Patent Application
20160347630
This invention relates to a system 20 and method for the simultaneous removal and recovery of ammonia and phosphorus from wastewater using magnesium chloride to precipitate phosphorus from wastewater.
Municipal and agricultural waste disposal is a major problem. Feedlots, animal barns, agroindustrial plants, municipal sewage, and farms that keep large numbers of animals are sources of enormous quantities of organic waste. The disposal of untreated organic waste causes serious pollution problems which include those tied to the wastes high content of chemically oxidizable components, expressed as COD or chemical oxygen demand, and BOD, biological or biochemical oxygen demand. When these pollutants reach bodies of water, either because they leach from disposal sites or as a consequence of being directly released or transported into water bodies, they deoxygenate the receiving waters and impair the receiving waters' capability to support aquatic life.
Acidity and high pathogen content add to the COD and BOD problems of untreated waste disposal. Acrid gases released into the atmosphere are not only unpleasant but they can also contribute to acid deposition, global greenhouse effects, and ozone depletion.
For agricultural animals, the animals are confined in high densities and lack functional and sustainable waste treatment systems. The liquid wastes are generally treated in large anaerobic lagoons with intermittent disposal through land applications (Stith, P. and Warrick, J., Boss Hog, North Carolina's pork revolution, The News & Observer, 1-3, Feb. ‘9-26, 1995; USEPA, Proposed regulations to address water pollution from concentrated animal feeding operations, EPA 833-F-00-016, January 2001, Office of Water, Washington, D.C., 20460). This system was developed in the early and mid-20th century prior to the current trend in high concentrated livestock operations. One of the main problems in sustainability is the imbalance of nitrogen (N) and phosphorus applied to land (USEPA, supra; Cochran et al., Dollars and Sense: An economic analysis of alternative hog waste management technologies, Environmental Defenses, Washington D.C., 2000). Nutrients in manure are not present in the same portion needed by crops, and when manure is applied based on a crop's nitrogen requirement, excessive phosphorus is applied resulting in phosphorus accumulation in soil, phosphorus runoff, and eutrophication of surface waters (Heathwaite et al., A conceptual approach for integrating phosphorus and nitrogen management at watershed scales, J. Environ. Qual., Volume 29, 158-166, 2000; Sharpley et al., Practical and innovative measures for the control of agricultural phosphorus losses to water: An overview, Journal Environ. Qual., Volume 29, 1-9, 2000; Edwards and Daniel, Environmental impacts of On-Farm Poultry Waste Disposal-A Review, Bioresource Technology, Volume 41, 9-33, 1992).
Conservation and recovery of nitrogen (N) and phosphorus from wastes is important in agriculture because of the high cost of commercial fertilizers. One of the largest environmental concerns with livestock and poultry production is the loss of ammonia gas (NH3) from manure (Aneja et al., Measurement and analysis of atmospheric ammonia emissions from anaerobic lagoons, Atmos. Environ., 35, 1949-1958, 2001; Paerl, Coastal eutrophication and harmful algal blooms: Importance of atmospheric deposition and groundwater as “new” nitrogen and other nutrient sources. Limnol. Oceanogr. 42, 1154-1165.1997) Phosphorus (P) build-up in soils to excessively high levels due to animal manures often results in eutrophication and pollution of surface waters. Nutrient pollution in the waterways is one of the United States’ most challenging environmental problems. It is caused by too much nitrogen and phosphorus runoff or discharges into the environment. Nutrient pollution has diverse and far-reaching effects on the economy of the United States, impacting many sectors that depend on clean water. The U.S. tourism industry loses about $1 billion each year, mostly from losses in fishing and recreational activities because of nutrient-polluted water bodies. As a result of phosphorus pollution, algal blooms in drinking water sources can drastically increase treatment costs and shortages in water supplies.
