System and method for treating biomass-containing wastewater for renewable energy

Abstract

A method for treating wastewater containing biomass and ammonia, comprising the steps of anaerobic digestion of the wastewater to produce a digestate, oxidizing dissolved sulfides in the digestate, mixing the digestate to form a mixed liquor, filtering the mixed liquor to produce a first filtrate, removing ammonia from the first filtrate to produce an ammonia-reduced filtrate, removing organic contaminants and divalent ions from the ammonia-reduced filtrate by nanofiltration to produce an organic-containing second retentate and an organic-reduced second filtrate, and A method of treating biomass and ammonia-containing wastewater is disclosed that includes removing additional organic contaminants from the organic-containing second retentate by a second nanofiltration operation to produce a third filtrate and a third retentate, removing inorganic ionic species from the organic-reduced second filtrate by reverse osmosis to produce a fourth filtrate and a fourth retentate, combining the third filtrate and the fourth retentate, and removing additional inorganic ionic species from the combined third filtrate and fourth retentate by a second reverse osmosis operation.

Description

[Technical field]

[0001] Aspects and embodiments disclosed herein relate generally to the treatment of wastewater containing flashed biomass, and more specifically to the recovery of water during the treatment of wastewater containing stillage produced during the production of ethanol. Summary of the Invention

[0002] According to one aspect, a method for treating biomass and ammonia-containing wastewater is provided, the method includes anaerobic digestion of biomass and ammonia-containing wastewater to produce biogas and a digestate, oxidizing dissolved sulfides in the digestate, mixing the digestate to form a mixed liquor, filtering a portion of the mixed liquor to produce a first filtrate and a first retentate, removing ammonia from the first filtrate to produce an ammonia-reduced filtrate, and removing organic contaminants and divalent ions from the ammonia-reduced filtrate by nanofiltration to produce a second retentate containing organic matter including divalent ions and a second retentate containing organic matter having reduced organic matter. removing additional organic contaminants from the organic-containing second retentate by a second nanofiltration operation to produce a third filtrate and a third retentate; removing inorganic ionic species from the organic-reduced second filtrate by reverse osmosis to produce a fourth filtrate and a fourth retentate; combining the third filtrate and the fourth retentate; and removing additional inorganic ionic species from the combined third filtrate and fourth retentate by a second reverse osmosis operation to form product water.

[0003] In some embodiments, the method further comprises performing a solid-liquid separation of a second portion of the mixed liquor and returning the resulting liquor to the vessel for oxidizing the dissolved sulfides.

[0004] In some embodiments, the method further comprises controlling the pH of the ammonia-reduced filtrate to about 7-9 and dosing the ammonia-reduced filtrate with a scale inhibitor.

[0005] In some embodiments, the method further includes processing the biogas to produce natural gas.

[0006] In some embodiments, the method further includes using energy produced by the biogas to power at least one operation of the method.

[0007] In some embodiments, the method further comprises adjusting the pH of the biomass and ammonia-containing wastewater to about 6 or greater prior to anaerobic digestion of the biomass and ammonia-containing wastewater.

[0008] According to another aspect, a system for treating biomass and ammonia-containing wastewater is provided, the system comprising: an anaerobic digester having an inlet fluidly connectable to a source of biomass-containing wastewater, a biogas outlet, and a digestate outlet; an oxidation tank having an inlet fluidly connected to the digestate outlet and an oxidation tank outlet; a softener source configured to deliver a softener to a mixing vessel having an inlet fluidly connected to the oxidation tank outlet and a mixing vessel outlet; a thickening tank having an inlet fluidly connected to the outlet of the mixing vessel and first and second mixed liquor outlets; a solid-liquid separator having an inlet fluidly connected to the first mixed liquor outlet of the thickening tank and a separated liquor outlet fluidly connected to the inlet of the oxidation tank; and a solid-liquid separator having an inlet fluidly connected to the second mixed liquor outlet of the thickening tank. a membrane filtration unit having an inlet, a filtrate outlet, and a retentate outlet; an ammonia reduction column having an inlet fluidly connected to the filtrate outlet, a countercurrent source of acid, and an ammonia-reduced filtrate outlet; a first nanofiltration unit having an inlet fluidly connected to the ammonia-reduced filtrate outlet, a filtrate outlet, and a retentate outlet; a second nanofiltration unit having an inlet and a filtrate outlet fluidly connected to the retentate outlet of the first nanofiltration unit; a first reverse osmosis unit having an inlet, a filtrate outlet, and a retentate outlet fluidly connected to the filtrate outlet of the first nanofiltration unit; and a second reverse osmosis unit having an inlet fluidly connected to the filtrate outlet of the second nanofiltration unit and the retentate outlet of the first reverse osmosis unit.

[0009] In some embodiments, the solid-liquid separator comprises a centrifuge.

[0010] In some embodiments, the system further comprises at least one of a coagulant source and a flocculant source located upstream of the centrifuge.

[0011] In some embodiments, the system further comprises a first pH adjuster source located upstream of the ammonia reduction column.

[0012] In some embodiments, the system further comprises a second source of pH adjuster located upstream of the first nanofiltration unit and / or a source of scale inhibitor located upstream of the first nanofiltration unit.

[0013] In some embodiments, the system is such that the anaerobic digester is a continuous stirred tank reactor (CSTR).

[0014] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component that is shown in various figures is represented by a similar numeral. For clarity, not every component is labeled in every drawing. In the drawings: [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a box diagram of a biomass-containing wastewater treatment system according to one embodiment. [Diagram 2] FIG. 1 is a box diagram illustrating a portion of a biomass-containing wastewater treatment system according to one embodiment. [Diagram 3] 3A-3B are box diagrams showing a portion of a system for treating biomass-containing wastewater according to one embodiment. [Figure 4] FIG. 1 is a box diagram of a biomass-containing wastewater treatment system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In one aspect, the present disclosure relates to systems and methods that can be used to reduce odor and recover biogas and water from flashed biomass, such as stillage, and more specifically to a closed system apparatus that provides anaerobic digestion of flashed biomass and minimizes freshwater consumption. The systems and methods disclosed herein generally relate to anaerobic digestion of biomass, such as stillage from ethanol production plants, and reducing or minimizing freshwater consumption. In particular, the amount of freshwater used by the disclosed systems and methods can be reduced or minimized by recovering and recycling wastewater from the process. The present disclosure relates to systems and methods for recovering and recycling wastewater. The wastewater treated by the systems and methods disclosed herein may be free of animal waste.

[0017] The systems and methods disclosed herein relate to the treatment of organic matter under anaerobic conditions. Anaerobic digestion of biomass has been practiced for many years. In anaerobic digestion, a mixed culture of bacteria breaks down the putrefactive parts of the organic matter, eventually into methane, carbon dioxide, and mineralized nutrients. In storage, the biomass begins the decomposition process leading to the production of intermediate compounds, which are volatile and often cause odors. These volatile intermediates accumulate in the stored biomass, as methanogenic microorganisms grow slowly and are present in limited numbers in fresh biomass. In an effective anaerobic digester, the growth of methanogens is promoted, resulting in the conversion of the intermediate compounds into biogas and nutrients, greatly reducing the odor potential of the biomass. Additionally, the biogas can be recovered and converted into thermal energy and used as heat for various processes within the facility, or the biogas can be converted into electrical energy in an internal combustion engine.

[0018] The primary means of promoting methanogen growth in the anaerobic digestion of biomass is to control the operating temperature and / or the residence time of the bacteria within the process. The types of anaerobic digesters that have been deployed in the digestion of biomass are fairly limited due to the nature of biomass as a substrate. Digestor types include a variety of batch and semi-continuous processes, including plug flow digesters, completely mixed digesters, covered lagoons, and continuously stirred reactors.

