3486 results about "Nitrification" patented technology

The present invention relates to an integrated closed loop system for aquaculture in at least one culturing tank and using continuous bioreactor technology for the biological treatment and removal of organic material, nitrogen and phosphorous, comprising: an integrated, partially or wholly closed loop system for waste water treatment, where the water contains nitrogen containing compounds and / or substances, comprising at least one production unit of such nitrogen containing compounds and / or substances and using continuous bioreactor technology for the biological treatment and removal of organic matter, nitrogen and phosphorous from the said water at continuous flow, comprising: a) at least one suspended carrier bioreactor for bacterial growth under anoxic conditions to cause anaerobic denitrification, with one or several compartments, preceding b) at least one suspended-carrier bioreactor for bacterial growth under oxic conditions to cause aerobic nitrification, c) the denitrification taking place after the production unit, and d) the nitrification taking place prior to the production unit in a by-pass mode as part of the continuous flow.

A method and process for the treatment of wastewater containing phosphorous and nitrogen. The wastewater is first anaerobically treated to produce an anaerobic effluent from which insoluble organic carbon is separated to form a sludge rich in organic carbon that is used as a substrate during anoxic treatment of the wastewater by de-nitrifying phosphorous accumulating organisms (DPAO's) and ordinary de-nitrifying organisms. The separation of insoluble organic carbon is normally conducted using a clarifier located intermediate the anaerobic and anoxic bio-reactors. In one embodiment, the ammonia rich clarifier supernatant is directed to an aerobic reactor for nitrification and the nitrate produced is recycled to the anoxic bio-reactor. The final effluent may be membrane filtered to retain nitrifying biomass within the aerobic bio-reactor. The invention reduces overall hydraulic residence time and sludge volume, which results in a smaller, less expensive wastewater treatment system.

An inclined plate coupled membrane bioreactor for treating feed water having excessive level of nutrients in particular chemical oxygen demand and total nitrogen and suspended solids has an aerobic bioreactor for nitrification and aerobic biodegradation in which membranes are submerged for permeate extraction, and an anoxic bioreactor for denitrification within which the inclined plates are outfitted to confine as much anoxic sludge as possible. An air oxygenating and an air scouring are continuously provided to the aerobic bioreactor to maintain a desired aerobic environment and to mitigate membrane fouling while an intermittent air blowing is provided to the anoxic bioreactor to blow out gaseous content generated through denitrification and to rectify the uniformed flow along the inclined plates. The aerobic sludge is recycled to the lower compartment of anoxic bioreactor and the supernatant of anoxic bioreactor is collected as weir effluent and delivered to the downstream aerobic bioreactor. Permeate is intermittently extracted from the membranes by a suction pump. There is no excess sludge withdrawn from the inclined plate coupled membrane bioreactor throughout the experiment.

The present invention relates to an integrated closed loop system for aquaculture in at least one culturing tank and using continuous bioreactor technology for the biological treatment and removal of organic material, nitrogen and phosphorous, comprising: an integrated, partially or wholly closed loop system for waste water treatment, where the water contains nitrogen containing compounds and / or substances, comprising at least one production unit of such nitrogen containing compounds and / or substances and using continuous bioreactor technology for the biological treatment and removal of organic matter, nitrogen and phosphorous from the said water at continuous flow, comprising: a) at least one suspended carrier bioreactor for bacterial growth under anoxic conditions to cause anaerobic denitrification, with one or several compartments, preceding b) at least one suspended-carrier bioreactor for bacterial growth under oxic conditions to cause aerobic nitrification, c) the denitrification taking place after the production unit, and d) the nitrification taking place prior to the production unit in a by-pass mode as part of the continuous flow.

Wastewater treatment systems and processes for: removal of solids, pathogens, nitrogen, and phosphorus from municipal and agricultural wastewater include nitrification of wastewater and increasing the pH of the nitrified wastewater by adding a metallic-containing salt and hydroxide to precipitate phosphorus to form a useable effluent having a specified nitrogen:phosphorus ratio that is useful as a fertilizer or spray for remediation of contaminated soils. The presence of infectious microorganism such as enteropathogenic bacteria and picarnoviruses will be reduced in the useable effluent. The precipitated phosphorus is recovered and used to form useable phosphorus products.