Phosphorus (P) build up in soils to excessively high levels due to animal manures often results in eutrophication and pollution of surface waters. Therefore, the ability to extract phosphorus from manure will be critical to the ability to accomplish waste utilization through land application without elevating soil phosphorus levels. Production of biogas from manure using anaerobic digesters (AD) is projected to be important in the future. If a new technology could be developed to recover concentrated phosphorus from AD effluents that can be removed from the watershed, then producers will also benefit from the sale of water quality credits in emerging nutrient credit programs being established through the United States of America. Another environmental and regulatory concern is the excess nitrogen (N) from the manure in confined livestock production, so farmers will be much more willing to adopt new technology for manure that addresses phosphorus and nitrogen in conjunction
U.S. Pat. No. 6,1777,077 (Lee et al.) and U.S. Pat. No. 6,200,469 (Wallace) both relate to the removal of nitrogen and phosphorus from wastewater wherein the phosphate is removed using microorganisms in aerobic tanks which absorb the phosphorus released from denitrified wastewater. See also U.S. Pat. No. 6,113,788 to Park et al; U.S. Pat. No. 6,117,323 to Haggerty; U.S. Pat. No. 6,139,743 to Park et al.
U.S. Pat. No. 6,893,567 (Vanotti et al.) is directed to a system for treating wastewater to at least reduce the amount of ammonia and phosphorus, as well as reducing the presence of infectious microorganisms by using a nitrification step to reduce or eliminate carbonate and ammonium buffers contained in the wastewater, precipitating phosphorus using an alkaline earth metal and increasing the pH of the wastewater. See also U.S. Pat. No. 7,674,379 (Vanotti et al.).
Szogi et al. developed a treatment process to recover nutrients from animal wastes. The process extracts phosphorus from solid animal wastes such as, for example, poultry litter or animal manure solids (Szogi et al., U.S. Pat. No. 8,673,046, Mar. 18, 2014). The first step of this process extracts phosphorus from solid animal wastes using mineral or organic acids. In the second step, phosphorus is recovered by the addition of liquid lime and an organic poly-electrolyte to the liquid extract to form a calcium-containing phosphorus precipitate.
While various systems have been developed for removing NH3 and phosphorus from wastewater, there still remains a need in the art for different abatement systems that removes both NH3 and phosphorus and recovers both in a concentrated pure form. The present invention, different from the related art,—provides such systems 20 using hydrophobic gas-permeable membranes and circulated stripping solutions to produce an effluent that can be treated with phosphorus precipitating compounds to recover up to 100% of the phosphorus present in wastewater.
It is therefore an object of the present invention to provide a system 20 for at least reducing levels of NH3 and phosphorus from ammonia- and phosphorus-containing liquid effluents and recovering nitrogen and phosphorus in a purified and concentrated form.
Another object of the present invention is to remove phosphorus using systems 20 that do not require large capacity airflow handling systems.
A still further object of the present invention is to provide a system 20 for at least reducing the levels of NH3 and phosphorus from ammonia- and phosphorus-containing effluents using systems 20 that captures NH3 in a circulated stripping solution in membrane manifold 15 and precipitates phosphorus by the addition of a phosphorus precipitating agent to liquid effluent that has reduced levels of NH3 and a high pH caused by low-rate aeration of the effluent.
A still further object of the present invention is to provide a system 20 for at least reducing the levels of NH3 and phosphorus from ammonia- and phosphorus-containing effluents using systems 20 that captures NH3 in a circulated stripping solution in membrane manifold 15 and precipitates phosphorus by the addition of MgCl2 to liquid effluent in said anaerobic digester 23.
Further objects and advantages of the invention will become apparent from the following description.
The present invention uses gas-permeable membrane technology disclosed in U.S. Pat. No. 9,005,333 (Apr. 14, 2015; herein incorporated by reference in its entirety) that captures and recovers the ammonia from wastewater. The ammonia removal is done with low-rate aeration in the reactors that increases the pH of the liquid and accelerates the rate of passage of NH3 through submerged microporous hydrophobic gas-permeable membrane manifold 15 (
In the second embodiment, the phosphorus precipitating compound is added to tank 46 and effluent containing precipitated phosphorus flows to tank 48 where the phosphorus solids are recovered from the treated effluent (
In the third embodiment, the phosphorus precipitating compound is added to tank 48 and the precipitated phosphorus is recovered from tank 48 (
As used in the specification and claims the singular form “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a membrane manifold” includes a plurality of membrane manifolds.
