CA2542894A1 - Multi-environment wastewater treatment method - Google Patents
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- CA2542894A1 CA2542894A1 CA002542894A CA2542894A CA2542894A1 CA 2542894 A1 CA2542894 A1 CA 2542894A1 CA 002542894 A CA002542894 A CA 002542894A CA 2542894 A CA2542894 A CA 2542894A CA 2542894 A1 CA2542894 A1 CA 2542894A1
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/30—Aerobic and anaerobic processes
- C02F3/301—Aerobic and anaerobic treatment in the same reactor
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/28—Anaerobic digestion processes
- C02F3/2806—Anaerobic processes using solid supports for microorganisms
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/30—Aerobic and anaerobic processes
- C02F3/302—Nitrification and denitrification treatment
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F3/00—Biological treatment of water, waste water, or sewage
- C02F3/02—Aerobic processes
- C02F3/06—Aerobic processes using submerged filters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/10—Biological treatment of water, waste water, or sewage
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Abstract
A single-tank wastewater treatment system has a multiplicity of zones with different environmental conditions including aerobic, anoxic and anaerobic, to reduce the strength of highly concentrated wastewaters in terms of their content of organic carbonaceous compounds and nutrients, notably nitrogen and phosphorus. The upper zone of the treatment system operates under alternatively aerobic and anoxic conditions controlled by the on-off operation of an air blower that introduces air through air diffusers placed at the bottom of the upper zone. The lower section of the treatment system contains oxygen--depleted zones including anoxic conditions at the bottom and anaerobic conditions above the anoxic zones and below the air diffusers. The upper and lower sections of the tank are in fluid communication. Within the volume of upper aerobic zone and lower oxygen-depleted zones, loose carrier material or stationary objects are disposed to support the attachment of microbial biomass and the formation of microbial biofilm. Thus, the treatment system includes both suspended and immobilized microorganisms.
Description
Multi-Environment Wastewater Treatment Method Field of the Invention The method and apparatus of this invention relate to the reduction in concentrations of organic compounds as well as nitrogen and phosphorus in a liquid or slurry of waste stream (e.g., wastewater or sludge) originated from municipal or industrial activities, or groundwater or landfill leachate. The organic material may contain sources of BOD and COD as well as hazardous chemicals such as aromatic hydrocarbons, including benzene, toluene, ethylbenzene, xylenes, phenols, cresols, polycyclic aromatic hydrocarbons (PAHs), and halogenated (e.g., chlorinated) hydrocarbons, such as tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane and similar xenobiotics, and inorganic material notably nitrogen and phosphorus.
Background of the Invention The treatment of wastewater and contaminated groundwater require the removal of organic and inorganic contaminants, usually present in solid and/or dissolved form, before their discharge into the receiving waters. The organic contaminants include sources of COD/BOD such as proteins, lipids and polysaccharides as well as hazardous compounds such as aromatic and aliphatic hydrocarbons.
Examples of the latter group include gasoline and diesel fuel, polycyclic aromatic hydrocarbons, phenols, chlorophenols, alkylated benzenes, tetrachloroethylene (PCE) and trichloroethylene (TCE). The nitrogenous and phosphorus compounds, which are among the most undesirable inorganic contaminants of wastewater and contaminated groundwater, also need to be removed during the treatment process.
The organic charge in the wastewater is often measured by chemical oxygen demand (COD) or biochemical oxygen demand (BOD). These parameters define the overall oxygen load that a wastewater will impose on the receiving water.
During biological treatment processes, organic substances are removed since these substances serve as the source of carbon and energy in the microbial metabolism. Nitrogen and phosphorus are also consumed by microorganisms as essential nutrients to support microbial growth during assimilatory processes, while excess amounts of nitrogenous compounds is removed during dissimilatory microbial nitrogen metabolism where they are transformed to molecular nitrogen and released into the atmosphere. The remaining phosphorus may be removed by the enhanced biological phosphorus removal (EBPR) or "luxury phosphorus uptake" process where special groups of microorganisms accumulate phosphorus and store it as poly-phosphorus compounds, thus removing it from the system during waste sludge disposal. Some nitrogen and phosphorus are also removed by the formation of chemical compounds that precipitate to the bottom of the tank.
Nitrogen and phosphorus have been recognized as major contributors to eutrophication, a process that supports the growth of algae and other undesirable organisms in the receiving waters and diminishes the concentration of dissolved oxygen, thus threatening aquatic life. Therefore, stringent criteria have been introduced demanding the reduction of these nutrients below certain levels that are established by the environmental agencies, before the effluent of treatment plants can be safely discharged to the receiving waters.
Biological removal of nitrogen involves two stages, nitrification and denitrification.
Nitrification involves the conversion of ammonia nitrogen to nitrite and nitrate nitrogen and requires an aerobic environment. This process is achieved in all aerobic reactors if the right operating conditions such as the dissolved oxygen concentration, liquid pH, carbonate concentration, and sludge retention time exist. Denitrification, i.e. the transformation of nitrate nitrogen to molecular
Background of the Invention The treatment of wastewater and contaminated groundwater require the removal of organic and inorganic contaminants, usually present in solid and/or dissolved form, before their discharge into the receiving waters. The organic contaminants include sources of COD/BOD such as proteins, lipids and polysaccharides as well as hazardous compounds such as aromatic and aliphatic hydrocarbons.
Examples of the latter group include gasoline and diesel fuel, polycyclic aromatic hydrocarbons, phenols, chlorophenols, alkylated benzenes, tetrachloroethylene (PCE) and trichloroethylene (TCE). The nitrogenous and phosphorus compounds, which are among the most undesirable inorganic contaminants of wastewater and contaminated groundwater, also need to be removed during the treatment process.
The organic charge in the wastewater is often measured by chemical oxygen demand (COD) or biochemical oxygen demand (BOD). These parameters define the overall oxygen load that a wastewater will impose on the receiving water.
During biological treatment processes, organic substances are removed since these substances serve as the source of carbon and energy in the microbial metabolism. Nitrogen and phosphorus are also consumed by microorganisms as essential nutrients to support microbial growth during assimilatory processes, while excess amounts of nitrogenous compounds is removed during dissimilatory microbial nitrogen metabolism where they are transformed to molecular nitrogen and released into the atmosphere. The remaining phosphorus may be removed by the enhanced biological phosphorus removal (EBPR) or "luxury phosphorus uptake" process where special groups of microorganisms accumulate phosphorus and store it as poly-phosphorus compounds, thus removing it from the system during waste sludge disposal. Some nitrogen and phosphorus are also removed by the formation of chemical compounds that precipitate to the bottom of the tank.
Nitrogen and phosphorus have been recognized as major contributors to eutrophication, a process that supports the growth of algae and other undesirable organisms in the receiving waters and diminishes the concentration of dissolved oxygen, thus threatening aquatic life. Therefore, stringent criteria have been introduced demanding the reduction of these nutrients below certain levels that are established by the environmental agencies, before the effluent of treatment plants can be safely discharged to the receiving waters.
Biological removal of nitrogen involves two stages, nitrification and denitrification.
Nitrification involves the conversion of ammonia nitrogen to nitrite and nitrate nitrogen and requires an aerobic environment. This process is achieved in all aerobic reactors if the right operating conditions such as the dissolved oxygen concentration, liquid pH, carbonate concentration, and sludge retention time exist. Denitrification, i.e. the transformation of nitrate nitrogen to molecular
2 nitrogen requires anoxic conditions and the presence of an easily degradable carbon source. If the treatment system cannot supply the required carbon source, then an external source such as methanol, ethanol, acetic acid or a different compound must be added. Biological nitrogen removal uses pre-denitrification or post-denitrification processes depending on whether the anoxic denitrification stage is before or after the aerobic nitrification stage, respectively.
When pre-denitrification is practiced, a recycle stream retums the nitrate-rich liquid from the aerobic zone to the anoxic zone for denitrification. In order to achieve phosphorus removal as well as nitrogen removal, the incorporation of an anaerobic zone in the treatment system is necessary. Anaerobic condition refers to the absence of molecular oxygen without traces of oxygen whereas anoxic environments may contain traces of oxygen, normally undetectable by commercial dissolved oxygen electrodes.
Combined anaerobiclanoxic/aerobic processes are frequently used in wastewater treatment systems for the removal of organic carbonaceous compounds and inorganic nitrogen and phosphorus. The presence of a diversified microbial population and different environmental conditions offered by the combined systems are particularly needed for the removal of nitrogen and phosphorus. However, combined systems are also used when high BOD/COD
concentrations are present in the wastewater since these systems offer a superior capacity and higher removal efficiencies compared to the aerobic, anoxic or anaerobic processes alone. In the combined processes, the excessive carbon and nitrogen materials are first hydrolyzed and partly degraded by anaerobic processes in the anoxic and/or anaerobic zones and then the remaining contaminating compounds are degraded and removed by aerobic processes in the follow-up aerobic zone. Moreover, in aerobic treatment processes, the reactor temperature often rises to the levels that it may inhibit microbial activities, especially the activity of nitrifying bacteria that are involved in the nitrification process. The incorporation of anaerobic processes lowers the reactor's temperature since anaerobic processes generate a lower amount of
When pre-denitrification is practiced, a recycle stream retums the nitrate-rich liquid from the aerobic zone to the anoxic zone for denitrification. In order to achieve phosphorus removal as well as nitrogen removal, the incorporation of an anaerobic zone in the treatment system is necessary. Anaerobic condition refers to the absence of molecular oxygen without traces of oxygen whereas anoxic environments may contain traces of oxygen, normally undetectable by commercial dissolved oxygen electrodes.
Combined anaerobiclanoxic/aerobic processes are frequently used in wastewater treatment systems for the removal of organic carbonaceous compounds and inorganic nitrogen and phosphorus. The presence of a diversified microbial population and different environmental conditions offered by the combined systems are particularly needed for the removal of nitrogen and phosphorus. However, combined systems are also used when high BOD/COD
concentrations are present in the wastewater since these systems offer a superior capacity and higher removal efficiencies compared to the aerobic, anoxic or anaerobic processes alone. In the combined processes, the excessive carbon and nitrogen materials are first hydrolyzed and partly degraded by anaerobic processes in the anoxic and/or anaerobic zones and then the remaining contaminating compounds are degraded and removed by aerobic processes in the follow-up aerobic zone. Moreover, in aerobic treatment processes, the reactor temperature often rises to the levels that it may inhibit microbial activities, especially the activity of nitrifying bacteria that are involved in the nitrification process. The incorporation of anaerobic processes lowers the reactor's temperature since anaerobic processes generate a lower amount of
3 heat compared to the aerobic processes. Besides, anaerobic processes have the capacity of operating at higher temperatures by using anaerobic thermophilic microorganisms that have a higher tolerance to elevated temperatures and efficiently degrade organic compounds at temperatures above 500 C. Therefore, anaerobic processes are often used prior to aerobic processes to reduce the concentration of organic compounds, especially in the treatment of highly concentrated wastewaters, before their final treatment by aerobic processes.
