Patent Application
20080076954
The invention is best understood from the following detailed description when read in connection with the accompanying drawing. Included in the drawing are the following figures:
The present invention generally provides a method of removing pharmaceutical active compounds (PACs), such as estrogen hormones and antibiotics, from aqueous solutions using ultrasound. Ultrasound has been applied for years to clean, enhance distribution, or extract. In recent years, ultrasound irradiation of certain power and frequency has been applied to destroy many organic pollutants in water and wastewater systems. Pharmaceutical and personal care product pollutants are a new environmental concern, however, and the possibility that such pollutants might be destroyed in aqueous systems using ultrasound has not been investigated. Specifically, the removal of estrogen hormones from water and wastewater is of importance due to their adverse effects on the ecosystem and potential risks to human health. Certainly, the optimized treatment units; the configuration of the sonicators, probes, reactors, and controlling systems; and the reaction conditions showing efficient effects have not been investigated.
According to the present invention, an ultrasound source of sufficient intensity and energy (power typically between 0.5 to 4 kW and frequency of about 20 kHz) is applied to destroy pharmaceutical pollutants such as estrogen hormones and antibiotics in water and wastewater. The intensity and energy of the ultrasound source are determined before the source is activated (i.e., predetermined). Used are both a 0.6 and a 2 kW system consisting of piezoelectric material. Both horn and probe tip attachments are used on the sonicator and are immersed into the reaction solution. The water containing pharmaceutical pollutants either flows through the reactor or is placed in a batch reactor. The flow rate is controlled to keep the retention time in the reactor at about 10 to 100 minutes (according to the sonication power and pollutant concentration). The flow-through vessel is made of stainless steel and the probe and horn tips are made of titanium alloy. The aqueous solution is irradiated with ultrasound by switching on the ultrasound. The sonication method is completely based on physical phenomena. No pH adjustment is needed and no other chemicals or materials need to be added to the solution.
The present invention also incorporates an analysis of the effect of operational conditions for a suitable sonication method such as temperature, pH, and pressure. The reaction rate of individual compounds in a mixture of estrogens was investigated. The effect of sonolysis on estrogen degradation in industrial wastewater was also examined.
The present invention is best discussed in the context of experimental examples. The following examples are included to more clearly demonstrate the overall nature of the invention. These examples are exemplary, not restrictive, of the invention.
The estrogen hormones used for purposes of experimentation were obtained from Sigma-Aldrich Co. of St. Louis, Mo.; Steriloids, Inc. of Wilton, N.H.; and from pharmaceutical companies. They were (minimum purities): 17α-estradiol (98%), estrone (100%), estriol (100%), equilin (99.9%), 17α-dihydroequilin (99.4%), 17β-estradiol (97.1%), 17α-ethinyl estradiol (99.1%), gestodene (99.3%), norgestrel (100%), levonorgestrel (100%), 3-O-methyl estrone (used as internal standard, 98%), and medrogestone (99.8%). All solvents were High Performance Liquid Chromatography (HPLC) grade and, along with other chemicals, were purchased from Fisher Scientific Company L.L.C. of Pittsburgh, Pa. Amber glass bottles were also obtained from Fisher Scientific. Varian Bond Elute 3 ml/500 mg solid-phase extraction (SPE) cartridges were obtained from Varian, Inc. of Palo Alto, Calif. All the glassware used for sonication reaction and analysis were silanized as described elsewhere. See, for example, R. Chimchirian et al., “Analysis of low level of free and conjugated synthetic and natural estrogen hormones in water and wastewater,” WEFTEC (Washington, D.C., 2005) (later, “R. Chimchirian et al., ‘Analysis’”). The wastewater was sampled from a pharmaceutical wastewater treatment plant effluent.
Two different sonication reactors, both 20 kHz, were used in this study: a 0.6 kW reactor and a 2 kW reactor. The 0.6 kW unit was used in a batch system in which the solution was kept under ultrasound irradiation for a certain reaction time. The 2 kW unit was used in a continuously flowing reactor in which the solution was passed with a flow rate corresponding to a certain retention time. Horn (45 mm diameter) and probe (10 mm diameter) tip attachments were tested in 250 ml solution in the 0.6 kW system. Approximately 0.28 kW power was applied to the reaction solution, which represents an ultrasound density of 1.12 W/ml. The ultrasound intensities were 18 and 357 W/cm2 for the horn and tip assemblies, respectively.
