WO2021155315A1

WO2021155315A1 - Wastewater treatment method

Info

Publication number: WO2021155315A1
Application number: PCT/US2021/015937
Authority: WO
Inventors: Benjamin T.W BOCHER; Victor A. Adamian
Original assignee: Ineos Us Chemicals Company
Priority date: 2020-01-31
Filing date: 2021-01-29
Publication date: 2021-08-05

Abstract

The present disclosure relates generally to processes and apparatuses for treating wastewater. Accordingly, one aspect of the disclosure provides a method for treating an effluent from a process for manufacturing an aromatic carboxylic acid, the effluent comprising organic matter and at least one sulfide-forming metal. The method includes contacting the manufacturing process effluent with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced amount of one or more sulfide-forming metals relative to the manufacturing process effluent. The method includes transferring at least a portion of the precipitation zone supernatant to an anaerobic zone comprising biomass; in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane and hydrogen sulfide; transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

Description

WASTEWATER TREATMENT METHOD

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 62/968,708, filed on January 31, 2020, the contents of which are hereby incorporated by reference in their entirety.

FIELD

[0002] The present disclosure relates generally to methods for treating wastewater.

More particularly, the present disclosure relates to methods for treating an effluent from a process for manufacturing an aromatic carboxylic acid.

TECHNICAL BACKGROUND

[0003] Wastewaters from industrial processes can contain organic matter and metals that must be removed before being discharged (e.g., to receiving water bodies).

[0004] Typically, conventional wastewater treatment systems first remove organic matter. For example, treatment systems can use microorganisms aggregated into a biomass to digest the organic matter. Such biological systems are typically one of two types — anaerobic (e.g., granular biomass) or aerobic (e.g., “activated sludge”). Anaerobic systems are generally more cost effective for removing the majority of organic matter, but often are unable to lower the concentration of organic matter to that required for discharge permits (e.g., no more than about 800 ppmw chemical oxygen demand (COD)).

Accordingly, aerobic reactions are typically used to bring the organic matter concentration to lower concentrations (e.g., about 100 ppmw chemical oxygen demand “COD”).

[0005] Anaerobic digestion of organic material produces a methane-rich biogas. Among other factors, the presence of H S produced by sulfur-reducing bacteria during anaerobic degradation limits the value of biogas, as the biogas stream can be corrosive and can cause fouling of biogas processing equipment.

[0006] Moreover, metals present in certain wastewaters — such as those from a process for manufacturing an aromatic carboxylic acid — can react with H S in an anaerobic reactor. The resulting metal-sulfide precipitates settle to the bottom of the reactor, forming a layer of biosolids and inert solids that must be physically removed after taking the reactor offline. Restarting the anaerobic reactor is complicated and can take several months. Additionally, recovery of precipitated metals from the biosolids-inert solids mixture is difficult and not practical. [0007] Conventional metal-removal methods for wastewater treatment include physical- chemical processes such as ion exchange, nanofiltration, and reverse osmosis. Such methods, which can be energy intensive, are necessarily performed at the end of a treatment process, where the partially treated water includes lower concentrations of organic matter that can interfere with metal removal. However, the preceding anaerobic and aerobic treatments can introduce biological by-products that can complicate the removal processes.

[0008] There accordingly remains a need to improve wastewater treatment processes for effluent from a process for manufacturing an aromatic carboxylic acid.

SUMMARY

[0009] The scope of the present disclosure is not affected to any degree by the statements within this summary.

[0010] In one aspect, the disclosure provides a method for treating a wastewater stream, the wastewater stream comprising organic matter and at least one sulfide-forming metal, the process comprising contacting the wastewater stream with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced concentration of one or more sulfide forming metals relative to the manufacturing process effluent; transferring at least a portion of the precipitation zone supernatant to an anaerobic zone comprising an anaerobic biomass; in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane, carbon dioxide, and hydrogen sulfide; and transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

[0011] In another aspect, the disclosure provides a method for treating an effluent from a process for manufacturing an aromatic carboxylic acid, the effluent comprising organic matter and at least one sulfide-forming metal, the process comprising contacting the manufacturing process effluent with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced concentration of one or more sulfide-forming metal relative to the manufacturing process effluent; transferring at least a portion of the precipitation zone supernatant to an anaerobic zone comprising an anaerobic biomass; in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane, carbon dioxide, and hydrogen sulfide; and transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

[0012] In certain embodiments of the methods as otherwise described herein, the aromatic carboxylic acid is terephthalic acid.

[0013] In certain embodiments of the methods as otherwise described herein, the at least one sulfide-forming metal is present in the wastewater stream or the manufacturing process effluent in a total concentration in the range of 0.5 to 500 ppm (e.g., in the range of 1-100 ppm, typically 2 to 20 ppm) by weight (ppmw).

[0014] In certain embodiments of the methods as otherwise described herein, the at least one sulfide-forming metal includes one or more of cobalt, manganese and iron,.

[0015] In certain embodiments of the methods as otherwise described herein, cobalt is present in the wastewater stream or the manufacturing process effluent in a combined concentration of at least 0.5 ppmw (ranging from 0.5 to 500- ppmw, typically 2 to 20 ppmw).

