2020; Zaied et al., 2020). The inclusion of recycled ZVI (e.g., 95.6% Fe) as an ingredient of the sorption media for the removal of contaminants is highly promising given its reactivity, large surface area, lower cost, and environmentally friendly nature (Khuntia et al., 2019). Furthermore, K and Ca (e.g., 1-2.5% and/or 0.7-1%) are also part of the chemical composition of the sorption media mixes, and thus, to some extent their presence can aid in a synergistic effect that can be helpful for the removal of contaminants.
Images of the media mixtures attained from SEM analysis are presented in
To further visualize the physical difference of the sorption media and analyze material morphology, and structure of the key elements of the media materials, SEM images of sand, clay, ZVI, and perlite are presented in
To meet the requirement imposed by the St. John River Management District for source water, color concentration of source water must be less than 40 Pt—Co color units. As the influent water influent concentration is 175±10 Pt—Co units the media needs to achieve about 77% color removal. The results are provided in terms of time (minutes) vs. color removal efficiency (%) and are presented in
The sorption media ZIPGEM, a media mix of ZVI, perlite, clay, and sand stood out at the final stage for the color removal. As shown in
Clogging and ponding may be associated with the ZVI particles undergoing oxidization resulting in iron oxide clogging of the pore space in the media mix and affecting the infiltration negatively. Given that some Al and Fe can be dissolved in water the major tannic acid removal mechanism could be chemical precipitation driven by the formation of solid organometallic complexes, the emergence of Al-tannate can also contribute to clogging issues. The higher the content of ZVI, the larger the chance to have a ponding effect due to accumulation of aluminum and iron salts on the surface of Si (found in sand). The ZVI and Sand ratio were calculated for IFGEM-1, IFGEM-4 and ZIPGEM based on the media matrix, as shown in TABLE 1, resulting in 0.04, 0.11 and 0.071 (ZVI/Sand percent by volume), with these results it can be recommended that, to avoid ponding issues, the ZVI to sand ratio should be less than 0.071. However, since the clogging issue in ZIPGEM occurred long after the media stopped efficiently treating the influent when the color exceeded 40-unit Pt—Co, this issue is not an immediate concern. The strong performance of ZIPGEM can be attributed to a larger surface area and hydraulic conductivity, high porosity, and better morphological structure among the media mixes, with stronger ionic interactions, van der Walls forces, and hydrogen bonding effect.
a4602
a52,480
aTerminal time points were reached due to clogging issues.
Tannic acid has a tendency to spontaneously adsorb to different surfaces to yield a hydrophilic coating (Ball and Meyer, 2016). Kaal et al. (2005) suggested the interactions between soil minerals and tannins result in adsorption. Wang et al. (2010) discovered that the adsorption mechanism is heterogeneous, and dependent on pH and ionic strength. Ball et al. (2016) indicated that the adsorption of tannic acid to silicate is completed after about 15 minutes revealing that it produces a thin layer on SiO2. The removal of tannic acids with clay is also related to adsorption. Attapulgite/CoFe2O4 was developed by Teng et al. (2019) for tannic acid removal, and the main mechanism responsible for the sorption was hydrogen bonding and surface complexation. As mentioned by Amari et al. (2021), however, attapulgite clay coated with chitosan was found to adsorb 95.3 mg g−1 of tannic acid driven by electrostatic interactions, hydrogen bonding, and Van der Waals forces (Deng et al., 2012). Furthermore, since the anionic functional groups of tannic acid include hydroxyl and carboxyl groups it can adsorb on oxide surfaces (Zhang et al., 2009). Tannic acid is negatively charged, hence Ca2+ can aid to bind negatively charged surfaces such as species of tannic acid (Perez-Benito, 2003; Zhang et al., 2009).
Besides, an Al ion has the possibility of interacting with multiple tannic acid molecules and the formation of insoluble complexes resulting from aluminum compounds such as Al—OH at low and high pH. While at pH between 5-6, when Al(OH)3 is the predominant form, complex formation is replaced by adsorption onto Al(OH)3 surface (Georgantas and Grigoropoulou, 2006). The coprecipitation of tannic acid with Al(OH)3. occurs in the presence of hydrous aluminum oxide (e.g., Al(OH)3) leading to soluble colloidal hydroxy-Al-tannate complexes (Omoike, 1999). In the case of humic substances, Al-humic complexes are formed, and charge neutralization occurs (Georgantas and Grigoropoulou, 2006). Similarly, since tannic acid is a polymeric molecule, it can chelate with Fe3+ ions, producing an insoluble complex where the structure is contingent on the solution pH (Al-Mayouf, 1997).
Given the composition of NOM present in natural water, the color removal mechanism encompasses the process of precipitation, charge neutralization, entrapment, adsorption, and complexation with coagulant metal ions into insoluble particles. The reduction in tannic acid in water can also be attained by precipitation leading to the formation of solid complexes which can be separated in processes like coagulation and sedimentation. Omoike (1999) examined the effect of tannic acid on phosphate and organism matter removal during wastewater treatment. Inorganic salts of aluminum or iron are primary coagulants in natural or engineered systems that can hydrolyze to generate insoluble precipitates and entrap particles, neutralizing the charge on the particles. As mentioned previously, accumulation of positively charged aluminum and iron salts (i.e., coagulating metal ions) on the surface of Si given the suitable pH values in water, could also attract negatively charged particles. NOM removal with ferric salts has been reported in a range for 29-70% (Uyak and Toroz, 2007) and NOM can also react with polyvalent metal cations producing soluble metal-NOM complexes (Li et al., 2016).
As shown in
The Yoon Nelson model is a kinetic empirical model that allows the estimation of the time needed for the media to reach 50% breakthrough (τ) (Ct/Co=50%). For CTS, IFGEM-1, IFGEM-4, CPS, and ZIPGEM this value was estimated as 2,152, 9,840, 3,382, 1,151 and 62,023 minutes, respectively. Alternatively, Thomas model parameters were selected for comparison as their predictions were consistent having an appropriate r-squared value for all media (R2>0.6). By comparing the qo it can be observed that ZIPGEM has the highest adsorption capacity (27.1 mg of Pt—Co·g−1) among the tested sorption media. Thus, the efficiency of the media can be categorized in descending order based on the adsorption capacities (qo) as ZIPGEM<IFGEM-1<IFGEM-4<CTS<CPS. Furthermore, in comparison to the Thomas model which predictions of qo for all the media were consistent, the MDR model showed an inconsistent prediction in qo for ZIPGEM (qo=421.52 mg of Pt—Co·g−1). Thus, despite the higher r-squared value for MDR model, it was not selected as the preferred model to estimate the dynamic adsorption capacity, as provided below in TABLE 6.
Comparison of ZIPGEM with Other Adsorbents
The advantages of low cost, feasible field application and easy maintenance motivated innovation of different adsorbents, including agricultural waste, activated carbon, activated alumina, and zero-valent iron among the most popular. The color removal using the activated sand showed an efficacy of 70% in the first 3 minutes while the non-modified sand had an efficacy of 40%. More comparisons of different adsorbents for color removal are summarized in TABLE 7.
Different electrochemical, physicochemical, and photocatalytic methods allow for the removal of dyes for industrial wastewater treatment. In the traditional technology hub, microfiltration, ultrafiltration, and nanofiltration for removal of humic substances have shown potential and can remove 90% of humic acids in water treatment plants (Lowe and Hossain, 2008). The removal of NOM (i.e., tannic and humic acid) by photocatalytic methods is an effective method too. An example is the degradation of dyes, detergents, and organic acids by TiO2 nanofilms (Albu et al., 2007) with the aid of UV light due to their photocatalytic activity (occurring at UV absorbance at the range of 254 nm˜370 nm) (Quan et al., 2005, Qaseem et al., 2020). In addition, the removal of tannic acid from wastewater by electrochemical oxidation was confirmed by Govindaraj et al. (2010). However, most of these existing technologies are costly and operationally complex due to regeneration and/or final disposal of sorbents while ZIPGEM can be used as daily coverage at landfills. It is helpful to estimate the replacement frequency upon the exhaustion of all adsorption capacity or reach the threshold (e.g., regulatory limit) to maintain reliable treatment.