[0019] During anaerobic treatment, the organic matter slurry may be sent to a tank or reactor containing anaerobic microorganisms. The anaerobic microorganisms convert the biodegradable material in the wastewater primarily into water, biogas, and biosolids. In particular, the anaerobic microorganisms promote the breakdown of polymeric organic matter into simpler compounds and biogas through methanogens. Examples of anaerobic microorganisms include methanogens and acetogens. The biogas produced is primarily carbon dioxide and methane, but may contain other components depending on the composition of the slurry.

[0020] Anaerobic treatment generally refers to a situation where the prevailing conditions of the slurry in a tank or reactor are anaerobic. The tank or reactor may be closed. The tank or reactor may be open. Even in embodiments where the anaerobic treatment tank or reactor is open, anaerobic treatment may occur without the addition of oxygen, particularly if the prevailing conditions in the water are anaerobic.

[0021] By adding microorganisms and / or dosing microbial nutrients during start-up, microbial growth can be promoted and odors of organic matter can be significantly reduced. Methanogenic growth in the anaerobic digestion of organic matter can be controlled by controlling the operating temperature, the residence time of the bacteria in the digester, and / or the mixing conditions.

[0022] Additionally, the biogas produced can be collected and converted into thermal energy, which can be used to heat various processes within the facility. The biogas can be converted into electrical energy using an internal combustion engine.

[0023] In addition to biogas recovery, minimizing water consumption is also an important factor. The process of treating biomass consumes a large amount of water. However, it is possible to minimize the amount of freshwater required by treating the wastewater and recovering most of the water. The systems and methods disclosed herein can be utilized to treat process wastewater and recover a portion of the water to reduce or minimize the amount of freshwater required. Anaerobic digestion of wastewater containing biomass can be performed in a batch or semi-continuous process. For example, anaerobic digestion can be carried out in plug flow digesters, complete mixed digesters, covered lagoons, or continuous stirred reactors.

[0024] Thus, according to one aspect, a system and method for treating wastewater containing flash biomass is provided. The biomass can include organic stillage. The stillage can be a waste product of ethanol production.

[0025] The wastewater to be treated may have high suspended and dissolved solids and may also have a high oxygen demand. For example, the wastewater may have a total suspended solids (TSS) of 4,000 mg / L or more, a volatile suspended solids (VSS) of 3,000-4,000 mg / L, a total dissolved solids (TDS) of 4,000-5,000 mg / L, a biochemical oxygen demand (BOD) of 35,000 mg / L or more, a soluble chemical oxygen demand (sCOD) of 55,000 mg / L or more, and a total chemical oxygen demand (COD) of 60,000 mg / L or more.

[0026] The method can include introducing wastewater into a holding tank and adjusting the pH of the wastewater in the holding tank, optionally by adding an acid or base, to bring the pH of the wastewater to a suitable pH for anaerobic digestion, for example, in the range of pH 6-8.

[0027] From the storage tank, the pH adjusted wastewater (or non-pH adjusted wastewater if it is determined that pH adjustment is not necessary) is introduced into the anaerobic bioreactor via a feed pump and a coarse screen (e.g., a ¼ inch mesh strainer). In some embodiments, the anaerobic bioreactor can be a BVF® Reactor from Evoqua Water Technologies, LLC. Organic matter in the wastewater is digested in the anaerobic bioreactor to produce biogas, sludge, and an anaerobically treated effluent that has a lower oxygen demand than the wastewater introduced into the anaerobic bioreactor. The anaerobically treated effluent may also have a reduced nitrogen content compared to the wastewater introduced into the anaerobic bioreactor. A portion of the sludge is returned to the inlet of the anaerobic bioreactor via a recycle pump to improve contact between the sludge and the inflowing wastewater and provide buffering effects for pH, alkalinity, organic load, and temperature. In some embodiments, a large portion of the sludge, e.g., an amount of sludge equal to 50%-100% of the inflowing wastewater volume, may be recycled to the inlet of the anaerobic bioreactor. Excess sludge may be disposed of or utilized as agricultural fertilizer. Biogas may be collected, used as fuel, or released to the environment. For example, biogas may be measured / collected / discharged via a biogas metering system and then discharged to the atmosphere outdoors. Biogas samples may be collected and used to measure the biogas composition (CH4, CO2, H2S, O2).

[0028] The anaerobically treated effluent is sent to an oxidation vessel for oxidizing dissolved sulfides in the anaerobically treated effluent. An oxygen-containing gas, e.g., air, is supplied to an aeration diffuser in the oxidation vessel using an air pump.

[0029] The effluent from the oxidation vessel is sent to a mixing tank where it is softened, for example by the addition of lime and / or caustic. A coagulant (e.g., ferric chloride) and / or a flocculant (e.g., a polymer) may also be mixed with the oxidation vessel effluent in the mixing tank.

[0030] After softening and coagulation, the partially treated wastewater is sent to a thickener tank where it is mixed to form a mixed liquor. A portion of the mixed fluid is removed from the thickener tank and processed through a solid-liquid separation device, such as a centrifuge. The low solids liquid or centrate separated from the solids / liquid separation unit may be returned to the oxidation vessel. The high solids portion separated from the solids / liquid separation unit may be discarded.

[0031] The remainder of the mixed fluid from the thickening tank is sent to a cross-flow filtration system, such as a cross-flow microfiltration system, to remove additional solids. Examples of cross-flow filtration systems include the MemTek® microfiltration system from Evoqua Water Technologies, LLC. The Evoqua MemTek® microfiltration system is a standalone PLC-controlled unit with a VFD-controlled feed pump and thickening tank. The membranes are made of PVDF with a nominal pore size of 0.1 μm. The membrane modules are of a tubular type with a cross-flow design. During operation, the total suspended solids are concentrated to 3-5%. The high solids concentrate produced in the cross-flow filtration system is periodically discharged to a sludge holding tank and can then be sent to a centrifuge to separate the solids and liquid. The solids are disposed of and the separated liquid is recycled to the front of the oxidation tank.

[0032] The filtrate from the cross-flow filtration system is processed through a gas separator, such as 3M's Liqui-Cell™ gas separation membrane device, to remove ammonia. Sulfuric acid can be added to the gas separator to react with the ammonia in the filtrate to produce and precipitate ammonium sulfate, which can be removed and disposed of.

[0033] After ammonia reduction, the filtrate is sent to a water recovery subsystem. Water recovery in the water recovery subsystem may include passing the filtrate from the ammonia reduction operation through a first nanofiltration (NF) unit and a brackish water reverse osmosis (BWRO) unit in a batch model. In some embodiments, antiscalants and / or pH adjusting acids (e.g., sulfuric acid) or bases may be added to the filtrate before entering the first NF unit and / or to the permeate of the first NF unit before entering the BWRO unit.

[0034] The waste or retentate from the first NF unit is further processed in a second NF unit, which is a loose-pore NF membrane unit designed for the removal of organic compounds. This step may be called nanofiltration waste recovery (NFRR).

[0035] After the NFRR, the permeate of the second NF unit is mixed with the BWRO waste and fed to a seawater RO (SWRO) skid after adding further antiscalants if necessary. The SWRO permeate is mixed with the BWRO permeate to become the final treated product water, which is used, for example, for yeast production and / or rich scrubber make-up. The waste from the second NF unit used in the NFRR step is combined with the SWRO waste and disposed of, for example, in a sewer or evaporation pond.

[0036] In some embodiments, the NF / RO skid is a microprocessor controlled unit and can mount multiple NF or RO modules. The skid includes VFD controlled pumps, flow meters, temperature gauges, and pressure gauges. Different membranes are used for the nanofiltration and RO steps.

