A nitration method and sewage treatment system for enriching AOB in side flow and reinforcing AOB in main flow

Abstract

The application discloses a nitration method for enriching AOB in a side stream and reinforcing an AOB in a main stream and a sewage treatment system, and the method comprises the following steps: inoculating activated sludge in an aerobic tank of a sewage treatment plant into a side stream short-cut nitrification reactor; starting the short-cut nitrification process to enrich nitrosation sludge, using sludge anaerobic digestion supernatant as the influent of the side stream short-cut nitrification reactor, controlling the dissolved oxygen concentration to be 0.1-0.5 mg / L, the pH to be 8.50-8.54, and the temperature to be 30-37 DEG C; after more than 50% of ammonia nitrogen in the influent of the side stream short-cut nitrification reactor is converted into nitrite nitrogen, nitrosation sludge is taken out from the side stream short-cut nitrification reactor every day and is put into a main stream nitrification reactor, and the nitrosation sludge accounts for 1.0-2.0% of the total mass of sludge in the main stream nitrification reactor, so as to realize the reinforcement of the nitrification capacity of the main stream nitrification reactor. According to the method, after AOB is enriched and cultured, the AOB is added into the main stream nitrification reactor to realize biological reinforcement nitrification, the nitrification capacity of the main stream reactor is enhanced, the ammonia nitrogen removal rate is improved, and the performance of the sewage treatment plant in dealing with the collapse of the nitrification system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of municipal wastewater treatment nitrification process, and particularly relates to a side stream enrichment / main stream AOB-strengthening nitrification method and a wastewater treatment system. BACKGROUND

[0002] Due to the increasingly stringent requirements of the state on water environment, especially the first level A standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002), which requires that the total nitrogen (TN) in the discharge of the municipal wastewater treatment plant should be lower than 15 mg / L, and the ammonia nitrogen should be lower than 5 mg / L. The limitation of the ammonia nitrogen concentration in the effluent is strengthened, which puts forward higher requirements on the stable operation of the wastewater treatment plant process and the effluent quality. In the traditional activated sludge process, the nitrification reaction is usually carried out in the main stream, that is, the organic matter degradation and nitrogen conversion are carried out simultaneously in the same reactor. However, due to the high concentration of organic matter in the main stream municipal wastewater, the activity and proliferation of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) are inhibited. In addition, the carbon source in the main stream municipal wastewater also promotes the growth of heterotrophic denitrifying bacteria (such as denitrifying bacteria and anaerobic ammonia oxidation bacteria), which competes with AOB and NOB for nitrogen source and oxygen source. Therefore, it often takes a long residence time, a high dissolved oxygen concentration and a large reactor volume to achieve complete nitrification in the main stream municipal wastewater.

[0003] In addition, the nitrification process is very sensitive to the temperature, load and other environmental factors (toxic substances, etc.) of the water quality. The illegal discharge of industrial wastewater can seriously affect the biochemical treatment system of the wastewater treatment plant, making the water quality composition complex and the toxicity increased. The nitrification system in wastewater treatment is a weak link, and the overload operation and other environmental factor changes faced by the wastewater treatment plant will make the nitrification system face the risk of collapse. Therefore, how to ensure and realize the efficient and stable operation of the wastewater treatment plant is the current research hotspot.

[0004] Anaerobic digestion of sludge in side-stream line is also involved in domestic sewage treatment plant. It is mainly through the action of microorganisms to degrade organic matter into more stable substances, such as methane, carbon dioxide and water, etc. It can reduce sludge quantity, reduce sludge moisture content, improve sludge stability, recover energy, etc. The supernatant of sludge anaerobic digestion refers to the part of the liquid rich in nitrogen flowing back to the main stream process from the sludge anaerobic digestion process, which usually accounts for 10% to 30% of the total nitrogen load of the main stream influent, but the water quantity is small, only accounting for 2% of the total water quantity. The ammonia nitrogen content of this wastewater is high (the total nitrogen concentration is generally 500-2000 mg / L), which can account for 15-30% of the daily nitrogen load of the sewage treatment plant, and the biochemical oxygen demand (BOD5) is generally between 50-200 mg / L; the chemical oxygen demand (COD) is only between 200-800 mg / L. Due to these characteristics of sludge digestion liquid, if it is directly returned to the main stream process for treatment, the following problems will be caused: increasing the nitrogen load of the main stream process, leading to the decrease of denitrification efficiency; increasing the consumption of oxygen and alkalinity, increasing the operation cost and energy consumption of the main stream process; increasing the emission of greenhouse gases such as CO2 and N2O, which will cause adverse effects on the environment. SUMMARY

[0005] In the traditional activated sludge process, nitrification is usually carried out in the main stream, i.e. organic matter degradation and nitrogen conversion are carried out simultaneously in the same reactor. However, due to the high concentration of organic matter in the main stream municipal wastewater, the activity and proliferation of AOB and NOB are inhibited. At the same time, denitrifying bacteria will compete with AOB and NOB for nitrogen source and dissolved oxygen. Therefore, complete nitrification in the main stream municipal wastewater often requires a long residence time, a high dissolved oxygen concentration and a large reactor volume. Based on this, the present application provides a side-stream enrichment / main-stream AOB-strengthened nitrification method to solve the problem that when the ammonia nitrogen concentration in wastewater suddenly increases to a certain upper limit, the sewage treatment plant faces overload operation and other environmental factors that may cause the collapse of the nitrification system, the ammonia nitrogen concentration in the effluent is too high, and the effluent cannot meet the national discharge standard.