As shown in
It is important to ensure that implementation of the sorption media as a pretreatment system does not have any side effect that can have any negative health or environmental impact. For instance, the long-term human exposure to aluminum can cause encephalopathy, anemia, and bone disease in dialyzed patients (Colonia and Peris-Sampedro, 2017). Moreover, iron is an essential element for living organisms as it contributes to oxygen transportation and electron transport. Yet, if the iron intake is excessive, it can lead to tissue damage (Abbaspour et al., 2014). The EPA in the US has established standards for iron and aluminum ion concentration under the secondary drinking water standards. Under these standards, the EPA has recommended that the concentration of aluminum and iron in drinking water should not exceed the concentrations of 0.2 and 0.3 mg·L−1, respectively. Moreover, the World Health Organization indicated that the aluminum levels in drinking water facilities using aluminum sulfate coagulation ranges from 0.1 to 2.7 mg·L−1.
Therefore, effluent samples from each column were analyzed in terms of dissolved aluminum and dissolved iron ion concentration to confirm that there was no harmful leachate with these metals from the sorption media. The results from CTS and CPS, as provided below in TABLE 8 and TABLE 11, respectively, indicate some increase in the dissolved aluminum ion concentration, yet the results did not exceed the concentration of aluminum found previously in drinking waters treated with aluminum sulfate coagulate. On the contrary, IFGEM-1, IFGEM-4 and ZIPGEM, as provided below in TABLE 9, TABLE 10, and TABLE 12, respectively effluents did not contain dissolved aluminum, on the contrary, they provided aluminum removal. Removal was observed in terms of dissolved iron in the ZIPGEM column. In IFGEM-4, iron concentration increase was observed after 69 hours potentially driven by clogging in the column as dissolved iron increased in the effluent.
The source water to be utilized for drinking water supply is oftentimes troubled by the presence of NOM (i.e., tannic and humic acid). Adsorption is still one of the most cost-effective treatment methods for the removal of color for drinking water treatment. A low maintenance alternative filtration media was proposed for any in-situ pretreatment of drinking water sources. Five low-cost sorption media were produced and tested by fixed bed column studies to determine the color removal efficiency. Given the influent condition of 175±10 Pt—Co units, the adsorption capacity can be ranked in terms of how long the proposed media sustained the color removal of ˜77% or greater. ZIPGEM was ranked the first followed by IFGEM-1, IFGEM-4, CTS, and CPS. ZIPGEM maintained the effluent below 40 Pt—Co units for about 14,000 minutes based on the media mix of 1,200 ml by volume and the prescribed adsorption capacity. Such performance can be attributed to the inclusion of both perlite and ZVI and synergetic effects between clay and sand. With the predicted Thomas model parameter, the adsorption capacity of ZIPGEM (e.g., 27.1 mg of Pt—Co·g−1) was superior to the adsorption capacity of the rest of the four sorption media. Moreover, observed morphology of ZIPGEM shown by SEM indicated a heterogenous surface further supporting the longer duration of color removal observed. Such synergistic interactions among the four components with unique morphological structure promoted color removal by improving physicochemical interactions via better dispersion and diffusion.
Differential Effect of Adsorption Ingredients for Phosphorous Removal from River Water
Three specialty adsorbents were studied to understand its potential to remove phosphate via physiochemical interactions. These media mixes include CPS, ZIPGEM, and BIPGEM. The components and media matrix in percent by volume as well as physical characteristics for each sorption media are presented in TABLE 13. The Zero-Valent Iron (ZVI) was obtained from Connelly-GPM, Inc. Iron Aggregate, with descriptive name ETI CC-1004 (−8+50). The ZVI composition is 87-93% metallic iron. Moreover, the perlite used is from Miracle-Go® and its description indicated that it contains 99.44% perlite. The biochar used is from Plantonix and it is derived from soft wood and tree trimmings. The physical characteristics including BET surface area and density were performed at the EMSL Analytical, Inc laboratories. Density and BET surface area were measured following methods ASTM D854 and ASTM B922. Moreover, the saturated hydraulic conductivity was measured at the University of Central Florida (UCF) Geotechnical laboratories following the constant head permeability test. The Point of Zero Charge (PZC) for each media was also measured by the salt addition method (Mahmood et al., 2011). The salt addition method determines the pH where the surface of the adsorbent is at ionic equilibrium, and it is the condition when the number of H+ and OH— at the surface of the particle are equal. The protocol followed is presented in detail in Ordonez et al. (2022) utilizing 0.2 M NaNO3 solution and adding NaOH or HNO3 for pH adjustment. The results are presented on
A series of isotherm tests were performed to obtain information on the adsorption capacity of the different green sorption media under different pH conditions. In the beginning the selected green sorption media including CPS, ZIPGEM, and BIPGEM were washed with DI water (3 Bed Volumes (BV)) and then dried for 24 hours at a temperature of 78° C. Subsequently, aliquots of 5 grams of media with 40 ml of DI water spiked to different concentrations (i.e., 0, 0.7, 2, 3, 4, 5, 15, 30, 60, 120, and 240 mg·L−1 PO43−) were prepared. The aliquots were then shaken for 6 hours on a shaker at 180 rpms and at room temperature. The procedure was repeated at three different pH conditions (i.e., pH of 4, 7 and 10) adjusted with NaOH or HNO3. At the completion of the shaking time, each aliquot was left to rest for 30 min and the supernatant was extracted, filtered via a membrane filter with pore size 0.45 μm and analyzed for phosphate concentrations in triplicate. An additional isotherm was performed following the same protocol but substituting the influent with surface canal water spiked with NO3— to a concentration of 2 mg·L−1, while the canal water was still spiked to different concentrations (i.e., 0, 0.7, 2, 3, 4, 5, 15, 30, 60, 120, and 240 mg·L−1 PO43−) to explore the competing effect between nitrate and phosphate.
Collected water samples were analyzed for TP using the Hach TNT 843, 844 and 845 analyze kit, which follows the Ascorbic Acid method (EPA method 365.1) at different detection ranges. Water samples were analyzed for Nitrate using the TNT 835 Hach kit, based on the Dimethylphenol method (EPA method 40 CFR 141). All samples were measured within 24 hours of collection. Additional information on the TNT kits measuring protocols can be found at Hach, (2021) and Hach (2022).
Isotherm studies allow the estimation of the adsorption capacity of a sorbent (i.e., sorption media) in an equilibrium condition. The four linear forms of the Langmuir isotherm model, and Freundlich linear models were applied to the isotherm data to obtain information of the adsorption capacity of the selected sorption media. The amount of phosphate adsorbed per unit weight of the sorption media (qe) was calculated in accordance with Eq. 11. Where m is the mass of the sorption media in grams, Co is the initial concentration on the solution in mg·L−1, Cc is the adsorbate concentration of the solution at equilibrium in mg·L−1 and V is the volume of the solution in L.
Langmuir isotherm model assumptions include monolayer adsorption onto a surface with finite number of adsorption sites (Hameed et al., 2007). The Langmuir nonlinear equation follows Eq. 12, where KL corresponds the Langmuir equilibrium constant or affinity constant (L·mg−1) and qm is the maximum adsorption capacity of the absorbent (mg·g−1) (Guo & Wang, 2019). Four different linear forms of the Langmuir isotherm can be found in the literature and are presented in Eq. 13 (denoted as Langmuir 1, hereafter), Eq. 14 (denoted as Langmuir 2, hereafter), Eq. 15 (denoted as Langmuir 3, hereafter) and Eq. 16 (denoted as Langmuir 4, hereafter).
The Freundlich model is an empirical model, its linear and nonlinear form are presented in Eq. 17 and Eq. 18, respectively. In both equations, the constant KF relates to the adsorption capacity, while the constant n relates to the adsorption intensity. If the n is greater than 1 then the adsorption is favorable (Campbell and Davies, 1995; Dada et al., 2012; Desta, 2013).
A triplicate set of columns of 5 inches (12.7 cm) in depth and 4 inches (10.2 cm) in diameter filled with 700 ml of sorption media with equivalent weight of gram of 1,000 grams of ZIPGEM media were set up to understand the dynamic removal of ZIPGEM. A filter and layer of pebbles were placed at the bottom of each media mix to prevent clogging, while a layer of pebbles was placed at the top of each column to aid in water distribution. Prior to the column study, each column was flushed with DI water for 3 BV and left to drain for about 8 hours. The dynamic column study consisted of feeding each column in downward flow with DI water spiked with phosphate standard solution to a concentration of 4 mg·L−1 PO43− until the media reached saturation. Water samples were collected from the effluent at different time intervals after 23 hours until the media reached exhaustion. Water samples were analyzed for TP using the Hach TNT 843.