As used in the specification and claims, the terms “about” and “approximately” mean to be nearly the same as a referenced number or value. As used herein, the terms “about” and “approximately” should be generally understood to encompass ±10% of a specified amount, frequency or value. Further, all number expressing the quantities used the specification and claims, for example, concentrations, reaction conditions, time, temperature and yield, are modified by the term “approximately” unless otherwise indicated. As used herein, when a numerical range is given, both ends of the range are included.
The term substantial or substantially mean of real worth or importance, or considerable value For example, a substantial increase or decrease means a change greater than 5% of the previous measured value.
For purposes of the present invention the recitation “low rate aeration” is defined as an aeration rate that is less than about 5% of the aeration rate used for biological ammonia removal/nitrification.
For purposes of the present invention, the term stripping solutions is defined as acids, such as organic acids including citric, oxalic, lactic, etc., for example; mineral acids including sulfuric, hydrochloric, nitric, phosphoric, for example; and mixtures of both mineral and organic acids and their precursors such as sodium bisulfate, sulfur, corn silage, molasses and carbohydrates and mixtures thereof. Approximately 1 normal acid solutions are preferred. Furthermore, stripping solutions can be water that is acidified by the fixation of gaseous carbon dioxide into the stripping water to form carbonic acid and further combination with gaseous ammonia to form ammonia bicarbonate.
For purposes of the present invention, a membrane manifold includes multiple membranes connected in parallel through a stripping solution splitter or in series through a connector (See U.S. Pat. No. 9,005,333, FIGS. 9A and 9B for example).
For purposes of the present invention the term liquid effluent is any liquid containing ammonia and phosphorus and includes water, municipal waste, livestock waste, manufacturing waste, etc.
For purposes of the present invention, the membrane assembly 15 functions as a passive getter for ammonia and as the ammonia is captured, production of more ammonia from non-volatile NH4 occurs until at least 50% of the NH4 is converted to NH3.
For purposes of the present invention the phosphorus precipitating agent is any chemical that precipitates phosphorus in a system that captures ammonia and uses a low-rate aeration to control pH in wastewater. Examples of a phosphorus precipitating agent include, but are not limited to, MgCl2, Mg(OH)2, Ca(OH)2, etc.
For purposes of the present invention the term stripping solution tank/ammonia concentrating reservoir 2 is defined as any size, non-reactive container for the storage of acid used in the present invention.
Modern animal production is an extremely sophisticated business and the management, treatment, purification, and appreciation of its by-products should also be so. As the practice of intensive production in enclosed areas grows, such as for example, stables, poultry houses, or pen facilities, there is an increasingly urgent need for effective and affordable alternatives for management of nutrient by-products.
The removal and recovery of NH3 and phosphorus is a desirable feature because it can be exported off the farm which solves the problems of nitrogen and phosphorus surpluses in concentrated livestock production regions. The present invention uses gas-permeable membranes manifold 15 that is submerged in wastewater. As shown in
The ammonia removal is done with low-rate aeration in the reactors that increases the pH of the liquid and accelerates the rate of passage of ammonia through the submerged gas-permeable membrane manifold and further concentration in an acid stripping solution. The effluent after ammonia treatment has a high pH of about greater than 9. The higher pH is the result of the destruction of the alkalinity with low aeration that strips the CO2 and the conversion of NH4+ to NH3 and removal of NH3 thru the membrane. Phosphorus precipitating compounds such as for example, magnesium chloride, MgCl2, is added to system either before or after ammonia removal.