[0016] In certain embodiments of the methods as otherwise described herein, organic matter is present in the wastewater stream or the manufacturing process effluent in concentration of at least 1000 ppmw chemical oxygen demand (e.g., 1000-15000 ppmw, or 5000-25000 ppmw).

[0017] In certain embodiments of the methods as otherwise described herein, the organic matter present in the wastewater stream or the manufacturing process effluent includes, but is not limited to, one or more of terephthalic acid, acetic acid, methanol, methyl acetate, benzoic acid, p-toluic acid, trimellitic acid, iso-phthalic acid, o-phthalic acid, p- carboxybenzaldehyde, and p-hydroxymethyl-benzoic acid.

[0018] In certain desirable embodiments of the methods as otherwise described herein, a concentration of cobalt present in the precipitation zone supernatant is no more than 50% (e.g., no more than 25%, no more than 20%, no more than 10%, or no more than 5%) of a concentration of cobalt present in the wastewater stream or manufacturing process effluent. In other embodiments, the concentration of cobalt in the precipitation zone supernatant is no more than 90% (e.g., no more than 75%) of the concentration of cobalt in the manufacturing process effluent.

[0019] In certain embodiments of the methods as otherwise described herein, organic matter is present in the anaerobic zone effluent in a concentration of no more than 10,000 ppm (e.g., no more than 7500 ppm, no more than 5000 ppm, no more than 1000 ppm, no more than 800 ppm, or no more than 500 ppm) chemical oxygen demand.

[0020] In certain embodiments of the methods as otherwise described herein, the method includes transferring at least a portion of an effluent of the anaerobic zone to an aerobic zone comprising activated sludge and an oxygen source. In certain such embodiments, the method further comprises in the aerobic zone, digesting at least a portion of the organic matter of the anaerobic zone effluent, transferring at least a portion of an effluent of the aerobic zone to a clarifier zone, and in the clarifier zone, forming a settled solids fraction and a clarifier zone supernatant having a reduced solids content.

[0021] In certain embodiments of the methods as otherwise described herein, organic matter is present in the aerobic zone effluent in a concentration of no more than 1000 ppmw (e.g., no more than 750 ppmw, or no more than 500 ppmw, or no more than 200 ppmw, or no more than 100 ppmw) chemical oxygen demand.

[0022] In certain embodiments of the methods as otherwise described herein, hydrogen sulfide from the biogas stream makes up at least 10 mol.% (e.g., at least 25 mol.%, or at least 50 mol.%, or at least 75 mol.%, or at least 80 mol.%, or at least 90 mol.%) of the sulfide of the sulfide source. The sulfide source can also include sulfide from other sources, e.g., external to the reaction processes described here. The person of ordinary skill in the art will understand that, as used herein, the sulfide source can be provided from one stream (e.g., solely the biogas stream, or a single stream combining the biogas stream with an external sulfide source), or a plurality of separate streams to the precipitation zone.

[0023] In certain embodiments of the methods as otherwise described herein, the method includes addition of sulfate to the anaerobic zone.

[0024] In certain embodiments of the methods as otherwise described herein, hydrogen sulfide and cobalt are present in the precipitation zone in a molar ratio of at least 1:1 hhSiCo (e.g., at least 1.1:1, or at least 1.25:1, or at least 1.5:1, or at least 1.75:1, or at least 2:1 H₂S:CO). [0025] In certain embodiments of the methods as otherwise described herein, at least 50 vol.% (e.g., at least 75 vol.%, or at least 85 vol.%, or at least 95 vol.%, or at least 99 vol.%) of the biogas stream is transferred to the precipitation zone. In certain embodiments, at least 10 vol.% (e.g., at least 25 vol.%, or at least 35 vol.%) of the biogas stream is transferred to the precipitation zone.

[0026] In certain embodiments of the methods as otherwise described herein, a methane-rich stream is recovered from the precipitation zone, the methane-rich stream comprising a reduced amount of hydrogen sulfide relative to the biogas stream.

[0027] In certain embodiments of the methods as otherwise described herein, the anaerobic zone comprises an upflow anaerobic sludge blanket reactor (UASB). But, as the person of ordinary skill in the art will understand, other types of reactors can be used in the anaerobic zone, e.g., fixed film anaerobic reactors and the anaerobic reactors available from Aqana under the tradename DACS.

[0028] In certain embodiments of the methods as otherwise described herein, the method further includes recovering at least one of the sulfide-forming metals from the precipitated fraction. The one or more sulfide-forming metals can beneficially be used in any suitable manner, depending on the metal. For example, in certain embodiments, the recovered metal is used as a catalyst in a process for manufacturing an aromatic carboxylic acid (e.g., recycled to the manufacturing process providing the effluent).

[0029] Other aspects of the disclosure will be apparent to those skilled in the art in view of the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a process flow diagram for the treatment of an effluent from a process for manufacturing an aromatic carboxylic acid, in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0031] In various aspects, the processes of the disclosure provide for efficient removal of organic materials and metals from an effluent from a process for manufacturing an aromatic carboxylic acid.

[0032] Additional features of the processes of the disclosure will now be described in reference to the drawing figures.

