Abstract: Systems and methods for aeration and mixing processes are disclosed.

Abstract: An automated produced water treatment system that injects ozone or an ozone-oxygen mixture upstream of produced water separators, with the dose rate changing dynamically as the produced water quality changes, as determined by continuous monitoring of the produced water quality by a plurality of sensors that detect water quality parameters in real time. The system may operate as a “slipstream” injection system, that draws a portion of produced water from the produced water pipeline and injects ozone or an ozone-oxygen mixture back into the pipeline with disrupting or slowing normal operations. Disinfectants or other additives may also be injected. The treatment system may be wholly or partially contained in mobile containers or trailers, for on-the-fly use in existing produced water treatment facilities.

Abstract: System and method of scum collection and removal in batch biological wastewater treatment systems.

Abstract: A high-concentration sewage treatment system for self-sufficiency of energy is provided. The system includes a hydrolysis acidification device, an anaerobic reactor, a sludge treatment device, a desulfurization tower, and a biogas power generation device. The hydrolysis acidification device includes a hydrolysis acidification tank, a first sedimentation tank, a first overflow water tank and an overflow pipe. The sludge treatment device includes a second sedimentation tank, a second overflow water tank, an inlet pipe and a dissolved oxygen meter. The second overflow water tank communicates with the hydrolysis acidification tank through a return pipe. The inlet pipe defines a jet hole. A regulating valve is connected to the inlet pipe. The regulating valve controls a speed and a height of mixed liquid in the jet hole. A high-concentration sewage treatment method for self-sufficiency of energy is also provided.

Abstract: A bioreactor for a water treatment system includes an aerator tank configured to receive an influent liquid, and a clarifier positioned in the aerator tank, the clarifier having a generally conical shape and defining a downwardly-facing opening. An interior of the clarifier is in communication with the aerator tank, external to the clarifier, at least via the downwardly-facing opening, and wherein the clarifier is positioned non-concentrically with the aerator tank. The bioreactor further includes a plurality of aeration vents positioned proximal to a bottom of the tank and configured to direct air into the aerator tank, and an effluent outlet positioned in the clarifier. A relatively clean effluent liquid, in comparison to the influent liquid in the aerator tank, exits from the clarifier via the effluent outlet.

Abstract: A wastewater treatment system includes a biological treatment plant and an auxiliary, non-biological treatment plant. The auxiliary plant receives overflow, which can be sanitary sewer overflow, combined sewer overflow or strictly storm overflow. Treatment is by coagulation and membrane separation, removing most bacteria. Following treatment the outflow can be discharged to streams.

Abstract: Systems and methods for actively treating mining wastewater, such as acid mine drainage, using a mixed culture of iron oxidizing bacteria, in a manner that results in both remediation of the water and the production of a useful end product. Exemplary systems and methods employ a reaction vessel where the bacteria can oxidize the iron in the mining wastewater for some amount of time, and a settling tank into which reacted water may be transferred and retained to permit iron oxyhydroxide contained in the water to settle as iron oxyhydroxide sludge. The iron oxyhydroxide sludge may be dried to produce iron oxyhydroxide solids that can be employed in the manufacture of a usable pigment.

Abstract: An automated produced water treatment system that injects ozone or an ozone-oxygen mixture upstream of produced water separators, with the dose rate changing dynamically as the produced water quality changes, as determined by continuous monitoring of the produced water quality by a plurality of sensors that detect water quality parameters in real time. The system may operate as a “slipstream” injection system, that draws a portion of produced water from the produced water pipeline and injects ozone or an ozone-oxygen mixture back into the pipeline with disrupting or slowing normal operations. Disinfectants or other additives may also be injected. The treatment system may be wholly or partially contained in mobile containers or trailers, for on-the-fly use in existing produced water treatment facilities. Ozone and/or nitrogen micro-bubbles and/or nano-bubbles may be introduced for friction reduction in oil and gas operations.