[0006] To achieve the above-mentioned purpose, the present application provides a side-stream enrichment / main-stream AOB-strengthened nitrification method, comprising the following steps:

[0007] (1) inoculating activated sludge from the aerobic tank of the sewage treatment plant into the side-stream short-cut nitrification reactor, so that the initial sludge concentration in the side-stream short-cut nitrification reactor is 2000-4000 mg / L;

[0008] (2) Start-up short-cut nitrification process to enrich nitrosation sludge, take sludge anaerobic digestion supernatant as the influent of side-stream short-cut nitrification reactor, the ammonia nitrogen concentration of the influent is 500-2000 mg / L, the chemical oxygen demand is 200-800 mg / L, and the concentration of dissolved oxygen is controlled to be 0.1-0.5 mg / L, the pH is 8.50-8.54, and the temperature is 30-37℃;

[0009] (3) After more than 50% of ammonia nitrogen in the influent of the side-stream short-cut nitrification reactor is converted into nitrite nitrogen, nitrosation sludge is taken from the side-stream short-cut nitrification reactor and put into the mainstream nitrification reactor every day, the nitrosation sludge accounts for 1.0-2.0% of the total mass of sludge in the mainstream nitrification reactor, so as to realize the enhancement of the nitrification capacity of the mainstream nitrification reactor; the influent of the mainstream nitrification reactor is domestic sewage, the chemical oxygen demand is 200-400 mg / L, the ammonia nitrogen concentration is 40-80 mg / L, and the temperature is controlled to be 5-25℃, and the concentration of dissolved oxygen is more than 2 mg / L.

[0010] As a further preferred technical solution of the present application, in step (1), the activated sludge is taken from the end of the aerobic tank of a sewage treatment plant.

[0011] As a further preferred technical solution of the present application, in step (1), the initial sludge concentration in the side-stream short-cut nitrification reactor is 3000 mg / L.

[0012] As a further preferred technical solution of the present application, in step (2), when the ammonia nitrogen concentration in the influent of the side-stream short-cut nitrification reactor is 1000 mg / L, the chemical oxygen demand is 500 mg / L, and the dissolved oxygen is controlled to be 0.2 mg / L.

[0013] As a further preferred technical solution of the present application, in step (2), in the initial stage after starting-up the short-cut nitrification process, the ammonia nitrogen concentration of the influent in the side-stream short-cut nitrification reactor is gradually increased.

[0014] The starting-up short-cut nitrification process refers to the start-up and operation of the side-stream short-cut nitrification reactor.

[0015] As a further preferred technical solution of the present application, in step (3), after more than 80% of ammonia nitrogen in the influent of the side-stream short-cut nitrification reactor is converted into nitrite nitrogen, the nitrosation sludge is taken and put into the mainstream nitrification reactor.

[0016] As a further preferred technical solution of the present application, in step (3), the nitrosation sludge put into the mainstream nitrification reactor every day accounts for 1.5-1.6% of the total mass of sludge in the mainstream nitrification reactor.

[0017] As a further preferred technical solution of the present application, in step (3), the dissolved oxygen is controlled at 2 mg / L or above by aeration, and the dissolved oxygen is 7-8 mg / L at the end of the aeration reaction.

[0018] According to another aspect of the present application, the present application also provides a sewage treatment system which adopts the above-mentioned side stream enrichment / main stream AOB-strengthened nitrification method.

[0019] Compared with the prior art, the present application can achieve the following beneficial effects by adopting the above technical solution:

[0020] 1) The present application uses the sludge anaerobic digestion supernatant containing high-concentration ammonia nitrogen to enrich and cultivate AOB nitrosation sludge in a side stream short-term nitrification reactor, and then adds it to a main stream nitrification reactor for treating municipal sewage to perform biological strengthening nitrification, so that the nitrification capacity of the main stream reactor is enhanced, thereby improving the ammonia nitrogen removal rate and improving the response performance of the sewage treatment plant when it is faced with overload operation and other environmental factors that may cause the nitrification system to collapse, and ensuring that the sewage can be discharged up to the standard.

[0021] 2) The present application uses the sludge anaerobic digestion supernatant containing high-concentration ammonia nitrogen to enrich and cultivate AOB nitrosation sludge in a side stream short-term nitrification reactor, and then adds it to a main stream nitrification reactor for treating municipal sewage to perform biological strengthening nitrification, so that the nitrification capacity of the main stream reactor is enhanced, thereby improving the ammonia nitrogen removal rate and improving the response performance of the sewage treatment plant when it is faced with overload operation and other environmental factors that may cause the nitrification system to collapse, and ensuring that the sewage can be discharged up to the standard.

[0022] 3) The present application uses the sludge anaerobic digestion supernatant containing high-concentration ammonia nitrogen to enrich and cultivate AOB nitrosation sludge in a side stream short-term nitrification reactor, and then adds it to a main stream nitrification reactor for treating municipal sewage to perform biological strengthening nitrification, so that the nitrification capacity of the main stream reactor is enhanced, thereby improving the ammonia nitrogen removal rate and improving the response performance of the sewage treatment plant when it is faced with overload operation and other environmental factors that may cause the nitrification system to collapse, and ensuring that the sewage can be discharged up to the standard.

[0023] 4) The present application uses the sludge anaerobic digestion supernatant containing high-concentration ammonia nitrogen to enrich and cultivate AOB nitrosation sludge in a side stream short-term nitrification reactor, and then adds it to a main stream nitrification reactor for treating municipal sewage to perform biological strengthening nitrification, so that the nitrification capacity of the main stream reactor is enhanced, thereby improving the ammonia nitrogen removal rate and improving the response performance of the sewage treatment plant when it is faced with overload operation and other environmental factors that may cause the nitrification system to collapse, and ensuring that the sewage can be discharged up to the standard. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0025] Figure 1NH4 + -N, NO2 - -N, NO3 - -N concentration.

[0026] Figure 2 Nitrite accumulation rate of side-stream short-cut nitrification reactor over time.