[0033] The present inventors have determined that contacting wastewater comprising one or more sulfide-forming metals and organic matter with a sulfide source upstream of an anaerobic reactor forms an recoverable metal-sulfide precipitate. Because the resulting supernatant has a reduced metals content, inactive-layer build-up in a downstream anaerobic zone (and accordingly, costly shutdown, layer removal, and startup) can be largely avoided. The present inventors have also determined that contacting the sulfide forming metals with a biogas stream of the downstream anaerobic zone desirably removes H2S from the biogas stream, and moreover decreases or even eliminates the need for an external sulfide source. Various embodiments are described below in the context of a wastewater stream that is an effluent from a process for manufacturing an aromatic carboxylic acid. The person of ordinary skill in the art will appreciate that the embodiments described herein can adapted for use with other wastewater streams containing organic matter and at least one sulfide-forming metal.

[0034] Accordingly, one aspect of the disclosure provides a method for treating an effluent from a process for manufacturing an aromatic carboxylic acid, the effluent comprising organic matter and at least one sulfide-forming metal. The method includes contacting the manufacturing process effluent with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced concentration of one or more sulfide-forming metals relative to the manufacturing process effluent. The method includes transferring at least a portion the precipitation zone supernatant to an anaerobic zone that includes an anaerobic biomass (e.g., a granular anaerobic biomass); in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane, carbon dioxide, and hydrogen sulfide; and transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

[0035] FIG. 1 is a process flow diagram for treating an effluent from a process for manufacturing an aromatic carboxylic acid, in accordance with one embodiment of the present disclosure. As shown in FIG. 1, a system for performing a method includes a precipitation zone 110 capable of precipitating one or more sulfide-forming metals to form a precipitated fraction comprising at least one metal sulfide and a precipitation zone supernatant comprising a reduced amount of one or more sulfide-forming metals; an anaerobic zone 120 capable of digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream. The system can in some embodiments further include, as shown in FIG. 1, an aerobic zone 130 capable of digesting at least a portion of the organic matter of an effluent of the anaerobic zone in the presence of an oxygen source; and a clarifier zone 140 capable of separating entrained solids from an effluent of the aerobic zone to form a settled solids fraction and a clarifier zone supernatant. [0036] Liquid and gaseous streams and materials used in the method represented in FIG. 1 may be directed and transferred through suitable transfer lines, conduits, and piping constructed, for example, from materials appropriate for process use and safety. It will be understood that particular elements may be physically juxtaposed and, where appropriate, may be have flexible regions, rigid regions, or a combination of both. In directed streams, intervening apparatuses and/or optional treatments may be included. By way of example, pumps, valves, manifolds, gas and liquid flow meters and distributors, sampling and sensing devices, and other equipment (e.g., for monitoring, controlling, adjusting, and/or diverting pressures, flows and other operating parameters) may be present. Other equipment is optionally present, including but not limited to: biogas handling equipment (e.g., water knock out drums; ultrafiltration equipment).

[0037] In the embodiment of FIG. 1 , an effluent from a process for manufacturing an aromatic carboxylic acid is transferred through a line 112 into the precipitation zone 110. In certain embodiments, the precipitation zone includes one or more contacting tanks (e.g., arranged in parallel and/or in series). As used herein, “processes for manufacturing aromatic carboxylic acids” include, for example, processes for manufacturing mono- and polycarboxylated species having one or more aromatic rings. In some embodiments, the aromatic carboxylic acids are manufactured by reaction of gaseous and liquid reactants in a liquid phase system. In some embodiments, the aromatic carboxylic acid comprises only one aromatic ring. In other embodiments, the aromatic carboxylic acid comprises a plurality (e.g., two or more) of aromatic rings that, in some embodiments, are fused (e.g., naphthalene, anthracene, etc.) and, in other embodiments, are not. In some embodiments, the aromatic carboxylic acid comprises only one carboxylic acid (e.g., -CO2H) moiety or a salt thereof (e.g., -CO2X, where X is a cationic species including but not limited to metal cations, ammonium ions, and the like). In other embodiments, the aromatic carboxylic acid comprises a plurality (e.g., two or more) of carboxylic acid moieties or salts thereof. Representative aromatic carboxylic acids include but are not limited to terephthalic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, benzoic acid, naphthalene dicarboxylic acids, and the like, and combinations thereof.

[0038] For example, in certain embodiments as otherwise described herein, an effluent from a process for manufacturing terephthalic acid (e.g., purified terephthalic acid, or so- called medium- purity terephthalic acids), isophthalic acid, trimellitic acid, or naphthalenedicarboxylic acid is transferred through a line 112 into the precipitation zone 110. In certain embodiments as otherwise described herein, the manufacturing process includes oxidation of a substituted aromatic hydrocarbon (e.g. p-xylene) to form the aromatic carboxylic acid (e.g., terephthalic acid), and the manufacturing process effluent is a liquid condensed from an off-gas of the oxidation reaction of the process (e.g., in an off-gas treatment zone) or a filtrate separated from solid aromatic carboxylic acid (e.g., in a recovery zone of the process). The effluent can be transferred to the precipitation zone directly (e.g., from an off-gas treatment zone or a recovery zone), or indirectly. For example, in certain embodiments, effluent is collected in a pressure equalization tank (not shown), and then transferred from the pressure equalization tank to the precipitation zone 110.