[0037] The systems and methods disclosed herein may include anaerobically digesting biomass-containing wastewater to produce biogas and digestate. Anaerobic digestion involves contacting an organic matter slurry with a microbial community in a substantially anaerobic environment. The anaerobic microbial community breaks down the organic matter in the wastewater and produces biogas. During anaerobic digestion, organic nitrogen may be converted to ammonia. The temperature of the anaerobic digestion may be controlled. In some embodiments, the temperature of the anaerobic digestion may be between 90-100°F (32-38°C) or 95-100°F (35-38°C), for example. The anaerobic microbial mixture in the digester may be agitated, for example, in a continuous stirred tank reactor.

[0038] For example, nutrients and / or alkaline agents, such as nitrogen, phosphorus, sodium bicarbonate, urea, phosphate, and combinations thereof, may be provided to the anaerobic microorganisms. Total Kjeldahl nitrogen (TKN) and ammoniacal nitrogen (NH3-N) measurements of the digestate may be used to determine whether sufficient nitrogen is available for the digestion process. Phosphorus-phosphate (PO4-P) measurements of the digestate may be used to determine whether sufficient phosphorus is available for the digestion process. Thus, the method may include measuring the nitrogen content and / or phosphorus content of the digestate. The method may include providing an effective amount of nutrients and / or alkaline agents in response to the measurements of the digestate.

[0039] The residence time of the mixed liquor in the anaerobic digester can be controlled. The wastewater can be contacted with the microbial population for a time sufficient to convert a predetermined amount of biomass into biogas. In some embodiments, the wastewater can be contacted with the microbial population for a time sufficient to discharge biogas production from the wastewater. The hydraulic residence time (HRT) of the mixed liquor in the anaerobic digester can be 15-35 days, for example, 20-30 days, about 15 days, about 20 days, about 25 days, about 30 days, or about 35 days.

[0040] The method may include collecting raw biogas produced by digestion. The raw biogas may include methane and carbon dioxide. The raw biogas may include water vapor. The raw biogas may include additional components or nutrients based on the composition of the wastewater. In some embodiments, the raw biogas may be at least 40% methane, at least 45% methane, at least 50% methane, at least 55% methane, at least 60% methane, or at least 65% methane. Carbon dioxide may make up the majority of the remainder of the biogas.

[0041] The method may include measuring a flow rate of raw biogas. The method may include measuring a composition of raw biogas produced by digestion. The composition of the raw biogas may depend on the composition of the wastewater. For example, the composition of the raw biogas may depend on the carbon to nitrogen ratio (C:N), pH, moisture, total solids, temperature, biological oxygen demand (BOD), loading rate, and HRT of the wastewater.

[0042] The method may include measuring the methane content of the raw biogas. The method may include controlling one or more parameters of the digestion in response to the methane measurement, for example controlling the temperature, mixing conditions, loading rate, or HRT of the digestion in response to the methane concentration being below a predetermined threshold, for example below 55%, below 50%, below 45%, or below 40%.

[0043] By controlling certain parameters, the methane content of the raw biogas may be increased. In an exemplary embodiment, the pH of the wastewater may be controlled to about 6-8. The temperature may be controlled to 90-100°F (32-38°C), for example 95-100°F (35-38°C). The mixing conditions of the mixed liquor in the digester may be controlled.

[0044] The systems and methods disclosed herein may use the energy produced by the biogas. In some embodiments, the energy produced by the biogas may be generated in the form of thermal energy. The thermal energy may be captured from the biogas by a boiler or a cogeneration process. The captured thermal energy may be used by one or more unit operations of the system. The captured thermal energy may be used in a unit operation of the facility. The thermal energy may be converted in a heat exchanger loop. For example, the thermal energy may be transferred to an energy demand using a heat exchanger loop. The energy demand may include one or more unit operations of the system and / or another unit operation of the facility.

[0045] In some embodiments, energy may be generated from the biogas in the form of electrical energy. The energy from the biogas may be converted to electrical energy by an internal combustion engine. The electrical energy may be used to operate one or more unit operations of the system and / or other unit operations of the facility.

[0046] In some embodiments, the method may include processing the raw biogas to produce natural gas. The raw biogas may be purified and converted to natural gas, e.g., renewable natural gas (RNG). The purification process may include removing, e.g., siloxanes, volatile organic compounds (VOCs), moisture, carbon dioxide, and trace levels of contaminants, including hydrogen sulfide, from the raw biogas. The purification process may include removing the nitrogen and oxygen content of the raw biogas. The purification process may produce natural gas having a methane content of at least 90%. In some embodiments, the methane content of the produced natural gas may be at least 92%, at least 94%, at least 96%, or at least 98%. The produced natural gas may be injected into a conventional natural gas pipeline or used as a replacement for fossil fuel natural gas in existing applications. For example, the produced natural gas may be used to generate electrical energy. The electrical energy may be used by one or more unit operations of the system and / or unit operations of the facility.

[0047] The digestate produced by anaerobic digestion may be wastewater containing sludge. The digestate may contain 1,500-3,000 ppm total suspended solids (TSS). The digestate may contain 3,500-6,000 ppm TDS. The digestate may contain 50-150 ppm calcium. The digestate may contain 200-300 ppm magnesium.

[0048] The method may include separating the digestate to produce digestate solids and a filtrate. The digestate solids may retain substantially all of the suspended solids and a portion of the dissolved solids from the digestate. Thus, the separation may reduce the TSS of the stream by at least 95%, at least 98%, at least 99%, at least 99.9%, or at least 99.99%. The separation may reduce the TDS of the stream by about 30%-65%, e.g., about 35%, about 50%, or about 65%. The separation may be performed by one or more of the following methods: centrifugation, thickening, filtration, sedimentation, and membrane filtration. The digestate solids may be collected to produce a solid product. The filtrate may be further processed as described below to produce product water.

[0049] The step of separating the digestate into digestate solids and filtrate may include administering at least one of a coagulant and a flocculant to the digestate to produce a digestate sludge. The coagulant may induce coagulation of suspended solids in the digestate. Coagulation may be induced by destabilization of colloidal and dispersed particles, inducing the growth of larger particle sizes. Exemplary flocculants may include anionic and cationic molecules. The flocculant may induce aggregation of suspended solids in the digestate. Flocculation may be induced by flocculating solids, such as coagulated solids and other suspended solids, into aggregates or complexes. Examples of flocculants include high molecular weight polymers with exposed binding groups for agglomerating suspended and coagulated solids. Certain separation additives may act as both coagulants and flocculants. Examples of separation additives include calcium hydroxide (lime), iron (III) sulfate, anionic polymers, and cationic polymers. One example of a separation additive is Alumafloc™ separation additive. Thus, the separation may include dosing the digestate with one or more of calcium hydroxide, ferrous sulfate, anionic polymers, cationic polymers. The digestate sludge containing the flocculated solids may be collected to produce a solid product.

[0050] In some embodiments, separating the digestate into digestate solids and filtrate may be performed by a series of separations. For example, separation may include administering at least one of a coagulant and a flocculant to the digestate to produce a digestate sludge containing large suspended solids. The digestate sludge may be separated from the digestate by at least one centrifuge and / or settling. Settling may separate the digestate into a digestate sludge and a supernatant. Additional water may be removed from the settled digestate sludge by a centrifuge. In some embodiments, separation may include concentrating the digestate prior to separation by centrifugation and / or settling. Suspended solids remaining in the digestate or in the supernatant from the settling operation are then separated by a filtration membrane, e.g., cross-flow filtration, to produce a retentate and a filtrate.

[0051] In an exemplary embodiment, the digestate may be administered calcium hydroxide. Calcium hydroxide may cause flocculation of suspended matter as a coagulant. Calcium hydroxide may also reduce the calcium and magnesium concentration of the solution as a softener. For example, the method may include administering to the digestate an amount of calcium hydroxide effective to produce a filtrate containing at least 90% less calcium and magnesium than the digestate. Additionally, calcium hydroxide may increase the pH of the solution. The pH may be controlled to remove ammonia, as described below.