The 2 kW unit had a working volume of 155 ml with the horn attachment (55 mm diameter) and 200 ml with the probe attachment (35 mm diameter). The power applied to the reaction solution was 0.32 kW, which represents ultrasound intensities of 13 and 33 W/cm2, and ultrasound densities of 2.06 and 1.60 W/ml, with the horn and probe assemblies, respectively. The flow-through vessel was made of stainless steel and the probe and horn tips were of titanium alloy. Both the 0.6 and 2 kW systems consisted of piezoelectric material. In the temperature-controlled experiments, a water bath was used outside the reactor to keep the temperature of the reaction solution at about 20° C.
The estrogen solution was prepared by spiking a certain volume of stock solution into water purified using a Milli-Q® ultrapure water system available from Millipore Corporation of Billerica, Mass. 200 ml of the solution was sampled periodically and placed into a silanized amber glass bottle. 3-O-methyl estrone was spiked in each sample as the internal standard. The samples were stored in the refrigerator for no more than 24 hours before extraction. The pH of the solutions was adjusted with HNO3 and NaOH.
The SPE was followed by Gas Chromatography/Mass Spectrometry (or GC/MS) for quantitative analysis of estrogen compounds. In simple terms, a GC/MS instrument represents a device that separates chemical mixtures (the GC component) and a very sensitive detector (the MS component) with a data collector (the computer component). The SPE was preformed using the Varian Bond Elute C-18 adsorbent cartridge. The cartridges were activated using 3 ml of methanol and rinsed with 3 ml of Milli-Q water prior to loading the sample. A 200 ml sample containing the estrogen compounds was passed through the SPE cartridge at a flow rate of 5 ml/min (with a vacuum pump). 3 ml of Milli-Q water was used to rinse the cartridges and then they were eluted with 3 ml of methanol into a test tube. For the wastewater sample, a 3 ml mixture of Milli-Q water and methanol (60:40, v/v) was used to rinse the cartridges in order to prevent interference from the background matrix. The eluent was completely dried using a Genevac EZ-2 personal evaporator and then derivatized by using bis(trimethylsilyl)trifluoro-acetamide for GC/MS analysis. For an explanation of this technique, see R. Chimchirian et al., “Analysis.”
The GC/MS analysis was performed using an Agilent 6890N GC and a 5973N MS. The auto split-less injections were made onto a Pursuit DB-225MS capillary column (30 m×0.25 mm×0.25 μm; J & W Scientific brand available from Agilent Technologies, Inc. of Santa Clara, Calif.) with an initial temperature of 50° C. for 1 minute, and a flow of 4.5 ml/minute, then ramped to 200° C. at 50° C./min with a flow of 4.5 ml/min and held for 45 minutes. Finally, the oven temperature was ramped to 220° C. at 10° C./min and held for 14 minutes. The post run was held at 240° C. for 10 minutes, with a flow of 4.8 mL/min. Helium was used as a carrier gas. The sample injection volume was 4 μl. The inlet and source temperature was 240° C. with a relative source voltage of 1447. The quad was set at 150° C.
Calibration standards were made by spiking appropriate amounts of hormones into 200 ml of Milli-Q water. The coefficient of determination (r2) value was 0.99 or greater for calibration curves. All the data reported were the average of duplicate analyses.
The previous study reported by R. Chimchirian et al., “Analysis,” has shown that, with the above analytical procedure, the recovery efficiencies of all the analytes were higher than 95%, with the exception of ethinyl estradiol and levonorgestrel/norgestrel (levonor/nor). The recovery efficiencies of these two cases were 86% and 81%, respectively. The relative standard deviation (RSD) was less than 2.5% in triplicate analysis. The quantization limit was 0.03 μg/L for all of the compounds using a 200 ml sample, except for equilin, levonorgestrel/norgestrel, and gestodene, in which cases the limits were 4.0 μg/L, 0.87 μg/L, and 0.87 μg/L, respectively. Levonorgestrel and norgestrel were reported together because they co-eluted from the GC column and had the same mass-to-charge ratios.
The destruction of estrogen compounds in the Milli-Q water is shown in
a)yalkowski 1992,
b)Hansch 1996,
c)Hansch 1995,
d)Meylan 1995,
e)Meylan 1996,
f)Merck 1996,
g)Meylan 1991,
h)Pinsuwan 1997.