[0039] As used herein, “sulfide-forming metals” include metals that can react (e.g., in aqueous solution) with a sulfide source to form a metal-sulfide product (e.g., having a lower solubility in water than that of the sulfide-forming metal). Also as used herein, “sulfide sources” include sulfides and sulfur-containing compounds capable of reacting with sulfide forming metals to form a metal-sulfide product. For example, cobalt can react with a sulfide source (e.g., H2S) to form cobalt sulfides (e.g., CoS, C0S2, C0₃S4, CogSs, CoS_x where x is 0.5-3, etc.). Similarly, manganese can react with a sulfide source (e.g., H2S) to form manganese sulfides (e.g., MnS, MnS2, MnS_x where x is 0.5-3, etc.).

[0040] In certain embodiments as otherwise described herein, the manufacturing process effluent comprises at least one sulfide-forming metal selected from cobalt, manganese, iron and chromium. In certain desirable embodiments, the manufacturing process effluent comprises cobalt and manganese.

[0041] In certain embodiments as otherwise described herein, the at least one sulfide forming metal is present in the manufacturing process effluent in a total concentration of at least 0.1 ppm by weight (ppmw), e.g., at least 0.5 ppmw, at least 1 ppmw, at least 2 ppmw, or at least 5 ppmw, or at least 10 ppmw. For example, in certain embodiments as otherwise described herein, the at least one sulfide-forming metal is present in the manufacturing process effluent in a concentration in the range of 0.1-500 ppmw, e.g., 0.5-500 ppmw, or 1- 500 ppmw, or 5-500 ppmw, or 10-500 ppmw, or 25-500 ppmw, or 0.1-100 ppmw, or 0.5-100 ppmw, or 0.1-50 ppmw, or 0.5-50 ppmw, or 0.1-25 ppmw, or or 0.5-25 ppmw, or 0.5-20 ppmw, or 2-500 ppmw, or 2-100 ppmw or 2-25 ppmw, or 2-20 ppmw. In certain embodiments as otherwise described herein, the manufacturing process effluent comprises cobalt as a sulfide-forming metal (e.g., in an amount as described above). In certain embodiments, cobalt is present in a concentration in an concentration of at least 0.5 ppmw (e.g., within the range 0.5-500 ppmw, or 2 to 20 ppmw). In certain embodiments as otherwise described herein, the manufacturing process effluent comprises manganese in a concentration as described above. In certain embodiments, manganese is present in a concentration of at least 0.1 ppmw (e.g., within the range 0.1-500 ppmw, or 2 to 20 ppmw). [0042] As used herein, “organic matter” includes carbon-containing impurities and byproducts from the process for manufacturing an aromatic carboxylic acid. For example, organic matter in an effluent of a manufacturing process including oxidation of a substituted aromatic hydrocarbon (e.g. p-xylene) to form the aromatic carboxylic acid (e.g., terephthalic acid) can include the aromatic carboxylic acid, partial oxidation products, and other by products of oxidation and purification steps of the process (e.g., in the case of PTA manufacturing, terephthalic acid, acetic acid, methanol, methyl acetate, benzoic acid, p- toluic acid, trimellitic acid, iso-phthalic acid, o-phthalic acid, p-carboxybenzaldehyde, p- hydroxymethyl-benzoic acid etc.). The person of ordinary skill in the art will appreciate that a concentration of organic matter can be expressed as a chemical oxygen demand (i.e. , an amount of oxygen necessary to completely oxidize the organic matter present in a sample).

[0043] In certain embodiments as otherwise described herein, organic matter is present in the manufacturing process effluent in a concentration of at least 1000 ppmw chemical oxygen demand (COD), e.g., 1000-15000 ppmw, or 5000-25000 ppmw COD.

[0044] In precipitation zone 110, the manufacturing process effluent contacts a sulfide source (e.g., at a pH ranging from 6 to 10, desirably6.5 to 8), forming a precipitated fraction comprising at least one metal sulfide and a precipitation zone supernatant comprising a reduced amount of one or more sulfide-forming metals relative to the manufacturing process effluent. The sulfide source comprises H S from a biogas stream produced in the anaerobic zone 120. In the embodiment of FIG. 1, the biogas stream is removed from the anaerobic zone 120 through a line 126, and then transferred to the precipitation zone 110 through line 114. The sulfide source can include sulfide other than H S from the biogas stream, such as H S from an external source (e.g., transferred to the precipitation zone 110 through the line 114). In certain embodiments, H S from the biogas stream makes up at least 10 mol.%

(e.g., at least 25 mol.%, or at least 50 mol.%) of the sulfide of the sulfide source. For example, in certain desirable embodiments, H S from the biogas stream makes up at least 70 mol.% (e.g., at least 80 mol.%, or at least 90 mol.%) of the sulfide of the sulfide source of the sulfide of the sulfide source.

[0045] In certain embodiments as otherwise described herein, hydrogen sulfide and cobalt are present in the precipitation zone in a molar ratio of at least 1:1 H S:Co, e.g., at least 1.1:1, or at least 1.25:1, or at least 1.5:1, or at least 1.75:1, or at least 2:1 H S:Co.

[0046] Contact of the sulfide source with the manufacturing zone effluent can be provided by mechanical agitation, gas sparging (with biogas or an additional carrier gas), recirculation pumping, static mixing, etc. A suitable mixing regime can be provided by one skilled in the art based on the present disclosure. In certain embodiments, contacting the manufacturing process effluent comprises sparging the manufacturing process effluent with the sulfide source.