Several designs of the combined anaerobic/anoxic/aerobic systems have been used with varying efficiencies for the treatment of animal wastes that commonly contain very high carbon and nitrogen concentrations (Kim et al, 2004; Poo et al., 2004; Choi et al. 2005). In these systems, anaerobic processes are initially used to hydrolyze the organic carbon and nitrogenous compounds and reduce the COD by degrading the carbon compounds. Some reductions in the nitrogen and phosphorus concentrations also take place in the anaerobic processes by their assimilation into the biomass cellular material and by the formation of chemical compounds such as struvite and hydroxyapatite. The remaining biodegradable carbonaceous and nitrogen compounds will be treated in an aerobic polishing stage to further reduce the COD and to oxidize the ammonia nitrogen. Higher nitrogen removal efficiencies will result by providing fluid communication between the aerobic and anoxiclanaerobic zones to accomplish denitrification.
The patent literature describes numerous techniques used to supply various environmental conditions for the removal of organic carbon and nutrients. In general, these techniques either include the creation of alternative aerobic-anoxic/anaerobic environments in a single zone/tank whereby controlled aeration provides alternating periods of aerobic and anoxiclanaerobic conditions or they include different zones/tanks having the required environmental conditions.
Examples of alternating aerobic-anoxic/anaerobic conditions in a single tank are found in US patents 5,266,200; 5,776,344; 6,905,602 and 6,936,170 while examples of multi-zone/multi-environment treatment technologies are described
Several designs of the combined anaerobic/anoxic/aerobic systems have been used with varying efficiencies for the treatment of animal wastes that commonly contain very high carbon and nitrogen concentrations (Kim et al, 2004; Poo et al., 2004; Choi et al. 2005). In these systems, anaerobic processes are initially used to hydrolyze the organic carbon and nitrogenous compounds and reduce the COD by degrading the carbon compounds. Some reductions in the nitrogen and phosphorus concentrations also take place in the anaerobic processes by their assimilation into the biomass cellular material and by the formation of chemical compounds such as struvite and hydroxyapatite. The remaining biodegradable carbonaceous and nitrogen compounds will be treated in an aerobic polishing stage to further reduce the COD and to oxidize the ammonia nitrogen. Higher nitrogen removal efficiencies will result by providing fluid communication between the aerobic and anoxiclanaerobic zones to accomplish denitrification.
The patent literature describes numerous techniques used to supply various environmental conditions for the removal of organic carbon and nutrients. In general, these techniques either include the creation of alternative aerobic-anoxic/anaerobic environments in a single zone/tank whereby controlled aeration provides alternating periods of aerobic and anoxiclanaerobic conditions or they include different zones/tanks having the required environmental conditions.
Examples of alternating aerobic-anoxic/anaerobic conditions in a single tank are found in US patents 5,266,200; 5,776,344; 6,905,602 and 6,936,170 while examples of multi-zone/multi-environment treatment technologies are described
4 in US patents 4,279,753; 4,800,021; 4,824,563; 4,895,645; 5,049,266;
5,196,111; 5,342,522; 5,534,147; 5,578,202; 5,578,214; 5,626,755; 5,645,725;
5,651,892; 5,676,828; 5,783,071; 5,811,008; 5,843,305; 6,054,044; 6,136,185;
5,651,892; 5,676,828; 5,783,071; 5,811,008; 5,843,305; 6,054,044; 6,136,185;
6,203,702 and 6,235,196.
US patent 5,776,344 describes a treatment system whereby wastewater passes through the biologically active material at least twice in two different directions.
The biologically active material comprises granular media to provide filtration sufficient to remove solid particulates from the wastewater flowing in the first direction and backwashing in the second direction to dislodge at least a portion of the particulates from the media. US patent 6,905,602 also relates to a biofilm system containing an anoxic tank for denitrification followed by an aerobic or altemating aerobic/anoxic treatment unit for nitrification. The anoxic tank contains a number of synthetic cords with a specific gravity lower than the specific gravity of the effluent providing support for the formation of fixed film organisms.
US patents 4,800,021; 4,895,645; 5,578,202; 5,626,755; 5,783,071 and 5,843,305 relate to treatment systems using a single multi-zone bioreactor containing different environmental conditions of aerobic, anoxic and/or anaerobic for the removal of organic carbon as well as nitrification and pre- or post-denitrification for nitrogen removal.
In US patent 4,800,021, microbial biomass is fixed in a multilayer bed of granular materials with at least partial aeration of the biomass creating a single upflow filtration reactor including a lower anaerobic zone and an upper aerobic zone separated by the injection of oxygenated gas. The oxygenated gas is sent intermittently into the bottom of the filter to reduce the level of phosphorus of the treated effluent.
US patent 4,895,645 describes a biological filter containing two distinct aerobic and anoxic zones. Pre-denitrification and anaerobic carbon removal take place in an upflow rock filter, while nitrification takes place in a downflow plastic filter making the system a fixed-film technology. Nitrified effluent is recycled back from the aerobic zone to the anaerobic zone along with the raw wastewater.
Liquid recirculation is used both for wetting of the plastic trickling filter media and for fumishing nitrate to the anaerobic filter.
US patent 5,578,202 relates to a processing vessel having an aerobic chamber, an anaerobic chamber containing blocks of buoyant filter material and a buffering chamber. A recycle stream returns a part of the water in the buffering chamber back to the anaerobic chamber.
In US patent 5,626,755 the three zones of aerobic, anoxic and anaerobic are established successively in vertical arrangement in a single tank. The aerobic zone at the bottom of the reactor is adjacent to the anoxic zone which is next to the anaerobic zone lying on the upper most section of the reactor. The environmental conditions in the three different biological zones are controlled by the introduction of microscopic gaseous bubbles and the quantity of air introduced into the aerobic zone.
US patent 5,783,071 provides an altemative design for a multi-environment treatment system comprising a single cylindrical tank having an outer anaerobic zone and an inner aerobic zone providing the passage of wastewater from the outer anaerobic zone to the inner aerobic zone-through holes in the inner wall that define the aerobic zone. An open ended conical hopper is positioned within the inner aerobic zone whose sides define a clarification zone.
US patent 5,843,305 relates to a wastewater treatment plant which comprises a compartmentalized bioreactor having an anaerobic zone, an aerobic zone and a middle compartment located between the anaerobic and aerobic compartments.
The middle compartment has a gas-solid separator for separating rising gas from anaerobic microorganisms. The aerobic zone contains a precipitation portion in an upper region for the separation of treated water from the system. A medium in a layered honeycomb type arrangement is provided in the anaerobic and aerobic zones for distributing the wastewater and for the attachment of microorganisms.
US patents 4,279,753; 5,049,266; 5,342,522; 5,578,214; 5,645,725; 5,651,892;
5,676,828; 5,811,008; 6,054,044; 6,136,185; 6,203,702; and 6,235,196 relate to treatment systems comprising several successive reactors having different levels of dissolved oxygen concentration to which wastewater is exposed sequentially for organic carbon and nutrient removal.
US patent 4,279,753 includes multiple series of altemating aerobic-anaerobic bioreactors in series. Each pair of bioreactor includes an upflow aerobic reactor and a downflow anaerobic reactor, all reactors containing support medium for fixed film microorganisms.
US patent 5,049,266 uses two fixed-film reactors for successive pre-denitrification and nitrification of wastewater after passing through a sedimentation compartment. Pre-denitrification takes place in an upflow fixed-bed anaerobic reactor while nitrification is carried out in a downflow fixed-bed aerobic reactor operating as a trickling filter. Recycle streams connect the two reactors for continuous operation.
US patent 5,342,522 uses three bioreactors in series. The first reactor contains aerobic and anaerobic zones for phosphorus removal, the second reactor has aerobic conditions for nitriifcation and the third reactor has anoxic conditions for denitriifcation. The nitrifying and denitrifying bioreactors are both fixed film reactors. An intermediate settling tank may be used after the first reactor to discharge phosphate-rich surplus sludge.
US patent 5,776,344 describes a treatment system whereby wastewater passes through the biologically active material at least twice in two different directions.
The biologically active material comprises granular media to provide filtration sufficient to remove solid particulates from the wastewater flowing in the first direction and backwashing in the second direction to dislodge at least a portion of the particulates from the media. US patent 6,905,602 also relates to a biofilm system containing an anoxic tank for denitrification followed by an aerobic or altemating aerobic/anoxic treatment unit for nitrification. The anoxic tank contains a number of synthetic cords with a specific gravity lower than the specific gravity of the effluent providing support for the formation of fixed film organisms.
US patents 4,800,021; 4,895,645; 5,578,202; 5,626,755; 5,783,071 and 5,843,305 relate to treatment systems using a single multi-zone bioreactor containing different environmental conditions of aerobic, anoxic and/or anaerobic for the removal of organic carbon as well as nitrification and pre- or post-denitrification for nitrogen removal.
In US patent 4,800,021, microbial biomass is fixed in a multilayer bed of granular materials with at least partial aeration of the biomass creating a single upflow filtration reactor including a lower anaerobic zone and an upper aerobic zone separated by the injection of oxygenated gas. The oxygenated gas is sent intermittently into the bottom of the filter to reduce the level of phosphorus of the treated effluent.
US patent 4,895,645 describes a biological filter containing two distinct aerobic and anoxic zones. Pre-denitrification and anaerobic carbon removal take place in an upflow rock filter, while nitrification takes place in a downflow plastic filter making the system a fixed-film technology. Nitrified effluent is recycled back from the aerobic zone to the anaerobic zone along with the raw wastewater.
Liquid recirculation is used both for wetting of the plastic trickling filter media and for fumishing nitrate to the anaerobic filter.
US patent 5,578,202 relates to a processing vessel having an aerobic chamber, an anaerobic chamber containing blocks of buoyant filter material and a buffering chamber. A recycle stream returns a part of the water in the buffering chamber back to the anaerobic chamber.
In US patent 5,626,755 the three zones of aerobic, anoxic and anaerobic are established successively in vertical arrangement in a single tank. The aerobic zone at the bottom of the reactor is adjacent to the anoxic zone which is next to the anaerobic zone lying on the upper most section of the reactor. The environmental conditions in the three different biological zones are controlled by the introduction of microscopic gaseous bubbles and the quantity of air introduced into the aerobic zone.
US patent 5,783,071 provides an altemative design for a multi-environment treatment system comprising a single cylindrical tank having an outer anaerobic zone and an inner aerobic zone providing the passage of wastewater from the outer anaerobic zone to the inner aerobic zone-through holes in the inner wall that define the aerobic zone. An open ended conical hopper is positioned within the inner aerobic zone whose sides define a clarification zone.