This invention discloses a method for deep denitrification treatment of high-concentration organic wastewater. The apparatus comprises an anaerobic decarbonization zone, an aerobic nitrosation / anaerobic ammoxidation denitrification zone, and a traditional nitrification / denitrification zone. In the anaerobic decarbonization zone, an anaerobic bioreactor is utilized to perform anaerobic biotreatment on the organic pollutants in raw water to remove the majority of organic matters. In the aerobic nitrosation / anaerobic ammoxidation denitrification zone, ammonia nitrogen and nitrite nitrogen are removed in the form of nitrogen gas. In the traditional nitrification / denitrification zone, nitrate in the water discharged from the aerobic nitrosation / anaerobic ammoxidation denitrification zone is subjected to denitrification and removed in the form of nitrogen gas. Excess organic matters are subjected to aerobic bioreaction and removed. The method can ensure COD; total nitrogen and ammonia nitrogen contents in the treated water are qualified for discharge. The method has such advantages as high decarbonization and denitrification efficiency, low energy consumption, and high running stability.

In a vertical shaft bioreactor, improved devices and methods are provided for enhanced secondary and / or tertiary treatment of wastewater, including residential, municipal and industrial wastewater. The devices and methods of the invention are useful for enhanced secondary wastewater treatment, including BOD and TSS removal. Tertiary treatment can alternately or additionally be achieved in the bioreactor with nitrification of ammonia, with nitrification and denitrification, and with nitrification, denitrification, and chemical phosphorus removal. A vertical shaft bioreactor is also provided which achieves thermophilic aerobic digestion and pasteurization of sewage sludges, optionally to produce class A biosolids.

The invention relates to an agrobacterium strain (Agrobacterium sp.) with heterotrophic nitrification-aerobic denitrification capability and an application thereof in nitrogenous effluent treatment. The bacterial strain is characterized in that: 16S rRNA gene contains nucleotide sequence shown in sequence table with a sequence length of 1418bp and a accession number FJ639330 in Genbank. The preservation number thereof is CGMCC No.2962. The agrobacterium of the invention has not only heterotrophic nitrification capability but also aerobic denitrification capability. During nitrogenous effluent treatment, and one aerobic phase can cause ammonian to change into gaseous product with high denitrification efficiency and easy operation and tremendous economic benefit compared with the traditional biological denitrification process.

The invention discloses a salt-tolerant microbial agent and a preparation method thereof. The microbial agent contains staphylococcus cohnii FSND-C, arthrobacter creatinolyticus FDN-1, flavobacterium mizutaii FDN-2, paracoccus denitrificans DN-3 and methylobacterium phyllosphaerae SDN-3. The microbial agent can achieve removal of ammonia nitrogen, total nitrogen and CODcr in the same reactor, has a good wastewater treatment effect, and can achieve short-cut nitrification and denitrification or simultaneous nitrification and denitrification while removing COD. Staphylococcus cohnii FSND-C can utilize various carbon sources, has certain salt tolerance, can be applied to the high-salinity wastewater treatment process, simultaneously can secrete a substance under environmental stimulus to enhance the flocculability of sludge, and further widens the application range of the microbial agent.

The invention belongs to the technical fields of environmental engineering and bioengineering and particularly relates to a sphingomonas strain and applications thereof in the aspects of shortcut nitrification-denitrification of nitrogen-containing industrial waste water and domestic sewage and treatment of a polluted water source. The sphingomonas strain is separated from a Taihu water in China,is a local strain and has high safety; and the strain can be grown in a basic medium, wherein in the basic medium, CO2 is used as a carbon source and energy or CO2 and an organism are used as a mixedcarbon source and energy, and ammonia nitrogen or nitrate nitrogen is used as a nitrogen source. The bacterium liquid, the dormancy cell and the immobilized strain of the sphingomonas can decompose ammonia nitrogen into nitrite nitrogen and simultaneously can decompose the ammonia nitrogen into nitrogen, can be used as denitrification microorganism for converting the ammonia nitrogen into the nitrite nitrogen and the nitrogen, thereby achieving the shortcut nitrification-denitrification. The strain can rapidly decompose the ammonia nitrogen and is suitable for treating the nitrogen-containingindustrial waste water and domestic sewage as well as polluted water source.