Abstract: The present invention relates to a method for simultaneous removal of heavy metals and organic matters from wastewater, including four steps: anoxic reaction, incubation reaction, aerobic reaction and sedimentation reaction, to solve tricky problems and shortcomings of current treatment technologies for industrial wastewater containing both heavy metals and organic substances. Compared with current technologies, in the present invention, by regulating and controlling heavy metal ions in wastewater, catalysts with function of activating molecular oxygen are in-situ generated, catalyzing dioxygen to produce strong oxidative species, thereby realizing catalytic oxidation of organic pollutants and crystallization and precipitation removal of heavy metals, which creatively treats waste using waste to achieve green oxidation, shortened treatment process, improvement of treating efficiency, reduction of economic cost and promotion of technology for industrial application.

Abstract: A process for aerobic treatment of wastewater is provided, which process comprises: (a) supplying a liquid influent comprising wastewater to a reactor containing granular biomass; (b) subjecting the reaction mixture to aerobic conditions comprising a concentration of dissolved oxygen from 0.1 mg/L to 4.0 mg/L, and a hydraulic retention time from 0.5 to 72 hours; (c) separating the reaction mixture into granular biomass and treated wastewater; and (d) recycling separated granular biomass to the reaction mixture. A bioreactor for the process is also disclosed, comprising a reaction vessel provided with an aeration means, a solids separation device with an inlet in the lower part of the reaction vessel having an outlet line for solids arranged to transport separated solids to a riser driven by airlift action and arranged to transport the solids to the upper part of the reaction chamber.

Abstract: A method for treating a circulating water in a wet paint booth, the method including adding a treatment agent including an aqueous solution including a tannin and an alkali metal hydroxide and/or an alkali metal carbonate to the circulating water in any of passages for the circulating water in the wet paint booth, wherein the passages include for supplying the circulating water from a water tank to a paint booth, for collecting an uncoated paint in the circulating water, and for returning the circulating water to the water tank; to detackify the uncoated paint collected in the circulating water.

Abstract: A method and device for using electrokinetic forces for thickening or dewatering municipal biosolids is provided. The method uses chlorine dioxide to accelerate and improve the efficiency of electrokinetic dewatering.

Abstract: Embodiments of the present disclosure describe an aquaculture environment control system comprising one or more control apparatuses positioned within a vessel at an angle relative to a proximal vessel wall and configured for scouring of the vessel, wherein each control apparatus has a discharge conduit and each discharge conduit has one or more orifices; and a fluid source in fluid communication with each of the control apparatuses. Embodiments of the present disclosure describe a method of controlling an aquaculture environment comprising supplying one or more of a fluid and gas to a control apparatus positioned within a vessel at an angle relative to a proximal vessel wall; and discharging one or more of the fluid and gas from the control apparatus at a fluid velocity sufficient for scouring of the vessel.

Abstract: A method for treating reverse osmosis concentrated water, comprises adding precipitant and oxidant to reverse osmosis concentrated water for treatment, filtering to obtain clear liquid, and adding catalyst for water treatment to clear liquid for catalytic oxidation to obtain a first-stage treated water. Optionally, the liquid may be subjected after catalytic oxidation to an adsorption treatment; performing reverse osmosis treatment on first-stage treated water to obtain second-stage reverse osmosis product water and second-stage reverse osmosis concentrated water; and adding oxidant to second-stage reverse osmosis concentrated water for oxidation treatment to obtain directly discharged effluent water. The obtaining of effluent water may further comprise subjecting liquid after oxidation treatment to adsorption treatment. The above method can recycle 75-85 wt % of water, and operates easily.

Abstract: Processes are disclosed for the microbial nitritation of ammonia that attenuate the production of at least one of nitrate anion and nitrous oxide. The processes use an ME biocatalyst having a highly porous, hydrophilic polymeric structure with ammonia-oxidizing microorganisms substantially irreversibly retained therein. The processes are particularly useful for integration with anammox processes.

Abstract: A mobile wastewater treatment system wherein a mobile carrier has mounted thereon a wastewater treatment plant. The wastewater treatment plant has a flow equalization tank, an aeration tank, a clarifying tank, a disinfection stage, and a pumping tank. The mobile carrier can be a trailer, a skid, a shipping container, or the like.