[0047] In the embodiment of FIG. 1, the precipitated fraction (i.e. , comprising at least one metal sulfide) settles to the bottom of a contacting tank of the precipitation zone 110, and is removed through a line 118. Advantageously, the present inventors have noted that the precipitated fraction can be conveniently separated from the precipitation zone supernatant, and valuable sulfide-forming metals such as cobalt and manganese can be recovered from the metal sulfides of the precipitated fraction.

[0048] A methane-rich stream comprising methane and other biogas components is removed from the precipitation zone (i.e., after contacting the H S of the biogas stream with the manufacturing process effluent) through a line 116. Desirably, the H S content of the methane-rich stream is significantly reduced relative to that of the biogas generated in the anaerobic zone; accordingly, corrosion and/or fouling of equipment used to handle or process stream 116 can be minimized, or even avoided. For example, in certain embodiments as otherwise described herein, H S is present in the sulfide source at a concentration in the range of 100-1000 ppm, e.g., 300-500 ppm; and H S is present in the methane-rich stream in a concentration no more than 100 ppm, e.g., 10-100 ppm. As the person of ordinary skill in the art will appreciate, the methane-rich stream can be used in a number of ways, e.g., as fuel to heat the anaerobic reactor, and/or as fuel for furnaces or boilers in other portions of an industrial plant.

[0049] Precipitation zone supernatant (i.e., comprising a reduced amount of one or more sulfide-forming metals relative to the manufacturing process effluent) is transferred to the anaerobic zone 120 through a line 122. In certain embodiments as otherwise described herein, the precipitation zone supernatant has a reduced amount of one or both of cobalt and manganese relative to the manufacturing process effluent. For example, in certain embodiments, the precipitation zone supernatant comprises a concentration of cobalt that is no more than 50% (e.g., no more than 25%, or no more than 20%) of a concentration of cobalt present in the manufacturing process effluent. In certain embodiments, the precipitation zone supernatant comprises a concentration of cobalt that is no more than 10% (e.g., no more than 5%) of a concentration of cobalt present in the manufacturing process effluent. However, the methods of the disclosure can be valuable even in cases when there is relatively less removal of cobalt from the precipitation zone, e.g., when the concentration of cobalt in the precipitation zone supernatant is no more than 90% (e.g., no more than 75%) of the concentration of cobalt in the manufacturing process effluent. [0050] The anaerobic zone 120 includes a biomass. In certain embodiments, the anaerobic zone 120 includes one or more anaerobic reactors (e.g., arranged in parallel and/or in series), each containing a biomass. As used herein, the “biomass” contained in the anaerobic zone includes microorganisms capable of digesting organic matter (i.e. , capable of reducing the chemical oxygen demand) present in the precipitation zone supernatant. In certain embodiments, the biomass comprises a slurry or a sludge. In certain embodiments, the biomass comprises solid granules.

[0051] For example, in certain desirable embodiments, the anaerobic zone comprises an upflow anaerobic sludge blanket (UASB) reactor containing a granular biomass. In certain such embodiments, digestion is conducted at a reactor temperature of 75-125 °F (e.g., about 100 °F). In certain such embodiments, the granular sludge inventory of the anaerobic zone (e.g., of one or more reactors of the anaerobic zone) is 4-10% (e.g., about 7%) total suspended solids, of which 50-90% is volatile suspended solids. In certain desirable embodiments, the average settling velocity of the granules is at least 20 m/hr (e.g., at least 50 m/hr, or at least 75 m/hr, or 20-125 m/hr, or 50-125 m/hr, or 75-125 m/hr). Suitable granular biomass is generally known in the art.

[0052] The person of ordinary skill in the art will appreciate that other types of reactors can be used in the anaerobic zone, e.g., fixed film anaerobic reactors and the anaerobic reactors available from Aqana under the tradename DACS. And the person of ordinary skill in the art will be able to provide anaerobic zone reaction conditions suitable to provide a desired conversion based on the description herein.

[0053] The biomass in the anaerobic zone 120 (e.g., in a UASB reactor of the anaerobic zone 120) digests at least a portion of the organic matter of the precipitation zone supernatant and contains the necessary sulfide-reducing bacteria, thereby forming a biogas comprising H2S CO2, and CFU. In certain embodiments as otherwise described herein, digestion removes at least 0.2 units of COD per day (e.g., 0.2-0.8 units of COD, or 0.3-0.5 units of COD) per unit of volatile suspended solids. Advantageously, the present inventors have determined that the reduced sulfide-forming metal content of the precipitation zone supernatant can minimize or even avoid build-up of an inactive solids layer in anaerobic reactors, desirably avoiding costly shutdowns for maintenance that necessitate a slow, complex start-up process.

[0054] In certain embodiments of the methods as otherwise described herein, the amount of hydrogen sulfide provided to the precipitation zone can be adjusted by addition of sulfate to the anaerobic zone. The sulfate can react in the anaerobic zone to form additional hydrogen sulfide. Sulfate addition to the anaerobic zone can be a safer and lower cost alternative to provide increased amounts of hydrogen sulfide to the precipitation zone than addition of sulfide to the precipitation zone from a different source. Sulfate can be added via any convenient sulfate source, e.g., an alkali metal sulfate such as sodium sulfate or an alkaline earth metal sulfate such as calcium sulfate or magnesium sulfate. Sulfate can be converted to sulfide in the anaerobic zone, with the sulfide becoming part of the biogas stream conducted to the precipitation zone.