[0027] Figure 3 Sludge settling performance and protein concentration of side-stream short-cut nitrification reactor.

[0028] Figure 4 Door level microbial community of side-stream short-cut nitrification reactor.

[0029] Figure 5 Genus level microbial community of side-stream short-cut nitrification reactor.

[0030] Figure 6 NH4 + -N, NO2 - -N, NO3 - -N concentration change.

[0031] Figure 7 COD concentration and COD removal rate of mainstream nitrification reactor.

[0032] Figure 8 Three nitrogen concentration changes of mainstream nitrification reactor in a typical period before bioaugmentation.

[0033] Figure 9 Three nitrogen concentration changes of mainstream nitrification reactor in a typical period after bioaugmentation.

[0034] Figure 10 Sludge settling performance and protein content of mainstream nitrification reactor.

[0035] Figure 11 Door level microbial community of mainstream nitrification reactor

[0036] Figure 12 Genus level microbial community of mainstream nitrification reactor.

[0037] The purposes, functional features and advantages of the present application will be further illustrated with reference to the accompanying drawings and in conjunction with embodiments. DETAILED DESCRIPTION

[0038] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0039] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0040] The sewage treatment system of municipal sewage is divided into a mainstream system and a side stream system, wherein: the mainstream system refers to a part for treating mainstream sewage, and the mainstream system is provided with a mainstream nitrification reactor for mainstream nitrification reaction, and an initial sedimentation tank and a secondary sedimentation tank connected to the water inlet end and the water outlet end of the mainstream nitrification reactor; the side stream system refers to a part for returning liquid rich in nitrogen from sludge treatment to the mainstream process for treatment, wherein the sludge mainly comes from the initial sedimentation tank and the secondary sedimentation tank of the mainstream system, and the side stream system is provided with a side stream short-cut nitrification reactor for short-cut nitrification reaction, and the sewage treated by nitrification through the side stream short-cut nitrification reactor can be returned to the initial sedimentation tank after subsequent other process treatment. The present application uses the side stream sludge digestion liquid containing high-concentration ammonia nitrogen to enrich and cultivate AOB in the side stream short-cut nitrification reactor, and then adds it to the mainstream nitrification reactor for treating municipal mainstream sewage to perform biological strengthening nitrification, so as to improve the nitrification capacity of the sewage treatment plant, cope with the risk that the overload operation and other environmental factors of the sewage treatment plant may cause the nitrification system to collapse, and ensure and realize the efficient and stable operation of the sewage treatment plant.

[0041] The present application provides a nitrification method for enriching AOB in the side stream and strengthening AOB in the mainstream applied to the above sewage treatment system, which comprises the following steps:

[0042] (1) inoculating activated sludge in an aerobic tank of a sewage treatment plant into the side stream short-cut nitrification reactor, so that the initial sludge concentration in the side stream short-cut nitrification reactor is 2000-4000 mg / L;

[0043] (2) starting the short-cut nitrification process to enrich nitrosation sludge, using sludge anaerobic digestion supernatant as the water inlet of the side stream short-cut nitrification reactor, the ammonia nitrogen concentration in the water inlet is 500-2000 mg / L, the chemical oxygen demand (COD) is 200-800 mg / L, the dissolved oxygen (OD) concentration is controlled to be 0.1-0.5 mg / L, the pH is 8.50-8.54, and the temperature is 30-37℃;

[0044] (3) When more than 50% of the ammonia nitrogen in the influent of the side-stream partial nitrification reactor is converted into nitrite nitrogen, nitrited sludge is taken from the side-stream partial nitrification reactor and fed into the main-stream nitrification reactor every day, and the amount of the nitrited sludge fed into the main-stream nitrification reactor accounts for 1.0-2.0% of the total mass of the sludge in the main-stream nitrification reactor, so as to enhance the nitrification capacity of the main-stream nitrification reactor; the influent of the main-stream nitrification reactor is domestic sewage, the chemical oxygen demand of which is 200-400 mg / L, the ammonia nitrogen concentration of which is 40-80 mg / L, and the temperature of which is controlled to be 5-25°C, and the concentration of the dissolved oxygen in the influent is higher than 2 mg / L.

[0045] The activated sludge taken from the aerobic tank of a sewage treatment plant contains ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), wherein: the ammonia-oxidizing bacteria (AOB) can oxidize ammonia nitrogen into nitrite nitrogen, and the main types of typical ammonia-oxidizing bacteria groups are shown in Table 1; the nitrite-oxidizing bacteria (NOB) can oxidize nitrite nitrogen into nitrate nitrogen, and the main types of typical NOB groups are shown in Table 2. Preferably, the activated sludge is taken from the end of the aerobic tank of a sewage treatment plant.

[0046] Table 1 Main types of typical AOB groups

[0047]

[0048] Table 2 Main types of typical NOB groups

[0049]

[0050] In order to improve the ammonia oxidation capacity of the side-stream partial nitrification reactor, nitrited sludge containing a large amount of AOB is enriched.

[0051] In a specific embodiment, the process for enriching nitrited sludge in the side-stream partial nitrification reactor is as follows:

[0052] By adding the activated sludge in step (1) above, the initial sludge concentration in the side-stream partial nitrification reactor is about 3000 mg / L, and the specific process for microbial culture in the side-stream partial nitrification reactor of step (2) is as follows: the temperature is controlled to be about 30-37°C, the influent is simulated high-ammonia-nitrogen wastewater for experiment, the composition of which is shown in Table 3, the C / N in the influent is controlled to be 0.5, the concentration of the dissolved oxygen is controlled to be 0.1-0.5 mg / L, the reactor is operated for 2 cycles every day, and each cycle is 12 h; each cycle includes influent for 600 min, aeration reaction for 60 min, standing for 30 min, effluent for 20 min, and idling for 10 min.