Abstract: A system and method for recovering a metal value from a metal-bearing ore material are provided. A metal-bearing ore can be mixed with certain substances and to form an agglomerated ore. In an intermediate state, between agglomeration and heap formation, bacteria can be added to the metal-bearing ore material to produce an augmented ore. The augmented ore can then be formed into a heap. Bacteria from the heap may be fortified to assist in bacterial growth.

Abstract: The present invention provides a method for reducing or controlling wastewater and pollutant from emulsion polymerization resin production, comprising the following steps: (1) optimizing an emulsion polymerization reactor to lengthen a cleaning interval of the reactor so as to reduce the volumes of reactor cleaning wastewater and pollutant discharge; (2) demulsifying latex filter cleaning wastewater and removing a latex material so as to reduce the volume of the pollutant discharge; (3) demulsifying the highly concentrated reactor cleaning wastewater, then performing flotation recovery; (4) mixing graft polymerization wastewater and 1,3-diene polymerization wastewater, then performing demulsification; (5) mixing the demulsified latex wastewater and condensation and drying wastewater, then performing a coagulation and dissolved air flotation treatment; and (6) implementing a biological treatment process on the effluent from the coagulation and dissolved air flotation treatment to remove an organic material, ni

Abstract: A method for clarification of wastewater that operates at least two alternating and equal process cycles in two or more clarifiers (1a, 1b), each process cycle consisting of a feed period with concurrent feeding and discharging and a reset period in which excess sludge is removed into a thickener (2a, 2b) and the remaining sludge blanket gets homogenized and pre-settled, wherein at each point of time in at least one clarifier (1a, 1b) the feed period is performed.

Abstract: A method for cleaning and preventing diffuser membrane fouling of an aeration system can include: transporting a liquid acidic solution into a downcomer pipe or a purge line positioned in a reservoir of an aeration system containing a body of water such that the liquid acidic solution flows into a manifold and air distribution pipes; allowing the liquid acidic solution to vaporize; and blowing the vaporized acidic solution into a plurality of diffusers supported by the air distribution pipes. An aeration system that can implement the method is also included.

Abstract: Sewage treatment is performed by using Sulphur to facilitate electron flow. A first cycle uses a sulphur composition having sulphur and/or sulphur compounds to transfer electrons from organic carbon to oxygen, nitrate and nitrite, and to convert phosphorus-containing compounds to solid material, which is retained in sewage sludge. The sulphur is further used to perform denitrification of nitrogen compounds. A further cycle uses oxygen to oxidize any ammonia present to nitrate and/or nitrite.

Abstract: A stream processing system, where the stream comprises a glycol based hydrate inhibitor and a kinetic hydrate inhibitor (KHI) is provided. The system comprises a thermal oxidation unit (31) and a processing unit comprising a stream inlet (9), a fluid inlet (11) and a mixture outlet (15) in fluid communication with the thermal oxidation unit.

Abstract: A device for purifying liquid wastewater, includes: a container suitable for retaining a granulate consisting of solid particles, and for enabling the contact between the solid particles of the granulate and the liquid wastewater flowing in the container between: an inlet for the liquid wastewater to flow into the container, and an outlet for substantially decontaminated water to flow out of the container; a community of microorganisms extending so as to be in contact with the solid particles of the granulate; at least one live benthic invertebrate whose mean size is greater than 250 ?m and which is distributed in the granulate; and at least one live benthic invertebrate whose mean size is from 50 ?m to 250 ?m and which is distributed in the granulate, characterized in that the community of macrobenthic organism and meiobenthic organism species includes a proportion of 60% to 80% of invertebrate detrivorous organisms.

Abstract: A process approach allows economical self-sustained operation of single vessel biotreatment systems for municipal wastewater treatment. The daytime solar powered treatment process is changed during darkness periods to operate the biotreatment system without electric grid powering.