[0055] As described above, biogas is removed from the anaerobic zone 120 through the line 126, and transferred to the precipitation zone 110 (through the line 114). In certain embodiments as otherwise described herein, at least 50 vol.%, e.g., at least 75 vol.%, or at least 85 vol.%, or at least 95 vol.%, or at least 99 vol.% of the biogas stream is transferred to the precipitation zone. In other embodiments, at least 10 vol.% (e.g., at least 25 vol.%, or at least 35 vol.%) of the biogas stream is transferred to the precipitation zone.

[0056] An effluent of the anaerobic zone 120 is transferred through a line 132 to aerobic zone 130. In certain embodiments as otherwise described herein, organic matter is present in the anaerobic zone effluent in a concentration of no more than 10,000 ppmw (e.g., no more than 7500 ppmw, no more than 5000 ppmw, no more than 1,000 ppmw, no more than 800 ppmw, or no more than 500 ppmw) chemical oxygen demand.

[0057] As described above, in certain embodiments of the methods as otherwise described herein, the method further includes transferring at least a portion of an effluent of the anaerobic zone to an aerobic zone comprising activated sludge and an oxygen source.

In the embodiment of FIG. 1 , the aerobic zone 130 includes an activated sludge and an oxygen source. In certain embodiments, the aerobic zone 130 includes one or more aerobic reactors (e.g., arranged in parallel and/or in series), each containing an activated sludge. As used herein, the “activated sludge” contained in the aerobic zone includes microorganisms capable of digesting organic matter (i.e., capable of reducing the chemical oxygen demand) present in the effluent of the anaerobic zone, in an aerobic environment. In the embodiment of FIG. 1, an oxygen source (e.g., air, pure oxygen, etc.) is introduced to the aerobic zone 130 through a line 134. In certain embodiments, air introduced through the bottom of one or more aerobic reactors rises through the activated sludge and the anaerobic zone effluent, promoting mixing thereof. Alternatively, air can be introduced from above if forced down through the activated sludge, before again rising to the top. Suitable aerobic reactors which may be employed in the aerobic zone, and operating conditions thereof, are generally known in the art.

[0058] An effluent of the aerobic zone 130 can be transferred through a line 142 to a clarifier zone 140. In certain embodiments as otherwise described herein, organic matter is present in the aerobic zone effluent in a concentration of no more than 1000 ppmw (e.g., no more than 750 ppmw, or no more than 500 ppmw, or no more than 200 ppmw, or no more than 150 ppmw) COD. For example, in certain embodiments, organic matter is present in the aerobic zone effluent in a concentration in the range of 10-1000 ppmw (e.g., 10-750 ppmw, or 10-500 ppmw, or 10-200 ppmw, or 10-150 ppmw) COD.

[0059] In the clarifier zone 140, entrained activated sludge and/or other solids present in the aerobic zone effluent settle (e.g., to the bottom of one or more clarifiers of the clarifier zone 140), forming a settled solids fraction and a clarifier zone supernatant having a reduced solids content. In the embodiment of FIG. 1 , the settled solids fraction is removed from the clarifier zone 140 through a line 144. In certain embodiments as otherwise described herein, the settled solids fraction including activated sludge is returned to the aerobic zone 130 (e.g., through the lines 146 and 132). In certain embodiments as otherwise described herein, the settled solids fraction is transferred to a downstream sludge processing zone (not shown), where the settled solids fraction is, for example, dewatered, dried, incinerated, landfilled, etc.

[0060] The clarifier zone supernatant is removed from the clarifier zone 140 through a line 152. In certain embodiments as otherwise described herein, the clarifier zone supernatant is transferred to a tertiary processing zone (not shown), in which the supernatant is further treated as is generally known in the art (e.g., by polishing ponds, membrane processes, etc.). In other embodiments, the clarifier zone supernatant is directly discharged from the clarifier zone (e.g., to a receiving water body). In certain embodiments as otherwise described herein, a portion of the clarifier zone supernatant is returned to a equalization tank upstream of the precipitation zone 110 (not shown).

[0061] Another aspect of the disclosure provides a system for treating an effluent from a process for manufacturing an aromatic carboxylic acid (e.g., capable of a treatment method as otherwise described herein) comprising a precipitation zone having an effluent inlet, a vapour inlet, and an effluent outlet; an anaerobic zone having an effluent inlet in fluid communication with the effluent outlet of the precipitation zone, a vapour outlet in fluid communication with the vapour inlet of the precipitation zone, and an effluent outlet. The system can further include an aerobic zone having an effluent inlet in fluid communication with the effluent inlet of the anaerobic zone and a vapour inlet in fluid communication with an oxygen source. In certain such embodiments, the system includes a clarifier zone having an effluent inlet in fluid communication with an effluent outlet of the aerobic zone.

