Abstract: The disclosure relates to a staggered electrode bio-electro-Fenton groundwater circulation well system, including a groundwater circulation well, a water pumping and injecting assembly and an in-well bio-electro-Fenton assembly. The water pumping and injecting assembly is configured to realize water pumping and injection between different screening sections of the groundwater circulation well. The bio-electro-Fenton assembly arranged in a first screening section of the groundwater circulation well includes at least one electrode device. A cathode and an anode of the electrode device form a spatially staggered arrangement according to different distribution areas.

Abstract: Disclosed is a method for the treatment and resource utilization of acidic organic wastewater, comprising: (1) performing activated sludge treatment on acidic organic wastewater; and (2) performing microalgae treatment on the acidic organic wastewater treated in step (1). By means of the combination of activated sludge treatment and microalgae treatment, the present invention can significantly reduce the COD of the acidic organic wastewater. In some embodiments, the use of acclimated activated sludge or activated sludge having a specific microbial flora structure can not only improve the treatment efficiency while shortening the treatment time, but also omit a pH value adjustment step without causing sludge accumulation.

Abstract: This present invention relates to compositions and methods of microbial enhanced oil recovery using Bacillus subtilis strains. The invention also relates to compositions and methods for performing oil degradation with Bacillus subtilis strains. The compositions and methods of the present invention are also used for enhanced commercial biosurfactant and enzyme production.

Abstract: An apparatus, method and system is provided for treating sewage sludge by dewatering the sewage sludge, heating the sewage sludge being treated to destroy pathogens, and then reducing volatile solids in the sewage sludge being treated through biochemical decomposition to produce a treated biosolids product that meets government regulations for pathogen reduction and vector attraction reduction.

Abstract: Disclosed is a method for treating water including: —an adsorption step which involves bringing the water into contact with a new adsorbant, the water being referred to as “pre-adsorbed water” before being brought into contact with the new adsorbant, and being referred to as “adsorbed water” after being brought into contact with the new adsorbant, and—a recirculation step which involves removing at least a portion of the new adsorbant brought into contact with the water during the adsorption step, the removed portion constituting a used adsorbant. During the recirculation step, the used adsorbant is brought into contact with the pre-adsorbed water. Also, the pre-adsorbed water does not undergo a clarification step that involves eliminating from the water at least a portion of the suspended matter that it contains. Also disclosed is a device for implementing such a method.

Abstract: The technology relates to an apparatus, methods and applications to grow microorganisms on-site to treat contaminated environments. The apparatus is designed to function under a wide range of environmental conditions including extreme cold, extreme heat and direct exposure to sunlight. Such environments normally reduce the shelf-life of the organisms in the storage chamber that feeds the fermenter where they are being grown. These environments can also lower the growth rate of the organisms in the fermenter causing diminished cell output. Quite often the optimum point of application for the organisms is outdoor and too far from structures with appropriate protection from ultraviolet radiation from the sun or from excessive cold or hot weather. The technology in the application addresses these issues.

Abstract: Geo-biological processes are designed to treat wastewater generated in animal feed lots when washing away feces, urine and other materials or in municipal wastewater systems. The present processes are focused on recovering a nutrient load in the wastewater for use as fertilizer and corresponding to separate mostly purified water for reuse. Alternate embodiments are algae and microbe based processes. The processes can be used individually or in various permutations.

Abstract: Disclosed is a flexible substrate/liquid electrolyte viscous composite material and preparation method therefor. The preparation method includes: adding a particular percentage by weight of a flexible substrate to a liquid electrolyte solution having a particular concentrate; fully stirring the solution at a particular temperature to dissolve and evenly disperse the substrate, so as to obtain a viscous liquid; and then standing the viscous liquid at a particular temperature for a particular period of time to obtain the material. The material has viscosity due to which the material can actively adhere to the surface of tissue of an organ, the mechanical property matching cardiac muscle, biocompatibility and security, and is used for treating acute and chronic myocardial infarction and heart failures, inhibiting the reconstruction, thinning, and fiberization of a ventricular wall, and improving the myocardial function. In addition, the material also features conductivity, in vivo degradability, and the like.