Data obtained from the dynamic column study was applied to Thomas (Eq. 19 and Eq. 20) and Yoon-Nelson (Eq. 21 and Eq. 22) dynamic model. The dynamic Thomas model (Thomas 1944) is one of the most popular models to predict the adsorption behavior of the adsorbent (green sorption media) (Nwabanne et al., 2022). The non-linear form of the Thomas model is presented in Eq. 19, while the linearized form is presented in Equation 20. Its constant (Kt, unitless) and media maximum adsorption capacity (qo, mg·g−1) are retrieved from the linear regression of ln
where Co is the influent concentration (in mg·L−1), Ct is the effluent concentration at time t (in mg·L−1), and t is time is minutes.
Yoon Nelson model (Yoon and Nelson, 1984) is one of the simplest dynamic models as it neglects the information of the physical characteristics of the physical bed and the absorbent. The non-linear form of the Yoon-Nelson model is presented in Eq. 21 and the linear form of the model is presented in Eq. 22. The parameters KYN and τ correspond to the Yoon-Nelson constant (in min−1) and the time required for the adsorbent to reach 50% breakthrough (in min) (Nwabanne et al., 2022).
A larger BET surface area and higher porosity can be good indicators of more available adsorbent sites resulting in better adsorption (Gupta et al., 2013). ZIPGEM has the larger BET surface area and higher porosity followed by BIPGEM and finally by CPS. Moreover, the saturated hydraulic conductivity of ZIPGEM was the highest among the three specialty absorbents, followed by CPS and BIPGEM, respectively. The saturated hydraulic conductivity is an important factor for appropriate treatment capacity (e.g., hydraulic loading rate) toward scale-up of the system, as it can indicate the required contact time of the adsorbent and adsorbate to obtain good removal efficiency.
Aside from the physical properties of the media, it is crucial to determine the chemical properties to obtain a holistic understanding of removal mechanisms of these specialty adsorbents. The PZC provides an insight on the surface charge of the media at different pH levels. This is, at pH levels below the PZC the surface of the media is positively charged, while at points above the PZC the surface of the media is negatively charged. The location of the PZC for CPS, ZIPGEM, and BIPGEM is located at pH of ˜5.6, ˜9.2 and ˜9.5, respectively (
The chemical composition of the three selected green sorption media mixes (i.e., CPS, ZIPGEM, and BIPGEM) were determined based on the X-ray Fluorescence (XRF) instrument. In TABLE 14, the results indicate that Si is the major element on the media matrix of the three sorption media mixes. For CPS, ZIPGEM, and BIPGEM, the percent content of Al is 10.5%, 8.4%, and 11.5%, respectively, being the second major element in the media matrix for CPS and the third major element for ZIPGEM and BIPGEM. The major difference among the chemical element composition is the presence of Fe in ZIPGEM and BIPGEM in comparison to CPS. The Fe percent content in ZIPGEM and BIPGEM is 12.1% and 12.8%, while it is only 0.4% in CPS. Another element that stands out in the chemical element composition of the media is Ca, as it can partake in the removal mechanism of PO43− via the different sorption media mixes.
The different specialty ingredients (i.e., media components) contribute to the overall physicochemical characteristics of each media mix in a synergistic way. Each specialty ingredient was carefully selected to obtain a sorption media mix capable of excelling in the removal of one or more contaminants (i.e., phosphate vs. nitrate) from different water matrices with cost-effective, scalable, and sustainable nature. For instance, silicate sand that has a low cost can maintain an appropriated flow rate (TABLE 13). Silicate sand is plentiful while providing an appropriate environment for microbial ecology to thrive, and it is simple to maintain and operate (Valencia et al., 2020). The adsorption of phosphorus to sand is mainly dependent on the Ca+2 content of the sand (Brix et al., 2001), as the negatively charged phosphorus is attracted to the positively charged Ca+2 (Eq. 22) (Deng et al., 2018, Lei et al., 2018). In the case of CPS, ZIPGEM, and BIPGEM, the percent content of Ca+2 is 1.1, 1.0, and 1.1% of the media in terms of element composition, respectively, suggesting that only some phosphorus removal can be associated with the electrochemical interaction of Ca2+ and phosphorus.
Nayak and Singh (2007) performed a XRF characterization on clay indicating that SiO3 and Al2O3 are present in major quantities in clay (48.12% and 34.54%, respectively), justifying the high content of Al in the sorption media (i.e., CPS, ZIPGEM and BIPGEM). Furthermore, the adsorption of phosphate to clay is the combination of physiochemical interactions because of ligand exchange and electrostatic attraction (Wang et al., 2018). Phosphate adsorption can also be associated with the results of the interaction between aluminum ion from the dissolution of clay that results on the chemical precipitation of aluminum phosphate following Eq. 23 and Eq. 24 (Edzwald et al., 1976).
Moreover, the percentage of Fe in ZIPGEM and BIPGEM is much higher than in CPS, owing to the inclusion of recycled ZVI as specialty ingredient of the green sorption media matrices. ZVI can be oxidized by oxygen in the presence of water to form ferrous iron (Eq. 25) which can further be oxidized to ferric iron with oxygen (Stumm & Lee, 1961) (Eq. 26). Subsequently, phosphate can precipitate with ferrous [Fe(II)] or ferric [Fe(III)] iron in accordance with Eq. 27, Eq. 28, and Eq. 29, further contributing to phosphate removal.
The removal of phosphate by perlite was disputable; for instance, Ma, et al, (2011) concluded that the removal of orthophosphate via perlite is negligible with an adsorption capacity of only 0.01 mg· g−1 found via a Langmuir isotherm test. Similarly, Williams et al. (2000) studied a peat-perlite medium and found that there is no phosphate adsorption. However, an examination by Ozel et al. (2012) found that expanded perlite as an in-situ landfill liner system has a PO43− removal efficiency of 91% from leachate. But Pradhan et al. (2020) treated greywater with perlite via a column study, and only achieved phosphate removals of up to 15%. The use of biochar for nutrient removal has increased due to its sustainable nature. The removal of phosphate by biochar is attributed to the large surface area, location of the PZC, and metal compounds (i.e., Al, Ca, Mg), supporting the main mechanism of removal (Almanassra et al., 2021; Veni et al., 2017; Yao et al., 2011).