[0053] Table 3 Composition of simulated high-ammonia-nitrogen wastewater for experiment

[0054]

[0055]

[0056] The following tests were conducted on the operation of the side-stream shortcut nitrification reactor and the enrichment of nitrosation sludge using the above process by means of laboratory simulation, as follows:

[0057] 1. Effluent quality and nitrite nitrogen accumulation rate, test ammonia nitrogen conversion rate

[0058] The total operation time of the side-stream shortcut nitrification reactor (hereinafter referred to as the reactor) was 180 days, which was divided into three stages. The changes in the ammonia nitrogen, nitrite nitrogen and nitrate nitrogen concentrations of the influent and effluent in the three stages are shown in Figure 1 and 3 .

[0059] From 0 to 20 days, the reactor was in the start-up period (Stage I), and the ammonia nitrogen and nitrate nitrogen concentrations gradually decreased to 7.57 mg / L and 102.95 mg / L, respectively, and the nitrite nitrogen gradually accumulated and reached 855.89 mg / L, with an accumulation rate of up to 90%. Under the low-dissolved oxygen condition of 0.1-0.5 mg / L, the competition advantage of AOB over NOB was better, indicating that the shortcut nitrification was successfully started.

[0060] From 20 to 115 days, it was Stage II. From 20 to 30 days, the nitrite nitrogen accumulation rate increased again, reaching 99%; after 30 days, the activity of NOB in the sludge increased, the effluent nitrate nitrogen concentration increased, and the effluent nitrite nitrogen concentration decreased, reaching 115.51 mg / L and 640.68 mg / L, respectively. It is possible that as the time extended and the DO in the water moderately decreased, the activity of AOB decreased, the activity of NOB increased, and the generation rate of nitrite nitrogen slowed down. At 62 days, the effluent nitrite nitrogen sharply decreased, the ammonia nitrogen concentration greatly increased, and reached 287.95 mg / L and 600.49 mg / L, respectively, and the pH value decreased to 6.8, which was mainly due to the insufficient alkalinity of the influent and the excessively low pH. The pH environment for the growth of AOB and NOB is different, and the decrease of the pH in the system to 6.8 indicates that NOB grows well but AOB does not. At 115 days, the ammonia nitrogen removal rate reached 92%, but the nitrate nitrogen increased to 247 mg / L, resulting in a decrease of the nitrite nitrogen accumulation rate to 70%. The reason is that in order to improve the ammonia nitrogen conversion rate, the aeration amount was increased, the DO was excessively used by NOB, the activity of NOB increased, which led to a decrease in the nitrite nitrogen concentration and an increase in the nitrate nitrogen concentration, and a decrease in the nitrite nitrogen accumulation rate. At this time, the sludge concentration was as high as 5870 mg / L, and the high sludge concentration would consume more dissolved oxygen, reducing the oxygen concentration in the shortcut nitrification process. The nitrification reaction requires sufficient oxygen supply, and if the sludge concentration is too high, it will lead to insufficient dissolved oxygen supply, affecting the activity of nitrifying bacteria and the nitrification reaction.

[0061] Stage III is from 115 to 133 days. At 115 days, 1.2 L of sludge is discharged to reduce the sludge concentration in the reactor, and the sludge concentration at this time is 3070 mg / L. Due to the sudden decrease in the content of nitrifying bacteria, the ammonia nitrogen content in the effluent increases to 289 mg / L, the nitrite nitrogen decreases to 569 mg / L, and the nitrite nitrogen accumulation rate increases to 85%. Starting from the 123rd day, the reactor is fed with water to 3 L every day, and the feeding is stopped at the 133rd day. After 126 days, the microorganisms gradually adapt to the change, the ammonia nitrogen concentration gradually decreases and is maintained at about 200 mg / L, the nitrite nitrogen concentration is about 700 mg / L, and the final nitrite nitrogen accumulation rate is maintained above 85%.

[0062] 2. Protein content of activated sludge

[0063] The trend of the change of the protein content of activated sludge is shown in Figure 3 The initial MLSS of the reactor during start-up is about 3070 mg / L, and the protein content is about 21.92 mg / L. During 0-65 days, the sludge amount does not increase significantly because at that time, the water is not refrigerated and light-protected, and sodium acetate is easily degraded at room temperature, resulting in a small amount of organic matter entering the system. From 65 days, the water is refrigerated and light-protected at 0-10 degrees to reduce the degradation rate of sodium acetate. During 65-115 days, the sludge amount increases significantly, and the MLSS is as high as about 5870 mg / L at 115 days. The sludge amount increases because there is a large amount of organic matter in the water entering the system, and a high content of organic matter in the water promotes the growth and reproduction of microorganisms, accelerating the sludge production rate. Organic matter is the main nutrient source for microorganisms, which provides carbon source, energy and other necessary nutrients, so that the metabolic activity of microorganisms is more active, and the sludge production rate is accelerated. The amount of sludge produced also increases accordingly, which accelerates the accumulation rate of sludge in the reactor, and at this time, the protein content in the sludge increases to 300 mg / L, which is about 30 times the initial concentration. At 115 days, the sludge amount in the reactor is discharged by 1.2 L, and at this time, the MLSS is reduced to 3260 mg / L, and the SV 30 value is also basically the same as at the beginning of start-up. However, the protein content is about 20 times the initial concentration after 115 days of sludge acclimation. The protein content decreases for a period of time in stage IV, and is as low as 100 mg / L at 160 days, but then gradually increases again. This indicates that the sudden reduction of sludge concentration in the system has a certain impact on the activity of microorganisms, but after a period of adaptation, the activity of microorganisms gradually recovers, and the protein concentration is increased to 178.61 mg / L at the end of the reactor operation. The supply of organic matter in the water can affect the number and activity of microorganisms, and a higher concentration of organic matter can provide more nutrients and energy to promote the reproduction and metabolic activity of microorganisms, thereby increasing the number and activity of microorganisms.