[0052] The method may include returning one or more dosing agents, such as, for example, a coagulant, a flocculant, or calcium hydroxide, to an upstream reaction tank.The method may include returning sludge, such as, for example, activated sludge, to the anaerobic digester or an upstream reaction tank.

[0053] The methods may include controlling the pH of the filtrate from the cross-flow filtration unit to less than about 10. For example, the methods may include controlling the pH of the filtrate to about 4 to about 10, about 7 to about 10, or about 9 to about 10. The methods may include administering an effective amount of a pH adjuster to the filtrate. The pH adjuster may include an acid or a base. Exemplary pH adjusters include strong bases such as sulfuric acid, hydrochloric acid, perchloric acid, and nitric acid. Other exemplary pH adjusters include, for example, potassium hydroxide, sodium hydroxide, sodium carbonate, ammonium hydroxide, calcium hydroxide, or magnesium hydroxide. In an exemplary embodiment, the pH may be controlled to less than about 10 by administering an effective amount of sulfuric acid to the filtrate.

[0054] The systems and methods disclosed herein may include removing ammonia from the filtrate to produce an ammonia-removed filtrate. During anaerobic digestion, the temperature and pH of the mixed liquor are generally maintained to favor digestion of organic matter into methane gas. Under such conditions, the ammonia is present substantially in the form of ammonium ions. After digestion, the pH may be controlled to a value effective to remove ammonia. For example, the pH may be controlled to greater than 9 by adding an effective amount of one or more pH adjusters. Certain separation additives, such as coagulants and flocculants, may increase the pH of the solution. In such an embodiment, an acidic pH adjuster may be used to lower the pH to less than 10. Exemplary pH adjusters are calcium hydroxide and sulfuric acid, as described above. In one exemplary embodiment, the ammonia may be removed by contacting the filtrate with an ammonia reduction column with sulfuric acid flowing countercurrently.

[0055] The method may include reducing the ammonia concentration in the filtrate to produce an ammonia-reduced filtrate. In some embodiments, the method may include reducing the ammonia concentration in the filtrate by at least about 90% to produce an ammonia-reduced filtrate. The ammonia-reduced filtrate may contain less than 100 ppm ammonia, e.g., less than 50 ppm ammonia, less than 10 ppm ammonia, less than 5 ppm ammonia, less than 2 ppm ammonia, or less than 1 ppm ammonia. The ammonia-reduced filtrate may have a TDS of 100 to 400 ppm.

[0056] The method can include controlling the pH of the ammonia-reduced filtrate to less than about 9, such as between about 4 and 9, or between about 7 and 9. The pH of the ammonia-reduced filtrate can be controlled by administering an effective amount of a pH adjuster to the ammonia-reduced filtrate, as described above.

[0057] The method may include administering a scale inhibitor to the ammonia-reduced filtrate. The scale inhibitor may be a silica, sulfate (e.g., barium sulfate, calcium sulfate, strontium sulfate), calcium carbonate, and / or calcium fluoride scale inhibitor. Thus, the ammonia-reduced filtrate may be administered an effective amount of a scale inhibitor to inhibit the formation of scale in one or more downstream unit operations, such as a microfiltration unit, a nanofiltration unit, and / or a reverse osmosis unit. In an exemplary embodiment, the scale inhibitor may include Vitec® 400 scale inhibitor (sold by Avista Technologies, Inc. of San Marcos, Calif.).

[0058] The method may include dosing the ammonia-reduced filtrate with potassium bisulfite, which may be used to neutralize chlorine, chloramines, and residual ammonia in the ammonia-reduced filtrate.

[0059] The systems and methods disclosed herein may include removing organic contaminants and divalent ions from the ammonia-reduced filtrate to produce an organic-containing waste and an organic-reduced filtrate. The organic contaminants and divalent ions may be removed by nanofiltration.

[0060] The organic-reduced filtrate may have 40-60% less TDS than the ammonia-reduced filtrate, e.g., 40-50% less TDS. The organic-reduced filtrate may have 2,000-5,000 ppm TDS, e.g., 3,500-4,500 ppm TDS. The organic-reduced filtrate may have less calcium and magnesium than the ammonia-reduced filtrate. In some embodiments, the organic-reduced filtrate may have, e.g., at least 90% less calcium and magnesium than the ammonia-reduced filtrate. The organic-reduced filtrate may have 10 ppm or less calcium, e.g., 5 ppm or less calcium, or 1 ppm or less calcium. The organic-reduced filtrate may have 10 ppm or less magnesium, e.g., 5 ppm or less magnesium, or 1 ppm or less magnesium.

[0061] The method can include controlling the pH of the organic-reduced filtrate to less than about 8, such as between about 4 and 8, or between about 6 and 8. The pH of the organic-reduced filtrate can be controlled by administering an effective amount of a pH adjuster to the organic-reduced filtrate, as described above.

[0062] The method can include dosing the organic-reduced filtrate with a scale inhibitor, which can be dosed with an effective amount of a scale inhibitor to inhibit the formation of scale in one or more downstream unit operations, such as a cross-flow filtration unit, a microfiltration unit, a nanofiltration unit, and / or a reverse osmosis unit.

[0063] The systems and methods disclosed herein may include concentrating the organic-reduced filtrate to produce a concentrated retentate and a permeate. The organic-reduced filtrate may be concentrated by reverse osmosis. The organic-reduced filtrate may be concentrated by brackish reverse osmosis. The method may concentrate the organic-reduced filtrate 2-5 times, e.g., about 2-fold, about 3-fold, about 4-fold, or about 5-fold, to produce a concentrated retentate.

[0064] The permeate may have a lower TDS than the reduced organics filtrate. In some embodiments, the permeate may have, for example, at least 90% more TDS than the reduced organics filtrate. The permeate may have a TDS of 10-500 ppm, for example, a TDS of 100-400 ppm, or a TDS of 200-300 ppm.

[0065] In some embodiments, to further recover water, organic contaminants and divalent ions may be separated from the organic-containing waste to produce a second organic-reduced filtrate. The organic-containing waste may be separated by a second nanofiltration operation.

[0066] The method can include administering a scale inhibitor to the organic-containing waste prior to separation. The organic-containing waste can be administered an effective amount of a scale inhibitor to inhibit scale formation in one or more downstream unit operations, such as a microfiltration unit, a nanofiltration unit, and / or a reverse osmosis unit.

[0067] The method can include combining the second organic-reduced filtrate and the concentrated retentate to produce a diluted retentate. The method can include administering a scale inhibitor to the diluted retentate. The diluted retentate can be administered an effective amount of a scale inhibitor to inhibit the formation of scale in one or more downstream unit operations, such as a microfiltration unit, a nanofiltration unit, and / or a reverse osmosis unit.

[0068] The method may include concentrating the diluted retentate to produce a second concentrated retentate and a second permeate. The diluted retentate may be concentrated by reverse osmosis. The diluted retentate may be concentrated by seawater reverse osmosis. The diluted retentate may be concentrated by saltwater recovery reverse osmosis. The method may include concentrating the diluted retentate 2-5 times, e.g., about 2-fold, about 3-fold, about 4-fold, or about 5-fold, to produce a second concentrated retentate.

[0069] The second permeate can have a lower TDS than the diluted retentate. In some embodiments, the second permeate can have, for example, at least 90% lower TDS than the diluted retentate. The second permeate can have a TDS of 500-1,000 ppm, for example, a TDS of 600-900 ppm, or a TDS of 700-900 ppm.

[0070] The method can include mixing a second permeate with the first permeate. The permeates can be mixed in amounts effective to provide a TDS of 200-500 ppm. For example, the mixed permeate can have a ratio of permeate to second permeate of 1:5 to 5:1, e.g., 2:1 to 5:1, 3:1 to 4:1, or 3:1 to 5:1.