In the first embodiment of the present invention, a phosphorus precipitating compound such as for example, MgCl2 is added to the effluent after ammonia removal in tank 48 in amounts equivalent to or higher than the phosphorus concentration in the effluent on a concentration basis. The amount of phosphorus in the effluent can be determined using an on-line phosphorus analyzers (not shown) (
In a second embodiment of the present invention, a phosphorus precipitating compound, such as for example, MgCl2 is added to the digester effluent in tank 46, mixed quickly using in-line mixers, mechanical mixers 17, or by the action of aeration turbulence inside the tank 46 (
In a third embodiment of the present invention, a phosphorus precipitating compound such as for example MgCl2, is added to the effluent after ammonia removal in tank 48 (
The following examples are intended only to further illustrate the invention and are not intended to limit the scope of the invention which is defined by the claims. Liquid swine manure and municipal wastewater and phosphorus precipitating compounds MgCl2 and Ca(OH)2 are used as a model to exemplify the system 20 of the present invention. System 20 can be used with any liquid effluent where NH3 and phosphorus is produced and/or accumulated.
In this example, MgCl2 is added to phosphorus recovery tank 48 (
In a second step, the treated effluent from tank 46 was then transferred to phosphorus separation tank 48 where it was mixed with MgCl2 to obtain a phosphorus precipitate and an effluent without phosphorus and ammonia. The rates of MgCl2 applied were calculated based on the initial phosphorus concentration in the wastewater which was about 400 mg/L to obtain a Mg:P ratio of about 1. One of the phosphorus separation tanks 48 received alkali, approximately 10 mmol NaOH, after the addition of MgCl2 to increase the pH to approximately 9.2. First the MgCl2 treatment was added to the effluent, then NaOH alkali was added to the same vessel 48 while mixing with a stirrer (not shown). The chemicals were reacted with the effluent by mixing with a stirrer (not shown) for about one minute. After about a 0.5 hours gravity sedimentation period, the treated effluent in both treatments were sampled in the supernatant and analyzed for phosphate, ammonium, total phosphorus, and total nitrogen. The phosphorus precipitate was dewatered using glass fiber filters, dried, and characterized for total N using TKN acid digestion; P, Mg, Ca, and K using ICP digestion; and plant available phosphorus using citrate soluble P. Mass balances were conducted to calculate recoveries of nitrogen and phosphorus by measuring flows and concentrations in the inflow and the outputs of system 20. All experiments were duplicated. The entire process was performed at room temperature of approximately 25 degrees C.
The effluent after ammonia treatment had a high pH of approximately 9.3 as a result of the destruction of the alkalinity by aeration that strips CO2 and the conversion of NH4→NH3+H+ and removal of NH3 thru the membrane. After rapid mixing with the MgCl2, the phosphorus quickly precipitated as a solid. Precipitate flocs were visible. Phosphorus mass recovery in the phosphorus precipitate was approximately 93% in the treatment that received only MgCl2 and 96% in the treatment that received MgCl2 and alkali NaOH. The process produced high quality phosphorus materials with very high phosphate and Mg content: approximately 46% P2O5 and approximately 16% Mg, and with low concentration of N, approximately 1.8%; Ca, approximately 0.4%; and K, approximately 1.7%. The plant available phosphorus material was also high, approximately 99%.
Results are shown in Tables 1-4.
In this example, MgCl2 is added first to the digester effluent in tank 46, (
With MgCl2 alone, no alkali addition, struvite phosphates, NH4MgPO4.6H2O, were produced containing approximately 4.5% N; approximately 26.4% P2O5, and approximately 9.9% Mg. The process provided quantitative recovery of the P in the solid form and yielded approximately 100% recovery. For ammonia, the combined process recovered approximately 91%; approximately 8% of the ammonia was recovered in the struvite precipitate and approximately 83% of the ammonia was recovered in the ammonia concentrate with the ammonia module 15. The initial pH of wastewater was approximately 8.4, after MgCl2 addition, it decreased to approximately 7.9 and increased to approximately 9.5 after aeration. The struvite formation is a widely used process for recovery of phosphate from wastewater streams implemented in several commercial processes. These processes typically use MgCl2 and NaOH or chemical combinations to add Mg and increase the process pH to produce struvite mineral containing P. However, these commercial processes recover only about <10% of the total nitrogen contained in the influent because all the N recovery is at the hands of the struvite formation that leaves about 90% of the N in the final effluent. In the process of the present invention, only about <3% of the ammonia remained in the final effluent with approximately 8% of the ammonia recovered in the struvite solids, and the majority of the ammonia, approximately 83%, being captured in the ammonia module 15, on a mass basis. The process of the invention uses low rate aeration without alkali to increase the pH that benefits both struvite formation and ammonia recovery. Most of the N and P are recovered in marketable products. The treatment with MgCl2 plus addition of alkali NaOH resulted in a final pH after aeration about the same as the treatment without NaOH: about 9.6-9.7 and 9.5., respectively. In all cases, the total phosphorus recovery efficiency in the phosphorus precipitate were high, approximately >99%, as well as the total N recovery efficiency of approximately >88%. In the process receiving MgCl2 with 3 mmol NaOH added, Mg phosphates were produced containing approximately 2.9% N, approximately 28.6% P2O5 with approximately 98.4% plant available, and approximately 19% Mg. In the process using MgCl2 with 117 mmol NaOH added produced Mg phosphates containing approximately 2.2% N, approximately 37.2% P2O5 of which approximately 98.9% is plant available, and approximately 14% Mg.