[0064] 3. Change of microbial community

[0065] 3.1 Changes in sludge microbiota at different stages of the phylum level

[0066] High-throughput sequencing was performed on the microorganisms in the seed sludge, stage II, stage III, and stage IV sludge, and the results are as follows: Figure 4 As shown in the figure. Experiments revealed that the relative abundances of Proteobacteria were 12.34%, 53.11%, 50.66%, and 68.64%, respectively. During the acclimation process, nitrifying bacteria showed an increasing trend, with an abundance approximately 4.6 times higher than that in the seed sludge. This indicates that sludge acclimation during short-cut nitrification is conducive to AOB enrichment, enhancing the growth and metabolic capacity of nitrifying bacteria, and promoting their reproduction and growth. The relative abundance of Proteobacteria decreased in stages II to III, likely due to the reduction in MLSS after two-fifths of the total sludge volume was removed from the reactor in stage III. Nitrospirota was found in the seed sludge with a relative abundance of 0.21%, but it was not detected in stages II, III, and IV of the acclimation process, possibly due to a decrease or disappearance of its content. Chloroflexi was present in all four sludge samples, with relative abundances of 28.15%, 7.47%, 10.38%, and 3.69%, respectively. Chloroflexi had the highest abundance in the seed sludge, with NOB being the dominant bacterium. The relative abundance of Chloroflexi showed an increasing trend from stage II to stage III. This may be because as the amount of sludge decreased, the abundance of other microbial communities may have declined, thus creating a better competitive environment for Chloroflexi and leading to its relative increase.

[0067] 3.2 Changes in sludge microbiota at different stages of the genus level

[0068] The sludge microbial community was analyzed, and the results are as follows: Figure 5The AOB in the sludge, the second-stage, the third-stage, and the fourth-stage sludge samples were dominated by Nitrosomonas, and the relative abundance was 0.39%, 20.07%, 20.17%, and 30.28%, respectively. During the short-cut nitrification domestication process, the operating conditions such as temperature, dissolved oxygen, and pH value were gradually adjusted to the range suitable for the growth of AOB, which provided a more favorable growth environment, and thus the relative abundance of Nitrosomonas gradually increased. It was shown that the nitrosation sludge containing a large amount of AOB was successfully enriched through the domestication of the short-cut nitrification process, the growth and metabolic capacity of AOB was enhanced, and the increase of AOB was promoted. The abundance of Nitrosomonas did not change from the second stage to the third stage due to the discharge of part of the sludge from the reactor in the third stage, which indicated that the number of AOB was continuously increasing between the two tests. The results showed that the short-cut nitrification domestication based on sludge digestion liquid (adding organic matter to the influent) could enrich the nitrosation sludge containing a large amount of AOB. The addition of an appropriate amount of organic matter could promote the growth of microorganisms, sludge formation, the generation of extracellular polymers, the formation of precipitates, and the increase of biological activity, thereby achieving the growth of sludge.

[0069] In the above test of the side-flow short-cut nitrification reactor, the ammonia nitrogen concentration of the influent was 1000 mg / L, the DO was less than 0.5 mg / L, the temperature was (35±2) °C, and 500 mg / L of sodium acetate was added to the influent as COD, which could promote the growth and reproduction of AOB. Over a period of 115 days, the MLSS increased from 3000 mg / L to 5870 mg / L. Over a period of 109 days, the protein content increased from the initial 21.92 mg / L to 300 mg / L before sludge discharge. After sludge discharge, the protein content increased from 106.33 mg / L to 178.61 mg / L at the end of the 20-day period. The relative abundance of Nitrosomonas in the microbial community increased from 0.39% to 30.28%; it could be seen that the nitrosation sludge containing a large amount of AOB obtained in the later stage of domestication could be used for strengthening the mainstream nitrification process.

[0070] In a specific embodiment, based on the conditions of 1000 mg / L of ammonia nitrogen concentration in the influent, DO less than 0.5 mg / L, and temperature (35±2) °C in step (2), 500 mg / L of organic matter (sodium acetate) is added to the influent as a carbon source to promote the growth and reproduction of AOB. The conversion of 100% ammonia nitrogen to nitrite nitrogen is used as the endpoint of short-cut nitrification of sludge anaerobic digestion supernatant, and AOB nitrosation sludge is obtained by enrichment in a side stream short-cut nitrification reactor. The AOB nitrosation sludge obtained by enrichment is put into the main stream nitrification reactor to realize the experiment of strengthening the nitrification capacity of the main stream nitrification reactor. The process of nitrification reaction in the main stream nitrification reactor is: using one-time water feeding mode, running 4 cycles per day, each cycle being 6 h; each cycle includes water feeding for 30 min, aeration for 270 min, sedimentation for 30 min, water discharge for 20 min, and idle for 10 min, wherein the dissolved oxygen is controlled to be above 2 mg / L by aeration, and the deoxygenation is 7-8 mg / L at the end of aeration reaction. The ammonia nitrogen concentration of the influent of the main stream nitrification reactor is 40-80 mg / L, and simulated municipal wastewater is used, and the composition of the wastewater is shown in Table 4. When the nitrosation sludge is put in, about 1.5% of the total amount of sludge in the main stream reactor is put into the main stream reactor every day.