Effect of Water Matrix on PO43− Adsorption
The effect that different pH values have on the adsorption capacity of CPS, ZIPGEM, and BIPGEM was realized via a series of isotherm experiments (
In general, higher PO43− adsorption was attained for all media mixes at lower pH (pH=4); however, when the pH increased to pH of 7 and 10 the adsorption capacity decreased, being the lowest at pH of 10 (
The Langmuir isotherm model is widely utilized for predicting the adsorption capacity of adsorbents. The data obtained from the isotherm studies were imputed into four different linear forms of the Langmuir isotherm. By comparing the experimental data and the simulated data obtained from the different forms of the linear Langmuir isotherm, it can be concluded that linear form present in Eq. 13 (Langmuir 1) is the most appropriate to predict the adsorption capacity of the media, followed by the linear form in Eq. 16 (Langmuir 4). These results are consistent with the findings by Guo and Wang (2019). The different parameters simulated by the Langmuir and Freundlich equation are summarized in TABLE 15. The qm values obtained for CPS at different water matrices ranged from 0.114 to 0.168 mg·g−1. The qm obtained for BIPGEM and ZIPGEM were close in range with each other, but over 10 times higher than that for CPS. The qm values for ZIPGEM ranged from 0.946 to 1.832 mg·g−1 and for BIPGEM the qm ranged from −0.131 to 1.824 mg·g−1. The negative adsorption capacity obtained for qm value for BIPGEM at pH of 10 is the result of an inappropriate fitting of the Langmuir model (
An isotherm test utilizing surface water collected from a canal water system in Florida, USA spiked with NO3— to a concentration of 2 mg L−1 was performed on CPS, ZIPGEM and BIPGEM to explore the adsorption capacity and the removal mechanism based on real world water matrices. Remarkably, the adsorption capacity of phosphate by CPS increased by 8 times its capacity when using canal water in comparison to DI water (TABLE 15 and TABLE 19). This can be related to the presence of calcium (79.03 mg·L− 1) and magnesium (14.10 mg·L−1) in the canal water which promoted PO43− precipitation (Eq. 22). However, the increase in PO43− adsorption capacity by ZIPGEM and BIPGEM when using canal water was only noticeable at high PO43− concentrations, as shown in
The nitrate adsorption capacity at equilibrium (qe) of CPS, ZIPGEM, and BIPGEM calculated in the different aliquots spiked with constant nitrate and varying phosphate concentrations (Eq. 1) remained consistent. The qe for ZIPGEM was the highest (0.0088±0.00023 mg·g−1) followed by BIPGEM and CPS with qe of 0.0075 (±0.001) and 0.0017 (±0.0005) mg·g−1. The simultaneous removal efficiency of the sorption media achieved in an isotherm using spiked water at constant nitrate concentration—(2 mg·L−1) and varying phosphate concentration (0, 0.7, 2, 3, 4, 5, 15, 30, 60, 120, and 240 mg·L−1) denoted as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11, respectively, is presented in
Fixed bed columns are a preferable experiment set up to determine the maximum adsorption capacities of green sorption media mixes as it considers axial dispersion, film diffusion resistance, and intraparticle diffusion resistance (Patel, 2019). The adsorption process of ZIPGEM was studied in a set of downflow dynamic columns, given its better performance in the isotherm studies in comparison against CPS and BIPGEM. Although the qm obtained for BIPGEM were almost equivalent to the qm obtained for ZIPGEM in the isotherm studies it was not selected because ZIPGEM has a lower production cost by excluding the biochar component and by considering the better performance of ZIGPEM at high pHs (pH of 10). The results from the dynamic column study of ZIPGEM are presented in
The R2 obtained from the linear regression curve of the Thomas and Yoon-Nelson model was 0.721 and 0.721. The KT constant from the Thomas models calculated from the linear regression is 2.50E (−6) and the calculated q0 is 7.65 mg·g−1. While the calculated KYN obtained from the linear regression of the data is 1E (−05) min−1 and the value of T is ˜166 days (239,110 min) for this column set up. By comparison the adsorption capacity of ZIPGEM with other adsorbents (TABLE 20), it can be concluded that ZIPGEM is more effective that other low-cost adsorbents such as zeolites and sponge iron.
The growth and production of plant crops require 16 essential elements including the macronutrients: nitrogen (N), phosphorus (P) and potassium (P), the secondary nutrients: calcium (Ca), magnesium (Mg) and sulfur(S) and the micronutrients: boron (B), chloride (CI), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn). Most plant crops required Fe in small quantities of about 0.44 kg to 0.68 kg (1 to 1.5 lb) Fe per 0.405 hectare (1 acre) (Hochmuth et al., 2011). While the application of chemical fertilizer as soil amendment increases crop production it can also cause side effects including water pollution from agricultural runoff, soil acidification, impact to the microbial ecology in the rhizosphere and affect nutritional balance (Lin et al., 2019). Alternatively, the application of organic fertilizers as soil amendment can prevent soil acidification and the long-term application of organic fertilizers can increase total soil organic carbon content (Wang et al., 2019), improve soil nutrients and can regulate and improve the structure of the microbial ecology in different soils (Cui et al., 2018, Lui et al., 2021).
Contemplating the use and reutilization of the exhausted ZIPGEM for local crop fields, instead of final disposal once ZIPGEM reaches saturation, would be more advantageous. Concurrently supporting the realization toward SDGs 2.3 to improve soil quality. The chemical element composition of the saturated ZIPGEM media is presented in TABLE 21, along with the chemical element composition of different fertilizers including fish manure (Ekinci et al., 2019), insect derived compost and commercial fertilizer (Choi et al., 2009). The re-use of the exhausted media as soil amendment is attributed to the sustainability and cost effectiveness of the new sorption media by lowering the cost and environmental impact in circular economy, reducing the ecological effects surrounding phosphorus mining (Koppelaar and Weikard, 2013) for chemical fertilizers and preserving the already limited phosphorus resources (Weikard and Seyhan, 2009). The search for low-cost fertilizer is currently needed given the 80% increase in price of fertilizer since 2020 (Bhadha et al., 2022). For instance, the current estimated cost to place fertilizer (N, P, K, Ca, Mg, Fe, Si, B, Cu, Mn and Zn) for sugarcane crops is 494 $ per acre (Bhabha et al., 2022).
With the accelerated increase in world population, the United Nations developed an agenda with Sustainable Development Goals to cover areas of concern including the production of clean water and sustainable food under the SDG 2.4 and 6.3. The present disclosure intends to propose three new green sorption media capable of removing nutrients from different water matrix to prevent eutrophication of aquatic system, while allowing the recycling of the adsorbed nutrients by direct applications of the exhausted media as soil amendment. The three green sorption media were explored in a series of isotherms, and the results were imputed into different forms of the Langmuir and Freundlich isotherm. The Langmuir 1 (Eq. 13) (Ce/qe VS. qe) linear form of the Langmuir isotherm model is preferable for estimating the qm of the sorption media (i.e., CPS, ZIPGEM and BIPGEM) given that the simulated data is the most similar to the experimental data. The predicted qm for CPS ranged from 0.114 to 0.938 mg·g−1, for ZIPGEM it ranged from 0.947 to 1.832 mg·g−1 and for BIPGEM it ranged from −0.131 to 1.824 mg·g−1. The sorption media ZIPGEM achieved higher PO43− adsorption capacities, and thus, its performance was the most excelled given its little variation on its performance under a wider range of influent water matrix (i.e., pH of 4, 7, and 10 and canal water). This supports its application in different water treatment systems. For instance, PO43− removals as high as 99% were attained for ZIPGEM at initial PO43− concentrations below 120 mg·L−1 in the presence of NO3− when using surface water (canal water). Moreover, 90% PO43− removals were attained for ZIPGEM at initial PO43− concentrations above 60 mg·L−1 within the different initial pH levels. A dynamic column study was performed using ZIPGEM to further characterize the dynamic adsorption capacity of the media. The maximum adsorption capacity of ZIPGEM estimated by the Thomas dynamic model in a column study was 7.56 mg·g−1.
The sustainable nature of the different ingredients of the media matrix and the high PO43− adsorption capacity and XRF chemical composition of the exhausted media further supports the direct application of ZIPGEM, BIPGEM, and CPS in sequence as soil amendment to aid in sustainable food production while contributing to improving soil quality. Finally, higher nitrate removal efficiency was attained by ZIPGEM, followed by BIPGEM, and CPS; however, the biological removal of nitrate was overlooked due to short contact time. Future work may be directed to understand the synthesis of microbiological and physiochemical nutrient removal mechanisms in the different green sorption media and how the different specialty ingredients of the media can further enhance the growth of microbial ecology (i.e., biochar), while further contributing to plant growth.
The adsorption capacities and removal mechanism of MC-LR of four green sorption media were explored. The sorption media CPS is composed of 92% sand, 5% clay, and 3% perlite in percentage by volume. ZIPGEM is composed of 85% sand, 5% clay, 5% ZVI, and 5% perlite in percent by volume. Both CPS and ZIPGEM were selected as control to investigate the differential effect of the inclusion of zero valent iron (ZVI) and biochar as media component. BIPGEM-1 is composed of 80% sand, 5% clay, 5% ZVI, 5% perlite, and 5% biochar in percentage by volume. While, BIPGEM-2 is composed of 60% sand, 5% clay, 5% ZVI, 5% perlite, and 25% biochar in percent by volume. The physical and chemical characteristics of the media were investigated for a better interpretation of the media removal mechanism. The density and Brunauer-Emmett-Teller (BET) surface area were analyzed by EMSL Analytical Laboratory. The saturated hydraulic conductivity and porosity were determined in a geotechnical laboratory at the University of Central Florida (UCF). The point of zero charge (PZC) was measured at a chemical laboratory at UCF following the salt addition method (Bakatula et al., 2018; Mahmood et al., 2011). The methodology was presented in detail by Ordonez et al. (022). Finally, the chemical composition of the media and the individual components was measured at the Advanced Materials Processing and Analysis Center at UCF via an X-ray fluorescence (XRF) analysis.
