Preparation method of carbon source of primary sludge in sewage plant

Abstract

The application discloses a kind of low carbon-nitrogen ratio sewage plant carbon source excavation and preparation method, it is related to sewage treatment field, carbon source in sewage plant is obtained by anaerobic acid production fermentation of primary sludge, rich in volatile fatty acid, effectively improve the denitrification and phosphorus removal efficiency of sewage treatment process.The application recycles organic matter in primary sludge while improving the carbon-nitrogen ratio of sewage influent, reducing the cost of additional carbon source, and also alleviating the problem of primary sludge disposal.The settling performance of the pretreated primary sludge is better, and it is easy to dewater and treat.The fermentation period is short, and the carbon source in the primary sludge can be obtained faster.Under the condition that the carbon-nitrogen ratio of the influent is supplemented to the same proportion, the denitrification and phosphorus removal effect of the carbon source is better, and it is suitable for denitrification and phosphorus removal treatment of low carbon-nitrogen ratio sewage.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a method for mining and preparing carbon sources in wastewater treatment plants with low carbon-to-nitrogen ratios. Background Technology

[0002] Reducing energy consumption during operation has become a crucial task for smart water plants. With the shrinking environmental capacity of most receiving water bodies in China and increasingly stringent environmental policies, more and more municipal wastewater treatment plants are required to meet the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002), and there is a trend towards further improvements in standards. According to the "Code for Design of Outdoor Drainage" (GB 50014-2006), the recommended carbon-to-nitrogen ratio (BOD5 / TKN) for biological denitrification should be >4. Currently, many regions in my country face insufficient raw water carbon sources and low carbon-to-nitrogen ratios, making it difficult and costly to achieve nitrogen and phosphorus discharge standards. To address the insufficient carbon source problem in nitrogen and phosphorus removal, many wastewater treatment plants have adopted measures to add external carbon sources. Common types of external carbon sources include methanol, acetic acid, sodium acetate, propionic acid, and glucose. Although these external carbon sources can significantly improve the nitrogen and phosphorus removal efficiency of wastewater treatment processes, methanol is biotoxic, and the cost of adding carbon sources such as sodium acetate and glucose is high, significantly increasing the financial burden on wastewater treatment plants, while also increasing carbon emissions.

[0003] In recent years, the number of urban wastewater treatment plants in my country has been increasing. According to the "2020 Statistical Yearbook of Urban and Rural Construction" published by the Ministry of Housing and Urban-Rural Development of China, 2,618 wastewater treatment plants have been built in cities nationwide, including 2,441 with secondary and tertiary treatment processes. These plants can treat 192.671 million cubic meters of wastewater per day. 3 Wastewater treatment facilities can process 11.38 million m³ of wastewater daily. With the increase in wastewater treatment capacity, the production of primary sludge has also increased rapidly. Statistics show that in 2019, my country's sludge production (80% moisture content) exceeded 60 million tons. Primary sludge is a crucial component of wastewater treatment plant sludge, and adopting appropriate methods for its treatment and disposal has become an urgent problem to solve.

[0004] Sludge anaerobic fermentation is a kind of effective sludge treatment and resource utilization technology. Sludge anaerobic fermentation reaction is very easy to carry out, and the organic matter content in the fermentation liquid after the reaction is high, and the main component is volatile fatty acid (VFAs, volatile fatty acid), and the denitrification rate is higher than that of traditional carbon source, which can effectively promote the denitrification and phosphorus removal efficiency of sewage plant sewage. Using sludge hydrolysis acidification liquid as external carbon source can not only reduce the cost of denitrification and phosphorus removal, but also realize the resource utilization of sludge, and has high commercial value and application range in practical application. However, the fermentation speed of primary sludge is slow, the settling performance is poor, the hydrolysis limiting step needs to be broken through, the dewatering effect needs to be improved, and the problem of increasing nitrogen and phosphorus treatment load caused by the reuse of fermentation acidification liquid needs to be reduced.

[0005] Therefore, those skilled in the art are committed to developing a technology for reducing the content of nitrogen and phosphorus and recycling the carbon source in the primary sludge in the sewage plant. SUMMARY

[0006] The purpose of the present application is to provide a low carbon-nitrogen ratio sewage plant carbon source mining and preparation method, characterized in that it comprises the following steps:

[0007] 1) Adjusting the sludge to be treated to isoelectric point;

[0008] 2) Dewatering the sludge treated by step 1) to retain the solid sludge, and resuspending the solid sludge by adding pure water;

[0009] 3) Anaerobic fermentation of the resuspended sludge to obtain the acidification liquid as a high-quality supplemental carbon source.

[0010] Further, in step 1), the sludge is the primary sludge generated in the primary sedimentation tank of the sewage treatment plant.

[0011] Further, in step 1), the sludge to be treated is adjusted to isoelectric point by hydrochloric acid.

[0012] Further, in step 1), after adjusting to isoelectric point, nitrite is added for pretreatment.

[0013] Further, after adding nitrite, the NO2 - The concentration of N in the sludge mixture system is 100-300 mg / L.

[0014] Further, the pretreatment needs to stir the sludge mixture under anaerobic conditions at 35℃.

[0015] Further, in step 2), the volume of the resuspended sludge is the same as that of the sludge to be treated in step 1) by adding pure water.

[0016] Further, in step 3), the initial pH of the anaerobic fermentation is 5; the anaerobic fermentation environmental conditions are that the sludge mixture is stirred under anaerobic conditions at 35℃.