[0071] Table 4 Composition of simulated municipal wastewater

[0072]

[0073] The following tests are carried out on the operation of the main stream nitrification reactor using the above process, as follows:

[0074] 1. Effluent water quality

[0075] 1.1 Ammonia nitrogen conversion rate

[0076] The main stream nitrification reactor is operated for 165 days, and the ammonia nitrogen change during the period is as follows: Figure 6As shown, from day 0 to 22, the ammonia nitrogen in the effluent showed an upward trend, rising from 0 mg / L to a maximum of 10.6 mg / L. As the microorganisms in the sludge gradually adapted to the environmental changes, the ammonia nitrogen concentration in the effluent decreased, the nitrate nitrogen concentration increased, and the nitrite nitrogen concentration was extremely low or even non-existent. At day 26, to prevent the biodegradation of sodium acetate in the influent, the influent was stored in a refrigerated container. The influent temperature was as low as 10℃ in summer, equivalent to a low-temperature shock to the sludge microorganisms with each influent intake. From day 26 to 71, the concentrations of ammonia nitrogen and nitrite nitrogen in the effluent increased slightly, reaching 7.34 mg / L and 2.47 mg / L respectively. This was mainly due to the sudden temperature shock to the microorganisms in the sludge, affecting their activity. However, after a period of adaptation, the activity returned to its previous state. To test the performance of sludge enriched with AOB in the side-flow culture, the influent ammonia nitrogen concentration in the main nitrification reactor was increased to 80 mg / L on day 71. The effluent ammonia nitrogen concentration increased significantly, reaching 37 mg / L, before decreasing and eventually stabilizing at around 20 mg / L. The ammonia nitrogen removal rate dropped to 75%, failing to meet the national Class A ammonia nitrogen discharge standard. On day 80, the sludge concentration reached a high of 7310 mg / L. Excessive sludge concentration can lead to insufficient dissolved oxygen supply, potentially affecting the activity of nitrifying bacteria and the nitrification reaction. Therefore, part of the sludge in the main nitrification reactor was discharged, resulting in a sludge concentration of 3180 mg / L. After sludge discharge, the nitrification capacity of the sludge improved, and the effluent ammonia nitrogen concentration decreased significantly, stabilizing at around 19 mg / L by day 100. Starting from day 100, 100 mL of AOB-enriched activated sludge from the side-flow short-cut nitrification reactor was added to the main nitrification reactor daily for 10 consecutive days. This resulted in a significant decrease in ammonia nitrogen concentration. After the added sludge adapted to the new environment, the main nitrification capacity improved, and the ammonia nitrogen concentration in the effluent gradually approached zero, achieving an ammonia nitrogen removal rate as high as 99%. At day 148, the system was subjected to a low-temperature shock at approximately 5°C. The experimental results showed that the system's nitrification function was stable, and its resistance to low-temperature shocks was enhanced. The nitrification capacity of the main nitrification reactor was significantly better than before the enhancement. This indicates that adding AOB-enriched nitrite sludge can, to some extent, compensate for the adverse effects of low temperature and high ammonia nitrogen, maintaining the efficient and stable operation of the nitrification system in wastewater treatment.

[0077] 1.2 COD removal rate

[0078] Changes in COD during the experiment are as follows Figure 7COD removal rate decreased from 90% to 80%, which indicated that the COD removal efficiency was related to temperature. When the low temperature shock started, the COD removal rate decreased, but after a period of adaptation, the COD removal rate returned to more than 90%. At 65 days, the influent COD content was increased from 200 mg / L to 300 mg / L, and the effluent COD content was significantly increased, with a maximum of 90 mg / L. After a short adaptation period, the COD removal rate returned to the previous level, indicating that the system could effectively resist the adverse environment of sudden increase of organic matter. At 71 days, a high ammonia nitrogen load shock was performed, and it could be seen that the increase of ammonia nitrogen concentration in the influent had little effect on the COD removal efficiency. From 100 days, sludge was added, and after biological strengthening, the sludge was subjected to low temperature shock, and the effect of temperature on COD removal rate was less than that of the sludge without previous strengthening. It was shown that the sludge after biological strengthening could stabilize the COD removal efficiency of the nitrification system.

[0079] 2. Comparison test of typical cycle system operation live

[0080] The concentration variation of three nitrogen in the effluent during a typical cycle was monitored before and after strengthening, respectively, and the results are shown in Figure 8 , 10 . Figure 8 The concentration variation of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen during a typical cycle without adding the AOB-enriched sludge is shown. It can be seen that the ammonia nitrogen concentration in the reactor gradually decreases with the reaction time, and after 150 min, the ammonia nitrogen concentration stabilizes at 15 mg / L until the end of the reaction. The ammonia nitrogen removal rate is only 70%. Before adding the AOB-enriched sludge, the removal efficiency of microorganisms in the sludge to ammonia nitrogen is low, and the effluent ammonia nitrogen content exceeds the national first-level A discharge standard. Figure 9 The concentration variation of three nitrogen during a typical cycle after adding the AOB-enriched sludge is shown. It can be seen that after adding the activated sludge enriched with AOB in the side stream, the ammonia nitrogen concentration in the effluent of the main stream nitrification reactor decreases to 0 mg / L after 180 min, and the ammonia nitrogen removal rate increases to more than 99%. From the comparison of the concentration variation of three nitrogen during a typical cycle before and after adding, it can be seen that the effect after adding is obviously better than that before adding, and after strengthening, the nitrification capacity of the main stream reactor is improved, and there is almost no residual ammonia nitrogen in the effluent, and the ammonia nitrogen removal rate is increased, so that the effluent meets the first-level A discharge standard. In both comparison tests, it can be seen that the nitrate nitrogen concentration shows an overall upward trend, but the nitrite nitrogen shows a trend of first increasing and then slowly decreasing. Throughout the reaction process, the nitrate nitrogen concentration is basically greater than the nitrite nitrogen concentration, and finally no nitrite nitrogen is accumulated, and all is converted into nitrate nitrogen, indicating that the dominant bacteria in the reaction system is NOB.