The MC-LR standard solution utilized for the isotherm studies was acquired from Sigma-Aldrich in liquid form with a concentration of 2.5 mM. The MC-LR standard for the column studies was obtained from Cayman chemical in a solid form. The MC-LR standard was first dissolved in methanol in accordance with its solubility point of 10 mg·m1-1. The formal name for the MC-LR is cyclo [2,3-didehydro-N-methylalanyl-D-alanyl-L-leucyl-(3S)-3-methyl-D-B-aspartyl-L-arginyl-(2S,3S,4E,6E,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoyl-D-y-glutamyl], and its molecular form is C49H74N10O12 (
A series of equilibrium isotherms were performed on the sorption media (i.e., CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2) to determine its MC-LR adsorption capacity and the effect the coexistence of phosphate (PO43−) or calcium (Ca2+) has on the MC-LR removal potential and adsorption capacity. In the first equilibrium isotherm (denoted as Case 1 hereafter), 5 aliquant on Erlenmeyer Flask were set with 10 g of media and m1 of DI water spiked with MC-LR to different initial concentrations ranging from 5-350 μg·L−1 (5, 35, 50, 100, and 350 μg L−1 denoted as Condition 1, Condition 2, Condition 3, Condition 4, and Condition 5, respectively). For BIPGEM-2 an additional condition (Condition 6) with a MC-LR concentration of 600 μg·L−1 MC-LR was included. In the second and third isotherm studies (denoted as Case 2 and Case 3, respectively, hereafter) the same protocol was followed; however, the initial conditions were modified by including PO43− to a concentration of 20 mg·L−1 (i.e., Case 2) or Ca2+ to a concentration of 30 mg·L−1 (i.e., Case 3) across all influent conditions (TABLE 22). The resultant solutions were shaken in a shaking platform for 24 hours at 160 rpm. At the conclusion of the shaking time the solutions were left to settle for 1 hour. Subsequently duplicate water samples with 100 mL of the resultant solutions were collected in a plastic bottle to be delivered to an external lab (i.e., Green Water Laboratories) for MC-LR analysis.
Water samples delivered to Green Water laboratory in Palatka, Florida were analyzed for total MC with a Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS) following the MMPB (2R-methyl-3S-methoxy-4-phenylbutanoic acid) method (Foss et al. 2). Guo et al. (2017) compared the analysis of MCs in drinking water by enzyme-linked immunoassay (ELISA) and LC-MS/MS method, finding that the LC-MS/MS results were more reliable than those from ELISA. An extra set of samples was collected and analyzed for PO43− or Ca2+ concentration via Hach measuring kits. The Hach product TNT844 was utilized to analyze the samples for PO43−, and the Hach product TNT869 was utilized to analyze the samples for Ca2+ concentrations. Water samples analyzed for PO43− or Ca2+ were previously filtered via a 0.45 μm membrane filter. To minimize the risk of the MC-LR adsorbing to the Erlenmeyer flask or sampling bottles, each of the flask and sampling bottles was rinsed 3 times with the spiked solution or the corresponding water sample prior to sample storage.
The different concentrations were selected given the wide range of concentrations at which MC-LR is found in different environments. For instance, the presence of MC-LR has been found in different drinking water sources or public reservoirs. In Sao Paulo, Brazil, concentrations ranging from 0.5-100 μg·L−1 were found in a public reservoir (Nobre, 1997), while concentrations up to 1.25 μg·L−1 were detected in Pará, in the Brazilian Amazonia (Vieira et al., 2005). Different aquatic systems have also been affected with high concentrations of MC; for instance, the concentrations of MC-LR in the Indian River Lagoon in the state of Florida ranged from 0.01-85.70 μg·L−1 between 2018 and 2019, with higher concentration detected during the wet season (May to October) (Laureano-Rosario et al., 2021). Moreover, Billam et al. (2006) reported MC-LR concentration in 2 lakes in Texas with concentrations ranging from 0.096-4.914 μg·L−1 in Buffalo Spring Lake and 0.2-5.83 μg·L−1 in Lake Ransom Canyon, and in both lakes higher concentrations were observed during the spring season. The issue with high concentrations of MC extends outside of the USA; for instance, in Beira Lake in Sri Lanka, MC-LR concentrations varied from 11,450-25,230 μg·L−1, with higher concentration targeted within the rainy season (Piyathilaka and Manage 2017).
Data collected for MC-LR concentration at different influent conditions were analyzed in terms of percentage removal as well as for its absorption capacity by the Langmuir and Freundlich isotherm models. The Langmuir isotherm is widely used to explore the adsorption capacity of different sorption materials (Languir, 1932; Ho and Chiang, 2001). Different linearization of the Langmuir model can be found in literature; however, Guo and Wang (2019) suggested that the linear form presented in Equation 30 and Equation 31 can better estimate the Langmuir parameters. In this equation the parameter qe is the amount of sorbate adsorbed per unit weight (μg·g−1) of the sorption media and it can be calculated following Equation 32. In Equation 3, m is the mass of the sorption media in grams, Co is the initial concentration on the solution in μg·L−1, Ce is the concentration of the solution at equilibrium in μg·L−1, and V is the volume of the solution in L. Moreover, the Langmuir parameters KL and qm correspond to the Langmuir equilibrium constant (L·μg−1) and the maximum adsorption capacity of the absorbent (μg·g−1), respectively, and are retrieved from the regression plot of
The Freundlich isotherm model is an empirical equation, and its nonlinear form is presented in Equation 33, while one of the most common linear forms is presented in Equation 34 (Freundlich, 1909; Appel, 1973). The linear form of the Freundlich equation is obtained from the linear regression In (qe) vs. In (Ce), where the slop of the line is 1/n and the KF is calculated form the x-interception. The 1/n parameter indicates the adsorption intensity where the adsorption is favorable If 1/n is between 0 and 1 (0<1/n>1) then the adsorption is unfavorable.
The thermodynamic parameters including Gibbs free energy (ΔG), enthalpy change ΔH° and entropy change 4S can aid in the explanation of the MC-LR removal mechanism by the sorption media. To determine these parameters a series of series of batch tests were performed with aliquots with 10 grams of media and 250 ml of DI water spike to Condition 5 for the three cases (Case 1, 2 and 3) at three different temperatures (17 C°, 23 C° and 35 C°). The same shaking and analysis protocol as the equilibrium isotherms was followed (Section 2.3).
The thermodynamic parameters can be determined from the Van't Hoff Equation (Equation 35) and the change in Gibbs free energy (ΔG) which can described in the form of Equation 36. Where keq is the equilibrium constant and can be calculated following Equation 37. The ΔS° is the standard entropy change (J/mol K), ΔH° is the standard enthalpy change (kJ/mol) and 4G° is the standard Gibbs free energy change (kJ/mol). When ΔS° is positive value it signifies affinity of adsorbent towards the aqueous solution, while a negative value relates to a lower affinity for adsorption. The change in enthalpy (ΔH) characterizes the total changes in bond energy between the adsorbent and adsorbate. For ΔH° an endothermic and exothermic reaction is represented by a positive and negative value, respectively. Moreover, a non-spontaneous and spontaneous reaction is inferred from a positive and negative value of ΔG, respectively.
Variance (ANOVA) test without replication with the data analysis module in Microsoft Excel. The one-way ANOVA was taken to verify if the differences in removal efficiency among the different sorption media (i.e., CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2) at the various influent cases were significant under a 95% confidence interval. The 2-null hypothesis (H0) and 2 alternative hypotheses (Ha) to be tested are as follows:
H0: There is not a significant difference in the removal efficiency means between sorption media. Ha: There is a significant difference in the removal efficiency between sorption media.
A 2-way ANOVA test was applied to the removal efficiency of each media at different influent conditions and cases to verify if the differences in removal efficiency are significant under a 95% confidence interval. The assumption considered by the 2-way ANOVA includes the homogeneity of variance, independence of observations, and normally distributed dependent variables, and the data should not have significant outliers (Knežević and Žmuk, 2021). The 2-null hypotheses (H01, H02) and 2 alternative hypotheses (Ha1, Ha2) to be tested are presented as follows:
Hoi: There is not a significant difference in the average removal efficiencies among the different initial influent MC-LR concentrations (i.e., Conditions 1-5 or Conditions 1-6) for CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2. (Ha1: There is a significant difference in the average removal efficiencies among the different initial influent MC-LR concentrations (i.e., Conditions 1-5 or Conditions 1-6) for CPS, ZIPGEM, BIPGEM-1, and BIPGEM-2.)