US patent 5,843,305 relates to a wastewater treatment plant which comprises a compartmentalized bioreactor having an anaerobic zone, an aerobic zone and a middle compartment located between the anaerobic and aerobic compartments.
The middle compartment has a gas-solid separator for separating rising gas from anaerobic microorganisms. The aerobic zone contains a precipitation portion in an upper region for the separation of treated water from the system. A medium in a layered honeycomb type arrangement is provided in the anaerobic and aerobic zones for distributing the wastewater and for the attachment of microorganisms.
US patents 4,279,753; 5,049,266; 5,342,522; 5,578,214; 5,645,725; 5,651,892;
5,676,828; 5,811,008; 6,054,044; 6,136,185; 6,203,702; and 6,235,196 relate to treatment systems comprising several successive reactors having different levels of dissolved oxygen concentration to which wastewater is exposed sequentially for organic carbon and nutrient removal.
US patent 4,279,753 includes multiple series of altemating aerobic-anaerobic bioreactors in series. Each pair of bioreactor includes an upflow aerobic reactor and a downflow anaerobic reactor, all reactors containing support medium for fixed film microorganisms.
US patent 5,049,266 uses two fixed-film reactors for successive pre-denitrification and nitrification of wastewater after passing through a sedimentation compartment. Pre-denitrification takes place in an upflow fixed-bed anaerobic reactor while nitrification is carried out in a downflow fixed-bed aerobic reactor operating as a trickling filter. Recycle streams connect the two reactors for continuous operation.
US patent 5,342,522 uses three bioreactors in series. The first reactor contains aerobic and anaerobic zones for phosphorus removal, the second reactor has aerobic conditions for nitriifcation and the third reactor has anoxic conditions for denitriifcation. The nitrifying and denitrifying bioreactors are both fixed film reactors. An intermediate settling tank may be used after the first reactor to discharge phosphate-rich surplus sludge.
7 US patent 5,578,214 discusses a two-tank apparatus for the treatment of wastewater with high concentrations of carbon and nitrogen contaminants. The first tank has a lower section with aeration means to create aerobic conditions and an upper section packed with vinylidene chloride fillers and an air supply agitation means for supplying air. The second tank has a section packed with charcoal and calcium carbonate fillers and an exhaust gas introduction diffuser for directing exhaust gases. The water under treatment is treated anaerobically in the lower portion of the first tank and continues treatment under aerobic or anaerobic conditions in the upper portion. Treatment further continues in the second tank under aerobic conditions. The exhaust gases from the first bioreactor are also treated in the second tank concomitant with the treatment of water. Nitrogen is removed by creating alternative aerobic and anaerobic conditions in the tanks. In an alternative design a membrane filter may be placed over the vinylidene chloride fillers in the first bioreactor.
In US patent 5,645,725 the anoxic zone contains porous mineral material particies and activated charcoal particles. Recycle streams in these treatment systems return a portion of the effluent from various stages of the process and connect reactors having different environmental conditions.
US patent 5,651,892 uses an aerobic vertical shaft bioreactor with an oxygen-containing gas for the removal of organic carbon from the liquid previously denitrified in an anoxic reactor. The effluent of the shaft bioreactor will be clarified and subsequently nitrified under aerobic condition. The treated liquid is clarified in a ciarification unit for final discharge.
US patent 6,054,044 has anoxic, anaerobic and aerobic cultures while US patent 5,811,008 contains aerobic and anaerobic cultures and an arrangement for controlling the residence time of the wastewater in the anaerobic reactor by varying the volume of this reactor.
g US patents 6,136,185 and 6,203,702 discuss a treatment system that has two treatment tanks and a holding reservoir. Each of the treatment tanks has an anaerobic zone that is two to five feet deep and an aerobic zone on top of the anaerobic zone that is at least twelve feet deep. Wastewater passes through the anaerobic zone to the aerobic zone of the first tank and continues treatment in the anaerobic and aerobic zones of the second tank.
US patent 6,235,196 discusses a wastewater bioprocessing system that comprises an anaerobic reactor, an aerobic reactor in direct communication with the anaerobic reactor, and a recycle loop for recycling a portion of the aerobic reactor effluent to the anaerobic reactor. The anaerobic and aerobic reactors can include a single reactor or a plurality of reactors. The recycle loop provides pH regulation, dilution of the feed, and nitrite-nitrate removal. The aerobic and anaerobic reactors may contain fixed-film microorganisms.
None of the known technologies offer a single-tank treatment system that comprises both pre-denitrification and post-denitrification operations for the removal of nitrogen; fixed-film combined with suspended microorganisms; three zones with flexible volumes and different environmental conditions, namely aerobic, anoxic and anaerobic, with controlled duration of aerobic and anoxic periods; and fluid communication between the zones. These features are all included in the treatment technology of the present invention offering significant reductions in the concentrations of organic carbon and nitrogen and reduction of phosphorus in a single easy-to-operate and maintain treatment tank with a small footprint. The treatment system of the present invention offers the presence of a diversified group of suspended and fixed-film microorganisms, high concentration and residence time of the microbial biomass, high specific and volumetric rates of contaminant removal, ease of operation and a relatively small footprint, and provides an intemal supply of carbon source for the denitriifcation process, eliminating the requirement for the supply of an external carbon source.
Summary of the invention The concept of multi-zone, multi-environment technology has been implemented in the design and development of a new wastewater treatment technology particularfy suitable to reduce the strength of highly concentrated wastewaters in terms of their content of organic carbonaceous compounds and nutrients, notably nitrogen and phosphorus, facilitating their further treatment. Very high organic and nitrogen loads of certain wastewaters render conventional treatment processes ineffective. The technology of the present invention reduces the concentrations of carbonaceous compounds and nitrogen and makes some reductions of phosphorus in a highly concentrated wastewater such as those produced in animal farms or slaughterhouses to the extent that the wastewater will be amenable to complete treatment by conventional technologies such as sequencing batch reactor (SBR) or activated sludge, conforming to environmental standards for effluent discharge. Thus, the technology of the present invention may serve either as a treatment technology if its effluent characteristics conform to local environmental standards, or as a pretreatment technology especially when dealing with highly concentrated wastewaters or stringent environmental standards. This is a major step in the treatment of high strength wastewaters since very high carbon and nitrogen concentrations often prohibit treatment.
The treatment process of the present invention contains a multiplicity of environmental conditions, including aerobic, anoxic and anaerobic, in a single, multi-zone tank to support the growth and proliferation of different groups of microorganisms and a variety of biochemical reactions involved in the removal of carbon, nitrogen and phosphorus contaminants. There are no baffles or walls to separate the zones. The influent wastewater is introduced into the treatment system at the bottom of the tank which is under anoxic conditions and flows upward passing through the anaerobic zone and continues its move towards the upper zone located above air diffusers. The upper zone operates under aerobic/anoxic conditions controlled by the ON/OFF action of an air blower.
Thus, in this treatment system the organic contaminants are first degraded by anaerobic processes in the anoxic and anaerobic zones reducing their concentration before further treatment in the aerobic zone. The ON/OFF cycle of the air blower will create a cyclic aerobic/anoxic zone in the upper section of the reactor supporting the degradation of organic carbonaceous compounds by aerobic microorganisms during the ON period as well as their anoxic degradation by facultative anaerobes during the OFF period while promoting nitrification and denitrification for nitrogen removal. Additional denitrification for a complete removal of nitrogen takes place at the bottom of the tank that is under anoxic conditions and is in fluid communication with the upper zone via a recycle stream. The treatment system includes both suspended and attached microorganisms, increasing cell retention time and enhancing the treatment capacity of the system. This design results in lower treatment temperatures, less production of microbial biomass and requires less oxygen for the aerobic degradation of the remaining compounds.
Brief Description of the Drawings The invention will be described in more detail in the following description in conjunction with the drawings in which:
Fig. I represents schematically an exemplary wastewater treatment system of the invention, Fig. 2 illustrates a relationship between the solid retention time (SRT) in different zones of the treatment system and the recycle ratio (r) under the first operating strategy, Fig. 3 represents schematically another embodiment of a wastewater treatment system of the invention, and Fig. 4. illustrates a relationship between the solid retention time (SRT) in different zones of the treatment system and the recycle ratio (r) under the second and third operating strategy.
Detailed Description of the Invention An example of the treatment system according to the invention is presented in FIG. 1. The system uses a single tank (1) containing multiple zones having different environmental conditions of aerobic, anoxic and anaerobic for the removal or considerable reductions in the concentrations of carbon and nitrogen and some reductions in the concentration of phosphorus contaminants. The tank (1) is divided into upper (2) and lower (3) sections by air diffusers (4) located horizontally inside the tank. The volumes of the two sections are not fixed and they are determined during the design stage based on the characteristics of the wastewater including the nature of the contaminants and their respective concentrations. Air is introduced into the system on a pre-determined schedule by an air blower or air compressor (5) through the air diffusers (4). The upper section (2) is aerobic when the air blower is ON and becomes anoxic when the air blower is tumed OFF. The durations of ON and OFF periods may or may not be equal and will be determined by the operator depending on the characteristics of the wastewater under treatment in order to adjust the required duration of aerobic and anoxic periods and the required efficiency of treatment. The periods can vary from minutes to hours. Examples include one hour ON and one hour OFF or 20 minutes ON and 40 minutes OFF, or 2 hours ON and three hours OFF.
The non-aerated lower section (3) below the air diffusers (4) has anoxic condition at the bottom (6) and anaerobic condition at the top (7), implying that the bottom of the treatment tank is under anoxic condition and the anaerobic zone is located above the anoxic zone and below the air diffusers (4). There are no walls or baffles to separate the different zones and there is a gradual change of the environmental conditions from anoxic to anaerobic in the bottom section imposed through the consumption of oxygen by the microorganisms and progressive depletion of oxygen as liquid moves upward. The division between the zones is naturally established by the change in dissolved oxygen concentration and redox potential in these zones. The wastewater to be treated (8) is introduced at the bottom of the tank which is under anoxic conditions (6) and gradually moves upward by natural flow of liquid towards the anaerobic zone (7) before entering the upper section of the tank (2) that operates under aerobic/anoxic conditions controlled by the ON/OFF action of the air blower (5). Air diffusers (4) deliver air on a pre-determined schedule to supply oxygen for the aerobic processes and also for the mixing of liquid. The treated effluent (9) leaves the treatment system on a continuous basis from the top of the treatment tank. A recycle stream (10) returns a part of liquid from the top of the treatment tank to the bottom. The recycle stream creates anoxic environment at the bottom of the tank due to the possible presence of traces of oxygen and nitrogen oxides. However, oxygen is completely depleted as liquid flows upward, creating anaerobic conditions in the area above the anoxic zone and below the diffusers.