[0071] In some embodiments, the recovered water may be used to clean or backwash at least one cross-flow filtration unit, nanofiltration unit, or reverse osmosis unit of the system. For example, the permeate and / or the second permeate (e.g., the combined permeate) may be used to backwash at least one cross-flow filtration unit, nanofiltration unit, or reverse osmosis unit of the system. The permeate may be mixed with a cleaning agent to form a cleaning solution. The cleaning agent may include, for example, one or more of potassium hydroxide, sulfuric acid, and hydrochloric acid. The clean-in-place waste may be collected to form a solid product. The clean-in-place waste, the concentrated retentate or the second concentrated retentate, the waste-containing organic matter or the waste-containing second organic matter, and the digested solids may be combined (with the digested sludge) to form a solid product.

[0072] The systems and methods disclosed herein may produce solids from biomass-containing wastewater. In some embodiments, the solids may be processed. For example, the solids may be dried. Residual moisture may be captured from the dryer and returned to the digestion or water recovery process. The solid product may be used to produce a Class A biosolids product. The solid product produced by the disclosed methods may comply with the requirements for Class A biosolids established by the U.S. Environmental Protection Agency (EPA). The solid product may be used as a fertilizer product. The solid product may be supplemented with nutrients and / or fertilizer. The solid product may be used as an organic product, such as a certified product suitable for organic farming. The fertilizer product produced by the disclosed methods may comply with the requirements outlined by the Organic Matter Review Institute (OMRI).

[0073] In certain embodiments, the dosage agents disclosed herein, such as coagulants, flocculants, softeners, pH adjusters, scale inhibitors, and detergents, may be acceptable for the production of Class A biosolids products. Solid products containing the dosage agents produced by the disclosed methods may comply with the requirements for Class A biosolids established by the EPA. The dosage agents may be suitable for the production of organic products, such as certified products suitable for organic farming. Fertilizer products containing the dosage agents produced by the disclosed methods may comply with the requirements outlined by OMRI.

[0074] Thus, according to another aspect, a system for treating wastewater containing biomass is provided. The system may include an organic matter digestion subsystem and a water recovery subsystem. The organic matter digestion subsystem may be configured to effectively digest the biomass and produce biogas, digested solids, and digested liquid. The water recovery subsystem may be configured to process the digested liquid and recover a quantity of water from the digested liquid. A portion of the recovered water may be returned to the biomass digestion subsystem to reduce the amount of fresh water required for digestion.

[0075] The biomass digestion subsystem may include an anaerobic digester having an inlet fluidly connected to a biomass-containing wastewater source, a biogas outlet, and a digestate outlet. The anaerobic digester may be a sealed or semi-sealed vessel that contains activated sludge containing anaerobic microorganisms. The anaerobic digester may include a temperature control unit including, for example, a temperature sensor, a heater, and / or a chiller. The temperature control unit may be configured to control the temperature of the mixed liquor in the anaerobic digester. The anaerobic digester may include elements for stirring the mixed liquor in the digester. In some embodiments, the anaerobic digester may be a continuous stirred tank reactor (CSTR).

[0076] The system may include a biogas processing unit fluidly connected to the biogas outlet. The biogas processing unit may include an energy collection unit. The energy collection unit may include a boiler or a cogeneration process. A heat exchanger and / or a heat pump may be used to transfer thermal energy from the energy collection unit to the energy demand. In some embodiments, the heat exchanger and / or the heat pump may be installed on-site. To capture as much thermal energy as possible, the distance between the biogas outlet of the anaerobic digester and the boiler or cogeneration process may be minimized. The energy demand may be a unit operation of the system, a unit operation of the facility, and / or an on-site energy demand, such as an ambient heating system of the facility.

[0077] The energy collection unit may include a combustion engine configured to generate electrical energy. The combustion engine may be installed on-site. The combustion engine may be configured to use biogas or natural gas generated from biogas as fuel. The combustion engine may be electrically connected to an energy demand, for example, an on-site energy demand. The energy demand may be an off-site energy demand. For example, electrical energy may be generated on-site to meet an off-site energy demand. In some embodiments, the combustion engine may be located off-site.

[0078] The biogas processing unit may include a biogas processing unit that may be configured to purify and convert the biogas to natural gas, as described above. In some embodiments, the biogas processing unit may be on-site. In other embodiments, the biogas processing unit may be located remotely.

[0079] The biomass digester subsystem may include a first solids-liquid separation subsystem with an inlet fluidly connected to the digestate outlet, at least one digestate solids outlet, and a low-solids liquid outlet. The first solids-liquid separation subsystem may be configured to produce digestate solids and a low-solids liquid. The first solids-liquid separation subsystem may include one or more of a centrifuge, a clarifier, and a membrane filter. The first solids-liquid separation subsystem may be configured to process approximately 1,000 gallons / min of digestate. In certain embodiments, the first solids-liquid separation subsystem may be configured to send 70-80% of the treated digestate (e.g., 700-800 gallons / min of low-solids liquid) to the water recovery subsystem. The first solids-liquid separation subsystem may be configured to send 20-30% of the treated digestate (e.g., 200-300 gallons / min of digestate solids) to a solids holding tank.

[0080] In some embodiments, the first solid-liquid separation subsystem may include a thickening tank having a first outlet and a second outlet. The first solid-liquid separation subsystem may further include a centrifuge having an inlet fluidly connected to the first outlet of the thickening tank, a digestate solids outlet, and a digestate liquid outlet. The centrifuge may be configured to separate the suspended solids into the digestate solids outlet and the remaining stream into the digestate liquid outlet. The biomass digestion subsystem may include a source of separation additive. For example, the biomass digestion subsystem may include at least one of a coagulant source and a flocculant source located upstream of the thickening tank and / or the centrifuge.

[0081] As an example, the first solid-liquid separation subsystem may include a source of calcium hydroxide located upstream of the thickening tank and / or centrifuge. The first solid-liquid separation subsystem may include a source of anionic polymer located upstream of the thickening tank and / or centrifuge. The first solid-liquid separation subsystem may include a source of ferrous sulfate located upstream of the thickening tank. The first solid-liquid separation subsystem may include a source of cationic polymer located upstream of the thickening tank. The thickening tank may be configured to mix the digestate with optional additives, such as, for example, calcium hydroxide, anionic polymer, cationic polymer, and / or ferrous sulfate, to generate a mixed liquor.

[0082] The system may include a solid product holding tank fluidly connected to the digested solids outlet of the first solid-liquid separation subsystem. In some embodiments, the system may include a solids return configured to direct the separated solids to an upstream reaction tank, such as an anaerobic digester or other upstream reaction tank. The system may include a dosing agent holding tank. The dosing agent holding tank may be configured to recover and reuse dosing agents, such as coagulants, flocculants, pH adjusters, etc. The dosing agent holding tank may be fluidly connected to an upstream reactor.

[0083] The water recovery subsystem may include a cross-flow filtration unit, for example, a cross-flow microfiltration unit. The cross-flow filtration unit may have an inlet fluidly connected to the outlet of the thickener tank, a retentate outlet, and a filtrate outlet. The cross-flow filtration unit may be a membrane filter, a hollow fiber membrane filter, a plate-and-frame membrane filter, a spiral membrane, a dead-end filter, a cross-flow filter, or other type of filter having pores sized to perform microfiltration. The average pore size of the cross-flow filtration membrane may be, for example, 0.02 μm to 0.1 μm. The cross-flow filtration unit may be configured to separate the mixed liquor from the thickener tank into a retentate and a filtrate. The cross-flow filtration unit may be configured to process 700 to 800 gallons per minute of liquid.