Abstract: A High Efficiency Treatment System (system) wastewater treatment system including a tank with a multi-chamber tank system that is designed to remove pollutants from domestic wastewater. Embodiments of the system consist of a pretreatment chamber, which is in fluid communication with an anoxic chamber, which is in fluid communication with an aeration chamber, which is in fluid communication with a clarification chamber, and which is in fluid communication with a polishing chamber. The system can be applied to remove suspended solids, BOD, ammonia, nitrate and TKN from wastewater.

Abstract: A method for removal and condensation of vapors from within an enclosed space is disclosed. An enclosed space containing hydrocarbonaceous material is surrounded by an insulative permeable layer having a lowering temperature gradient between the inner surface and the outer surfaces. The insulative layer may also be covered by an impermeable layer. Heating the material in the enclosed space causes the formation of vapors at a positive pressure within the enclosed space. Vapors pass through the inner surface of the insulative permeable layer and contact the permeable materials and are condensed by the lowering temperature within the insulative layer. The condensate liquid passes downwardly through the insulative layer and is then collected.

Abstract: The invention is directed to systems and methods of biological and chemical treatment of wastewater comprising organic nitrogen compounds. Systems may include: an aerobic reactor, a first separation module for separating liquid and solid components of the wastewater; an oxidation module for removing organic materials from the wastewater; and a post-anoxic reactor for denitrifying at least a portion of the wastewater. Systems may include a second separation module and various feedback recycle lines between the components. Methods may include: degrading by the aerobic reactor more than 95% of organic compounds to ammonia, oxidizing by the oxidation module at least a portion of the ammonia to nitrates, and degrading by the post-anoxic reactor at least a portion of the nitrates to nitrogen gas and water. Systems and methods may reduce total organic carbon of the wastewater by more than 90%, and total nitrogen of the wastewater by more than 90%.

Abstract: Bioconversion processes are disclosed in which two or more biocatalysts including microorganisms or isolated enzymes that are substantially irreversibly retained in the interior of an open, porous, highly hydrophilic polymer are used in a common aqueous medium. In one exemplary embodiment, one biocatalyst produces a chemical product that is a substrate to at least one other biocatalyst. In another exemplary embodiment, the feed includes two or more substrates and one biocatalyst bioconverts at least one substrate and another biocatalyst bioconverts at least one other substrate. This aspect is particularly useful for treating water including disparate contaminants by metabolic degradation in a bioreaction zone including multiple types of biocatalysts.

Abstract: A system of treating high nitrogen content waste water is disclosed, where the system includes a precipitation and conditioning subsystem, an ammonia stripper subsystem, and a denitrification subsystem. The system is adapted to reduce nitrogen contamination to level below about 10 ppm and in certain embodiments below 3 ppm.

Abstract: In some embodiments, a wastewater treatment system may reduce contaminants in water. A system may include one or more bioreactors which include a substrate that supports a biofilm. The bacteria used to form the biofilm may be selected to maximize the reduction of contaminants in water. Various components of the wastewater treatment system may be optimized to improve the efficiency and energy consumption of the wastewater system.

Abstract: There is provided a shaped article made of porous hydrogel that contains a polyvinyl alcohol acetalized with a dialdehyde, wherein the shaped article after freeze-drying has a pore size of 0.1 to 50 ?m. Preferably, the shaped article made of porous hydrogel further contains a water-soluble polysaccharide. Also preferably, an acetalization degree of the polyvinyl alcohol is 1 to 50 mol %. Also preferably, the shaped article made of porous hydrogel is in the form of particles with a sphere-equivalent diameter of 1 to 20 mm. Such a shaped article made of porous hydrogel exhibits high strength and good survivability of microorganisms.

Abstract: A method of supplying engineered water for drilling or hydraulic fracturing of wells, where the water comes from either fresh sources or is recycled from drilling or hydraulic fracturing operations whereby the water is treated for example with a mechanical vapor recompression unit or other treating apparatuses and methods to significantly reduce the concentration of constituents that are deleterious to drilling or hydraulic fracturing chemistries while keeping desirable constituents, such as semi-volatile antimicrobial constituents. The final composition of the engineered water is designed to contain constituents that are optimal for drilling or hydraulic fracturing operations.

Abstract: A ballasted anaerobic system for treating wastewater including at least one anaerobic treatment reactor. A weighting agent impregnation subsystem is configured to mix weighting agent with the biological flocs to form weighted biological flocs to create a weighted anaerobic sludge blanket in the at least one anaerobic treatment reactor. A weighting agent recovery subsystem is configured to recover the weighting agent from excess sludge and reintroduce the weighting agent to the weighting agent impregnation subsystem.