The delivery system for the influent wastewater (8) may be a simple pipe or it may be a complex manifold consisting of several perforated pipes along the width of the tank or some means to distribute the influent across the tank. In very wide tanks, a pump may be placed inside the tank and at the bottom to distribute the wastewater as much as possible around the width of the tank and to provide mixing of wastewater and sludge, accumulated at the bottom of the tank.
The particulate carbon and nitrogenous material in the wastewater are initially hydrolyzed in the bottom anoxic (6) and anaerobic (7) zones by facultative and anaerobic microorganisms generating easily biodegradable COD which is partly degraded by anaerobic processes. The remaining COD is degraded by aerobic processes in the upper section of the treatment system.
The presence of aerobic and anoxic environmental conditions in this treatment system implies that it has the potential of removing excessive nitrogen by biological nitrification/denitrffication along with the removal of COD. This is important if the concentration of nitrogen in the wastewater increases to such an extent that it can no longer be removed simply by incorporation into the microbial cells. Under this condition, ammonia nitrogen is oxidized in the upper zone under aerobic conditions during the nitrification process producing nitrites and nitrates, collectively known as nitrogen oxides. The nitrified liquid is partially denitrified under anoxic conditions in the upper zone when the air blower turns OFF and this zone turns anoxic. The hydrolyzed carbonaceous compounds will supply the required COD for the post-denitriifcation processes in this zone.
The remaining nitrites and nitrates in the nitrified liquid are transferred by a recycle stream (10) to the bottom anoxic zone where they will be reduced and denitrified during pre-denitrification processes and removed as nitrogen gas. The introduction of raw wastewater at the anoxic zone implies that biodegradable COD will be available in this zone to support the pre-denitrification processes.
In addition to the removal of nitrogen, the exposure of wastewater to alternating aerobic and anaerobic conditions promotes the growth and proliferation of phosphorus accumulating microorganisms (PAOs) thus enabling the removal of phosphorus by enhanced biological phosphorus removal (EBPR) process.
Excess phosphorus will be removed from the treatment system by the waste sludge removed from the bottom of the tank (11) on an occasional basis.
The lower section of the treatment tank (3) contains immobile solid support material (12) to create a fixed-bed environment for the attachment of microbial culture and formation of fixed-film biomass. Solid support material (13) has also been placed in the upper section of the treatment tank (2) preferably in the form of floating objects for the immobilization of microorganisms and formation of fixed-film biomass. The presence of attached-growth microorganisms in addition to the suspended-growth biomass increases the degradation capacity of the system by increasing the concentration of biomass and its retention time. The presence of attached-growth or fixed-film biomass in the aerobic zone increases the nitrification capacity of the treatment system by ensuring that the slow-growing nitrifying bacteria, needed in the nitrification process, will persist in the treatment system and will not be washed out even in the event of extreme operating conditions such as cold temperatures. A screen placed in front of the exit ports in the upper section of the treatment tank for the outward flow of the effluent (9) or the recycle stream (10) will ensure the retention of the support material inside the upper section. Thus in the treatment system of the present invention, aerobic, facultative and anaerobic biomass exist in both attached and suspended forms, increasing biomass concentration and the overall rate of biodegradation of contaminants while facilitating the retention of microorganisms.
The solid support media in the lower section of the tank are arranged in such a way that they also act as baffles to retain the accumulated sludge at the bottom of the tank, preventing its rise to the upper areas that may upset the operation of the system.
The ON/OFF cycle of air blower offers the following operational advantages:
- It prevents the accumulation in the upper zone of the nitrification products, nitrite and nitrate, that may exert inhibitory effects on the microbial culture.
- It provides longer periods for denitrification and renders the treatment system both post-denitrification as well as pre-denitrification, enabling a higher efficiency of nitrogen removal.
- During the OFF period of the air blower, the heavy flocs of microorganisms containing aerobic and facultative microorganisms will travel downward from the upper zone and will pass through the anaerobic and anoxic zones. The strict aerobic microorganisms will mostly die or become de-activated under oxygen-depleted conditions while the facultative microorganisms will survive and continue to degrade the contaminants by anaerobic processes. The aerobic microorganisms will be digested anaerobically producing easily biodegradable COD for further biodegradation by the microbial biomass in the lower section, particularly the denitrifying and phosphorus accumulating organisms that require easily biodegradable COD for their continued activities. The remaining undigested biomass accumulates at the bottom of the tank and will be removed as waste solid sludge.
- When the air blowers are turned ON, the action of air blower will create pressure difference across the air diffusers, carrying a fraction of microbial biomass upward from the lower section of the tank to the upper section.
The strict anaerobic microorganisms traveled to this zone will die or become de-activated while facultative anaerobes will continue degradation of contaminants by aerobic processes. Under aerobic conditions, aerobic microorganisms will grow and produce young and active cells with high physiological activities and high rates of biodegradation. Simultaneously, strict anaerobic microorganisms grow in the anaerobic zone under the air diffusers, producing young and active anaerobic cells. Thus due to the imposed ON/OFF operation of the air blower, the microorganisms will be rejuvenated on a continuous basis in all different zones, ensuring the persistence of young and active microbial biomass and removal of old and slow biomass.
The simultaneous presence of pre-denitrification and post-denitrification in this treatment system offers a higher efFciency of nitrogen removal and eliminates the requirement for the addition of an external carbon source for nitrogen removal. The presence of suspended as well as fixed-film microbial biomass provides adequate mixing, homogeneity of environment, high transfer rates of oxygen and nutrients through cellular membrane as well as high biomass concentrations and high cell retention times, particularly important to support a high efficiency of nitrification.
Another advantage offered by the treatment system of the present invention is that it operates under lower temperatures compared to the levels normally achieved under aerobic treatment operations such as activated sludge processes. This is due to the presence of anoxic and anaerobic environments and the resulting generation of less heat by this treatment system. In general, the generated heat during anaerobic microbial processes is less than that produced during aerobic processes. Consequently, the initial degradation of carbonaceous compounds by anaerobic processes, as practiced in the treatment system of the present invention, will considerably reduce the wastewater's COD concentration generating less heat and preventing the rise of reactor's temperature to prohibiting levels. This is particularly important during the treatment of wastewaters with high COD concentrations since the excessive rise of temperature will often deactivate the microbial biomass seriously impairing the treatment process.
In addition, the produced sludge in the treatment system of the present invention is less than that formed in aerobic treatment systems since anaerobic processes have a lower biomass yield (up to 5 times less) compared to aerobic processes.
The produced sludge will be partly digested in the bottom anaerobic zone and the rest will be removed on an occasional basis as waste sludge.
Operation of the Treatment System The treatment system of the present invention may operate under three different operating conditions presenting three "operating strategies", enabling it to maintain a relatively high efFciency of COD and nitrogen removal under various influent wastewater conditions. These operating strategies depend on the characteristics of the wastewater under treatment and in particular on the ratio of chemical oxygen demand to total nitrogen (COD:TN). The COD:TN ratio plays an important role in controlling the efficiency of nitrogen removal by nitrification/denitrification processes in a biological treatment system. The highest nitrogen removal efficiencies are normally obtained when the COD:TN
ratio is above 5, preferably in the range of 6-8. Under this condition, the carbon concentration is sufficient to support a complete denitrification, and a high efficiency of nitrogen removal will be obtained. Lower COD:TN ratios of less than diminish the removal efficiency of nitrogen by denitrification and are often corrected by the addition of an external carbon source to increase the COD
concentration. The imposed changes in the operating conditions of the treatment system of the present invention represented by the three "operating strategies"
will enable it to vary the involved biological processes, supporting a high efficiency of carbon and nitrogen removal even when the COD:TN ratio is significantly less than 5 or even less than 0.5.
The first operating strategy applies when the COD:TN ratio is above 5. Under this condition, the treatment system operates at a liquid pH range preferably between 7 and 8.5 in all the different zones and at DO concentrations preferably above 2 mg/L in the aerobic zone. Nitrogen removal is carried out by the traditional method of complete ammonia oxidation to nitrate followed by its further reduction to nitrogen gas during the denitriflcation process. Nitrification takes place in the upper section of the treatment tank of the present invention during the ON period while denitrification takes place under anoxic conditions, initially in the upper section of the treatment tank during the OFF period and also at the bottom of the tank which constantly remains under anoxic conditions. The presence of fixed-film biomass supports the establishment of adequate solid retention time (SRT) in the range of 3 to 10 days, or occasionally longer, which is needed for the retention of slow-growing nitrifying bacteria and a complete nitrification in the aerobic zone. The solid retention time (SRT) in both upper and lower sections of the treatment tank shows a strong dependence on the recycle ratio (r) as presented in Figure 2. The recycle ratio is defined as the ratio between the flow rates of the recycle stream (from the upper to the lower section) and the influent wastewater. This dependence implies that the solid retention time (SRT) in the upper aerobic/anoxic zone and the bottom anoxic-anaerobic zones can be controlled by the recycle ratio. Exemplary dimensions and operating conditions of the treatment plant are presented in Table 1.
The second operating strategy applies when the COD:TN ratio is below 5 but above 0.5. Under this condition, often encountered in industrial operations producing high-nitrogen-concentration wastewaters such as slaughterhouses, the nitrification stage is controlled in such a way that ammonium ions are oxidized to nitrite and further nitrite oxidation to nitrate is inhibited. The produced nitrite is subsequently denitrified under anoxic conditions, releasing nitrogen gas.
Ammonia oxidation to nitrite, also known as nitritation, takes place under aerobic conditions at relatively low DO concentrations, while nitrite reduction, referred to as denitritation, takes place under anoxic conditions. The oxidation of ammonium to nitrite is usually controlled by the operating conditions of the system as described by Abeling and Seyfried (1992); Yoo et al. (1999); Gibbs et al. (2004); and Jenicek et al. (2004). The most important parameters controlling the transformation of ammonium to nitrite are liquid pH preferably equal to or greater than 7.0, dissolved oxygen (DO) concentration during the aeration period preferably less than 2.0 mg/L, and a relatively low solid retention time (SRT) preferably between 1 and 2 days in order to favor the retention of ammonia oxidizing bacteria (AOB) and allow for the wash out of nitrite oxidizing bacteria (NOB) that, under these conditions, grow more slowly than the ammonia oxidizing bacteria. The length of the aeration period is also important since in combination with aeration it controls the population of ammonia oxidizers versus nitrite oxidizers.
If the wastewater characteristics demand the operation of the treatment system according to the second operating strategy, then the upper zone of the treatment system of the present invention should operate without solid support material in order to establish a low solid retention time. An example of the treatment system of the invention operating at the second operating strategy is presented in FIG. 3.
The variations of solid retention time (SRT) with the recycle ratio (r) under the second operating strategy are presented in Figure 4.