[0084] The water recovery subsystem may include an ammonia reduction column having an inlet fluidly connected to the filtrate outlet, a countercurrent source of acid, and an ammonia-reduced filtrate outlet. The ammonia reduction column may be configured to remove ammonia from the filtrate and produce an ammonia-reduced filtrate. The column may comprise hollow fibers. In an exemplary embodiment, the filtrate may flow through the shell side (outside) of the hollow fibers while an acid solution may flow countercurrently through the lumen side (inside) of the hollow fibers. The countercurrent acid may be sulfuric acid. In such an embodiment, the ammonia removed from the column may be in the form of ammonium sulfate. The captured ammonium sulfate may be collected for the solid product.

[0085] In an exemplary embodiment, the ammonia reduction column can be a Liqui-Cel® membrane contactor (sold by 3M, St. Paul, Minnesota).

[0086] The water recovery system may include a source of pH adjuster located upstream of the ammonia reduction column. The source of pH adjuster may be an acid or a base. In an exemplary embodiment, the source of pH adjuster may be sulfuric acid.

[0087] The water recovery subsystem can include a second solid-liquid separation subsystem having an inlet fluidly connected to the ammonia-reduced filtrate outlet, at least one retentate outlet, and at least one permeate outlet. The second solid-liquid separation subsystem can be configured to process the ammonia-reduced filtrate to produce a concentrated retentate and an organics-reduced filtrate outlet.

[0088] The second solid-liquid separation subsystem may include a first nanofiltration unit having an inlet fluidly connected to the ammonia-reduced filtrate outlet, a retentate outlet, and an organics-reduced filtrate outlet. The nanofiltration unit may be a membrane filter, a hollow fiber membrane filter, a plate-and-frame membrane filter, a spiral membrane, a dead-end filter, a cross-flow filter, or other type of filter having pores sized to perform nanofiltration. The average pore size of the nanofiltration membrane may be, for example, 0.02 μm to 0.1 μm. The nanofiltration unit may be configured to separate the ammonia-reduced filtrate into an organics-containing waste containing organic contaminants and divalent ions and an organics-reduced filtrate.

[0089] The water recovery subsystem may include a second pH adjuster source located upstream of the second solid-liquid separation subsystem, e.g., upstream of the nanofiltration unit. The second source of pH adjuster may be an acid or a base. In one embodiment, the second source of pH adjuster may include sulfuric acid. The system may additionally or alternatively include a source of scale inhibitor located upstream of the second solid-liquid separation subsystem, e.g., upstream of the nanofiltration unit.

[0090] The water recovery subsystem may include a first reverse osmosis unit having an inlet fluidly connected to the organics-reduced filtrate outlet, a retentate outlet, and a permeate outlet. The reverse osmosis unit may use a partially permeable membrane to separate ions and other small molecules from a stream under pressure. The reverse osmosis unit may be a brackish reverse osmosis unit. The brackish reverse osmosis unit may operate under a pressure of about 200 psi. The reverse osmosis unit may be configured to concentrate the waste containing organics and produce a concentrated retentate containing dissolved solids and a permeate.

[0091] The water recovery system may include a third pH adjuster source located upstream of the first reverse osmosis unit. The second pH adjuster source may be an acid or a base. As an example, the second source of pH adjuster may include sulfuric acid. The water recovery subsystem may additionally or alternatively include a second source of scale inhibitor located upstream of the reverse osmosis unit. The water recovery subsystem may additionally or alternatively include a source of potassium bisulfite located upstream of the reverse osmosis unit.

[0092] The system may include a product water storage tank having an inlet fluidly connected to a permeate outlet of the first reverse osmosis unit. The product water storage tank may be configured to direct the permeate to the wash-in-place liquid holding tank.

[0093] In some embodiments, the water recovery subsystem can include a second nanofiltration unit having an inlet fluidly connected to the retentate outlet of the first nanofiltration unit, a third retentate outlet, and a second organic-reduced filtrate outlet. The second nanofiltration unit can be configured to separate the organic-containing waste to produce a second organic-containing waste and a second organic-reduced filtrate.

[0094] The water recovery subsystem may include a third source of antiscalant located upstream of the second nanofiltration unit.

[0095] The water recovery subsystem may further include a second reverse osmosis unit having an inlet fluidly connected to the retentate outlet of the first reverse osmosis unit and the second organic-reduced filtrate outlet of the second nanofiltration unit, a fourth retentate outlet, and a second permeate outlet fluidly connected to the product water storage tank. The second reverse osmosis unit may be a seawater reverse osmosis unit. The seawater reverse osmosis unit may be configured to operate under a pressure of about 1,000 psi. The second reverse osmosis unit may be a saltwater recovery reverse osmosis unit. The second reverse osmosis unit may be configured to concentrate the diluted retentate (formed by the combination of the concentrated retentate and the second organic-reduced filtrate) to produce a second concentrated retentate comprising dissolved solids and a second permeate. The second permeate may be sent to the product water storage tank and mixed with the permeate from the first reverse osmosis unit.

[0096] The water recovery subsystem may include a fourth source of antiscalant located upstream of the second reverse osmosis unit.

[0097] The system may include a solids processing subsystem. The solids processing subsystem may be located onsite downstream of the solids holding tank. The solids processing subsystem may be located at a remote location. The solids processing subsystem may be configured to process the solids to produce a Class A biosolids product. The solids processing subsystem may be configured to process the solids to produce a fertilizer product. In some embodiments, the solids processing subsystem may include a dryer. The solids processing subsystem may include a source of nutrients and / or fertilizer.

[0098] The system may be comprised of one or more clean water-in-place holding tanks. The clean water-in-place holding tank may be fluidly connected to the product water storage tank. The clean water-in-place holding tank may direct recovered water (e.g., permeate) or cleaning solution (e.g., recovered water dosed with at least one cleaning agent) to backwash at least one microfiltration unit, nanofiltration unit, or reverse osmosis unit of the system to perform a clean-in-place operation. The clean water-in-place storage tank may be fluidly connected to a source of cleaning agent. The clean water-in-place storage tank may be configured to direct clean-in-place waste to the solids holding tank.

[0099] The system may include one or more pumps or valves configured to direct fluids through the unit operations. The system may include one or more sensors, e.g., composition sensors, configured to measure a composition of the one or more fluids. The system may include one or more pH sensors configured to measure a pH of the one or more fluids. In some embodiments, the system may include a digestate composition sensor. The sensor may be configured to measure one or more of TKN, NH3-N, and PO4-P in the digestate. In some embodiments, the system may include a biogas composition sensor. The sensor may be configured to measure methane content of the biogas. In some embodiments, the system may include a biogas flow sensor. In some embodiments, the system may include a wastewater composition sensor. The sensor may be configured to measure one or more of pH, total solids, BOD, and C:N of the wastewater.

[0100] The system may include a controller operably connected to one or more sensors and configured to alert a user if the sensor measures a value outside a predetermined range of acceptable ranges. The controller may be operably connected to one or more pumps or valves. For example, the controller may be configured to direct dosing of a dosage agent according to a measured value, e.g., a measured pH unit. In some embodiments, the controller may be operably connected to a temperature control unit of the anaerobic digester. The controller may be operably connected to an agitator of the anaerobic digester.

[0101] In exemplary embodiments, the controller may be configured to dose nutrients and / or alkalinity to the wastewater depending on the composition of the digestate, e.g., the TKN, NH3-N, and / or PO4-N concentrations of the digestate. In some embodiments, the controller may be configured to vary the mixing conditions of the anaerobic digester depending on the methane content of the biogas or the biogas flow rate.