[0081] 3. Protein content of activated sludge

[0082] The changes in sludge settling properties and protein content during the experiment are as follows: Figure 10 As shown, the mainstream nitrification reactor exhibited normal sludge settling, a clear sludge-water interface, and clear supernatant throughout the entire operation period. From day 0 to 26, the sludge concentration and protein content remained relatively constant, possibly due to the influent being placed at room temperature, leading to rapid organic matter degradation. Therefore, on day 26, the influent was refrigerated to slow down the rate of organic matter degradation. From day 26 to 65, the sludge volume increased, and MLSS rose significantly, but the protein concentration remained essentially unchanged. On day 65, the COD concentration was increased from 200 mg / L to 300 mg / L, and on day 71, the ammonia nitrogen concentration was increased to 80 mg / L. From day 71 to 100, MLSS and protein content increased dramatically, reaching 7310 mg / L and 358.84 mg / L, respectively. This indicates that the addition of appropriate amounts of organic matter and the increase in ammonia nitrogen concentration have a certain impact on the number and activity of microorganisms, promoting microbial proliferation and enhancing microbial activity. The sludge protein concentration increased from 195.21 mg / L to 358.84 mg / L, more than double the initial concentration. Excessive MLSS at day 80 led to increased effluent ammonia nitrogen concentration and decreased ammonia nitrogen removal rate. Therefore, sludge was removed from the reactor, reducing the sludge protein concentration to 194.42 mg / L. However, the protein concentration rapidly increased again with prolonged operation. At day 100, 100 mL of mixed sludge was added daily from the SBR2 reactor to enhance nitrification. Between days 100 and 120, the protein concentration showed a slight decreasing trend. This may be due to the introduction of a new microbial population, competing with or coexisting with other microbial populations in the reactor, potentially causing changes in the number or activity of microorganisms. After day 120, the protein concentration began to gradually increase again, indicating that the microorganisms may have gradually adapted to the newly introduced nitrifying sludge. This adaptation process may be accompanied by increased microbial activity. Alternatively, the newly introduced nitrifying sludge may have a competitive advantage, gradually becoming dominant after competing with existing microorganisms, leading to an overall increase in microbial activity. AOB may also synergize with other microbial populations in the nitrification reactor, promoting the overall activity of the microbial community. At 148 days, a low-temperature shock of approximately 5°C was applied to the system, and the sludge protein concentration still increased, albeit at a slower pace. This indicates that the microorganisms in the system, after bioaugmentation, have better resistance to low-temperature shocks and exhibit stronger activity than during the initial startup phase, resulting in more stable nitrification process operation.

[0083] 4. Changes in the microbial community

[0084] 4.1 Changes in sludge microbiota at different stages of the phylum level

[0085] The microbial phylum structure classification in the seed sludge, stage II (before sludge discharge), stage III (before enhancement), stage IV (after enhancement), and stage V sludge is shown in Table 1. Figure 11 As can be seen, the main phylum is Proteobacteria, and the relative abundance is 23.37%, 56.99%, 53.78%, 49.91%, and 61.45%, respectively.

[0086] After enhancement, Proteobacteria shows a downward trend, and the difference between the nitrosation sludge and the original microbial community in the nitrification reactor is one of the reasons for the decrease of Proteobacteria. Other microbial groups in the nitrosation sludge may compete for nutrients and living space, thereby inhibiting the growth of Proteobacteria. However, in stage V, Proteobacteria gradually increases, and the relative abundance is higher than that before enhancement. The relative abundance of Chloroflexi in the five sludge samples is 24.6%, 6.97%, 2.11%, 1.62%, and 1.58%, respectively.

[0087] 4.2 Changes in microbial community at the genus level in each stage of sludge

[0088] The microbial community structure classification at the genus level in the seed sludge, stage II (before sludge discharge), stage III (before enhancement), stage IV (after enhancement), and stage V sludge is shown in Table 2. Figure 12Nitrospira was found in the sludge, phase II, III, IV, V, and the relative abundance was 2.56%, 0.53%, 0.05%, 0.18%, 1.36% respectively, which indicated that the nitrification capacity of the system gradually decreased before the enhancement, resulting in the decrease of ammonia removal rate. It might be because that the ammonia concentration of the influent was increased to 80 mg / L in phase II, which exceeded the nitrification capacity of the sludge, and might have an inhibitory effect on NOB, thereby reducing its activity and relative abundance, which was consistent with the rapid increase of ammonia concentration in the effluent. At this time, the sludge concentration in the mainstream nitrification reactor was relatively high, and another possibility was considered whether the high sludge concentration led to insufficient nitrification capacity, resulting in the decrease of ammonia removal rate. Therefore, the sludge in the reactor was partially discharged on the 80th day, and the sludge concentration in the system was 3180 mg / L. Although the ammonia concentration in the effluent decreased, Nitrospira in the sludge in phase III showed a downward trend, and the ammonia concentration in the effluent did not meet the standard. This indicated that the nitrification capacity of the nitrifying bacteria in the system might be insufficient to treat the ammonia in the wastewater, resulting in high ammonia concentration in the effluent. The relative abundance of Nitrosomonas related to AOB in the five samples was 0.38%, 0.13%, 1.09%, 4.40%, 1.79% respectively. In phase I and II, Nitrosomonas was relatively less, and the microorganisms in the nitrification system were mainly NOB. After sludge discharge, the relative abundance of Nitrospira showed an upward trend, which was consistent with the decrease of ammonia concentration in the effluent, indicating that the high MLSS would affect the nitrification capacity of the nitrification system. However, the ammonia concentration in the effluent was still too high to meet the discharge standard. In phase IV, after adding nitrosation sludge for biological enhancement of nitrification, the abundance of Nitrosomonas in the system increased significantly. This indicated that a large number of AOB entered the nitrification system after the enhancement to strengthen the mainstream nitrification capacity, and the nitrification efficiency gradually increased after the enhancement, which was consistent with the decrease of ammonia concentration in the effluent or even complete removal. In phase V after the biological addition, the abundance of Nitrospira gradually increased, the activity of NOB was restored, the nitrification capacity of the reaction system was enhanced, and the ammonia concentration in the effluent was always kept at a very low level, which could meet the discharge standard of level A.