The second operating strategy is particularly suitable when the wastewater has high nitrogen concentrations, for example above 1000 mg/L, and the concentration of carbon source in the wastewater is not sufficient to support a complete denitrification via nitrate. The low COD:TN ratio precludes a complete nitrogen removal via denitrification due to low COD availability, or requires the addition of external carbon sources. The denitritation process which refers to nitrite reduction as opposed to nitrate reduction, will improve the efficiency of nitrogen removal resulting in savings in carbon source of about 40% and oxygen savings of about 25% according to the following stoichiometric relationships:
Nitritation: NH4+ + 1.5 02 --> NOZ + 2 H+ + H20 Nitrification NH4+ + 2.0 02 --+ N03 + 2 H+ + H20 Denitritation 2 N02 + 6 H+ + 6 e' --+ 2 OH" + N2 + 2 H20 Denitrification 2 N03 + 10 H+ + 6 e-+ 2 OH" + N2 + 4 H20 The third operating strategy applies when the wastewater possesses very high nitrogen concentration and low COD concentrations, drastically lowering the COD:TN ratio to values under 0.5. Under these conditions, nitrogen removal is significantly impaired since high concentrations of nitrates and nitrites either inhibit further ammonia oxidation, or a complete nitrogen removal will be prevented even via denitritation due to the extremely low COD concentrations.
In this operating strategy, ammonium is partially oxidized to nitrite in the upper aerobic zone followed by the conversion of the remaining ammonia into molecular nitrogen under anaerobic conditions while the produced nitrite serves as the electron acceptor. The concept presented in the third operating strategy has been described in the literature. Anaerobic ammonia oxidation is known as the Anammox process (Jetten et al., 1999), while the combined nitritation/(anaerobic ammonia oxidation) has been described by Volcke et al.
(2005) and Caffez et al. (2005) and has been used in a single reactor in a process known as CANON (Strous, 1999). The combined process uses two groups of autotrophic bacteria: one for ammonium oxidation to nitrite (Nitrosommonas) and the second group for anaerobic ammonia oxidation through the Anammox process, thus minimizing organic carbon requirements.
The employment of the combined nitritation and Anammox process, permitted by the design of the treatment system of the present invention, addresses nitrogen removal even under very low COD:TN ratios. The combined process offers up to 63% savings in aeration energy, and does not require the addition of external carbon sources for nitrogen removal while minimizing sludge production compared to conventional nitrification-denitrification processes. The important operating parameters include aerobic zone DO concentration <2.0 mg/L for nitritation and < 0.1 mg/L for Anammox in the anoxic and anaerobic zones, liquid pH preferably between 7 and 8 and the nitrite:ammonium molar ratio around 1.0 in the anoxic and anaerobic zones to support a high efficiency of the Anammox process. Relatively high cell residence times preferably greater than 15 days are also needed for the slow-growing Anammox bacteria. If the wastewater characteristics demand the operation of the treatment system according to the third operating strategy, then the system will adopt the design depicted in Figure 3 without the requirement of solid support material in the upper zone. The relationship between the solid retention time (SRT) and the recycle ratio (r) under the third operating strategy is also illustrated in Figure 4.
As presented in Figures 2 and 4, the solid retention time (SRT) can be controlled by the recycle ratio to reach values that are in accordance with the requirements of the three operating strategies. The three possible operating strategies enable the treatment system of the present invention to adopt various operating procedures depending on the characteristics of the wastewater and particularty the COD:TN ratio, implying that it has the capacity of removing nitrogen with a very low supply or availability of carbon.
The effluent leaving the treatment system of the present invention may often need additional treatment before discharge if the raw wastewater contains extremely high concentrations of carbon and nutrients or if stringent environmental criteria are enforced for effluent discharge. Under these conditions, the present invention is used for pretreatment to enable the effluent to be readily treated by conventional treatment methods downstream. An obvious example of this would be treating industrial wastewaters prior to discharge to the local municipal wastewater treatment plant. Of course, the required type and extent of additional treatment depends on the characteristics of the raw wastewater under treatment and the imposed treatment standards. It may consist of a simple solid-liquid separation downstream the treatment system of the present invention for effluent clarification, or tertiary treatment plants to further reduce the concentration of nutrients, nitrogen and phosphorus, as well as solid digestion and pathogen removal. The high capacity of the treatment system of the present invention in the reduction of wastewaters' carbon and nitrogen concentrations will make this technology extremely useful in the industrial waste treatment market particularly in the treatment of animal wastes and slaughterhouse and food-processing effluents.
REFERENCES:
- Abeling, U. and Seyfried, C F. (1992) Wat. Sci. Tech. 26(5-6) 1007-1015.
- Caffez, S., Canziani R., Lubello, C. and Santianni, D. (2005) Wat. Sci.
Tech.
52(4) 9-17.
- Choi, E., Kim, D., Eum, Y., Yun, Z. and Min, K. -S. (2005) Wat. Environ.
Res., 77(4) 381-389.
- Gibbs, B.M., Shephard, L.R., Third, K.A.; and Cord-Ruwisch, R. (2004) Wat.
Sci. Tech. 50(10) 181-188.
- Jenicek, P., Svehla, P., Zabranska J. and Dohanyos, M. (2004). Wat. Sci.
Tech. 49(5-6) 73 - 79.
- Jetten, M.S.M, Strous, M., Van De Pas-Schoonen, K., Schalk, J., Van Dongen, U.G.J.M., Van de Graaf, A.A., Logemann, S., Muyzer, G., Van Loosdrecht, M.C.M. and Kuenen,J.G. (1999) Fems Microbiol. Rev., 22, 421-437.
- Kim D.-H., Choi, E., Yun, Z. and Kim S.-W. (2004) Wat. Sci. Technol. 49(5-6) 165-171.
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(2004) Wat. Sci. Technol. 49(5-6) 315 - 323 - Strous, M., Kuenen, J.G. and Jetten, M.S.M (1999) Appli. Environ. Microbiol.
65, 3248-3250.
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and Vanrolleghem P.A. (2005) Wat. Sci. Tech. 52(4) 107-115.
- Yoo, H., Ahn K.-H., Lee H.-Jõ Lee K.-H., Kwak Y.-J. and Song K.-G. (1999) Wat. Res. 33(1), 145-154.
Table 1. Example of dimensions and operating conditions of the treatment plant Parameter value Wastewater flow rate m3/d 100 Overall treatment tank volume m 300 Aerobic/anoxic zone volume m 120 Anoxic/anaerobic zone volume m 180 Chemical oxygen demand k/m 4.0 Nit en concentration o eratin strategy 1) k/m 0.6 Nitrogen concentration o eratin strategy 2) k/m 1.3
In US patent 5,645,725 the anoxic zone contains porous mineral material particies and activated charcoal particles. Recycle streams in these treatment systems return a portion of the effluent from various stages of the process and connect reactors having different environmental conditions.
US patent 5,651,892 uses an aerobic vertical shaft bioreactor with an oxygen-containing gas for the removal of organic carbon from the liquid previously denitrified in an anoxic reactor. The effluent of the shaft bioreactor will be clarified and subsequently nitrified under aerobic condition. The treated liquid is clarified in a ciarification unit for final discharge.
US patent 6,054,044 has anoxic, anaerobic and aerobic cultures while US patent 5,811,008 contains aerobic and anaerobic cultures and an arrangement for controlling the residence time of the wastewater in the anaerobic reactor by varying the volume of this reactor.
g US patents 6,136,185 and 6,203,702 discuss a treatment system that has two treatment tanks and a holding reservoir. Each of the treatment tanks has an anaerobic zone that is two to five feet deep and an aerobic zone on top of the anaerobic zone that is at least twelve feet deep. Wastewater passes through the anaerobic zone to the aerobic zone of the first tank and continues treatment in the anaerobic and aerobic zones of the second tank.
US patent 6,235,196 discusses a wastewater bioprocessing system that comprises an anaerobic reactor, an aerobic reactor in direct communication with the anaerobic reactor, and a recycle loop for recycling a portion of the aerobic reactor effluent to the anaerobic reactor. The anaerobic and aerobic reactors can include a single reactor or a plurality of reactors. The recycle loop provides pH regulation, dilution of the feed, and nitrite-nitrate removal. The aerobic and anaerobic reactors may contain fixed-film microorganisms.
None of the known technologies offer a single-tank treatment system that comprises both pre-denitrification and post-denitrification operations for the removal of nitrogen; fixed-film combined with suspended microorganisms; three zones with flexible volumes and different environmental conditions, namely aerobic, anoxic and anaerobic, with controlled duration of aerobic and anoxic periods; and fluid communication between the zones. These features are all included in the treatment technology of the present invention offering significant reductions in the concentrations of organic carbon and nitrogen and reduction of phosphorus in a single easy-to-operate and maintain treatment tank with a small footprint. The treatment system of the present invention offers the presence of a diversified group of suspended and fixed-film microorganisms, high concentration and residence time of the microbial biomass, high specific and volumetric rates of contaminant removal, ease of operation and a relatively small footprint, and provides an intemal supply of carbon source for the denitriifcation process, eliminating the requirement for the supply of an external carbon source.
Summary of the invention The concept of multi-zone, multi-environment technology has been implemented in the design and development of a new wastewater treatment technology particularfy suitable to reduce the strength of highly concentrated wastewaters in terms of their content of organic carbonaceous compounds and nutrients, notably nitrogen and phosphorus, facilitating their further treatment. Very high organic and nitrogen loads of certain wastewaters render conventional treatment processes ineffective. The technology of the present invention reduces the concentrations of carbonaceous compounds and nitrogen and makes some reductions of phosphorus in a highly concentrated wastewater such as those produced in animal farms or slaughterhouses to the extent that the wastewater will be amenable to complete treatment by conventional technologies such as sequencing batch reactor (SBR) or activated sludge, conforming to environmental standards for effluent discharge. Thus, the technology of the present invention may serve either as a treatment technology if its effluent characteristics conform to local environmental standards, or as a pretreatment technology especially when dealing with highly concentrated wastewaters or stringent environmental standards. This is a major step in the treatment of high strength wastewaters since very high carbon and nitrogen concentrations often prohibit treatment.
The treatment process of the present invention contains a multiplicity of environmental conditions, including aerobic, anoxic and anaerobic, in a single, multi-zone tank to support the growth and proliferation of different groups of microorganisms and a variety of biochemical reactions involved in the removal of carbon, nitrogen and phosphorus contaminants. There are no baffles or walls to separate the zones. The influent wastewater is introduced into the treatment system at the bottom of the tank which is under anoxic conditions and flows upward passing through the anaerobic zone and continues its move towards the upper zone located above air diffusers. The upper zone operates under aerobic/anoxic conditions controlled by the ON/OFF action of an air blower.