The effect of pH on estrogen degradation in the 2.0 kW sonolysis system was examined with a total initial estrogens concentration of 50 μg/L. The results are shown in
The kinetics of sonication of estrogen compounds was studied in the 2.0 kW system with initial individual compound concentrations of 1 and 10 μg/L, and pH levels of 3, 7, and 9. The first or zero-order reaction sonolysis degradation rates of many pollutants have been reported. See Y. Adewuyi, “Sonochemistry: Environmental Science.” It is also reported that the degradation rate constant might be variable with the initial concentration of some pollutants. The first order rate constants tend to decrease, while zero-order rate constants increase, when the initial concentration increases. See Y. Adewuyi, “Sonochemistry: Environmental Science”; see also A. Kotronarou et al., “Oxidation of hydrogen sulfide in aqueous solution by ultrasonic irradiation,” Environmental Science and Technology, 26, pp. 2420-26 (1992). Y. Adewuyi also discussed the change from zero-order to first order degradation rate.
It was observed that the degradation of all estrogen compounds under the tested concentrations and pH could be described with the pseudo first-order kinetics. The pseudo first-order rate constant of each compound under these conditions (including 2.0 kW sonolysis of a mixture of the compounds in Milli-Q water with an ultrasound density of 2.06 W/ml) is shown in Table 2. The order of degradation tendency at pH 7 was: 17α-dihydroequilin>17α-estradiol>equilin>estrone>17β-estradiol>ethinyl estradiol>gestodene>levonorgestrel/norgestrel.
Table 2 shows that, in the estrogen multi-component system, the reaction rate constant K for the individual estrogen compound does not change significantly with pH or initial concentration in the range of 1 to 10 μg/L. For example, at pH levels of 3, 7, and 9, the first-order rate constant for 17α-estradiol was 0.17, 0.14, and 0.14 per minute, respectively, for an initial concentration of 10 μg/L. When its initial concentration decreased from 10 to 1 μg/L at pH 7, the first-order rate constant changed from 0.14 to 0.15 per minute. From the results in Table 2, it can be determined that the average of the rate constants for all estrogens at 1 μg/L initial concentration was 0.13±0.04 per minute at pH-7. The average of the rate constants for all estrogens at 10 μg/L initial concentration were 0.17±0.07, 0.11±0.06, and 0.11±0.03 per minute at pH levels of 3, 7, and 9, respectively.
The octanol-water partition coefficient, Kow, is the ratio of the concentration of a chemical in octanol and in water at equilibrium and at a specified temperature. Octanol is an organic solvent that is used as a surrogate for natural organic matter. This parameter is used in many environmental studies to help determine the fate of chemicals in the environment. An example would be using the coefficient to predict the extent a contaminant will bioaccumulate in fish. The octanol-water partition coefficient has been correlated to water solubility; therefore, the water solubility of a substance could be used to estimate its Kow.
No good correlation (r2 higher than 0.8) was observed between rate constants and physicochemical properties, seen in Table 1, such as solubility, Kow, and Henry constant. This may be partly due to possible inaccuracies in the literature-reported property data. There have been some concerns about the quality of the basic physicochemical data such as Kow and solubility. See, for example, R. Renner, “The Kow controversy,” Environmental Science and Technology, pp. 411A-413A (2002).
An acceptable correlation between the rate constants (K) and molecular weights (MW) of the estrogens was observed in clean water under the tested conditions, however, and is shown in
Estrone is one of the most frequently detected estrogen compounds in natural systems. It can be produced naturally in the body, or from the breakdown of other estrogens. In this study, the ultrasound-induced degradation rate constant of estrone was applied to predict that of the other estrogens. The correlation between rate constant and molecular weight is shown in
K/K
estrone
=a×(MWe/MWestrone)+b (Equation 1)
In Equation 1, K is the rate constant of any estrogen compound and Kestrone is the experimental rate constant of estrone. MWe and MWestrone are the molecular weights of estrogen and estrone, respectively. Using Equation 1, the first order rate constant of any other estrogen compound during ultrasound-induced degradation can be predicted based on the experimental rate constant of estrone, as shown in Equation 2, in which Kpredict is the predicted rate constant for any estrogen compound. The values of constants a and b were determined to be −3.9155 and 4.9509, respectively, under pH 7 conditions.
K
predict
=[a×(MWe/MWestrone)+b]×Kestrone (Equation 2)
Table 3 lists the predicted rate constant of each estrogen compound, using Equation 2, and the percentage error. The data were generated using sonolysis of a mixture of estrogen compounds in Milli-Q water. The initial concentration of the individual compounds was 10 μg/L, the ultrasound density was 2.06 W/ml, and the pH was 7.