[0089] In the above-mentioned test of the mainstream nitrification reactor, the nitrosation sludge enriched with AOB after cultivation was continuously added to the mainstream nitrification reactor in a certain amount per day for strengthening the nitrification process. Compared with before the strengthening, the ammonia nitrogen concentration in the effluent decreased from about 17 mg / L to about 1 mg / L, and the ammonia nitrogen removal rate increased from 78% to 98%. Over a period of 74 days, the sludge protein concentration increased from 150.88 mg / L to 358.84 mg / L before sludge discharge, which was more than twice the initial concentration. After sludge discharge for 19 days, the protein concentration gradually increased from 194.42 mg / L to 304.23 mg / L. Over a period of 65 days after biological strengthening, the protein concentration increased to 551.45 mg / L. After the strengthening, compared with before the strengthening, the relative abundance of the microorganism genus Nitrospira related to NOB increased from 0.05% to 0.18%, and the relative abundance of Nitrosomonas related to AOB increased from 1.09% to 4.40%. The nitrification capacity of the reaction system was enhanced, and the ammonia nitrogen concentration in the effluent was always kept at a very low level, which could reach the first-level A discharge standard. Moreover, the nitrification system after the strengthening was subjected to a low-temperature impact of about 5°C, and the nitrification capacity of the system was relatively stable, and the ammonia nitrogen concentration in the effluent was about 0.08 mg / L, indicating that this biological strengthening method could guarantee the efficient and stable operation of the wastewater treatment system to a certain extent.

[0090] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these are only illustrative, and various changes or modifications can be made to the present embodiments without departing from the principles and essence of the present application, and the protection scope of the present application is only defined by the appended claims.

Claims

1. A nitrification process with side-stream enrichment / main-stream augmentation of AOB, characterized in that, The method comprises the following steps: (1) inoculating activated sludge from an aerobic tank of a sewage treatment plant into a side-stream partial nitrification reactor to make the initial sludge concentration in the side-stream partial nitrification reactor 2000-4000 mg / L; (2) starting the partial nitrification process to enrich nitrosation sludge, using the supernatant of sludge anaerobic digestion as the influent of the side-stream partial nitrification reactor, the ammonia nitrogen concentration in the influent being 500-2000 mg / L, the chemical oxygen demand being 200-800 mg / L, the dissolved oxygen concentration being controlled at 0.1-0.5 mg / L, the pH being 8.50-8.54, and the temperature being 30-37℃; (3) after more than 50% of the ammonia nitrogen in the influent of the side-stream partial nitrification reactor is converted into nitrous nitrogen, taking nitrosation sludge from the side-stream partial nitrification reactor and putting it into a mainstream nitrification reactor every day, the nitrosation sludge accounting for 1.0-2.0% of the total sludge mass in the mainstream nitrification reactor, so as to strengthen the nitrification capacity of the mainstream nitrification reactor; the influent of the mainstream nitrification reactor is domestic sewage, the chemical oxygen demand being 200-400 mg / L, the ammonia nitrogen concentration being 40-80 mg / L, and the temperature being controlled at 5-25℃, the dissolved oxygen concentration being more than 2 mg / L.

2. The process for nitrification of side stream enrichment / main stream augmentation AOB as claimed in claim 1 wherein, In step (1), the activated sludge is taken from the end of the aerobic tank of the sewage treatment plant.

3. The process for nitrification of side stream enrichment / main stream augmentation AOB as claimed in claim 1 wherein, In step (1), the initial sludge concentration in the side-stream partial nitrification reactor is 3000 mg / L.

4. The process for nitrification of side stream enrichment / main stream augmentation AOB according to claim 3, characterized in that, In step (2), when the ammonia nitrogen concentration in the influent of the side-stream partial nitrification reactor is 1000 mg / L, the chemical oxygen demand is 500 mg / L, and the dissolved oxygen is controlled at 0.2 mg / L.

5. The process for nitrification of side stream enrichment / main stream augmentation AOB as claimed in claim 3 wherein, In step (2), in the initial stage after starting the partial nitrification process, the ammonia nitrogen concentration in the influent of the side-stream partial nitrification reactor is gradually increased.

6. The process for nitrification of side stream enrichment / main stream augmentation AOB as claimed in claim 1 wherein, In step (3), after more than 80% of the ammonia nitrogen in the influent of the side-stream partial nitrification reactor is converted into nitrous nitrogen, the nitrosation sludge is taken and put into the mainstream nitrification reactor.

7. The process for nitrification of side stream enrichment / main stream augmentation AOB according to claim 6, characterized in that, In step (3), the nitrosation sludge put into the mainstream nitrification reactor every day accounts for 1.5-1.6% of the total sludge mass in the mainstream nitrification reactor.

8. The process for nitrification of side stream enrichment / main stream augmentation AOB as claimed in claim 1 wherein, In step (3), the dissolved oxygen is controlled at more than 2 mg / L by aeration, and the dissolved oxygen is 7-8 mg / L at the end of the aeration reaction.

9. A sewage treatment system characterised in that, The method for enriching AOB in a side-stream and strengthening nitrification in a mainstream according to any one of claims 1-8 is adopted.

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