[0102] The controller may be a computer or a mobile device. The controller may include a touchpad or other operating interface. For example, the controller may be operated via a keyboard, a touchscreen, a trackpad, and / or a mouse. The controller may be configured to run software on an operating system known to those skilled in the art. The controller may be electrically connected to a power source. The controller may be digitally connected to one or more components. The controller may be connected to one or more components via a wireless connection. For example, the controller may be connected via a wireless local area network (WLAN) or short wavelength ultra-high frequency (UHF) radio waves. The controller may be operably connected to additional pumps or valves in the system, for example, the controller may direct fluids or additives as needed. The controller may be coupled to a memory storage device or cloud-based memory storage.

[0103] Multiple controllers may be programmed to operate the system in cooperation. For example, a controller may be programmed to cooperate with an external computing device. In some embodiments, the controller and the computing device may be integrated. In other embodiments, one or more of the processes disclosed herein may be performed manually or semi-automatically.

[0104] Referring to FIG. 1, a system 10 for treating biomass-containing wastewater is shown. The system 10 includes an organic matter digestion subsystem 1000 and a water recovery subsystem 2000. The organic matter digestion subsystem 1000 includes an anaerobic digester 120 and a solid-liquid separation subsystem 130. The anaerobic digester 120 may be a BVF® reactor from Evoqua Water Technologies, LLC. The water recovery subsystem 2000 includes an ammonia reduction column 210 and a second solid-liquid separation subsystem 220. The organic matter digestion subsystem 1000 has a solids outlet fluidly connected to a solids product subsystem 3000 that includes a holding tank. The solids product subsystem 3000 may include a solids product processing subsystem. Biogas produced by the anaerobic digester 120 is sent to a biogas processing subsystem 4000. The biogas processing subsystem 4000 may include an energy collection unit and / or a biogas processing unit. The water recovery subsystem 2000 has a product water outlet configured to direct the recovered water to a point of use. The water recovery subsystem 2000 has a retentate outlet to direct the retentate to a retentate treatment system, such as a sewer. The system 10 may operate to recover water from the digestion process and minimize liquid waste.

[0105] 2, an exemplary biomass digestion subsystem 1001 is shown. The biomass digestion subsystem 1001 includes an anaerobic digester 120, an oxidation tank 125, and a solid-liquid separation subsystem 130. A portion of the sludge produced in the anaerobic digester 120 may be returned to the anaerobic digester as return activated sludge (RAS) via pump P. The anaerobic digester 120 may be supplied with water and / or a pH adjuster to maintain the pH within the anaerobic digester at a level suitable for anaerobic digestion of the biomass in the wastewater.

[0106] The oxidation tank 125 receives the digestate from the anaerobic digester 120 and is supplied with an oxygen-containing gas, such as air, from a gas source 127. The oxidation tank 125 may be used to oxidize dissolved sulfides in the digestate from the anaerobic digester 120.

[0107] The solid-liquid separation subsystem 130 includes a source of separation additive 132, a reaction tank 134 for mixing the separation additive 132 with the effluent from the oxidation tank 125, a thickening tank 136, and a solid-liquid separation device 138, such as, for example, a centrifuge. The separation additive may be a softener, a coagulant, and / or a flocculant. The separation additive may include, for example, calcium hydroxide (lime), iron(III) sulfate, anionic polymers, and / or cationic polymers.

[0108] The thickener tank 136 may be used to mix the digestate from the anaerobic digester 120 with the separated additives to form a mixed liquor. A portion of the mixed liquor may be sent to the centrifuge 138. The remainder of the mixed liquor from the thickener tank 136 is provided to the water recovery subsystem 2000.

[0109] The solids from the centrifuge 132 are sent to the solids generation subsystem 3000. The separated liquid, or centrate, is returned from the centrifuge 138 to the oxidation tank 125. The biogas from the anaerobic digester 120 is sent to the biogas treatment subsystem 4000.

[0110] 3A, an exemplary water recovery subsystem 2001 is shown. The water recovery subsystem 2001 includes a filtration module 205, e.g., a cross-flow filtration unit such as a MemTek® Cross-Flow Microfiltration System from Evoqua Water Technologies LLC, an ammonia reduction column 210, and a solid-liquid separation subsystem 220. Retentate from the filtration module 205 may be removed and used, for example, as make-up water for a biogas scrubber used to scrub the biogas produced in the anaerobic digester 120. The ammonia reduction column 210 may be supplied with sulfuric acid from a sulfuric acid source 212, which reacts with the ammonia in the liquid stream to precipitate ammonium sulfate.

[0111] The solid-liquid separation subsystem 220 includes a first dosing agent source 223, a nanofiltration unit 222, a second dosing agent source 225, and a reverse osmosis unit 226. The dosing agents may include, for example, a pH adjuster, a scale inhibitor, and / or potassium bisulfite. The reverse osmosis unit 226 includes a permeate / product water outlet. The nanofiltration unit 222 and the reverse osmosis unit 226 have a retentate outlet that is directed to a retentate treatment subsystem 5000, such as a sewer or evaporation pond.

[0112] Referring to FIG. 3B, an alternative exemplary water recovery subsystem 2002 is shown. The water recovery subsystem 2002 is similar to the water recovery subsystem 2001, but the solid-liquid separation subsystem 220 includes a third dosing agent source 227 and a second nanofiltration unit 224 located downstream of the retentate outlet of the first nanofiltration unit 222. The second nanofiltration unit 224 can be a small-pore NF membrane unit designed to remove organic compounds to perform the NFRR process. The solid-liquid separation subsystem 220 also includes a fourth dosing agent source 229 and a second reverse osmosis unit 228 located downstream of the retentate outlet of the first reverse osmosis unit 226. The first reverse osmosis unit 226 can be a BWRO unit and the second reverse osmosis unit 228 can be a SWRO unit, both of which can be used to remove inorganic ionic species from the water being treated. The second nanofiltration unit 224 has a filtrate outlet directed to the second reverse osmosis unit 228. The second reverse osmosis unit 228 has a permeate outlet that directs the permeate to mix with the permeate from the first reverse osmosis unit 226 to form product water. The second nanofiltration unit 224 and the second reverse osmosis unit 228 have retentate outlets that are directed to the retentate waste subsystem 5000.

[0113] Referring to FIG. 4, a system 11 for treating biomass-containing wastewater is shown. System 11 is similar to system 10, except that system 11 includes a clean-in-place tank 600 fluidly connected downstream of the product water outlet. Clean-in-place tank 600 is configured to send a cleaning solution to solid-liquid separation subsystem 130 (e.g., for cleaning a cross-flow filtration unit) and solid-liquid separation subsystem 220 (e.g., for providing makeup water to an ammonia reduction column or for providing cleaning solution to a nanofiltration unit or a reverse osmosis unit). Clean-in-place tank 600 is configured to send clean-in-place waste to a solid waste holding tank, such as solid product subsystem 3000, for disposal. System 11 also includes a controller 700. Controller 700 may be operatively connected to one or more pumps, valves, or sensors of the system and configured to direct fluids (e.g., to dose separation additives or dosing agents) or control temperature within the system (e.g., using a temperature control unit of an anaerobic digester). EXAMPLES

[0114] The function and advantages of these and other embodiments may be better understood from the following examples, which are illustrative in nature and are not intended to limit the scope of the invention.

[0115] (Example 1: Mass balance of biomass-containing wastewater treatment system) A biomass-containing wastewater treatment plant was designed based on the pilot plant data. The plant will treat approximately 1157 gpm of biomass-containing wastewater. The plant has an organic matter digestion subsystem 1001, shown in Figure 2, upstream of the water recovery subsystem, shown in Figure 3B.

[0116] Influent wastewater is first screened through a 1 / 4-inch mesh basket strainer before being sent to an anaerobic digester. The anaerobic digester has a capacity of 5.73 million ft 3 / day of biogas and 59 gpm of sludge with 3-4% TSS.