H02: There is not a significant difference in the average removal efficiencies among the different cases (i.e., Cases 1, 2, and 3) for CPS, ZIPGEM, BIPGEM-1, and BIPGEM-2 (Ha2: There is a significant difference in the average removal efficiencies among the different cases (i.e., Cases 1, 2, and 3) for CPS, ZIPGEM, BIPGEM-1, and BIPGEM-2.)
The acceptance or rejection of the null hypotheses was determined by comparison of the F and Fcrit values. If the F value was greater than the Fcrit value, then the null hypothesis was rejected and the alternative hypothesis was chosen.
A fixed-bed column study for CPS, ZIPGEM and BIPGEM-1 was performed to collect information on its removal efficiency and adsorption capacity for MC-LR treatment in a dynamic environment. The experimental setup consisted of a polyvinyl chloride column of 12.7 cm depth (5 inches) and 10.2 cm (4 inches) diameter in triplicate for each sorption media. Each column contained a filter and layer of pebbles at the bottom to prevent clogging, followed by 1,300 mL of media (i.e., CPS, ZIPGEM, BIPGEM-1) and topped with a layer of pebbles to aid in water distribution at the surface of the column. The column was operated in a downflow manner with peristaltic pump to provide a constant flowrate of 14 mL·min−1. Each column has 1,300 ml of media. The hydraulic loading rate is 2,517 1·day−1·m−2 (60.939 gallons·day−1·ft−2). The influent consisted of spiked surface water at a concentration of 70 μg·L−1 of MC-LR that reflects the typical high range of MC-LR concentrations in natural environments. The media reach 50% breakthrough at 40 hours (50% removals were obtained at this point).
Water samples were collected at different times to capture the breakthrough curve of CPS, ZIPGEM and BIPGEM-1 for MC-LR adsorption. The collected water samples were delivered to Green Water laboratory for analysis for total MC with a LC-MS/MS. Moreover, a set of triplicate samples collected from surface water was sent to Eurofins Flowers Chemical Laboratories, Inc. for analysis of basic water parameters (i.e., dissolved iron, dissolved aluminum, nitrogen kjeldahl, nitrate, nitrite, total nitrogen, total phosphorus, and chlorophyll a). A separate set of triplicate water samples was sent to ALS testing laboratories to test the concentration of tannic acid in the water.
Information on the breakthrough curve for all sorption media (i.e., CPS, ZIPGEM and BIPGEM-1) was imputed into 2 dynamic models, namely Thomas and Modified Dose-Response (MDR) model. The Thomas model is commonly used to produce a general analysis of the adsorption process in a fixed bed column. The Thomas model was developed based on the Langmuir isotherm equilibrium and second-order reversible kinetics (Gonzalez-Lopez et al., 2021). The linear form of the Thomas model is presented in Equation 35 and can be obtains from the linear regression of ln
where t is time in minutes; Co and Ct are the influent MC-LR concentration and the effluent concentration at time t in μg·L−1, respectively; m is the mass of media along the fixed bead in grams; Q is the influent flow rate in L·min−1; KT is the Thomas constant in L·minutes−1·μg−1; and q, is the maximum adsorption capacity of the media in μg·L−1
The MDR model is an empirical model, which is more suitable for asymmetric breakthrough curves and thus minimizes the error from the Thomas model (Song et al., 2011). The linear form of the MDR model is presented in Equation 36; from this equation the constants Ct, Co, Q, m, qo, and t keep the same meaning and units as in the Thomas model, however, the constant amdr corresponds to the MDR constant (unitless).
The characteristics of the sorption media CPS, ZIPGEM, BIPGEM-1, and BIPGEM-2 are summarized in TABLE 23. The results indicate that the sorption media BIPGEM-2 has the highest BET surface area, followed by ZIPGEM, BIPGEM-1 and CPS. ZIPGEM has the highest saturated hydraulic conductivity followed by CPS, BIPGEM-1, and BIPGEM-2, respectively. The difference in the physical characteristics among CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2 can be attributed to the inclusion of ZVI or ZVI and biochar as media components and the different media matrices. A larger surface area and higher porosity can be beneficial for adsorption processes because it can provide more active sites (Bhatnagar and Jain, 2005; Rong et al., 2017; Subramaniam et al., 2017), while a lower saturated hydraulic conductivity can be beneficial for adsorption process because it extends the contact time of the media and the adsorbate. However, a lower density can be beneficial for application purposes given the inverse relationship between density and volume (pore space). The location of the PZC for the media can also impact the removal mechanisms. The PZC for CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2 occurs at pH of 5.6, 9.2, 9.6, and 10, respectively. At the PZC the charge at the surface of the sorption media is zero, however, when the pH drops below the PZC the surface charge is positively charged, whereas when the pH is above the PZC the charge in the surface of the media is negatively charged (Bhatnagar and Jain, 2005).
The location of the PZC for ZIPGEM can be attributed to the presence of ZVI because the PZC for iron hydroxides ranges from 7-9 (Wu et al., 2017). However, the higher location of the PZC in BIPGEM-1 and BIPGEM-2 can be attributed to the presence of biochar, given that the PZC for biochar (as disclosed herein) is located at a pH of 10.6 (TABLE 23)
The chemical elemental composition of the different components of the media matrix were explored by an XRF analyzer to explore how each material can contribute to the removal mechanism of the sorption media (TABLE 24). The main component of these green sorption media is sand, followed by clay and perlite, whereas ZVI is a component of ZIPGEM, BIPGEM-1 and BIPGEM-2 and biochar is a component of BIPGEM-1 and BIPGEM-2. Sand (the main component of all media) is made of ˜91% Si, and clay (the second main component in the all-media matrix) is made of ˜38% and ˜52% Al and Si, respectively. The composition of perlite is mainly Si, K, and Al, accounting for ˜57%, ˜19%, and ˜9%, respectively. ZVI is composed of ˜95% of Fe, while the main components of biochar are Ca and K, accounting for ˜50.9% and ˜23.8% respectively.
In TABLE 25, the chemical elemental composition for CPS, ZIGEM, BIPGEM-1 and BIPGEM-2 is presented. The major difference in the elemental composition among the media is the presence of Fe in ZIPGEM, BIPGEM-1 and BIPGEM-2 in comparison to CPS. In ZIPGEM, BIPGEM-1 and BIPGEM-2, Fe accounts for ˜12.1%, ˜12.8% and ˜5.6%, respectively of the media's chemical elemental composition, in comparison to CPS, in which Fe only accounts for ˜0.4% of its elemental composition. With the increased Fe percentage in ZIPGEM, the percentage of Si decreases as evidence of the lower content of sand in ZIPGEM, BIPGEM-1 and BIPGEM-2.
A series of isotherm studies were performed to understand the removal efficiency and the effect that different influent concentrations have on the MC-LR removal by the different sorption media (i.e., CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2). Additionally, 3 different cases were selected to investigate the effect that the coexistence of PO43− and Ca2+ has on the MC-LR removal efficiency of sorption media. In Case 1, MC-LR alone was spiked in the influent at different concentrations, while in Case 2, PO43− at a constant concentration was spiked in the influent with varying MC-LR concentrations and in Case 3, Ca2+ at a constant concentration was included along the spiked influents with different MC-LR concentrations. The different influent concentrations ranged from 5-600 μg·L−1 and are denoted as Condition 1-6 as explained in TABLE 22. In general, in Case 1, Case 2 and Case 3 (
In Case 2, the simultaneous removal of phosphorus was studied, and it was observed that ZIPGEM outperformed the other sorption media in terms of phosphate removal, with removals ranging from 49.4-60.6%. The PO43− removal by BIPGEM-2 ranged from 43.9-54.09%, while for BIPGEM-1 it ranged from 33.7-43.13%. Lower PO43− removal were obtained by CPS ranging between 10.3-20.6%. In Case 3, occurrence of Ca2+ was studied, and no significant change in effluent concentration, in comparison to the influent concentration, was observed among the 4 different sorption media.