Abstract: In one embodiment, a bioremediation agent and method of bioremediation of an oil spill are disclosed. The bioremediation agent contains oil-digesting bacteria and bacterial nutrients in a buoyant water semi-insoluble and biodegradable casein product. The bioremediation agent may be distributed by boats or seeded by aircraft to remediate oil from coastlines after an oil spill.

Abstract: A system of treating high nitrogen content waste water is disclosed, where the system includes a precipitation and conditioning subsystem, an ammonia stripper subsystem, and a denitrification subsystem. The system is adapted to reduce nitrogen contamination to level below about 10 ppm and in certain embodiments below 3 ppm.

Abstract: The present invention provides a method for treating wastewater in which the majority of solids and biological oxygen demand compounds are separated from the wastewater feed using a primary separation process, to produce a solids phase and a water phase. The solids phase is irradiated to reduce the level of pathogens such that it is safe to use as a soil substitute and/or additive so that the solids can thus be disposed of in an environmentally-friendly manner. In additional embodiments, the solids that have been disinfected by radiation are mixed with a suitable inert filler material to produce a soil substitute, fertilizer, compost, or other soil additive. The liquid phase is treated in a substantially smaller system than would be required for treating the full-strength wastewater that can include a suspended media biological regeneration reactor system.

Abstract: In some embodiments, a wastewater treatment system may reduce contaminants in water. A system may include one or more bioreactors which include a substrate that supports a biofilm. The bacteria used to form the biofilm may be selected to maximize the reduction of contaminants in water. Various components of the wastewater treatment system may be optimized to improve the efficiency and energy consumption of the wastewater system.

Abstract: A biological wastewater treatment system includes a tank or reactor for holding and treating wastewater. Disposed in the tank or reservoir is an array of biofilm carriers for supporting biomass that remove pollutants and contaminates from the wastewater. A screen structure is mounted to the tank for screening treated wastewater flowing from the tank and preventing the biofilm carriers from being discharged from the tank. The screen structure includes a vertical screen made up of a plurality of screen modules disposed in side-by-side relationship and disposed upstream of an outlet formed in the tank. Further this screen structure may include a plurality of auxiliary screens that project form the vertical screen inwardly towards the interior area of the tank thereby providing increased screening area through which wastewater is discharged during a wastewater treatment process.

Abstract: Systems and methods for removing organic contaminants from water may be used, for example, to treat produced water from a steam assisted heavy oil recovery operation. The treated produced water may be re-used to create steam. Alternatively, the produced water may be a blowdown stream treated to facilitate further treatment in a thermal crystallizer. The treatments may include pH adjustment or separating de-solubilized organics or both. Other treatments may include one or more of oxidation, sorption and biological treatments. The treatments may be used alone or in various combinations. One exemplary combination includes reducing the pH of produced water, separating de-solubilized organics from the produced water, and oxidizing the produced water or contacting the produced water with activated carbon.

Abstract: The present invention provides a bio-augmentation composition for improving the hydrocarbon degradation efficiency of effluent treatment plant for hydrocarbon degradation in wastewater generated from hydrocarbon processing industry and a method thereof. The composition comprises a synergistic combination of selective microorganisms to develop a consortium enabling effective degradation of hydrocarbons present in wastewater and converting thereof into harmless and environment friendly substances. The invention also provides for the said microorganisms and their isolations.

Abstract: The present invention provides a method for treating wastewater in which the majority of solids and biological oxygen demand compounds are separated from the wastewater feed using a primary separation process, to produce a solids phase and a water phase. The solids phase is irradiated to reduce the level of pathogens such that it is safe to use as a soil substitute and/or additive so that the solids can thus be disposed of in an environmentally-friendly manner. In additional embodiments, the solids that have been disinfected by radiation are mixed with a suitable inert filler material to produce a soil substitute, fertilizer, compost, or other soil additive. The liquid phase is treated in a substantially smaller system than would be required for treating the full-strength wastewater that can include a suspended media biological regeneration reactor system.