Thus, in this treatment system the organic contaminants are first degraded by anaerobic processes in the anoxic and anaerobic zones reducing their concentration before further treatment in the aerobic zone. The ON/OFF cycle of the air blower will create a cyclic aerobic/anoxic zone in the upper section of the reactor supporting the degradation of organic carbonaceous compounds by aerobic microorganisms during the ON period as well as their anoxic degradation by facultative anaerobes during the OFF period while promoting nitrification and denitrification for nitrogen removal. Additional denitrification for a complete removal of nitrogen takes place at the bottom of the tank that is under anoxic conditions and is in fluid communication with the upper zone via a recycle stream. The treatment system includes both suspended and attached microorganisms, increasing cell retention time and enhancing the treatment capacity of the system. This design results in lower treatment temperatures, less production of microbial biomass and requires less oxygen for the aerobic degradation of the remaining compounds.
Brief Description of the Drawings The invention will be described in more detail in the following description in conjunction with the drawings in which:
Fig. I represents schematically an exemplary wastewater treatment system of the invention, Fig. 2 illustrates a relationship between the solid retention time (SRT) in different zones of the treatment system and the recycle ratio (r) under the first operating strategy, Fig. 3 represents schematically another embodiment of a wastewater treatment system of the invention, and Fig. 4. illustrates a relationship between the solid retention time (SRT) in different zones of the treatment system and the recycle ratio (r) under the second and third operating strategy.
Detailed Description of the Invention An example of the treatment system according to the invention is presented in FIG. 1. The system uses a single tank (1) containing multiple zones having different environmental conditions of aerobic, anoxic and anaerobic for the removal or considerable reductions in the concentrations of carbon and nitrogen and some reductions in the concentration of phosphorus contaminants. The tank (1) is divided into upper (2) and lower (3) sections by air diffusers (4) located horizontally inside the tank. The volumes of the two sections are not fixed and they are determined during the design stage based on the characteristics of the wastewater including the nature of the contaminants and their respective concentrations. Air is introduced into the system on a pre-determined schedule by an air blower or air compressor (5) through the air diffusers (4). The upper section (2) is aerobic when the air blower is ON and becomes anoxic when the air blower is tumed OFF. The durations of ON and OFF periods may or may not be equal and will be determined by the operator depending on the characteristics of the wastewater under treatment in order to adjust the required duration of aerobic and anoxic periods and the required efficiency of treatment. The periods can vary from minutes to hours. Examples include one hour ON and one hour OFF or 20 minutes ON and 40 minutes OFF, or 2 hours ON and three hours OFF.
The non-aerated lower section (3) below the air diffusers (4) has anoxic condition at the bottom (6) and anaerobic condition at the top (7), implying that the bottom of the treatment tank is under anoxic condition and the anaerobic zone is located above the anoxic zone and below the air diffusers (4). There are no walls or baffles to separate the different zones and there is a gradual change of the environmental conditions from anoxic to anaerobic in the bottom section imposed through the consumption of oxygen by the microorganisms and progressive depletion of oxygen as liquid moves upward. The division between the zones is naturally established by the change in dissolved oxygen concentration and redox potential in these zones. The wastewater to be treated (8) is introduced at the bottom of the tank which is under anoxic conditions (6) and gradually moves upward by natural flow of liquid towards the anaerobic zone (7) before entering the upper section of the tank (2) that operates under aerobic/anoxic conditions controlled by the ON/OFF action of the air blower (5). Air diffusers (4) deliver air on a pre-determined schedule to supply oxygen for the aerobic processes and also for the mixing of liquid. The treated effluent (9) leaves the treatment system on a continuous basis from the top of the treatment tank. A recycle stream (10) returns a part of liquid from the top of the treatment tank to the bottom. The recycle stream creates anoxic environment at the bottom of the tank due to the possible presence of traces of oxygen and nitrogen oxides. However, oxygen is completely depleted as liquid flows upward, creating anaerobic conditions in the area above the anoxic zone and below the diffusers.
The delivery system for the influent wastewater (8) may be a simple pipe or it may be a complex manifold consisting of several perforated pipes along the width of the tank or some means to distribute the influent across the tank. In very wide tanks, a pump may be placed inside the tank and at the bottom to distribute the wastewater as much as possible around the width of the tank and to provide mixing of wastewater and sludge, accumulated at the bottom of the tank.
The particulate carbon and nitrogenous material in the wastewater are initially hydrolyzed in the bottom anoxic (6) and anaerobic (7) zones by facultative and anaerobic microorganisms generating easily biodegradable COD which is partly degraded by anaerobic processes. The remaining COD is degraded by aerobic processes in the upper section of the treatment system.
The presence of aerobic and anoxic environmental conditions in this treatment system implies that it has the potential of removing excessive nitrogen by biological nitrification/denitrffication along with the removal of COD. This is important if the concentration of nitrogen in the wastewater increases to such an extent that it can no longer be removed simply by incorporation into the microbial cells. Under this condition, ammonia nitrogen is oxidized in the upper zone under aerobic conditions during the nitrification process producing nitrites and nitrates, collectively known as nitrogen oxides. The nitrified liquid is partially denitrified under anoxic conditions in the upper zone when the air blower turns OFF and this zone turns anoxic. The hydrolyzed carbonaceous compounds will supply the required COD for the post-denitriifcation processes in this zone.
The remaining nitrites and nitrates in the nitrified liquid are transferred by a recycle stream (10) to the bottom anoxic zone where they will be reduced and denitrified during pre-denitrification processes and removed as nitrogen gas. The introduction of raw wastewater at the anoxic zone implies that biodegradable COD will be available in this zone to support the pre-denitrification processes.
In addition to the removal of nitrogen, the exposure of wastewater to alternating aerobic and anaerobic conditions promotes the growth and proliferation of phosphorus accumulating microorganisms (PAOs) thus enabling the removal of phosphorus by enhanced biological phosphorus removal (EBPR) process.
Excess phosphorus will be removed from the treatment system by the waste sludge removed from the bottom of the tank (11) on an occasional basis.
The lower section of the treatment tank (3) contains immobile solid support material (12) to create a fixed-bed environment for the attachment of microbial culture and formation of fixed-film biomass. Solid support material (13) has also been placed in the upper section of the treatment tank (2) preferably in the form of floating objects for the immobilization of microorganisms and formation of fixed-film biomass. The presence of attached-growth microorganisms in addition to the suspended-growth biomass increases the degradation capacity of the system by increasing the concentration of biomass and its retention time. The presence of attached-growth or fixed-film biomass in the aerobic zone increases the nitrification capacity of the treatment system by ensuring that the slow-growing nitrifying bacteria, needed in the nitrification process, will persist in the treatment system and will not be washed out even in the event of extreme operating conditions such as cold temperatures. A screen placed in front of the exit ports in the upper section of the treatment tank for the outward flow of the effluent (9) or the recycle stream (10) will ensure the retention of the support material inside the upper section. Thus in the treatment system of the present invention, aerobic, facultative and anaerobic biomass exist in both attached and suspended forms, increasing biomass concentration and the overall rate of biodegradation of contaminants while facilitating the retention of microorganisms.
The solid support media in the lower section of the tank are arranged in such a way that they also act as baffles to retain the accumulated sludge at the bottom of the tank, preventing its rise to the upper areas that may upset the operation of the system.
The ON/OFF cycle of air blower offers the following operational advantages:
- It prevents the accumulation in the upper zone of the nitrification products, nitrite and nitrate, that may exert inhibitory effects on the microbial culture.
- It provides longer periods for denitrification and renders the treatment system both post-denitrification as well as pre-denitrification, enabling a higher efficiency of nitrogen removal.
- During the OFF period of the air blower, the heavy flocs of microorganisms containing aerobic and facultative microorganisms will travel downward from the upper zone and will pass through the anaerobic and anoxic zones. The strict aerobic microorganisms will mostly die or become de-activated under oxygen-depleted conditions while the facultative microorganisms will survive and continue to degrade the contaminants by anaerobic processes. The aerobic microorganisms will be digested anaerobically producing easily biodegradable COD for further biodegradation by the microbial biomass in the lower section, particularly the denitrifying and phosphorus accumulating organisms that require easily biodegradable COD for their continued activities. The remaining undigested biomass accumulates at the bottom of the tank and will be removed as waste solid sludge.
- When the air blowers are turned ON, the action of air blower will create pressure difference across the air diffusers, carrying a fraction of microbial biomass upward from the lower section of the tank to the upper section.
The strict anaerobic microorganisms traveled to this zone will die or become de-activated while facultative anaerobes will continue degradation of contaminants by aerobic processes. Under aerobic conditions, aerobic microorganisms will grow and produce young and active cells with high physiological activities and high rates of biodegradation. Simultaneously, strict anaerobic microorganisms grow in the anaerobic zone under the air diffusers, producing young and active anaerobic cells. Thus due to the imposed ON/OFF operation of the air blower, the microorganisms will be rejuvenated on a continuous basis in all different zones, ensuring the persistence of young and active microbial biomass and removal of old and slow biomass.
The simultaneous presence of pre-denitrification and post-denitrification in this treatment system offers a higher efFciency of nitrogen removal and eliminates the requirement for the addition of an external carbon source for nitrogen removal. The presence of suspended as well as fixed-film microbial biomass provides adequate mixing, homogeneity of environment, high transfer rates of oxygen and nutrients through cellular membrane as well as high biomass concentrations and high cell retention times, particularly important to support a high efficiency of nitrification.
Another advantage offered by the treatment system of the present invention is that it operates under lower temperatures compared to the levels normally achieved under aerobic treatment operations such as activated sludge processes. This is due to the presence of anoxic and anaerobic environments and the resulting generation of less heat by this treatment system. In general, the generated heat during anaerobic microbial processes is less than that produced during aerobic processes. Consequently, the initial degradation of carbonaceous compounds by anaerobic processes, as practiced in the treatment system of the present invention, will considerably reduce the wastewater's COD concentration generating less heat and preventing the rise of reactor's temperature to prohibiting levels. This is particularly important during the treatment of wastewaters with high COD concentrations since the excessive rise of temperature will often deactivate the microbial biomass seriously impairing the treatment process.
In addition, the produced sludge in the treatment system of the present invention is less than that formed in aerobic treatment systems since anaerobic processes have a lower biomass yield (up to 5 times less) compared to aerobic processes.
The produced sludge will be partly digested in the bottom anaerobic zone and the rest will be removed on an occasional basis as waste sludge.
Operation of the Treatment System The treatment system of the present invention may operate under three different operating conditions presenting three "operating strategies", enabling it to maintain a relatively high efFciency of COD and nitrogen removal under various influent wastewater conditions. These operating strategies depend on the characteristics of the wastewater under treatment and in particular on the ratio of chemical oxygen demand to total nitrogen (COD:TN). The COD:TN ratio plays an important role in controlling the efficiency of nitrogen removal by nitrification/denitrification processes in a biological treatment system. The highest nitrogen removal efficiencies are normally obtained when the COD:TN
ratio is above 5, preferably in the range of 6-8. Under this condition, the carbon concentration is sufficient to support a complete denitrification, and a high efficiency of nitrogen removal will be obtained. Lower COD:TN ratios of less than diminish the removal efficiency of nitrogen by denitrification and are often corrected by the addition of an external carbon source to increase the COD
concentration. The imposed changes in the operating conditions of the treatment system of the present invention represented by the three "operating strategies"
will enable it to vary the involved biological processes, supporting a high efficiency of carbon and nitrogen removal even when the COD:TN ratio is significantly less than 5 or even less than 0.5.