The MC-LR percentage removals obtained by each sorption media in each case were subject to a 1-way ANOVA at a 95% critical interval. By comparing the resultant F and Fcrit values, it was concluded that there is a significant difference among the mean values of these removal efficiencies across the 4-sorption media. This conclusion was attained via the acceptance of the alternative hypothesis. Furthermore, the percentage removals across the 3 different cases (i.e., Cases 1, 2, and 3) and conditions (i.e., Conditions 1-5 or Conditions 1-6) within each media were further compared by a 2-way ANOVA test with a 95% critical interval. The test was performed to determine if there was a significant difference among the MC-LR percentage removals attained at the different cases and conditions within each media. The acceptance or rejection of the null hypothesis was determined based on the comparison of the F and Fcrit value. For BIPGEM-2, ZIPGEM and CPS, both null hypotheses (H01 and H02) were accepted, leading to the conclusion that there were not significant differences in the MC-LR percentage removals obtained among the different MC-LR influent concentrations and cases. On the contrary, for BIPGEM-1 the first null hypothesis was rejected (H01), allowing for acceptance of the first alternative hypothesis, leading to the conclusion that there were significant differences across MC-LR percentage removals attained by the different influent MC-LR conditions (Condition 1-5). Moreover, for BIPGEM-1, the second null hypothesis was accepted, generating the conclusion that there were not significant differences in the MC-LR removals across the different cases.
To further characterize the MC-LR adsorption capacity of the sorption media (i.e., CPS, ZIPGEM, BIPGEM-1, and BIPGEM-2), the isotherm results were imputed into the Langmuir and Freundlich isotherm models, and the results are presented in TABLE 26 and TABLE 27. High correlation efficiencies (R2) were obtained for CPS, ZIPGEN and BIPGEM-1 from the linear regression following the Freundlich isotherm, while for BIPGEM-2 R2 was only observable in Case 1. For the Langmuir isotherm model, high value of R2 was only obtained from the linear regression of BIPGEM-1 (all cases) and CPS and BIPGEM-2 in Case 1, and an acceptable R2 was obtained for ZIPGEM case 1. The low R2 for CPS, ZIPGEM and BIPGEM-2 in Case 2 and Case 3 can be explained by the first and second assumption of the Langmuir isotherm that states that the adsorption is entirely of a monolayer at the surface and that only one adsorbed molecule can be adsorbed at each site. Considering these results, it can be concluded that for CPS and ZIPGEM the adsorption is monolayer on homogeneous sites when MC-LR is alone in the influent, whereas, when MC-LR coexists with other contaminants (i.e., PO43− and Ca2+), the adsorption is multilayer on heterogeneous sites according to the assumption of the Freundlich isotherm model. Such conclusion cannot be made for BIPGEM-1, given that high R2 were attained from the linear regression of both Langmuir and Freundlich models.
The adsorption capacities in Case 1 for CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2 obtained by the Langmuir model are 0.74 μg·g−1, 1 μg·g−1, 4.63 μg·g−1, and 29.49 μg·g−1, respectively. BIPGEM-2 had the higher adsorption capacity followed by BIPGEM-1, ZIPGEM and CPS. Moreover, the n value derived from the Freundlich isotherm model indicates whether the adsorption is favorable or unfavorable. Based on the n values from CPS, the adsorption for Case 1 and Case 3 is favorable, while the adsorption in Case 2 is not favorable. On the contrary, for ZIPGEM, BIPGEM-1 and BIPGEM-2 the adsorption is favorable for all cases (Case 1, Case 2, and Case 3). The adsorption capacity of BIPGEM-1 and BIPGEM-2 are compared to different adsorbents in the literature and is summarized in TABLE 28.
Phosphate adsorption capacity (qe) of the sorption media CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2 is presented in TABLE 29, along with the shared phostaphe adsorption capacity, when MC-LR is present in the water matrix (qe_shared). The phosphate adsorption capacity of BIPGEM-1 was the least affected by the presence of MC-LR as the qe and qe_shared estimated is 0.210 and 0.123 mg·g−1, respectively. For both, ZIPGEM and BIPGEM-1, the qe reduced by about 0.038 and 0.044 mg·g−1, respectively, in the presence of MC-LR. The decrease in the qe,shared from the qe can be explained by a competition between phosphate and MC-LR for the available adsorption sites in the surface of the media. While, the qe, shared slightly increases in CPS by 0.015 mg·g−1. Given the low qe and a higher standard deviation in the qe,shared in CPS, such difference can be more relatable with a variation in the media phosphate adsorption capacity that with the effect by the presence of MC-LR. The maximum adsorption capacity of the sorption media (qo) (i.e., CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2) calculated by the Langmuir isotherm are presented in TABLE 26. In general, a decrease in the MC-LR q0 of the sorption media was observed in Case 2, under the coexistence of MC-LR and phosphate, further implying a competition for the available sorption sites in the surface of the media.
The ΔG°, ΔH° and ΔS° are possible indicators of the nature of adsorption. Given the outperformance of BIPGEM-1 and BIPGEM-2 in the MC-LR adsorption capacity, the thermodynamic properties were further investigated. The ΔH° values for BIPGEM-1 in all cases are positive, indicating that the adsorption is endothermic. While for BIPGEM-2, the ΔH° value indicated that the adsorption is exothermic when the water matrix contains only MC-LR, but when the water matrix phosphate or calcium the adsorption becomes endothermic. The endothermic nature of the MC-LR adsorption to biochar has previously been confirmed by Li et al., (2014). Given the increase in the MC-LR removal efficiency in BIPGEM-1 and BIPGEM-2 and the endothermic nature of the MC-LR adsorption to the sorption media, it can be suggested that the inclusion of biochar was the main contributor in the media for MC-LR removal. The ΔS° indicates affinity between the sorption media BIPGEM-1- and BIPGEM-2 and the aqueous solution. While ΔG° indicates that the MC-LR adsorption to BIPGEM-2 is spontaneous, and in the contrary the MC-LR adsorption to BIPGEM-1 is unspontaneous.
MC-LR in water at most pH (3<pH<12) is mostly negatively charged because of the deprotonation of the carboxyl group (Lawton et al., 2003; Lee and Walker, 2006). On the contrary the surface charge of CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2 are positively charged at pH below 5.6, 9.2, 9.6. and 10, respectively, in accordance with its PZC (TABLE 23). The location of the PZC in ZIPGEM, BIPGEM-1 and BIPGEM-2 can be attributed to the presence of ZVI and ZVI and biochar as part of the sorption media matrix. This is because the location of PZC for iron hydroxide usually lies between 7 and 9 (Wu et al., 2017) and at pH of 10.6 for biochar (as disclosed herein). By considering the force of attraction between oppositely charged particles or Coulombic attraction, the higher adsorption capacity based on the Langmuir isotherm model for ZIPGEM, BIPGEM-1 and BIPGEM-2 in comparison to CPS can be justified (TABLE 26). Previous researchers have explained the interactions between MC-LR and iron particles. For instance, the removal of MC-LR onto iron oxide nanoparticles was examined by Lee and Walker (2011), who concluded that pH strongly affected the adsorption of MC-LR, indicating that the adsorption of MC-LR increased with decreasing pH, thus contributing to the adsorption of MC-LR to iron oxide particles (maghenite) mainly via electrostatic interactions. Moreover, Gao et al. (2012) suggested that the adsorption of MC-LR to iron oxide nanoparticles was spontaneous and endothermic. Additionally, the presence of clay can further aid in the MC-LR adsorption capacity of the sorption media.
The removal efficiency and adsorption capacity of BIPGEM-2 and BIPGEM-1 were the highest among all 4 sorption media, and such improvement can be attributed to the inclusion of biochar in the media. The adsorption of MC-LR to biochar, as shown in
In nature, MC-LR is commonly presented with other compounds including PO43− and Ca2+; for this reason, it is important to understand how its presence can affect the removal efficiency of the sorption media. Based on the fitting of the Langmuir isotherm model, it can be assumed that when MC-LR is alone (Case 1) the adsorption of MC-LR in ZIPGEM and CPS is monolayer, whereas when MC-LR is present with other components (e.g., phosphate and calcium ions), the adsorption is multilayer. Moreover, based on the Freundlich equation, the major effect on the adsorption capacity was observed under the presence of PO43− for CPS because the n value indicated that the adsorption was not favorable. The larger PZC and better physical and chemical characteristics of ZIPGEM, BIPGEM-1, BIPGEM-2 can explain whether in accordance with the Freundlich model, the adsorption was maintained as favorable in the presence of PO43−. By comparing the percentage removal, in these different conditions prescribed, a decrease in the MC-LR removal rates in Case 2 for all sorption media (i.e., CPS, ZIPGEM, BIPGEM-1, BIGPEM-2) can be observed. Such a decrease in removal efficiency of different adsorbents has been previously observed, and it can be attributed to a competition effect of PO43− and MC-LR for the available positive adsorption sites (Li et al., 2014). However, the removal of PO43− was not affected by the presence of MC-LR, suggesting that the interaction in the surface media will favor PO43−.