Abstract: A method of detecting Hg2+ in an aqueous solution. The method includes contacting the aqueous solution with a composition containing a plant extract and biosynthesized silver nanoparticles. The composition has an average particle size of 30-50 nm. A color change following the contacting indicates the presence of Hg2+ in the aqueous solution. The composition is preferably synthesized by reduction of a silver salt with an extract of Ocimum basilicum.

Abstract: A flow equalization reactor for a multi-stage activated sludge process for treating industrial wastewater and/or municipal sewage is divided into two or more treatment zones. An outflow from a first treatment zone is mixed with an outflow from the second treatment zone in a mixer and conveyed to a third stage reactor containing anaerobic, autotrophic ammonia oxidizing anammox bacteria for converting nitrite nitrogen to nitrogen gas. The relative amounts of the outflows from the first and second treatment zones are controlled to promote and optimize the growth and accumulation of the anammox biomass in the third stage reactor.

Abstract: A selective removal of chlorine and phosphorus that are detrimental to subsequent hydrothermal hydrocatalytic conversion from the biomass feed prior to carrying out catalytic hydrogenation/hydrogenolysis/hydrodeoxygenation of the biomass in a manner that does not reduce the effectiveness of the hydrothermal hydrocatalytic treatment while minimizing the amount of water used in the process is provided.

Abstract: Digestion of cellulosic biomass solids can be enhanced in the presence of a phenolic solvent. Methods for digesting cellulosic biomass solids can comprise providing cellulosic biomass solids in a digestion medium comprising water and an organic solvent; heating the cellulosic biomass solids and the digestion medium in a digestion unit in the presence of molecular hydrogen and a slurry catalyst capable of activating molecular hydrogen, thereby forming an alcoholic component and liberating lignin, the lignin forming a phenolics liquid phase partitioned from the digestion medium and at least a portion of the slurry catalyst accumulating in the phenolics liquid phase; removing at least a portion of the phenolics liquid phase and accumulated slurry catalyst from the digestion unit; converting at least a portion of the phenolics liquid phase into a phenolic solvent; and returning at least a portion of the phenolic solvent and the slurry catalyst to the digestion unit.

Abstract: In a wastewater treatment system, feed water is processed by anaerobic digestion, preferably in an anaerobic moving bed bioreactor (AnMBBR). Effluent from the AnMBBR passes through one or more solid-liquid separation units. A solids portions is treated by hydrolysis or suspended growth anaerobic digestion. A liquid portion of the hydrolysis or suspended growth anaerobic digestion effluent is returned to the AnMBBR or blended with effluent from the AnMBBR. The AnMBBR effluent may be treated with an aerobic moving bed bioreactor (MBBR) before the one or more solid-liquid separation steps. Membrane filtration may provide a first solid-liquid separation step. A thickened waste stream may be withdrawn from a recirculation loop flowing from the first solid-liquid separation unit to the MBBR. Optionally, a solids portion separated from the feed water upstream of the AnMBBR may also be treated by hydrolysis or suspended growth anaerobic digestion.

Abstract: A process for treating water containing dissolved organic compounds, including naphthenic acids, for example, oil sands process water, using petroleum coke is provided, comprising: removing petroleum coke from a coking operation; forming a petroleum coke/water slurry by adding the water containing dissolved organic compounds to the petroleum coke; adding a pH-lowering agent to the petroleum coke/water slurry either during slurry formation or after slurry formation to form a treated petroleum coke/water slurry; and allowing the treated petroleum coke/water slurry to mix for a sufficient time in a carbon adsorption reactor to allow the petroleum coke to adsorb a substantial portion of the dissolved organic compounds from the water.

Abstract: Ultrapure water of high purity having extremely low TOC concentration is produced by efficiently degrading urea in raw water by biological activated carbon treatment even when the raw water contains ammonium nitrogen. The ultrapure water production method, where raw water is treated in a primary pure water system, and then the resulting water is treated in a subsystem, contains a step of treating pretreated water with chlorine based oxidizer added by a biological treatment means installed upstream to the subsystem. Chlorine based oxidizer is added so that the chlorine based oxidizer concentration is 5 times or more than the ammonium nitrogen concentration of water treated in the biological treatment means in terms of Cl2.