A wastewater treatment system includes a tidal, sequential vertical flow marsh cell system having at least three marsh cells in serial forward fluid communication. Incoming wastewater to be treated is channeled to at least the first and a second marsh cell, and a portion of water exiting a final marsh cell, to the first marsh cell surface. Each marsh cell is alternately flooded and drained for enhancing aeration of incoming water and marsh cell contents, which include media and plant roots having biofilms growing thereon, the biofilms including a population of nitrifying and denitrifying bacteria, for achieving substantially simultaneous nitrification and denitrification of the wastewater.

The invention relates to aerobic denitrifying paracoccus denitrificans and application thereof. A bacterial strain provided in the invention is paracoccus denitrificans DN-3CGMCC No. 3658; the Paracoccus denitrificans can carry out aerobic denitrification by using nitrate nitrogen under both aerobic and oxygen-limited conditions and can also carry out heterotrophic nitrification-aerobic denitrification by using ammonia-N, and a total nitrogen removal rate on above mentioned occasions is greater than 90%. The paracoccus denitrificans provided in the invention has stable hereditary features, isapplicable to treatment of a variety of nitrogen-containing waste water and produces a good nitrogen removal effect.

The invention discloses a method for quickly starting a completely autotrophic nitrogen removal over nitrite process on sewage on the conditions of constant temperature and low ammonia nitrogen and belongs to the field of city sewage treatment and reutilization. The completely autotrophic nitrogen removal over nitrite (CANON) process is started in a biological filter tank reactor and comprises the following steps: firstly, nitrifying sludge by using an inoculating part, and performing aerobic nitrification start with sufficient oxygen supply to build a nitrosobacteria-dominated and nitrobacterium-dominated microorganism system; inhibiting the growth of nitrobacterium through intermittent aeration / anaerobism and enriching anaerobic ammonium oxidation bacteria; and finally, performing continuous aeration, controlling ammonia nitrogen to be oxidized to a stage of nitrous acid through restrictive oxygen supply, and optimizing microenvironment where nitrosobacteria and anaerobic ammonium oxidation bacteria coexist so as to successfully start the CANON process. By using the method, the problem that the growth enrichment of the anaerobic ammonium oxidation bacteria is slower for a long term can be solved; moreover, the starting way is simple and feasible, and the difficulty of the start of a single-stage autotrophic nitrogen removal system is reduced; and therefore, a method is provided to start the CANON process on stimulated waste water on the conditions of constant temperature and low ammonia nitrogen.

A process for the recovery of nitrogen from anaerobically digested liquid waste and for the collection of the nitrogen as nitrate compounds that can be used to produce fertilizer and compost, includes stripping ammonia from anaerobically digested liquid waste, and converting the ammonia into nitrates via nitrification.

The nitrobacteria growth promoter consists of molasses 100 weight portions, metal salt 0.2-2.5 weight portions and adsorbent 1-8 weight portions. The metal salt includes component A of FeSO4 or FeCl2, and component B of MgSO4 and / or CaCl2, in the molar ratio of 10 to (0.5-5). The adsorbent is zeolite powder, diatomite, powdered active carbon, fly ash or their mixture. The nitrobacteria growth promoter is used in biological nitrification process of eliminating ammonia nitrogen and thrown into sewage directly to promote the propagation and growth of nitrobacteria in sewage. It has raised ammonia nitrogen eliminating rate and low cost.

The invention discloses a device for autotrophic nitrogen removal by combining A / O shortcut nitrification of sludge digestion liquid and anaerobic ammonium oxidation of granular sludge and a method thereof. The device of the invention comprises a digestion liquid tank, an A / O shortcut nitrification tank, a sedimentation tank, a middle water tank, an anaerobic ammonium oxidation tank, wherein, the digestion liquid tank is communicated with a first cancellus as an anoxic zone of the A / O shortcut nitrification tank by the inlet pump of the A / O shortcut nitrification tank; the sedimentation tank the upper part of which is communicated with the middle water tank by a water pipe is provided with a central pipe and the anaerobic ammonium oxidation tank is provided with a water bath sleeve and a granular sludge bed. In addition, the method of the invention comprises the following steps of starting the A / O shortcut nitrification tank; starting the anaerobic ammonium oxidation tank of the granular sludge; operating an autotrophic biological nitrogen removal system in series after the starting of the A / O shortcut nitrification tank and the anaerobic ammonium oxidation tank is respectively completed. The device and the method of the invention are applicable to the shortcut nitrification and the nitrogen removal of the sludge digestion liquid in a sewage treatment plant and have the advantages of advanced technology, simple structure of the device, convenient operation and good treatment effect of water purification.