Table 3 shows that the predicted data were quite close to the experimental data. The error was not more than 18%, indicating the effectiveness of a prediction method using molecular weights. In
Due to cavitation effects, the temperature of the solution can increase in batch systems during the sonolysis process if there is no temperature control. Under 0.6 kW sonolysis in the batch system, the temperature of the solution reached 85° C. from 20° C. in 30 minutes with a horn attachment, and reached 37° C. in 30 minutes with a probe attachment, absent temperature control.
The horn-attached system has a higher surface area and correspondingly lower ultrasound intensity (18 W/cm2) compared with the probe-attached system (357 W/cm2).
The application of a probe versus horn assembly was evaluated for transferring the ultrasound energy into the water for both 0.6 and 2 kW sonicator units. Batch experiments were performed with a 0.6 kW unit operating at 20 kHz; the unit delivered between 130 to 140 watts to the solution containing estrogens. Horn (45 mm) and a probe (10 mm) tip attachments were tested in 250 ml solution with the 0.6 kW system, and the results were compared. Approximately 0.28 kW power was imparted to the reaction solution, which represents an ultrasound density of 1.12 W/ml. The ultrasound intensities were 18 and 357 W/cm2 for the horn and probe assemblies, respectively.
The effect of fluid pressure on degradation was tested in the 2 kW system where the pressure in the flow-through vessel was increased from 0 to 30 psig by manipulating the hydraulic system. The higher fluid pressure had an adverse effect on degradation of the compounds. The first reason may be due to the retarded cavitation effects. An increase in pressure within the system would require more energy to create a cavity, as may be determined from Equation 3, and cause lower frequency or efficiency of bubble formation. See Y. Adewuyi, “Sonochemistry: Environmental Science.”
I=Pa
2/2ρc (Equation 3)
In Equation 3, I represents the acoustic intensity (W/cm2), Pa is the acoustic pressure (pressure in the bubble at the moment of transient collapse), ρ is the density of the fluid (water in this study), and c is the speed of sound in the fluid (1500 m/s in water). The term ρc reflects the acoustic impedance of the medium and is 1.5×106 kg/m2s. At higher fluid pressure, Pa increases and higher ultrasound intensity is needed to achieve cavity collapse.
A second possible reason why higher fluid pressure had an adverse effect on degradation of the compounds is that, with the flow rates that were used, the increase in transferred power also increased the solution temperature which is detrimental to the reaction rate as stated earlier. Specifically, with the fluid pressure at 30 psig, the temperature of the system increased to nearly 40° C.
The destruction of estrogen hormones in wastewater was also examined using a 0.6 kW sonolysis system. In this study, the estrogen compounds were spiked into a pharmaceutical wastewater, which was then irradiated with ultrasound.
Table 4 shows that, in the wastewater system with higher initial concentration, the reaction rate was slower than that in the clean water systems with lower initial concentration. This may result from lower ultrasound power, higher estrogen concentration, and the matrix effects in the wastewater samples. The reaction was also slower due to possible interference of the accumulated by-products in the system. Furthermore, the presence of many other organic and inorganic chemicals (unidentified) may create competition for free radicals. The competition may not affect each estrogen identically. Therefore, matrix effects may be important and should be considered when evaluating sonication for use in wastewater treatment systems.
The average of first-order rate constants of all estrogens in the wastewater was 0.011±0.005 per minute, which was only 10% the average of the rate constant observed in clean water. Moreover, the difference (deviation of 0.005 per minute) among the reaction rate constants in wastewater at higher initial concentration was insignificant when compared to the clean water systems (deviation of 0.06 per minute) at pH 7 with 10 μg/L initial concentration. It may be possible to enhance degradation rate with higher-power ultrasound systems.
In summary, a sonication method as defined by the present invention is an effective method for removal of estrogen hormones in aqueous system. The ultrasound-induced destruction of estrogen compounds in aqueous solutions was studied in a batch reactor using a 1.12 W/ml sonication unit and in a continuous flow reactor using a 2.06 W/ml sonication unit. The degradation of the compounds can be simulated with the pseudo first-order reaction in both clean water and wastewater. The order of degradation tendency at pH 7 in clean water was: 17α-dihydroequilin>17α-estradiol>equilin>estrone>17β-estradiol>ethinyl estradiol>gestodene>levonorgestrel/norgestrel. The average rate constants at 10 μg/L initial concentration were 0.17±0.07, 0.11±0.06, and 0.11±0.03 per minute at pH 3, 7, and 9, respectively.