Results are shown in Tables 5-10 below.
This example illustrates how the low aeration rate in the ammonium separation tank 46 increases the pH and enhances both the N recovery and the P recovery. Aeration versus no aeration of tank 46 is compared using the system shown in
Table 11 shows mass balances for recovery of ammonia from digested swine effluent in two farms by gas-permeable membrane module 15 with and without aeration of module 15 (
See also
This example illustrates the use of other phosphorus precipitating agents, such as Mg(OH)2 and Ca(OH)2 (hydrated lime), that can be used in the present invention to recover phosphorus in conjunction with the ammonia separation and recovery. System 20 includes ammonium separation tank 46, N concentration tank 2, and phosphorus separation tank 48 which were constructed and operated the same as described in Example 1, using the same wastewater influent. The only difference with Example 1 is that in step 2, hydrated lime (Ca(OH)2 was used as precipitating agent instead of MgCl2. The wastewater influent contained an ammonia (NH4+) concentration of 2216 mg N/L and a phosphate concentration of 15 mmol P/L. The Ca(OH)2 was applied at rates of approximately 10, 20, 40 and 80 mmol/L and the corresponding Ca:P molar ratios were approximately 0.67, 1.33, 2.67, and 5.33.
In the nitrogen capture and recovery step, the ammonia concentration was reduced from approximately 2,216 to 55 mg N/L (98%) and recovered in the stripping reservoir 2. The treated effluent from the ammonia separation tank 46 had high pH of approximately 9.5±0.2 as a result of the destruction of the alkalinity by aeration that strips the CO2 and the conversion of NH4→NH3+H+ and removal of NH3 thru the membrane (not shown). After rapid mixing with the Ca(OH)2, the phosphorus quickly precipitated as a solid. Precipitate flocs were whitish in color and visible. The phosphorus removal was low, approximately 7-9%, with Ca:P molar ratios of approximately 0.77 and 1.33. The system responded to higher lime rates. At Ca:P ratios of approximately 2.67 and 5.33 the P removal was increased to approximately 45% and 68%, respectively. Since in all treatments the pH was higher, approximately >10, than the pH needed to optimize precipitation of soluble phosphorus using Ca(OH)2, it is concluded that the limitation in the example was the amount of Ca available and not the pH, which was already high before lime application. Therefore, the process pH is not useful to optimize chemical application and the chemical dosage should be based on amount of phosphate in the liquid. This concentration can be determined using on-line phosphate analyzers (i.e. Phosphax Analyzer, Hach Company, Loveland, Colo.) or rapid colorimetric tests kits for phosphate (Hach Company, Loveland, Colo.). Alternatively, the phosphorus can be measured in the treated effluent and dosage of lime adjusted in the process to meet a desired phosphorus concentration level.