The nitrobacteria culture promoter consists of molasses 100 weight portions, ferrous salt 0.2-2.5 weight portions and adsorbent 1-8 weight portions. The ferrous salt includes is sulfate or hydrochloride. The adsorbent is zeolite powder, diatomite, powdered active carbon, fly ash or their mixture. The nitrobacteria culture promoter is used in biological nitrification process of eliminating ammonia nitrogen and thrown into sewage directly to promote the propagation and growth of nitrobacteria in sewage. Through combination with sewage temperature regulation, dissolving oxygen, regulating pH, etc, the nitrification may be completed in short period. It has raised ammonia nitrogen eliminating rate and low cost.

The invention belongs to the environmental microorganism field, and in particular relates to a heterotrophic nitrification microorganism agent, a method for cultivating the same, and a use of the same in culture wastewater treatment. The microorganism agent contains Stenotrophomonas maltophilias strain DN1.1 and Pseudomonas putida strain DN1.2 which have the preservation registration numbers respectively as CCTCC M 207074 and CCTCC M 207075. The microorganism agent can effectively remove ammonia nitrogen and total nitrogen in a water body, accumulates no nitrite or nitrate during denitrification, and can simultaneously remove CODCr in organic wastewater, which is applicable to the treatment of high-concentration culture wastewater. The use of the microorganism agent in treating culture wastewater is simple in process and stable in effect.

A nitrification-denitrification process using magnetic seeding and magnetic separation to treat water is provided. The process includes biologically converting ammonia to nitrates with a biofilm disposed on magnetic seed. Suspended solids are removed by mixing flocculant and magnetic seeds with the water and magnetically removing floc formed floc from the water.

Biological nutrient removal (BNR) in municipal wastewater treatment to remove carbonaceous substrates, nutrients and phosphorus, has recently become increasingly popular worldwide due to increasingly stringent regulations. Biological fluidized bed (BFB) technology, which could be potentially used for BNR processes, can provide some advantages such as high efficiency and compact structure. This present invention incorporates the fixed-film biological fluidized bed technology with the biological nutrient removal in a liquid-solid circulating fluidized bed, which has achieved the simultaneous elimination of organic carbon, nitrogen and phosphorus, in a very efficient manner and with very compact space requirements. The BNR-LSCFB has two fluidized beds, running as anoxic / anaerobic and aerobic processes to accomplish simultaneous nitrification and denitrification and to remove carbonaceous substrates, nutrients and phosphorus, with continuous liquid and solids recirculation through the anoxic / anaerobic bed and the aerobic bed. The new BNR-LSCFB system is not only an excellent alternative for conventional activated sludge type BNR technologies but is also capable of processing much higher loadings and suitable for industrial applications.

The nitrobacteria growth promoter consists of molasses 100 weight portions, metal salt 0.2-2.5 weight portions and adsorbent 1-8 weight portions. The metal salt includes component A of MnSO4 or MnCl2, and component B of MgSO4 and / or CaCl2, in the molar ratio of 10 to (0.5-5). The adsorbent is zeolite powder, diatomite, powdered active carbon, fly ash or their mixture. The nitrobacteria growth promoter is used in biological nitrification process of eliminating ammonia nitrogen and thrown into sewage directly to promote the propagation and growth of nitrobacteria in sewage. It has raised ammonia nitrogen eliminating rate and low cost.

The invention discloses a device and a method for nitrogen and phosphorus removal for low CN ratio urban sewage through nitrosation and anaerobic ammonia oxidation coupling denitrifying phosphorus removal intensification, and belongs to the field of biological sewage treatment. The device comprises an urban sewage raw water tank, a denitrifying phosphorus removal reactor, an adjusting water tank, a sedimentation tank, and an integrated partial nitrification and anaerobic ammonia oxidation reactor; when the urban sewage enters the denitrifying phosphorus removal reactor, phosphorus-accumulating bacteria utilizes organic carbon source in the urban sewage for anaerobic phosphorus release, sedimentation and water drainage are performed, the amount of output water is adjusted by the adjusting water tank, then the output water enters the integrated partial nitrification and anaerobic ammonia oxidation reactor, contained NH4<+>-N is converted into N2 to be effectively removed through partial nitrification and anaerobic ammonia oxidation, contained PO4 <3-> and a small amount of NO3<->-N produced in the anaerobic ammonia oxidation flow back with the output water to the denitrifying phosphorus removal reactor for denitrifying phosphorus removal, and then micro-aeration is carried out for a period of time. The method reduces oxygen consumption and energy consumption, improves the nitrogen and phosphorus removal rate, and avoids the problem of insufficient carbon source.