No significant change in degradation rate constant occurred for different initial analyte concentrations of 1 μg/L or 10 μg/L. The degradation rate constant decreased slightly with molecular weight increase. Accordingly, the destruction of estrogens can be predicted, with acceptable agreement, based on the experimental degradation of estrone. Higher solution temperatures and fluid pressures were detrimental to destruction efficiencies. The order of degradation tendency in wastewater was somewhat different from that in clean water, probably due to high estrogen concentration and matrix effects in wastewater samples. The order of degradation tendency of estrogens in wastewater is 17α-dihydroequilin>equilin>ethinyl estradiol>levonorgestrel/norgestrel>gestodene>17α-estradiol=17β-estradiol>estriol=estrone. The average first-order rate constants of all estrogens in the wastewater under 0.6 kW sonolysis was 0.011±0.005 per minute.
The ultrasound method according to the present invention has a number of practical applications. For purposes of illustration, and without limitation, a number of those applications are highlighted below.
The method can be used to destroy PPCPs in water and wastewater systems, including surface water, groundwater, raw drinking water, municipal wastewater, and industrial wastewater (hospital, pharmaceutical). More specifically, the ultrasound method can efficiently decontaminate (e.g., destroy estrogen hormones in) high strength and small volume wastewaters at hospitals, nursing homes, and pharmaceutical production plants where the wastewater containing hormones and pharmaceuticals is initially generated. It can also be used to destroy natural hormones present in the wastewater generated at the International Space Station where the goal is to capture and recycle all the fluid excreted from the human body.
The method can be applied during drinking water treatment procedures to remove any PPCPs in the water source, especially those PPCPs that cannot be removed with conventional drinking water treatment methods. The method can be applied for drinking water purification to remove trace level estrogen compounds that have potential adverse effects on human health. Thus, the method can remove trace levels of pharmaceutical contaminants from drinking water.
With the application of the method, release of pharmaceutical pollutants from pharmaceutical industries and municipal wastewater treatment plants and other sources can be minimized if not eliminated. The ultrasound method of destroying hormones can also be used as a supplement to other existing conventional (e.g., municipal) wastewater treatment techniques, either pre-treatment to remove toxic compounds to favor biodegradation, or post-treatment to remove environmental unfriendly chemicals before the effluent enters receiving water bodies or is reused for irrigation. More specifically, the method can be applied as the post-treatment after conventional biological treatment units to remove any remaining PPCPs in the system.
The method can be applied prior to conventional biological units during industrial and municipal wastewater treatment for PPCPs destruction. It is of benefit to remove the targeted pharmaceutical compounds from the wastewater influent, to desorb the adsorbed PPCPs from solid particles, and to degrade the toxic or high strength PPCP compounds to smaller molecules that have enhanced bio-degradability for the following bio-treatment steps. In addition, treatment of the influent stream will prevent the sorption of PPCPs to the biosolids (sludge). Hence, the production of contaminated sludge can be prevented.
An important potential application observed from experiments conducted is that the ultrasound method has the ability to destroy chemicals that are sorbed onto contaminated sludge in wastewater. Hence, the method can be used to clean contaminated sludge in wastewater treatment plants. Data show that a pharmaceutical compound sorbed to (“stuck on”) wastewater sludge can be destroyed using the ultrasound method, i.e., the sludge can be “cleaned” by destroying the sorbed contaminant with ultrasound.
To test experimentally whether ultrasound helps in the degradation of the pharmaceutical compound hexachlorophene (HXC) present in sludge, the solid and liquid phases of sludge were analyzed individually both before and after the application of ultrasound. Sludge was initially spiked with HXC and a part of the sludge was taken for unsonicated sludge tests (i.e., dry suspended solid, or DSS, concentration) and analysis of the concentration of HXC in the two phases of the unsonicated sludge. The solid and liquid phases from the unsonicated sludge were analyzed. The remaining spiked sludge was sonicated. After 90 minutes of sonication, the sonicated sludge was analyzed for DSS and HXC concentration in a similar manner as done for the unsonicated sludge.