Abstract: The present disclosure relates to an apparatus and method for anaerobic wastewater treatment with a membrane, which effectively generates biogas and suppresses fouling on a membrane surface by performing anaerobic treatment to wastewater. The apparatus for anaerobic wastewater treatment with a membrane includes: an anaerobic reactor for performing anaerobic treatment to wastewater and generating biogas; an anaerobic membrane bio-reactor for filtering wastewater discharged from the anaerobic reactor by means of a membrane module and providing an additional anaerobic treatment space for the wastewater; submerged membrane modules provided in the anaerobic membrane bio-reactor to filter wastewater; rotating disks provided at both sides of the submerged membrane module to induce turbulence to the wastewater by means of rotation; and a second media provided in the anaerobic membrane bio-reactor to circulate according to the flow of the wastewater so that foulants on a surface of the membrane module are detached.

Abstract: In some embodiments, a wastewater treatment system may reduce contaminants in water. A system may include one or more bioreactors which include a substrate that supports a biofilm. The bacteria used to form the biofilm may be selected to maximize the reduction of contaminants in water. Various components of the wastewater treatment system may be optimized to improve the efficiency and energy consumption of the wastewater system.

Abstract: Methods for enhancing an activated sludge process including at least one biological reactor. A weighting agent impregnation subsystem is coupled to the biological reactor for mixing biological flocs and weighting agent to impregnate the weighting agent into the biological flocs to form weighted biological flocs. A weighting agent recovery subsystem is configured to recover the weighting agent from the weighted biological flocs and reintroducing the recovered weighting agent to the weighting agent impregnation subsystem.

Abstract: A coupling bioreactor in the form of a tower type seal structure filled with a suspended carrier. A water inlet pipe, an air inlet pipe, and a first microporous aerator are arranged at the bottom of the coupling reactor. The water inlet pipe is connected to a water distributor. The air inlet pipe is connected to the first microporous aerator. A gas inlet pipe and a second microporous aerator are arranged at the middle part of the coupling bioreactor and are connected with each other. An annular overflow weir is arranged at the upper part of the coupling bioreactor and is connected to a water outlet pipe. A gas outlet pipe is arranged at the top of the coupling bioreactor. The ratio of the height to the diameter of the coupling bioreactor is between 3 and 10.

Abstract: An anthropogenic sorbent material modified for sequestering and/or attenuating multiple chemical and/or biological pollutant species, both organic and inorganic, in an aqueous environment is disclosed as well as a method of sequestering and/or attenuating multiple chemical and/or biological pollutant species, both organic and inorganic, in an aquatic ecosystem by capping at least a portion of a sedimentary basin of the aquatic ecosystem.

Abstract: In one embodiment, a grey water treatment system includes an oxidation reactor for oxidizing grey water. The grey water treatment system also includes a biological reduction and precipitation system with microbes designed to remove one or more target components from the oxidized grey water.

Abstract: A ballasted sequencing batch reactor system for treating wastewater including one or more sequencing batch reactors. A weighting agent impregnation subsystem is configured to mix biological flocs and weighting agent to form weighted biological flocs. A weighting agent recovery subsystem is configured to recover weighting agent from the weighted biological flocs and reintroduce the recovered weighting agent to the weighting agent impregnation subsystem.

Abstract: A method for treating wastewater through the use of powdered natural lignocellulosic materials (PNLM) and/or powdered kenaf (PK). The method includes mixing particulate kenaf with microorganisms to form an effector composition, mixing the effector composition with influent wastewater, oxygenating the wastewater, reacting the wastewater and clarifying the wastewater, resulting in improvement in the microbial population effector composition in the wastewater.

Abstract: A biological purifier of the present invention includes chaff retaining sulfate-reducing bacteria. A biological purification system of the present invention includes a treatment container in which anaerobic conditions are maintained, and the above biological purifier is stored; a supply system for supplying the untreated waste water into the treatment container; and an discharge system for discharging treated water from which the heavy metal ions have been removed in the treatment container by the purifier, from the treatment container. In a biological purification method of the present invention, the biological purifier and the untreated waste water are brought into contact with each other under anaerobic conditions, thereby precipitating and removing the heavy metal ions as sulfide from the untreated waste water.