The invention relates to a biological denitrification method for salt-containing sewage, which comprises the following steps: adding a denitrification microbial inoculant into a biochemical sewage treatment system, and simultaneously starting the nitrification-denitrification biological denitrification treatment processes, wherein the sewage treatment temperature is 18-40 DEG C, the dissolved oxygen is 0.1-5 mg / L, and the pH value is 7.0-9.0. The denitrification microbial inoculant contains one or two of Staphylococcuscohnii FSDN-C, Arthrobactercreatinolyticus FDN-1 and Flavobacteriummizutaii FDN-2, and also contains one or two of Paracoccusdenitrificans DN-3 and Methylobacteriumphyllosphaerae SDN-3. The method provided by the invention can effectively treat high-salt-content sewage, enhances the adsorptivity and flocculence for sludge, has wide application range for wastewater quality and high impact resistance to salt-containing sewage, and obviously enhances the sewage treatment effect on the premise of removing pollutants, such as ammonia nitrogen, COD (chemical oxygen demand) and the like.

The invention relates to a device and method for a sludge digestive juice semi-partial nitrification anaerobic ammonia oxidation denitrification and denitrifying phosphorus removal coupling system and belongs to the technical field of biological sewage treatment. The device comprises a raw water tank, a denitrifying phosphorus removal reactor, a first regulating water tank, a semi-partial nitrification reactor, a second regulating water tank, an anaerobic ammonia oxidation reactor and a water discharging water tank; the method for the sludge digestive juice semi-partial nitrification anaerobic ammonia oxidation denitrification and denitrifying phosphorus removal coupling system comprises the steps that sludge digestive juice firstly enters the denitrifying phosphorus removal reactor, phosphorus-accumulating bacteria release phosphorus by utilizing a carbon source in raw water, then NO3-N in refluxed anaerobic ammonia oxidation effluent is utilized for carrying out denitrifying phosphorus removal, effluent is discharged into the semi-partial nitrification reactor and the anaerobic ammonia oxidation reactor for realizing removal of ammonia nitrogen in the raw water; one part of effluent of the anaerobic ammonia oxidation reactor is discharged, one part of the effluent of the anaerobic ammonia oxidation reactor is refluxed into the denitrifying phosphorus removal reactor for being used during denitrifying phosphorus removal. The method for the sludge digestive juice semi-partial nitrification anaerobic ammonia oxidation denitrification and denitrifying phosphorus removal coupling system can be applied to biological nitrogen and phosphorus removal of high ammonia nitrogen waste water with low CN ratio, oxygen consumption and energy consumption are reduced compared with the traditional denitrification and phosphorus removal technology, and denitrification and phosphorus removal efficiency is greatly improved.

The invention discloses a device and a method for denitrification of single stage autotroph in low-cellulose nitrate (CN) high-ammonia nitrogen waste water. The device comprises a raw water tank, a water inlet pump, a reactor, a secondary sedimentation tank and a sludge reflux pump, wherein overcurrent holes are arranged in the water flow direction of the reactor in an up-and-down alternative form and connected with various grid chambers, an anoxic zone grid chamber is arranged at the front end of the reactor, and an aerobic zone grid chamber is arranged at the back end of the reactor; the anoxic zone grid chamber is provided with a stirrer and an agitator blade; the aerobic zone grid chamber is provided with the stirrer, the agitator blade, an aeration riser pipe and an intermediate perforated clapboard; and the aeration riser pipe is internally provided with an aeration head, and sponge filling material is filled below the intermediate perforated clapboard, wherein filling ratio is 30-50%. In the method, shortcut nitrification is achieved above the aerobic zone through low dissolved oxygen (DO is 0.5 <-1>mg / L) and free ammonia (FA) inhibition so that ammonia nitrogen is converted to nitrite nitrogen; and anoxicammoxidation biomembrane acts on the lower part of the aerobic zone, the nitrite nitrogen and ammonia nitrogen are converted to nitrogen, thereby achieving denitrification of autotroph. The method has the advantages of low oxygen consumption, less sludge output and no extra carbon source.