Results are shown in
In this example, MgCl2, is added to phosphorus recovery tank 48 with alkali NaOH using the third embodiment described above (
Three cases were evaluated using this configuration with municipal wastewater. A fourth case was a control treatment that precipitated the phosphorus with MgCl2 and NaOH without previous N recovery module or aeration. All cases were tested using the same municipal wastewater. In case #1, the N recovery was done during 3 days before the phosphorus precipitation step (Tables 12-13). In case #2, the N recovery was done during 9 days before the phosphorus precipitation step (Tables 14-15 and
In all cases, the phosphorus separation tanks 48 received 5.42 mmol/L of MgCl2 and alkali after the addition of MgCl2 to increase the pH to an end-point of approximately 9.2. Cases 1-3 received approximately 3-10 mmol/L NaOH and the control (Case #4) approximately 33 mmol/L NaOH to reach the pH 9.2. First the MgCl2 treatment was added to the effluent, then NaOH alkali was added to the same vessel 48 while mixing with a stirrer (not shown). The chemicals were reacted with the effluent by mixing with a stirrer (not shown) for about one minute. After about a 0.5 hours gravity sedimentation period, the treated effluent in all treatments were sampled in the supernatant and analyzed for ammonia (NH4—N) and phosphorus. NH4—N analysis of the influent, effluent and N recovered by the membrane was done by colorimetry (Standard Method 4500-NH3 G, Technicon Instruments Corp., 1977). Phosphorus content of the liquid samples was done by ICP analysis of nitric acid digestion extracts. The precipitated solids were separated from the supernatant and dried in an oven at 100 degrees C. Nitrogen in the solids was determined using Total Kjeldal N (TKN) determinations using acid digestion and the salicylate methods (Standard Method 4500-Norg D) adapted to digested extracts (Technicon Instruments Corp., Industrial Method 337-74W/B). Phosphorus, Mg, Ca and K in the solids was determined using nitric acid digestion and ICP analysis. Plant available phosphorus in the solids was determined using citrate soluble P. Mass balances were conducted to calculate recoveries of nitrogen and phosphorus by measuring flows and concentrations in the inflow and the outputs of system 20. All experiments were duplicated. The entire process was performed at room temperature of approximately 25 degrees C.
In case #1, the effluent after ammonia treatment had a high pH of approximately 8.5 as a result of the destruction of the alkalinity by aeration that strips CO2 and the conversion of NH4→NH3+H+ and removal of NH3 thru the membrane. After addition of small amounts of NaOH (5 mmol/L) to increase pH to 9.2 and rapid mixing with the MgCl2, the phosphorus quickly precipitated as a solid. Precipitate flocs were visible. System 20 removed 83.2% of N and 96.3% of P. The percentage of nutrient recovered divided by nutrient removed was 112.0% and 82.4% for N and P respectively. Total Recovery (percentage of nutrient recovered divided by initial nutrient) was approximately 93% for N and 79% for P (Table 12). The process produced high quality phosphorus materials with very high phosphate and Mg content: approximately 44% P2O5 and approximately 14% Mg, and with low concentration of N, approximately 2.8%; Ca, approximately 0.9%; and K, approximately 0.7% (Table 13).
Results are shown in Tables 12 and 13 below.
In case #2, the N recovery period was extended to 9 days before P precipitation. Compared with case #1 (N recovery period=3 days), the extended N recovery period further reduced the ammonia concentration of the liquid effluent 6 leaving the ammonia separation tank 46. The effluent after N recovery treatment had a lower pH of approximately 6.59 as a result of the continued destruction of the alkalinity by aeration and the additional conversion of NH4→NH3+H+ and removal of NH3 thru the membrane. After addition of the MgCl2 and small amounts of NaOH (10 mmol/L) to increase pH to 9.2, and rapid mixing, the phosphorus quickly precipitated as a solid. Precipitate with whitish flocs was visible. System 20 removed 91.8% of N and 85% of P. The percentage of nutrient recovered divided by nutrient removed was 85.1% and 125% for N and P respectively. Total Recovery (percentage of nutrient recovered divided by initial nutrient) was approximately 79% for N and 106% for P (Table 14). After N recovery, both ammonia and carbonate alkalinity concentrations were low, approximately 71 and 92 mg/L, respectively, compared with the initial side-stream wastewater containing approximately 730 mg NH4—N/L and 2900 mg carbonate alkalinity/L. With low ammonia and alkalinity in the liquid, the P precipitation process produced high quality phosphorus materials with very high phosphate and Mg content: approximately 42% P2O5 and approximately 15% Mg, and with low concentration of N, approximately 2.6%; Ca, approximately 1.4%; and K, approximately 1.9%. The precipitated P was approximately 98% plant available (Table 15).