That said, the presence of cations in the water matrix can enhance the removal of MC-LR, which was observed by comparing the removal efficiencies in Case 3 with the removals in Case 1 for all sorption media. In Case 2, the Ca2+ removal was null, and the concentration maintained constant throughout the isotherm studies, regardless of the influent condition. Gao et al. (2012) suggested that calcium ions slightly enhanced the MC-LR adsorption capacity of the iron oxide nanoparticle. Meanwhile, Liu et al. (2019a) found that metal cation (i.e., Ca2+) on clay surface altered MC-LR adsorption by strengthening the ligand exchange and electrostatic interactions favoring MC-LR adsorption onto surface of kaolinite at lower pH.
Whereas a decrease in the MC-LR removal efficiency of the sorption media is seen in the presence of PO43−, an increase in the MC-LR removal efficiency when Ca2+ is present in water can be observed. However, its difference is not statistically significant within 95% critical interval in accordance with a 2-way ANOVA. These results support the application of the sorption media in a field scale, especially with BIPGEM-1 due to its high simultaneous removal efficiency of MC-LR and PO43− and low production cost.
Dynamic Removal Efficiency with Canal Water:
The dynamic removal efficiency of sorption media with canal water as influent condition was investigated to simulate the adsorption behavior on a field scale. The results of the MC-LR percentage removal by the sorption media CPS, ZIPGEM, and BIPGEM-1 are presented in
The results from the dynamic column studies for CPS, ZIPGEM, and BIPGEM-1 were imputed into the Thomas and MDR dynamic models, and the results are presented in TABLE 29. Given the short removal time for CPS, the MDR dynamic model was not applicable. Conversely, the adsorption capacity (qo) of CPS predicted by the Thomas model was 0.15 μg·g−1; however, given that the Thomas model is based on the Langmuir model, the R2 obtained from the linear regression was low (0.35). For ZIPGEM, the Thomas and MDR models were applied, obtaining R2 of 0.651 and 0.776, respectively. The qo value predicted for ZIPGEM by the Thomas model was 0.97 μg·g−1 and by the MDR model was 0.016 μg·g−1. The R2 for BIPGEM-1 obtained by the Thomas and MDR models were 0.417 and 0.965, and the predicted q0 values were 1.04 and 1.19 μg·g−1, respectively. The lower R2 from the Thomas model fitting can be associated with the assumption of monolayer adsorption in the Langmuir isotherm, which, based on the results of the isotherm study, is not a valid assumption when there are other elements in the water matrix.
By comparing the qo from the dynamic models and the qm predicted from the Langmuir equilibrium isotherms, it can be observed that the adsorption capacities obtained in a dynamic condition are lower (TABLE 27 and TABLE 29). The water matrix characterization used as influent condition in the dynamic column study was performed by the research team. The decrease in the adsorption capacity of the sorption media can be explained by the presence of other contaminants in the influent water matrix because it can result in competition for the available sites between the adsorbents and the adsorbates. For instance, Gao et al. (2012) studied the removal efficiency of MC-LR to iron oxide nanoparticles and concluded that there is a competitive adsorption effect with other compounds, especially compounds containing carboxyl groups (i.e., citric acid, benzoic acid, and oxalic acid) with the effect increasing with a rising number of carboxyl groups. Moreover, Li et al. (2014) and Xiao et al. (2012) indicated that the presence of dissolved organic matter, especially tannic acid, inhibits the MC-LR adsorption capacity of biochar because they can compete for the available mesopore or macropore regions. Furthermore, Dixit et al. (2019) showed that inorganic ions (i.e., nitrate, bicarbonate, and sulphate) compete with MC-LR for the available sites in ionic exchange removal mechanisms, resulting in a reduction of MC-LR removal efficiency. Finally, the negative effect that the presence of phosphate has in the MC-LR removal efficiency of CPS, ZIPGEM, and BIPGEM-1 was further explained.
To respond to the increasing drinking water demand and changing water quality, it is crucial to develop proper treatment for surface water affected by nutrients, metals, and algal blooms. The MC-LR removal efficiencies, and adsorption capacities of 4 sorption media denoted as CPS, ZIPGEM, BIPGEM-1 and BIPGEM-2 for MC-LR at different water matrices were presented. The first advantage of these green sorption media is the low cost of operation and sustainable nature due to the use of recycled materials (e.g., ZVI and biochar). Additionally, these green sorption media have been proven to treat different pollutants simultaneously.
In terms of MC-LR adsorption capacity, the sorption media BIPGEM-2 outperformed BIPGEM-1, ZIPGEM and CPS. The MC-LR adsorption capacity of BIPGEM-2, based on the Langmuir isotherm in Case 1, Case 2 and Case 3 was 29.29, 18.45, and 16.9 μg·g1, respectively. While, given the low production cost of BIPGEM-1, in comparison to BIPGEM-2, the MC-LR adsorption in a dynamic model was investigated and resultant qo is 1.19 μg·g−1 based on the MDR dynamic model. The adsorption capacity of BIPGEM-1 in a dynamic environment is comparable with other adsorbents in literature. For example, in TABLE 30, it can be observed that the adsorption capacity of BIPGEM-1 is comparable with the adsorption capacity of GAC studied in a dynamic environment. The best performance of BIPGEM-2 and BIPGEM-1 for the MC-LR removal can be attributed to a large BET surface area, lower saturated hydraulic conductivity, high porosity, and the location of the PZC. Moreover, the inclusion of biochar in the media mix increases the MC-LR removal efficiency by its pore structure and high PZC in BIPGEM-1 and BIPGEM-2.
However, in a dynamic environment facing a real water matrix, the adsorption capacity of CPS, ZIPGEM, and BIPGEM-1 could be compromised given the presence of dissolved organic matter and inorganic ions, causing a competition for the available adsorption sites. Such an occurrence was also observed in the isotherm studies, indicating that the presence of PO43− decreases the MC-LR removal efficiency of the sorption media. However, the presence of Ca2+ resulted in an increase in the MC-LR removal efficiency. Although these trends were represented by the observed change in the percentage removals, the application of a 2-way ANOVA test concluded that these changes are not significant under a 95% confidence interval, further supporting the application of the sorption media in different environments.
The removal of PO43− was not affected by the presence of MC-LR, and in terms PO43− removal the sorption media ZIPGEM outperformed BIPGEM-1 and CPS. The removal efficiency of ZIPGEM ranged from 55-60%. Although this researcher slightly studied the PO43− removal efficiency of the sorption media, its efficiency to treat PO43− suggests further research to find the adsorption capacity of ZIPGEM and BIPGEM-1. Finally, it can be concluded that the sorption media ZIPGEM, BIPGEM-1 and BIPGEM-2 are a good alternative to treat MC-LR and phosphate in-situ. Given the results, the water matrix needs to be studied before deciding on the appropriate sorption media. For instance, in water with high concentrations of PO43− but low concentrations of algal toxin, the sorption media ZIPGEM may be more appropriate. But, in water with high concentration of algal toxins and DOM but lower PO43− concentration, the filtration media BIPGEM-1 may be more appropriate.
The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and/or take precedence over any such contradictory material.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
This nonprovisional application is a Continuation-in-Part of and claims priority to U. S. Nonprovisional patent application Ser. No. 18/303,973 entitled “COLOR REMOVAL WITH ZIPGEM FILTRATION MEDIA FOR WATER AND WASTEWATER TREATMENT” filed Apr. 20, 2023 by the same inventor, which claims priority to U. S. Provisional Patent Application No. 63/333,310 entitled “COLOR REMOVAL WITH ZIPGEM FILTRATION MEDIA FOR WATER AND WASTEWATER TREATMENT” filed Apr. 21, 2022 by the same inventor, all of which are incorporated herein by reference, in their entireties, for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 63333310 | Apr 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18303973 | Apr 2023 | US |
| Child | 18770246 | US |