[0117] The anaerobic digester effluent is mixed with 209 gpm of centrate from the downstream centrifuge and treated in the oxidation tank for sulfide oxidation. 1,307 gpm of in-process wastewater is discharged from the oxidation tank and dosed with lime and polymer flocculant. Solids from the in-process wastewater are allowed to settle in a thickener tank from which 240 gpm of sludge with 4% TSS is removed, dosed with additional polymer, and sent to the centrifuge. The centrifuge separates the sludge from the thickener tank into 34 gpm of 25% solids which is discarded and 209 gpm of centrate which is returned to the oxidation tank.

[0118] The mixed fluid from the thickening tank is sent to a cross-flow filtration system where the mixed fluid is separated into 20 gpm retentate and 1067 gpm filtrate. The filtrate is treated in an ammonia reduction column which outputs 18.2 gpm of 20-25% ammonium sulfate solution. The 1067 gpm ammonia reduced wastewater is sent to the first NF unit after being dosed with scale inhibitors and sulfuric acid. The 800 gpm filtrate from the first NF unit is sent to the first RO unit after being dosed with additional scale inhibitors and sulfuric acid. After adding additional scale inhibitors, 267 gpm retentate is sent from the first NF unit to the second NF unit. The 200 gpm filtrate from the second NF unit and 96 gpm retentate from the first RO unit are sent to the second RO unit. The first RO unit produces 704 gpm of permeate and the second RO unit produces 252 gpm of permeate that are mixed to form product water. 67 gpm of retentate from the second NF unit and 44 gpm of retentate from the second RO unit are sent out of the system for disposal.

[0119] Thus, from 1152 gpm of influent wastewater, the process produces 956 gpm of clean product water, 34 gpm of sludge for disposal, and 111 gpm of retentate.

[0120] Example 2: Digestion of biomass A wastewater sample containing ethanol production stillage was treated in the system disclosed herein. Some parameters of the wastewater and the wastewater after being treated in different unit operations of the system are shown in Table 1 below.

[0121] As shown, the system was able to reduce the wastewater TSS from 4,266 mg / L to undetectable levels in the final product water (RO permeate) and reduce the wastewater VSS from 3,839 mg / L to undetectable levels in the final product water. The wastewater TDS was reduced from 4,769 mg / L to 330 mg / L in the final product water. Sodium, calcium, sulfate, carbonate, and ammonia were all significantly reduced after treatment. Biogas was produced with a COD of 6.39 Scfd / lb.

[0122] [Table 1]

[0123] The phrases and terms used herein are for descriptive purposes and should not be considered limiting. The term "plurality" as used herein refers to two or more items or components. The terms "comprise," "include," "carry," "have," "contain," and "include" are open-ended terms in the written description, claims, and the like, meaning "including but not limited to." Thus, the use of such terms is meant to encompass the items listed thereafter, their equivalents, and additional items. With respect to the claims, only the transitional phrases "consisting of" and "consisting essentially of" are closed or semi-closed transitional phrases, respectively. The use of ordinal numbers such as "first," "second," and "third" to modify elements of a claim does not, in and of itself, imply that the element of a claim has priority, precedence, or order over elements of other claims, or the chronological order in which the actions of a method are performed, but is merely used as a label to distinguish an element of a claim having a particular name from another element having the same name (other than the use of the ordinal number) and to distinguish the elements of the claim.

[0124] Having thus described several aspects of at least one embodiment, it will be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Features described in any embodiment may be included in or substituted for features of other embodiments. Such changes, modifications, and improvements are intended to be part of this disclosure and within the scope of the invention. Accordingly, the foregoing description and drawings are for illustrative purposes only.

[0125] Those skilled in the art will understand that the parameters and configurations described herein are exemplary, and that the actual parameters and / or configurations will vary depending on the particular application in which the disclosed methods and materials are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, equivalents to the specific embodiments disclosed.

Claims

1. 1. A method for treating biomass and ammonia-containing wastewater, comprising: anaerobic digestion of the biomass and ammonia-containing wastewater to produce biogas and digestate; oxidizing dissolved sulfides in the digestate; mixing the digest to form a mixture; filtering a portion of the mixture to produce a first filtrate and a first retentate; removing ammonia from the first filtrate to produce an ammonia-reduced filtrate; removing organic contaminants and divalent ions from the ammonia-reduced filtrate by nanofiltration to produce a second retentate containing organics including divalent ions and a second organic-reduced filtrate; removing additional organic contaminants from the organic-containing second retentate by a second nanofiltration operation to produce a third filtrate and a third retentate; removing inorganic ionic species from the organic-reduced second filtrate by reverse osmosis to produce a fourth filtrate and a fourth retentate; combining the third filtrate and the fourth retentate; removing additional inorganic ionic species from the combination of the third filtrate and the fourth retentate by a second reverse osmosis operation to form product water; 1. A method for treating biomass and ammonia-containing wastewater, comprising:

2. 10. The method of claim 1, further comprising performing a solid-liquid separation of a second portion of the mixed liquor and returning the resulting liquor to a vessel for oxidizing dissolved sulfides.

3. 10. The method of claim 1, further comprising controlling the pH of the ammonia-reduced filtrate to about 7-9 and dosing the ammonia-reduced filtrate with a scale inhibitor.

4. The method of claim 1 further comprising processing the biogas to produce natural gas.

5. 5. The method of claim 4, further comprising using energy produced by the biogas to power at least one operation of the method.

6. 10. The method of claim 1, further comprising adjusting the pH of the biomass and ammonia-containing wastewater to about 6 or greater prior to anaerobic digestion of the biomass and ammonia-containing wastewater.

7. 1. A system for treating biomass and ammonia-containing wastewater, comprising: an anaerobic digester having an inlet fluidly connectable to a source of biomass-containing wastewater, a biogas outlet, and a digestate outlet; an oxidation tank having an inlet fluidly connected to the digestate outlet and an oxidation tank outlet; a softening agent source configured to deliver a softening agent to a mixing vessel having an inlet fluidly connected to the oxidation tank outlet and a mixing vessel outlet; a concentrate tank having an inlet fluidly connected to the outlet of the mixing vessel and first and second mixed liquor outlets; a solid-liquid separator having an inlet fluidly connected to the first mixed liquor outlet of the thickening tank and a separated liquor outlet fluidly connected to the inlet of the oxidation tank; a membrane filtration unit having an inlet fluidly connected to the second mixed liquor outlet of the concentration tank, a filtrate outlet, and a retentate outlet; an ammonia-reduction column having an inlet fluidly connected to the filtrate outlet, a countercurrent source of acid, and an ammonia-reduced filtrate outlet; a first nanofiltration unit having an inlet fluidly connected to the ammonia-reduced filtrate outlet, a filtrate outlet, and a retentate outlet; a second nanofiltration unit having an inlet fluidly connected to the retentate outlet of the first nanofiltration unit and a filtrate outlet; a first reverse osmosis unit having an inlet fluidly connected to the filtrate outlet of the first nanofiltration unit, a filtrate outlet, and a retentate outlet; a second reverse osmosis unit having an inlet fluidly connected to the filtrate outlet of the second nanofiltration unit and the retentate outlet of the first reverse osmosis unit; A system for treating biomass and ammonia-containing wastewater comprising:

8. The system of claim 7 , wherein the solid-liquid separator comprises a centrifuge.

9. The system of claim 8 , further comprising at least one of a coagulant source and a flocculant source located upstream of the centrifuge.

10. 8. The system of claim 7, further comprising a first pH adjuster source located upstream of the ammonia reduction column.

11. 11. The system of claim 10, further comprising a second source of pH adjuster located upstream of the first nanofiltration unit and / or a source of scale inhibitor located upstream of the first nanofiltration unit.

12. 8. The system of claim 7, wherein the anaerobic digester is a continuous stirred tank reactor (CSTR).

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