Abstract: A device for mixing and aerating a body of water, the device includes a microbial fuel cell comprising an anode and a cathode; an electricity management subsystem electrically connecting the anode and the cathode; and a mixing subsystem electrically connected to the electricity management subsystem. The device can be used to mix or aerate a body of water containing organic material while simultaneously reducing the requirements for aeration. The body of water may provide organic material to the microbial fuel cell to produce electricity to power the mixing subsystem.

Abstract: The present invention relates to a method of selectively obtaining phosphorus from solids containing heavy metals and phosphate. In this method, the solid is treated under acidic aerobic conditions using microorganisms comprising leaching microorganisms and polyphosphate-accumulating microorganisms, so that the heavy metals and the phosphates are released from the solid and the released phosphates may be taken up by the polyphosphate-accumulating microorganisms. The phosphorus-enriched biomass that is obtained in this manner is separated and may be utilized, e.g., as organic fertilizer.

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 methods for increasing soluble chemical oxygen demand (sCOD) in sewage sludge. These methods include passing the sewage sludge through one or more devices that contains (a) a hollow body provided with a straight-through passage of substantially constant cross-section, the passage having an inlet end and an outlet end for the entry and discharge respectively of the sewage sludge, (b) a transport fluid nozzle substantially circumscribing and opening into the passage intermediate the inlet and outlet ends thereof, (c) a transport fluid inlet communicating with the transport fluid nozzle for the introduction of a transport fluid, and (d) a mixing chamber being formed within the passage downstream of the transport fluid nozzle. The sewage sludge is then passed through a digester.

Abstract: A method and system for controlling dissolved oxygen levels in a secondary treatment system of a wastewater treatment facility that can employ a membrane bioreactor in which oxygen introduction into mixed liquor is controlled to prevent bulking and minimize generation of extra cellular polymeric substances. The control is exercised by insuring that dissolved oxygen levels within the mixed liquor do not fall below a minimum system level at which microorganism stress would occur. This is done by setting a minimum dissolved oxygen level control point equal to a sum of the minimum system level and an adjustment factor determined on the basis of oxygen uptake rate and time delays inherent in sensing oxygen levels and changes thereof within the mixed liquor. The minimum system dissolved oxygen level can be continually calculated on the basis of an inferred food to mass ratio that would vary with sensed mixed liquor suspended solids.

Abstract: A system and method includes an aeration subsystem that excites enzymes in the liquid waste passing through the septic system. The aeration subsystem includes a compressor section that compresses the liquid waste. The method includes mixing enzymes into the fluid waste material, compressing the fluid waste material with the compressor, injecting air into the compressed fluid waste material, and determining whether the fluid waste material is at a desired cleanliness, and if not, recirculating the fluid waste material through the compressor.

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: The present invention provides an aeration lateral system designed to be site specific for new septic disposal areas or retro fitting to existing septic disposal areas to break up the biological clogging sludge mat at the interface of the wastewater and imported sand or native soil fill under or adjacent to disposal areas of a typical septic system. The lateral system provides uniform or other site specific distribution of fluids about the bio-mat of a wastewater disposal area, with lateral spacing and hole spacing varying based on the type of disposal area being utilized. The lateral system can also be utilized to provide continuous low volume air supply system to a wastewater disposal area or peat filter module. The air lateral installation includes methods to minimize airflow disturbance of the soil and methods to prevent air leakage.

Abstract: A rapidly installed intermittent flow and storm water treatment method and apparatus employing rapid solids separation and sulfur dioxide chemical dewatering technology to produce disinfected reclaimed storm water with heavy metals removed and diluted nutrients suitable for open stream or land application.

Abstract: A process for treating water that includes ammonium. The water is directed to a biological reactor and the quantity of nitrates formed in the reactor and the quantity of ammonium reduced in the reactor is determined. A ratio of the quantity of nitrates formed to the quantity of ammonium reduced is determined. Further, the percentage of ammonium reduced is also determined. The water in the biological reactor is aerated by injecting oxygen into the reactor where the amount of oxygen injected is a function of the ratio and the percentage of ammonium reduced in the reactor.