The invention discloses a fresh water scale pond ecological breeding system. The system comprises five parts, namely a breeding pond, a pond water normal-position distributed treatment part, a pond discharge water abnormal-position centralized treatment part, a backwater function recovery treatment part and a pond water quality compensation treatment part. Breeding water aquatic ecology, pond breading and an aquaculture engineering technology are integrated organically; and pond microcirculation is formed through absorption, decomposition and nitrification functions of microorganisms, algae and the aquatic plants, particularly continuous removal of aquatic plants with growth and intermittent water supply, so that the utilization rate of pond eutrophic substances is improved, and breeding backwater is restored. The system has the remarkable effects of water saving and emission reduction and provides the high-efficiency pond ecological breeding system which is novel in process and is high in operability and economic and practical and has a unique structure for fishery industrialization and scale production.

The invention belongs to the technical field of biological wastewater treatment, and particularly relates to a bioelectrochemical synchronous nitrification / denitrification denitriding reactor and an application method thereof. The reactor comprises a bed, a biological anode, a biological cathode, a filler, a gas flowmeter, an aerator, an aeration head, a circulating pump and a direct-current stabilized-voltage power supply, wherein the biological cathode and the biological anode are respectively arranged at both sides in the reactor and are respectively connected with the negative pole and the positive pole of the direct-current power supply; the filler is filled in the bed; the aeration head is arranged at the middle upper part of the bed; both ends of the bed are respectively provided with a water inlet and a water outlet and are connected with a circulating pipeline for internal circulation through the circulating pump; and the top of the reactor is provided with a gas outlet through which the reactor is communicated with the outside. The application method of the reactor comprises the following steps: forming an anode ammoxidation biological film and a cathode denitrification biological film, and starting the reactor after the films are successfully formed; carrying out nitrification and denitrification reaction under the condition of 0.2-1.0mg / L of dissolved oxygen; and carrying out denitriding reaction while applying a micro voltage of 0.2-0.5V and keeping a cathode potential of (-100)-(-250)mV. The invention has the advantages of good treatment effect, energy saving, environment friendliness, high start speed, convenient operation process and the like.

Embodiments include a method and apparatus for recovering ammonia and nitrogen from a waste stream. Embodiments further include recovering ammonia using an ammonia recovery process and a biological nitrogen recovery process. In some embodiments, a return stream from the ammonia recovery process may be used to provide alkalinity, carbon substrate, and / or biological oxygen demand to the biological nitrogen recovery process. In some embodiments, a hydrothermal sludge process may be used to further treat the waste stream and provide additional return to the ammonia recovery system. Other embodiments include an ammonia recovery system for conducting the ammonia recovery process, a biological nitrification and / or denitrification system for conducting the biological nitrogen recovery process, and an optional hydrothermal sludge processing system.

The invention discloses an integrated pre-denitrification and denitrogenation biological filter sewerage treatment process. The integrated process is characterized in that: the process is realized by combining an anoxic denitrification biological filter and an aerobic nitrification biological filter in tandem, first, sewage with organic substances and ammonia nitrogen is mixed with part of effluent water of the aerobic nitrification biological filter which flows back to a water inlet end, then the sewage and the effluent water pass the anoxic denitrification biological filter together, and the organic substances in the sewage are taken as a carbon source by denitrifying bacteria adhesively growing on bio-ceramsite in the anoxic denitrification biological filter to reduce nitrate nitrogen from the return water of the aerobic nitrification biological filter into nitrogen gas, thus realizing denitrification function; and the effluent water of the anoxic denitrification biological filter flows to the aerobic nitrification biological filter, and a filter material in the aerobic nitrification biological filter is adhered with special growing aerobic decarbonization microbes and the growing denitrifying bacteria which further degrade the organic substances and the ammonia nitrogen from the anoxic denitrification biological filter, thus causing content indicators of the organic substances, the ammonia nitrogen, total nitrogen and the like in the effluent water of the aerobic nitrification biological filter to meet the discharge requirement.