Abstract: A method of prevention of acid rock drainage excludes oxygen from waste rocks that contain ferrous sulfides by building an oxygen bio-barrier over exposed surfaces of the waste rock. The bio-barrier may be formed by applying a slurry to the rock. The slurry may contain several components such as microbial material, one or more nutrients, water or another fluid, and optionally water-absorbent material. The microbial material may include bacteria, algae, fungi or a combination thereof. Additionally, the slurry may contain one or more acid-neutralizing compounds, one or more cellulose-containing substances, and one or more UV protecting agents.

Abstract: The present invention provides systems and methods for in-situ remediation of soil and groundwater having contaminants such as but not limited to organic compounds perhaps providing adsorption, chemical oxidation, and even biodegradation of contaminants with novel treatments such as but not limited to mixtures of granular activated carbon, calcium peroxide, sodium persulfate, and nitrate perhaps in various concentrations.

Abstract: The present invention refers to a hollow microsphere having a porous circumferential wall comprised of nanofilaments.

Abstract: A method for treating wastewater comprises biologically treating the wastewater in a fixed-biomass biological reactor and then treating the wastewater in a ballasted flocculation system. The ballasted flocculation system produces a clarified effluent and sludge containing inert granular material having biomass accumulated thereon and suspended solids. The inert granular material having biomass accumulated thereon is separated from the suspended solids and then cleaned with a cleaning solution. After separating the biomass from the cleaned inert granular material, the cleaned inert granular material is recycled for use in the ballasted flocculation system.

Abstract: The present invention provides an apparatus and method for biologically treating fluids, in particular municipal or industrial wastewater or the like, the apparatus comprising a pair of reservoirs each containing growth medium having a biofilm thereon, the apparatus being arranged to pump the wastewater from one reservoir to another such as to alternatively expose the biofilms within the reservoirs to air and wastewater, thus making it possible to achieve sequential aerobic, anoxic and anaerobic conditions in the biofilms.

Abstract: The invention relates to a biological wastewater purification method using a reactor including a first compartment (2) and a second compartment (4), the lower parts of which are communicated with one another. The water to be treated enters the first compartment, while the second compartment houses aerobic granular sludge at atmospheric pressure. Oxygen-laden gas is injected into the lower part of the second compartment. The granular sludge forms a bed (5) in the second compartment (4) and the reactor operates in a sequential, discontinuous manner in a cycle comprising two phases, namely: a first anaerobic phase during which the first compartment (2) is vacuum-filled with the water to be treated, after which the pressure is abruptly brought to atmospheric pressure in order to discharge a volume of water rapidly into the second compartment (4); and a second aerobic phase during which gas containing oxygen is injected into the second compartment (4).

Abstract: Systems and methods for the bioremediation of soluble sulfates from an environmental effluent, include a first chamber including lactic acid bacteria immobilized on a first matrix and a second chamber including sulfate-reducing bacteria immobilized on a second matrix. The methods include providing the lactic acid bacteria a suitable medium for the production of lactic acid, which is directed to the culture of sulfate-reducing bacteria for use as a substrate/electron donor for the reduction of sulfates present in the environmental effluent.

Abstract: Integrated membrane treatment systems for treatment of an aqueous solution. In embodiments, components, such as an MBR, are integrated with means to recover energy from the system, for example from an RO concentrate, to operate the other components. In embodiments including biological treatment, RO is integrated with other components, such as an MBR with the ROs ability to remove inorganic nitrogen enabling biological treatment to be performed with only partial nitrification and the MBR operated without active pH control. In embodiments, RO is integrated with a chlorine generator to convert chlorides present in the RO concentrate for an in-situ source of oxidizing biocides for disinfection purposes. Chloramines may be generated in-situ from residual ammonia and chlorides in the RO reject. In embodiments, carrier media is employed in a membrane tank to enhance removal of residual organics by the MBR and to also improve effectiveness of membrane scouring.

Abstract: Anaerobic Wastewater treatment system and process in which the influent is passed through a mixing chamber and then through a series of filters of progressively smaller size to separate the materials carrying the colonized bacteria from finer solids in the influent and separate the materials according to size in a completely enclosed and flooded environment. The materials from the filters are progressively reduced to a smaller size, the materials of smaller size are returned to the mixing chamber, and new influent is inoculated with the colonized bacteria carried by the materials returned to the mixing chamber.

Abstract: Disclosed are compositions of matter comprising at least one anaerobic degrading microorganism, particulate active carbon and a polymeric solid support wherein the anaerobic degrading microorganism and particulate active carbon are entrapped in the polymeric support and processes for preparing the same. The disclosed compositions of matter are used in processes of anaerobic degradation of waste materials resulting in high yields of biogas production.