Abstract: A system for treating wastewater including at least one water-treatment pathway having at least one wastewater inlet, at least one oxygen-permeable, water-impermeable wall, separating an interior of the pathway from outside air, and at least one treated wastewater outlet and arranged for at least aerobic treatment of the wastewater as it flows from the at least one wastewater inlet to the at least one treated wastewater outlet, at least one wastewater supply conduit, supplying the wastewater to the at least one wastewater inlet of the water-treatment pathway and at least one treated wastewater conduit, supplying treated wastewater from the at least one treated wastewater outlet of the at least one water-treatment pathway.

Abstract: A plant effluent treatment method includes a mixing treatment step that mixes a microorganism activating agent into plant effluent containing organic compounds as discharged from a chemical plant, petroleum plant or petrochemical plant and discharges it as mixing treatment effluent, and an aerobic treatment step that subjects the mixing treatment effluent to aerobic biological treatment and solid-liquid separation treatment in a membrane bioreactor tank.

Abstract: A lagoon batch wastewater treatment system for a wastewater treatment lagoon wherein a containment tank expands and contracts during a sewage treatment process reducing erosion of the berm or bank of the lagoon.

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 method for bioremediation of contaminants, comprising contacting a contaminant with composite particles including at least one microbial available nutrient species and at least one fatty acid species, and contacting the contaminant with oxygenated water including greater than about 4 parts per million dissolved oxygen. Water may be oxygenated on-site using various oxygenating devices, such as an aspirator, aerator, impeller and diffuser. Optionally, the oxygenated water may be prepared with wastewater that is being remediated. The method may be used to maintain a dissolved oxygen concentration of greater than a setpoint concentration, such as at least 4 ppm. A preferred oxygenated water stream or source has a dissolved oxygen concentration of greater than 50 ppm. Where the contaminant is in a wastewater, the dissolved oxygen concentration in the remediation zone or the oxygenated water stream may be measured with a dissolved oxygen sensor.

Abstract: Aerator kit comprising a body defining a fluid-flow channel, and a nozzle insert disposed inside said body as such forming together a venturi aerator which is useful for aerating aqueous waste. The aerator can be used submerged as a part of an aerobic digester, in which gas or air flow into the nozzle inlet while drawing liquid through a peripheral hole in the aerators body and cause mixing. The aerator can be also used as an above ground aerator in which liquid is pumped into the nozzle inlet while drawing air through said peripheral hole. In an another embodiment the aerator could be also used for adding additive to a gas or liquid.

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 method of treating wastewater includes removing BOD and ammonium from the wastewater. The wastewater is directed into a tank where it is mixed with mixed liquor or activated sludge from an activated sludge wastewater treatment system. The mixture of wastewater and mixed liquor or activated sludge forms a mixed liquor stream. The mixed liquor stream is directed to a ballasted flocculation system where suspended solids is removed from the wastewater. This produces a clarified effluent that is directed to a zeolite tank. Clarified wastewater from the ballasted flocculation system is directed into the zeolite tank and mixed with zeolite. Zeolite is effective to remove ammonium from the wastewater. Thus, the process as a whole is effective in removing suspended solids, soluble BOD as a result of mixing the mixed liquor or activated sludge with the wastewater, and ammonium.

Abstract: Methods of controlling a nitrification reaction in a biological nitrogen removal reactor to favor partial nitrification of ammonia to nitrite instead of complete oxidation of ammonia to nitrate are disclosed. In some embodiments, the methods include the following: maintaining a pH in the reactor within a range that promotes growth of ammonia oxidizing bacteria; maintaining a concentration of dissolved oxygen in the reactor within a range that limits the ammonia oxidizing bacteria from completing nitrification; selecting an operational solids retention time within a range suitable for maintaining increasing concentrations of the ammonia oxidizing bacteria in the reactor while reducing concentrations of nitrite oxidizing bacteria in the reactor; and increasing a concentration of free ammonia in the reactor thereby inhibiting growth of the nitrite oxidizing bacteria in the reactor.