Sludge contaminated with HXC was treated with ultrasound, and the results are shown in Table 5. The amount of contaminant sorbed onto the sludge before and after the sonication process was measured. The experiment was conducted twice to test the reproducibility of the experiment. The results are reproducible because the percentage of the pharmaceutical compound removed is 74 to 82%. Results show that the mass of the contaminant in the sludge (liquid and solid phases combined) dropped by 70-80%, showing the degradation effect of ultrasound on contaminant present in the sludge.
Along with the destruction of the pharmaceutical compound in the sludge, a side outcome observed was the enhancement in the biodegradability and dewaterability of the sludge. This may be observed from Table 5, column 5, as the amount of solids in the sludge reduced tremendously after sonication. This result suggests the feasibility of a sludge-less reactor. Because sludge disposal is a costly problem, minimizing the sludge to almost zero sludge would be a positive direction in the reduction of operational costs in wastewater treatment facilities.
Biological oxidation demand (BOD) tests on the unsonicated and sonicated sludge were also performed. BOD commonly serves as a measure of pollution. From BOD tests completed for sludge before and after sonication,
The volatile suspended solids (VSS) during aerobic processes of unsonicated and sonicated sludge were also measured. VSS indicates the biodegradable fraction of the sludge. Higher VSS content indicates the higher bacteria activity and higher degradability of the background pollutants. From VSS tests completed in similar aerobic reactors for sludge before and after sonication,
There have been some recent studies reported by others regarding application of ultrasound in improving the biodegradability of sludge and zero sludge reactors. As to the former, see P. Marjoleine et al., “Evaluation of current wet sludge disintegration techniques,” Journal of Chemical Technology & Biotechnology, 73(2), pp. 83-92 (1998); and U. Neis, “Ultrasound in water, wastewater and sludge treatment,” Water 21, 4, pp. 36-39 (2000). As to the latter, see S. Yoon et al., “Incorporation of ultrasonic cell disintegration into a membrane bioreactor for zero sludge production,” Process Biochemistry, 39(12), pp. 1923-29 (2004). There have also been research papers on the application of ultrasound to increase sludge dewaterability, by studying the decrease in capillary suction time of the sludge after the application of ultrasound. See T. Hall, “Sonication induced changes of particle size and their effects on activated sludge dewaterability,” Environmental Technology Letters, 3, pp. 79-88 (1982); and X. Yin et al., “A review on the dewaterability of bio-sludge and ultrasound pretreatment,” Ultrasonics Sonochemistry, 11(6), pp. 337-48 (2004).
The experimental data outlined above support an improvement, however, namely the simultaneous benefit of “cleaning” or decontaminating the sludge by destroying the pharmaceutical contaminants, while converting the sludge into a form which is easily biodegradable. This process of ultrasound is applicable to decontaminate sludge or sediments generated from drinking water, municipal wastewater, and industrial wastewater treatment plants.
In addition to the advantages outlined above for the ultrasound method according to the present invention, among the other advantages are:
a. The method is simple to use. The user simply activates (typically, using a switch) the reactor to treat the water. There is no hazardous or complicated operation requiring skilled labor. Thus, the method can be easily operated with immediate on/off by central control.
b. The equipment necessary to implement the method is reliable.
c. The equipment necessary to implement the method has a small footprint and is modular in design, such that additional units can be added easily. Unlike some other methods, the implementing equipment does not need much space. Instead, the method is very convenient to apply in small areas such as in hospitals and pharmaceutical manufacturing rooms where the estrogen-contaminated wastewater is first generated.
d. The method provides a high destruction effect on toxic and highly potent pharmaceutical and personal care chemicals and, more specifically, can destroy a variety of different estrogen hormones.
e. The method does not require any chemical additives.
f. The method does not require any pH adjustment.
g. The method does not require any filtration.
h. The method does not produce any waste sludge. This is a major advantage over biological processes which generate sludge that mandates disposal—generally as hazardous waste.
i. The method does not produce any off gases. This is a major advantage over processes such as those using ozone in which the unused ozone in the off-gas must be destroyed and the residual ozone in the treated water must be removed.
j. The method is not limited by water and wastewater characteristics such as turbidity, color, or suspended solids.
k. The method can be applied as either a pre-treatment or a post-treatment in combination with other water purification processes.
l. It is feasible to apply the method to different environmental matrices and work sites.
Although illustrated and described above with reference to certain specific embodiments and examples, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention. It is expressly intended, for example, that all ranges broadly recited in this document include within their scope all narrower ranges which fall within the broader ranges.