[0062] Additional aspects of the disclosure are provided by the following enumerated embodiments, which can be combined in any number and in any fashion that is not technically or logically inconsistent. Embodiment 1. A method for treating an effluent from a process for manufacturing an aromatic carboxylic acid, the effluent comprising organic matter and at least one sulfide forming metal, the method comprising contacting the manufacturing process effluent with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced concentration of one or more sulfide-forming metals relative to the manufacturing process effluent; transferring at least a portion of the precipitation zone supernatant to an anaerobic zone comprising a biomass; in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane, carbon dioxide, and hydrogen sulfide; and transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

Embodiment 2. The method of embodiment 1, wherein the aromatic carboxylic acid is terephthalic acid.

Embodiment 3. The method of embodiment 1 or 2, wherein the at least one sulfide forming metal is present in the manufacturing process effluent in a total concentration of at least 0.1 ppmw, e.g., in the range of 0.1-500 ppmw, or 1-500 ppmw, or 5-500 ppmw, or IQ- 500 ppmw, or 25-500 ppmw).

Embodiment 4. The method of any of embodiments 1-3, wherein the at least one sulfide-forming metal includes one or more of cobalt, manganese and iron.

Embodiment 5. The method of any of embodiments 1-4, wherein cobalt is present in the manufacturing process effluent in a total concentration of at least 0.5 ppmw (e.g., 0.5- 500 ppmw, or 2 to 20 ppmw).

Embodiment 6. The method of any of embodiments 1-5, wherein organic matter is present in the manufacturing process effluent in a concentration of at least 1,000 ppmw (e.g., 1,000-15,000 ppmw, or 5,000-25,000 ppmw) chemical oxygen demand. Embodiment 7. The method of any of embodiments 1-6, wherein the organic matter present in the manufacturing process effluent includes, but is not limited to one or more of terephthalic acid, acetic acid, methanol, methyl acetate, benzoic acid, p-toluic acid, trimellitic acid, iso-phthalic acid, o-phthalic acid, p-carboxybenzaldehyde, and p-hydroxymethyl- benzoic acid.

Embodiment 8. The method of any of embodiments 1-7, wherein a concentration of cobalt present in the precipitation zone supernatant is no more than 50% (e.g., no more than 30%, no more than 20%, no more than 10%, or no more than 5%) of a concentration of cobalt present in the manufacturing process effluent.

Embodiment 9. The method of any of embodiments 1-8, wherein organic matter is present in the anaerobic zone effluent in a concentration of no more than 10,000 ppmw (e.g., no more than 7,500 ppmw, no more than 5,000 ppmw, no more than 1,000 ppmw, no more than 800 ppmw, or no more than 500 ppmw) chemical oxygen demand.

Embodiment 10. The method of any of embodiments 1-9, further comprising transferring at least a portion of an effluent of the anaerobic zone to an aerobic zone comprising activated sludge and an oxygen source.

Embodiment 11. The method of embodiment 10, further comprising, in the aerobic zone, digesting at least a portion of the organic matter of the anaerobic zone effluent, transferring at least a portion of an effluent of the aerobic zone to a clarifier zone, and in the clarifier zone, forming a settled solids fraction and a clarifier zone supernatant having a reduced solids content.

Embodiment 12. The method of embodiment 11 , wherein organic matter is present in the aerobic zone effluent in a concentration of no more than 1 ,000 ppmw (e.g., no more than 750 ppmw, or no more than 500 ppmw, or no more than 200 ppmw, or no more than 150 ppmw) chemical oxygen demand.

Embodiment 13. The method of any of embodiments 1-12, wherein hydrogen sulfide from the biogas stream makes up at least 10 mol.% (e.g., at least 25 mol.%, or at least 50 mol.%, or at least 70 mol.%, or at least 80 mol.%, or at least 90 mol.%) of the sulfide of the sulfide source. Embodiment 14. The method of any of embodiments 1-13, further comprising adding sulfate to the anaerobic zone.

Embodiment 15. The method of any of embodiments 1-14, wherein hydrogen sulfide and cobalt are present in the precipitation zone in a molar ratio of at least 1:1 hhSiCo (e.g., at least 1.1:1, or at least 1.25:1, or at least 1.5:1, or at least 1.75:1, or at least 2:1 hhS o).

Embodiment 16. The method of any of embodiments 1-15, wherein at least 50 vol.% (e.g., at least 75 vol.%, or at least 85 vol.%, or at least 95 vol.%, or at least 99 vol.%) of the biogas stream is transferred to the precipitation zone.

Embodiment 17. The method of any of embodiments 1-16, further comprising recovering a methane-rich stream from the precipitation zone, the methane-rich stream comprising a reduced amount of hydrogen sulfide relative to the biogas stream.

Embodiment 18. The method of any of embodiments 1-17, further comprising recovering at least one of the sulfide-forming metals from the precipitated fraction.

Embodiment 19. The method of embodiment 18, further comprising using the recovered metal as a catalyst in the manufacture of an aromatic carboxylic acid.

Embodiment 20. The method of any of embodiments 1-19, wherein the anaerobic zone comprises an upflow anaerobic sludge blanket reactor (UASB).