Abstract: A system and process for treating an industrial wastewater stream is provided using a membrane biological reactor in which granular activated carbon material is introduced into an aeration portion and maintained upstream of a membrane operating system. The size of the granules of activated carbon is selected so that they can be screened or otherwise readily separated from the mixed liquor stream before the mixed liquor enters the membrane operating system tank(s) containing the submerged membranes, thereby preventing abrasion of the membrane by the carbon granules. The aeration portion includes a waste discharge port whereby a portion of spent granular activated carbon can be removed when the effluent concentration of chemical oxygen demand compounds approaches limits typically set by governmental agencies, and replaced by addition of fresh or regenerated granular activated carbon having greater adsorbent capacity.

Abstract: The present invention is related to a method and system for cleaning a media support structure in a filter cell in a liquid filter system, wherein a cleaning solution does not significantly enter a filter media zone. The method comprises supplying a cleaning solution to a filter cell to a level sufficient to submerge the media support structure, but not to significantly enter the filter media zone. Additionally, the cleaning solution level is monitored to ensure the cleaning solution does not significantly enter the filter media zone. Alternatively, the cleaning solution may be continuously recirculated and reintroduced to the filter cell during the cleaning operation.

Abstract: A nitrification carrier having made nitrifying bacteria dominant therein and a denitrification carrier having made anaerobic ammonium-oxidizing bacteria dominant therein are mixed in a treatment tank. Both of a nitrification reaction with the nitrification carrier and a denitrification reaction with denitrification carrier are allowed to proceed in the treatment tank to decompose ammonium nitrogen in wastewater to nitrogen gas. The ratio of the bacterial loads of the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria can be easily controlled by immobilizing the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria on different carriers from each other (nitrification carrier and denitrification carrier) and by controlling the volume ratio (ratio of the feeding amounts) of the nitrification carrier and the denitrification carrier.

Abstract: The invention relates to a method for biologically cleaning wastewater (A), comprising the following steps: providing a treatment basin (B) having a floor (1) and at least one wall (2) extending from the floor at a wall height (W), having an inlet opening (3) and having at least one outflow opening (9) in the range from 0 to a maximum of 0.5 times the wall height (W), feeding the wastewater (A) through the inlet opening (3) into the treatment basin (B), bringing the wastewater (A) into contact with microorganisms seeded in loose growth bodies (12) received in the treatment basin (B), and discharging the wastewater (A) at least partially cleaned by the action of the microorganisms from the treatment basin (B) through the outflow opening (9), wherein the growth bodies (12) are retained in the treatment basin (B).

Abstract: A wastewater treatment method for treating wastewater containing ammonium nitrogen, includes the steps of: charging an unacclimated denitrification carrier containing anaerobic ammonium-oxidizing bacteria into a treatment tank; charging an unacclimated nitrification carrier containing nitrifying bacteria into the treatment tank; acclimating the unacclimated denitrification carrier in the treatment tank under an anaerobic condition; acclimating the unacclimated nitrification carrier in the treatment tank under an aerobic condition, after having acclimated the denitrification carrier; nitriting the ammonium nitrogen in the wastewater to generate nitrite with the acclimated nitrification carrier; and denitrifying the nitrite generated by nitriting the ammonium nitrogen with the acclimated denitrification carrier, while using the ammonium nitrogen in the wastewater as a hydrogen donor.

Abstract: A method of biologically treating wastewater with an integrated fixed film activated sludge process. The integrated fixed film activated sludge process includes biomass suspended in mixed liquor and biomass disposed on carriers. Under certain conditions the dissolved oxygen concentration in a reactor that includes the mixed liquor, biomass suspended in the mixed liquor, and the biomass on the carriers, biological treatment is performed primarily by the biomass in the mixed liquor. This is achieved by controlling or maintaining the dissolved oxygen concentration in the reactor at a relatively low concentration. When the biomass suspended in the mixed liquor is unable to adequately biologically treat the mixed liquor, the dissolved oxygen concentration in the reactor is controlled or maintained at a relatively high concentration. This enables biomass on the carriers to contribute more to the biological treatment of the mixed liquor than when the dissolved oxygen concentration was maintained relatively low.