Addition of 5-10 mmol/L of NaOH to the side-stream municipal effluent after the N recovery step significantly increased both the amount of solids precipitated in the phosphorus separation tank 48 and amount of P recovered in the solids using precipitating agent MgCl2 (Table 16).
The results are shown in Tables 14, 15 and 16 below.
See also
In case #3, the initial side stream effluent (before N recovery) was supplemented with the addition of 1000 mg/L of carbonate alkalinity using 2 g/L of potassium bicarbonate (KHCO3)(Tables 16-17). The N recovery step was also done during 9 days as in case #2. The effluent after N recovery treatment had the lowest ammonia concentration (12 mg N/L) and a higher pH of approximately 8.5. After addition of small amounts of NaOH (5 mmol/L) to increase pH to 9.2 and rapid mixing with the MgCl2, the phosphorus quickly precipitated as a solid. Precipitate flocs were visible. The addition of carbonate alkalinity to the wastewater improved N removal but decreased performance of the phosphorus recovery process, both in quantity and quality of the phosphorus product. System 20 removed 98.8% of N and 42.8%% of P. The percentage of nutrient recovered divided by nutrient removed was 85.8% and 113.6% for N and P respectively. Total Recovery (percentage of nutrient recovered divided by initial nutrient) was approximately 85% for N and 64% for P (Table 17). Case #3 with 1000 mg/L carbonate alkalinity supplementation reduced the phosphorus grade of the precipitated solid materials: approximately 27.4% P2O5 and approximately 13% Mg, and with low concentration of N, approximately 1.4%; Ca, approximately 2.2%; and K, approximately 8.7% (Table 18).
The results are shown in Tables 17 and 18 below.
In case #4 (Control), the P precipitation was done directly in the side-stream effluent without receiving previous N recovery treatment (Tables 19-20). Therefore, the effluent contained high ammonia concentration, approximately 756 mg/L and a pH of 7.84. The side-stream municipal effluent required large amounts of NaOH (28 mmol/L) to increase the pH from 7.8 to 9.2 end-point. After rapid mixing with the MgCl2, the phosphorus quickly precipitated as a solid. Precipitate flocs were visible. The process removed 17.5% of N and 93.1% of P. The percentage of nutrient recovered divided by nutrient removed was 16.2% and 106.4% for N and P respectively. Total Recovery (percentage of nutrient recovered divided by initial nutrient in the effluent) was low for N, approximately 2.8%, and high for P, approximately 98.7% (Table 19). Since there was no N recovery module, the small N recovery was done in the precipitated solids. The final effluent contained significant amounts (624 mg/L) of ammonia compared with the influent (756 mg/L). The precipitation of phosphorus with high ammonia and alkalinity produced a solid material with approximately 29.9% P2O5 and approximately 10.5% Mg, and with low concentration of N, approximately 2.8%; Ca, approximately 0.45%; and K, approximately 0.39% (Table 20).
The results are shown in Tables 19 and 20 below
Alkali titrations were performed to compare the effect of alkali addition on pH of side-stream municipal wastewater during precipitation of phosphorus with MgCl2 and NaOH (
The relationship between wastewater alkalinity consumption and ammonia removal using gas-permeable membranes and aeration during N recovery was determined using a variety of wastewater types (anaerobically digested swine wastewater, raw swine wastewater and anaerobically digested side-stream municipal wastewater) (Table 22 and
The results are shown in Tables 22 below and
It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed above, but that various changes and modifications thereof are possible without departing from the scope Index of the invention as defined in the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| 62169387 | Jun 2015 | US |