The first operating strategy applies when the COD:TN ratio is above 5. Under this condition, the treatment system operates at a liquid pH range preferably between 7 and 8.5 in all the different zones and at DO concentrations preferably above 2 mg/L in the aerobic zone. Nitrogen removal is carried out by the traditional method of complete ammonia oxidation to nitrate followed by its further reduction to nitrogen gas during the denitriflcation process. Nitrification takes place in the upper section of the treatment tank of the present invention during the ON period while denitrification takes place under anoxic conditions, initially in the upper section of the treatment tank during the OFF period and also at the bottom of the tank which constantly remains under anoxic conditions. The presence of fixed-film biomass supports the establishment of adequate solid retention time (SRT) in the range of 3 to 10 days, or occasionally longer, which is needed for the retention of slow-growing nitrifying bacteria and a complete nitrification in the aerobic zone. The solid retention time (SRT) in both upper and lower sections of the treatment tank shows a strong dependence on the recycle ratio (r) as presented in Figure 2. The recycle ratio is defined as the ratio between the flow rates of the recycle stream (from the upper to the lower section) and the influent wastewater. This dependence implies that the solid retention time (SRT) in the upper aerobic/anoxic zone and the bottom anoxic-anaerobic zones can be controlled by the recycle ratio. Exemplary dimensions and operating conditions of the treatment plant are presented in Table 1.
The second operating strategy applies when the COD:TN ratio is below 5 but above 0.5. Under this condition, often encountered in industrial operations producing high-nitrogen-concentration wastewaters such as slaughterhouses, the nitrification stage is controlled in such a way that ammonium ions are oxidized to nitrite and further nitrite oxidation to nitrate is inhibited. The produced nitrite is subsequently denitrified under anoxic conditions, releasing nitrogen gas.
Ammonia oxidation to nitrite, also known as nitritation, takes place under aerobic conditions at relatively low DO concentrations, while nitrite reduction, referred to as denitritation, takes place under anoxic conditions. The oxidation of ammonium to nitrite is usually controlled by the operating conditions of the system as described by Abeling and Seyfried (1992); Yoo et al. (1999); Gibbs et al. (2004); and Jenicek et al. (2004). The most important parameters controlling the transformation of ammonium to nitrite are liquid pH preferably equal to or greater than 7.0, dissolved oxygen (DO) concentration during the aeration period preferably less than 2.0 mg/L, and a relatively low solid retention time (SRT) preferably between 1 and 2 days in order to favor the retention of ammonia oxidizing bacteria (AOB) and allow for the wash out of nitrite oxidizing bacteria (NOB) that, under these conditions, grow more slowly than the ammonia oxidizing bacteria. The length of the aeration period is also important since in combination with aeration it controls the population of ammonia oxidizers versus nitrite oxidizers.
If the wastewater characteristics demand the operation of the treatment system according to the second operating strategy, then the upper zone of the treatment system of the present invention should operate without solid support material in order to establish a low solid retention time. An example of the treatment system of the invention operating at the second operating strategy is presented in FIG. 3.
The variations of solid retention time (SRT) with the recycle ratio (r) under the second operating strategy are presented in Figure 4.
The second operating strategy is particularly suitable when the wastewater has high nitrogen concentrations, for example above 1000 mg/L, and the concentration of carbon source in the wastewater is not sufficient to support a complete denitrification via nitrate. The low COD:TN ratio precludes a complete nitrogen removal via denitrification due to low COD availability, or requires the addition of external carbon sources. The denitritation process which refers to nitrite reduction as opposed to nitrate reduction, will improve the efficiency of nitrogen removal resulting in savings in carbon source of about 40% and oxygen savings of about 25% according to the following stoichiometric relationships:
Nitritation: NH4+ + 1.5 02 --> NOZ + 2 H+ + H20 Nitrification NH4+ + 2.0 02 --+ N03 + 2 H+ + H20 Denitritation 2 N02 + 6 H+ + 6 e' --+ 2 OH" + N2 + 2 H20 Denitrification 2 N03 + 10 H+ + 6 e-+ 2 OH" + N2 + 4 H20 The third operating strategy applies when the wastewater possesses very high nitrogen concentration and low COD concentrations, drastically lowering the COD:TN ratio to values under 0.5. Under these conditions, nitrogen removal is significantly impaired since high concentrations of nitrates and nitrites either inhibit further ammonia oxidation, or a complete nitrogen removal will be prevented even via denitritation due to the extremely low COD concentrations.
In this operating strategy, ammonium is partially oxidized to nitrite in the upper aerobic zone followed by the conversion of the remaining ammonia into molecular nitrogen under anaerobic conditions while the produced nitrite serves as the electron acceptor. The concept presented in the third operating strategy has been described in the literature. Anaerobic ammonia oxidation is known as the Anammox process (Jetten et al., 1999), while the combined nitritation/(anaerobic ammonia oxidation) has been described by Volcke et al.
(2005) and Caffez et al. (2005) and has been used in a single reactor in a process known as CANON (Strous, 1999). The combined process uses two groups of autotrophic bacteria: one for ammonium oxidation to nitrite (Nitrosommonas) and the second group for anaerobic ammonia oxidation through the Anammox process, thus minimizing organic carbon requirements.
The employment of the combined nitritation and Anammox process, permitted by the design of the treatment system of the present invention, addresses nitrogen removal even under very low COD:TN ratios. The combined process offers up to 63% savings in aeration energy, and does not require the addition of external carbon sources for nitrogen removal while minimizing sludge production compared to conventional nitrification-denitrification processes. The important operating parameters include aerobic zone DO concentration <2.0 mg/L for nitritation and < 0.1 mg/L for Anammox in the anoxic and anaerobic zones, liquid pH preferably between 7 and 8 and the nitrite:ammonium molar ratio around 1.0 in the anoxic and anaerobic zones to support a high efficiency of the Anammox process. Relatively high cell residence times preferably greater than 15 days are also needed for the slow-growing Anammox bacteria. If the wastewater characteristics demand the operation of the treatment system according to the third operating strategy, then the system will adopt the design depicted in Figure 3 without the requirement of solid support material in the upper zone. The relationship between the solid retention time (SRT) and the recycle ratio (r) under the third operating strategy is also illustrated in Figure 4.
As presented in Figures 2 and 4, the solid retention time (SRT) can be controlled by the recycle ratio to reach values that are in accordance with the requirements of the three operating strategies. The three possible operating strategies enable the treatment system of the present invention to adopt various operating procedures depending on the characteristics of the wastewater and particularty the COD:TN ratio, implying that it has the capacity of removing nitrogen with a very low supply or availability of carbon.
The effluent leaving the treatment system of the present invention may often need additional treatment before discharge if the raw wastewater contains extremely high concentrations of carbon and nutrients or if stringent environmental criteria are enforced for effluent discharge. Under these conditions, the present invention is used for pretreatment to enable the effluent to be readily treated by conventional treatment methods downstream. An obvious example of this would be treating industrial wastewaters prior to discharge to the local municipal wastewater treatment plant. Of course, the required type and extent of additional treatment depends on the characteristics of the raw wastewater under treatment and the imposed treatment standards. It may consist of a simple solid-liquid separation downstream the treatment system of the present invention for effluent clarification, or tertiary treatment plants to further reduce the concentration of nutrients, nitrogen and phosphorus, as well as solid digestion and pathogen removal. The high capacity of the treatment system of the present invention in the reduction of wastewaters' carbon and nitrogen concentrations will make this technology extremely useful in the industrial waste treatment market particularly in the treatment of animal wastes and slaughterhouse and food-processing effluents.
REFERENCES:
- Abeling, U. and Seyfried, C F. (1992) Wat. Sci. Tech. 26(5-6) 1007-1015.
- Caffez, S., Canziani R., Lubello, C. and Santianni, D. (2005) Wat. Sci.
Tech.
52(4) 9-17.
- Choi, E., Kim, D., Eum, Y., Yun, Z. and Min, K. -S. (2005) Wat. Environ.
Res., 77(4) 381-389.
- Gibbs, B.M., Shephard, L.R., Third, K.A.; and Cord-Ruwisch, R. (2004) Wat.
Sci. Tech. 50(10) 181-188.
- Jenicek, P., Svehla, P., Zabranska J. and Dohanyos, M. (2004). Wat. Sci.
Tech. 49(5-6) 73 - 79.
- Jetten, M.S.M, Strous, M., Van De Pas-Schoonen, K., Schalk, J., Van Dongen, U.G.J.M., Van de Graaf, A.A., Logemann, S., Muyzer, G., Van Loosdrecht, M.C.M. and Kuenen,J.G. (1999) Fems Microbiol. Rev., 22, 421-437.
- Kim D.-H., Choi, E., Yun, Z. and Kim S.-W. (2004) Wat. Sci. Technol. 49(5-6) 165-171.
- Poo, K. M., Jun, B. H., Lee, S. H., Im, J. H., Woo, H.J. and Kim, C.W.
(2004) Wat. Sci. Technol. 49(5-6) 315 - 323 - Strous, M., Kuenen, J.G. and Jetten, M.S.M (1999) Appli. Environ. Microbiol.
65, 3248-3250.
- Voicke, E.I.P., Van Hulle, S.W.H., Donckels, B.M.R., Van Loosdrecht, M.C.M.
and Vanrolleghem P.A. (2005) Wat. Sci. Tech. 52(4) 107-115.
- Yoo, H., Ahn K.-H., Lee H.-Jõ Lee K.-H., Kwak Y.-J. and Song K.-G. (1999) Wat. Res. 33(1), 145-154.