Embodiment 21. A method for treating a wastewater stream, the wastewater stream comprising organic matter and at least one sulfide-forming metal, the process comprising contacting the wastewater stream with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced concentration of one or more sulfide forming metal relative to the manufacturing process effluent; transferring at least a portion of the precipitation zone supernatant to an anaerobic zone comprising an anaerobic biomass; in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane, carbon dioxide, and hydrogen sulfide; and transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

Embodiment 22. A system for treating a wastewater stream (e.g., an effluent from a process for manufacturing an aromatic carboxylic acid), the system comprising a precipitation zone having an effluent inlet, a vapour inlet, and an effluent outlet; an anaerobic zone having an effluent inlet in fluid communication with the effluent outlet of the precipitation zone, a vapour outlet in fluid communication with the vapour inlet of the precipitation zone, and an effluent outlet.

Embodiment 23. The system of embodiment 22, further comprising an aerobic zone having an effluent inlet in fluid communication with the effluent inlet of the anaerobic zone and a vapour inlet in fluid communication with an oxygen source.

Embodiment 24. The system of embodiment 23, further comprising a clarifier zone having an effluent inlet in fluid communication with an effluent outlet of the aerobic zone.

[0063] The entire contents of each and every patent and non-patent publication cited herein are hereby incorporated by reference, except that in the event of any inconsistent disclosure or definition from the present specification, the disclosure or definition herein shall be deemed to prevail.

[0064] The foregoing detailed description and the accompanying drawings have been provided by way of explanation and illustration and are not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

[0065] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding claim — whether independent or dependent — and that such new combinations are to be understood as forming a part of the present specification.

Claims

1. A method for treating an effluent from a process for manufacturing an aromatic carboxylic acid, the effluent comprising organic matter and at least one sulfide-forming metal, the method comprising contacting the manufacturing process effluent with a sulfide source in a precipitation zone to form a precipitated fraction comprising at least one metal sulfide, and a precipitation zone supernatant comprising a reduced concentration of one or more sulfide-forming metals relative to the manufacturing process effluent; transferring at least a portion of the precipitation zone supernatant to an anaerobic zone comprising a biomass; in the anaerobic zone, digesting at least a portion of the organic matter of the precipitation zone supernatant and forming a biogas stream comprising methane, carbon dioxide, and hydrogen sulfide; and transferring at least a portion of the biogas stream to the precipitation zone; wherein the sulfide source of the precipitation zone comprises hydrogen sulfide from the biogas stream.

2. The method of claim 1, wherein the aromatic carboxylic acid is terephthalic acid.

3. The method of claim 1, wherein the at least one sulfide-forming metal is present in the manufacturing process effluent in a total concentration in the range of 0.1-500 ppmw.

4. The method of claim 1, wherein the at least one sulfide-forming metal includes one or more of cobalt, manganese and iron.

5. The method of claim 1, wherein the organic matter present in the manufacturing process effluent includes, but is not limited to one or more of terephthalic acid, acetic acid, methanol, methyl acetate, benzoic acid, p-toluic acid, trimellitic acid, iso-phthalic acid, o-phthalic acid, p- carboxybenzaldehyde, and p-hydroxymethyl-benzoic acid; and the organic matter is present in the manufacturing process effluent in a concentration of 1,000-15,000 ppmw chemical oxygen demand.

6. The method of claim 1, wherein a concentration of cobalt present in the precipitation zone supernatant is no more than 50% of a concentration of cobalt present in the manufacturing process effluent.

7. The method of claim 1 , wherein organic matter is present in the anaerobic zone effluent in a concentration of no more than 10,000 ppmw chemical oxygen demand.

8. The method of claim 1, further comprising transferring at least a portion of an effluent of the anaerobic zone to an aerobic zone comprising activated sludge and an oxygen source.

9. The method of claim 8, further comprising, in the aerobic zone, digesting at least a portion of the organic matter of the anaerobic zone effluent, transferring at least a portion of an effluent of the aerobic zone to a clarifier zone, and in the clarifier zone, forming a settled solids fraction and a clarifier zone supernatant having a reduced solids content.

10. The method of claim 9, wherein organic matter is present in the aerobic zone effluent in a concentration of no more than 1,000 ppmw chemical oxygen demand.

11. The method of claim 1, wherein hydrogen sulfide from the biogas stream makes up at least 10 mol.% of the sulfide of the sulfide source.

12. The method of claim 1, further comprising adding sulfate to the anaerobic zone.

13. The method of claim 1, wherein at least 50 vol.% of the biogas stream is transferred to the precipitation zone.

14. The method of claim 1, further comprising recovering a methane-rich stream from the precipitation zone, the methane-rich stream comprising a reduced amount of hydrogen sulfide relative to the biogas stream; recovering at least one of the sulfide-forming metals from the precipitated fraction; and using the recovered metal as a catalyst in the manufacture of an aromatic carboxylic acid.

15. A system for treating a wastewater stream, the system comprising a precipitation zone having an effluent inlet, a vapour inlet, and an effluent outlet; an anaerobic zone having an effluent inlet in fluid communication with the effluent outlet of the precipitation zone, a vapour outlet in fluid communication with the vapour inlet of the precipitation zone, and an effluent outlet; an aerobic zone having an effluent inlet in fluid communication with the effluent inlet of the anaerobic zone and a vapour inlet in fluid communication with an oxygen source; and a clarifier zone having an effluent inlet in fluid communication with an effluent outlet of the aerobic zone.