Table 1. Example of dimensions and operating conditions of the treatment plant Parameter value Wastewater flow rate m3/d 100 Overall treatment tank volume m 300 Aerobic/anoxic zone volume m 120 Anoxic/anaerobic zone volume m 180 Chemical oxygen demand k/m 4.0 Nit en concentration o eratin strategy 1) k/m 0.6 Nitrogen concentration o eratin strategy 2) k/m 1.3
Claims (21)
1. A process for treating wastewater containing liquid and solids, comprising the steps of: providing a single process vessel for containing said liquid and solids; establishing a plurality of oxygen-depleted zones in the lower portion of said processing vessel; establishing an aerobic zone above said plurality of oxygen-depleted zones; feeding the wastewater into said processing vessel at the oxygen-depleted zones; supplying air in a controlled on-off operation to create alternatively aerobic and anoxic conditions in the upper portion of said processing vessel; maintaining anoxic conditions at the bottom of said oxygen depleted zones;
maintaining anaerobic conditions above the anoxic zone and below the aerobic zone; withdrawing substantially treated effluent from said upper portion; feeding a portion of said withdrawn effluent into about the bottom of said oxygen-depleted zones; and withdrawing substantially solids from the bottom of said oxygen-depleted zones.
maintaining anaerobic conditions above the anoxic zone and below the aerobic zone; withdrawing substantially treated effluent from said upper portion; feeding a portion of said withdrawn effluent into about the bottom of said oxygen-depleted zones; and withdrawing substantially solids from the bottom of said oxygen-depleted zones.
2. The process as recited in claim 1 whereby the aerobic zone contains solid support material for the attachment of microorganisms and formation of microbial biofilm.
3. The process as recited in claim 1 whereby the oxygen-depleted zones in the lower portion of the processing vessel contain solid support material for the attachment of microorganisms and formation of microbial biofilm.
4. The process as recited in claim 1 whereby the solid support material in the lower portion of the processing vessel are arranged in such a way as to retain the sludge and prevent its rise to the upper zone.
5. The process as recited in claim 1 whereby the aerobic zone in the upper portion of said processing vessel contains both suspended as well as immobilized microorganisms.
6. The process as recited in claim 1 whereby the oxygen-depleted zones in the lower portion of said processing vessel contain both suspended as well as immobilized microorganisms.
7. The process as recited in claim 1 including the step of feeding wastewater at the bottom of said oxygen-depleted zones creating upward flow of liquid in said processing vessel.
8. The process as recited in claim 1 further including the step of withdrawing substantially treated effluent from the top of said upper portion.
9. The process as recited in claim 1 further including the step of feeding air at the bottom of said upper portion in a controlled on-off operation through aeration means such as air diffusers.
1O.The process as recited in claim 1 whereby the oxygen-depleted zones below the aerobic zone include an anoxic zone at the bottom and an anaerobic zone above the anoxic zone and below the aerobic zone.
11. The process as recited in claim 1 whereby the volumes of aerobic zone in the upper portion of said processing vessel and oxygen-depleted zones in the lower portion of said processing vessel are not fixed and may be adjusted by the position of aeration means.
12. The process as recited in claim 1 whereby nitrogen is removed by either of the following processes:
a) Nitrification/denitriifcation b) Nitritation/denitritation c) Nitritation/anaerobic ammonia oxidation
a) Nitrification/denitriifcation b) Nitritation/denitritation c) Nitritation/anaerobic ammonia oxidation
13.A process for treating wastewater containing liquid and solids, comprising:
a) providing a multi-zone vessel;
b) providing an inlet for feeding wastewater into said vessel;
c) creating in an upper portion of said vessel a zone having alternative aerobic and anoxic conditions;
d) creating in a lower portion of said vessel below the aerobic zone a plurality of oxygen-depleted zones;
e) providing an air inlet for feeding air into said aerobic zone;
f) feeding air through said air inlet in a controlled on-off operation to create alternatively aerobic and anoxic conditions in the upper portion of said treatment vessel;
g) establishing an anoxic zone at the bottom of said oxygen-depleted zones in the lower portion of said treatment vessel;
h) establishing an anaerobic zone in said oxygen-depleted zones above the anoxic zone and below the aerobic zone;
i) feeding said wastewater into the bottom portion of said oxygen-depleted zones through said wastewater inlet;
j) providing an effluent outlet for withdrawing substantially treated liquid from said aerobic zone;
k) withdrawing substantially treated effluent from said system through said effluent outlet;
l) feeding a portion of said effluent withdrawn from said aerobic zone into at about the bottom of said oxygen-depleted zones;
m) providing a substantially solids outlet disposed at about the bottom of said oxygen-depleted zone;
n) withdrawing substantially solids from said system through said substantially solids outlet; and
a) providing a multi-zone vessel;
b) providing an inlet for feeding wastewater into said vessel;
c) creating in an upper portion of said vessel a zone having alternative aerobic and anoxic conditions;
d) creating in a lower portion of said vessel below the aerobic zone a plurality of oxygen-depleted zones;
e) providing an air inlet for feeding air into said aerobic zone;
f) feeding air through said air inlet in a controlled on-off operation to create alternatively aerobic and anoxic conditions in the upper portion of said treatment vessel;
g) establishing an anoxic zone at the bottom of said oxygen-depleted zones in the lower portion of said treatment vessel;
h) establishing an anaerobic zone in said oxygen-depleted zones above the anoxic zone and below the aerobic zone;
i) feeding said wastewater into the bottom portion of said oxygen-depleted zones through said wastewater inlet;
j) providing an effluent outlet for withdrawing substantially treated liquid from said aerobic zone;
k) withdrawing substantially treated effluent from said system through said effluent outlet;
l) feeding a portion of said effluent withdrawn from said aerobic zone into at about the bottom of said oxygen-depleted zones;
m) providing a substantially solids outlet disposed at about the bottom of said oxygen-depleted zone;
n) withdrawing substantially solids from said system through said substantially solids outlet; and
14.The process as recited in claim 13 further comprising feeding air into at about the bottom of said aerobic zone.
15.The process as recited in claim 13 further comprising withdrawing said treated effluent from about the top of said aerobic zone.
16. A method for wastewater treatment comprising the steps of:
creating a plurality of oxygen-depleted zones in the lower portion of a single treatment vessel; introducing wastewater at about the bottom of said treatment vessel; providing upward flow of wastewater in said treatment vessel; providing solid support material for the attachment of microorganisms and formation of microbial biofilm in said oxygen-depleted zones; creating suspended and immobilized microbial biomass in said oxygen-depleted zones; employing said oxygen-depleted zones for facultative and strict anaerobic processes including hydrolysis of long-chain and heavy carbonaceous material and partial degradation of the resulting carbonaceous material by facultative and strict anaerobic processes, reduction of nitrogen oxides for the removal of nitrogen, anaerobic ammonia oxidation, formation of volatile fatty acids by fermentation processes and uptake of volatile fatty acids by phosphorus accumulating organisms;
creating a zone with alternative aerobic/anoxic condition in the upper portion of said single treatment vessel; introducing air at the bottom of said upper zone in a controlled on-off operation to create alternative aerobic and anoxic conditions in said upper zone; providing solid support material for the attachment of microorganisms and formation of microbial biofilm in said upper zone; creating suspended and immobilized microbial biomass in said upper zone; employing said upper zone with alternative aerobic/anoxic conditions for processes including further degradation of carbonaceous compounds in the wastewater transferred from said lower portion, nitritation, nitrification, denitrification and phosphorus accumulation;
providing means for the withdrawal of substantially treated effluent;
providing means for transfer of a portion of withdrawn effluent to at about the bottom of oxygen-depleted zones to create communication between the upper and lower portions of said vessel for nitrogen and phosphorus removal; providing means for withdrawal of substantially solids from at about the bottom of said lower portion.
creating a plurality of oxygen-depleted zones in the lower portion of a single treatment vessel; introducing wastewater at about the bottom of said treatment vessel; providing upward flow of wastewater in said treatment vessel; providing solid support material for the attachment of microorganisms and formation of microbial biofilm in said oxygen-depleted zones; creating suspended and immobilized microbial biomass in said oxygen-depleted zones; employing said oxygen-depleted zones for facultative and strict anaerobic processes including hydrolysis of long-chain and heavy carbonaceous material and partial degradation of the resulting carbonaceous material by facultative and strict anaerobic processes, reduction of nitrogen oxides for the removal of nitrogen, anaerobic ammonia oxidation, formation of volatile fatty acids by fermentation processes and uptake of volatile fatty acids by phosphorus accumulating organisms;
creating a zone with alternative aerobic/anoxic condition in the upper portion of said single treatment vessel; introducing air at the bottom of said upper zone in a controlled on-off operation to create alternative aerobic and anoxic conditions in said upper zone; providing solid support material for the attachment of microorganisms and formation of microbial biofilm in said upper zone; creating suspended and immobilized microbial biomass in said upper zone; employing said upper zone with alternative aerobic/anoxic conditions for processes including further degradation of carbonaceous compounds in the wastewater transferred from said lower portion, nitritation, nitrification, denitrification and phosphorus accumulation;
providing means for the withdrawal of substantially treated effluent;
providing means for transfer of a portion of withdrawn effluent to at about the bottom of oxygen-depleted zones to create communication between the upper and lower portions of said vessel for nitrogen and phosphorus removal; providing means for withdrawal of substantially solids from at about the bottom of said lower portion.
17.The method according to claim 16 wherein nitrification and denitrification conditions are established alternatively in the upper zone of said vessel;
18.The method according to claim 16 wherein removal of nitrogen is accomplished by three possible processes of nitrification/denitriifcation, nitritation/denitritation and nitritation/(anaerobic ammonia oxidation);
19.The method according to claim 16 wherein removal of phosphorus is accomplished by enhanced biological phosphorus removal (EBPR) process.
20.A single vessel system for treating wastewater, comprising: vessel means;
a source of wastewater; a plurality of treatment zones having various levels of dissolved oxygen concentration and redox potential in said vessel means including an upper zone having alternative aerobic/anoxic conditions; lower zones disposed below the upper zone having a plurality of oxygen-depleted conditions including anoxic and anaerobic conditions;
solid support material for microbial immobilization in the upper zone and the lower oxygen-depleted zones; an inlet for feeding said wastewater into said vessel means at about the bottom of said lower zones; an air source;
aeration means for feeding air from said air source in a controlled on-off operation into said upper zone; a passage fluidly interconnecting said upper zone with said lower oxygen-depleted zones; a liquid outlet for withdrawal of substantially treated effluent from said upper zone; an outlet for withdrawal of substantially solids from at about the bottom of said lower portion.
a source of wastewater; a plurality of treatment zones having various levels of dissolved oxygen concentration and redox potential in said vessel means including an upper zone having alternative aerobic/anoxic conditions; lower zones disposed below the upper zone having a plurality of oxygen-depleted conditions including anoxic and anaerobic conditions;
solid support material for microbial immobilization in the upper zone and the lower oxygen-depleted zones; an inlet for feeding said wastewater into said vessel means at about the bottom of said lower zones; an air source;
aeration means for feeding air from said air source in a controlled on-off operation into said upper zone; a passage fluidly interconnecting said upper zone with said lower oxygen-depleted zones; a liquid outlet for withdrawal of substantially treated effluent from said upper zone; an outlet for withdrawal of substantially solids from at about the bottom of said lower portion.
21. The system as recited in claim 20 wherein the solid support material in the lower portion of the processing vessel are arranged in such a way as to retain the sludge and inhibit its rise to the upper zone.
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