[0017] The technical effects of the present application are as follows:

[0018] 1. The primary sludge can be pretreated by adjusting the pH value to the isoelectric point, which can significantly improve the settling and dewatering properties of the sludge, reduce the water content of the sludge, and reduce the volume of the sludge.

[0019] 2. The addition of nitrite in the pretreatment process can effectively reduce the dissolution of ammonia and phosphorus elements, and can improve the recovery rate of organic matter and nitrogen and phosphorus elements in the sludge. The optimal dosage is 300 mg / L NO2 - -N, and the optimal pretreatment time is 1 h;

[0020] 3. After the pretreatment of the primary sludge is completed, the initial pH is adjusted to 5 for anaerobic fermentation, and the fermentation effect of the sludge is optimal, with a VFAs content of 2000-3000 mg COD / L, mainly acetic acid type fermentation, and a fermentation period of about 6 d;

[0021] 4. The fermentation liquid of the primary sludge can be used as a supplemental carbon source in the inverted A 2 / O to improve the carbon-nitrogen ratio of the influent. The addition of carbon source does not significantly increase the nitrogen and phosphorus treatment load, and the components in the liquid carbon source can be completely degraded without the risk of secondary pollution.

[0022] 5. After the primary sludge fermentation liquid is added to the influent, the COD removal rate reaches 87%-93%, the NH4 + -N removal rate is 91%-98%, and the TN removal rate is 76%-88%. All of the above indicators can stably reach the first level A standard. Under the condition of not adding phosphorus removal agents, the PO4 3- -P removal rate is as high as 88%-94%. Phosphorus removal can be strengthened, and the demand for phosphorus removal agents can be greatly reduced.

[0023] 6. The reuse of the fermentation liquid can effectively increase the types of microorganisms in the wastewater treatment system, and can adjust the microbial community structure of each part, thereby more effectively removing nitrogen and phosphorus. DETAILED DESCRIPTION

[0024] The present application will be further described below with reference to the examples, but should not be understood as limiting the above-mentioned subject matter of the present application to only the following examples. Various substitutions and modifications can be made according to ordinary technical knowledge and conventional means in the art without departing from the above-mentioned technical idea of the present application, and all of them should be included in the protection scope of the present application.

[0025] Example 1:

[0026] A method for carbon source mining and preparation in a low carbon-nitrogen ratio sewage plant, comprising the following steps:

[0027] 1) adding hydrochloric acid to adjust the primary sludge generated in the primary sedimentation tank of the sewage treatment plant to the isoelectric point.

[0028] Nitrite sodium is added to the sludge for pretreatment. In the example, the addition of nitrite sodium makes the NO2 - -N concentration is 300 mg / L (the amount of nitrite sodium added is determined accordingly). The pretreatment time is 1 h, and the pretreatment conditions are: 35℃, anaerobic environment, stirring at 140 rpm.

[0029] 2) The sludge treated by step 1) is subjected to dewatering treatment, and the solid phase sludge is reserved. Pure water is added to resuspend the solid phase sludge. In the example, the addition of pure water makes the volume of the resuspended sludge the same as the initial time (the amount of pure water added is determined accordingly).

[0030] 3) The resuspended sludge is subjected to anaerobic fermentation: hydrochloric acid / sodium hydroxide is added to adjust the initial pH to 5, and the anaerobic fermentation environmental conditions are: 35℃, 140 rpm stirring. The anaerobic fermentation time is 6 days.

[0031] In this example, the anaerobic environment should use nitrogen or helium to blow gas into the reaction system to discharge oxygen, so that it reaches the anaerobic condition.

[0032] In the sewage treatment process, the product of the above anaerobic fermentation can be added as a carbon source into the water, and the water inlet position is the anaerobic tank section.

[0033] Example 2:

[0034] A method for carbon source mining and preparation in a low carbon-nitrogen ratio sewage plant, comprising the following steps:

[0035] 1) adding hydrochloric acid to adjust the primary sludge generated in the primary sedimentation tank of the sewage treatment plant to the isoelectric point.

[0036] Nitrite sodium is added to the sludge for pretreatment. In the example, the addition of nitrite sodium makes the NO2 - -N concentration is 100 mg / L (the amount of nitrite sodium added is determined accordingly). The pretreatment time is 1 h, and the pretreatment conditions are: 35℃, anaerobic environment, stirring at 140 rpm.

[0037] 2) The sludge treated by step 1) is subjected to dewatering treatment, and the solid phase sludge is reserved. Pure water is added to resuspend the solid phase sludge. In the example, the addition of pure water makes the volume of the resuspended sludge the same as the initial time (the amount of pure water added is determined accordingly).

[0038] 3) Resuspend the sludge and perform anaerobic fermentation: add hydrochloric acid / sodium hydroxide to adjust the initial pH to 5, and the anaerobic fermentation conditions are: 35℃, 140 rpm stirring. The anaerobic fermentation time is 6 days.

[0039] In this embodiment, the anaerobic environment should use nitrogen or helium to blow gas into the reaction system to discharge oxygen, so as to achieve anaerobic conditions.

[0040] In the sewage treatment process, the product of the above anaerobic fermentation can be added as a carbon source into the water at the anaerobic tank section.

[0041] Example 3:

[0042] A low carbon-nitrogen ratio sewage plant carbon source excavation and preparation method, comprising the following steps:

[0043] 1) Add hydrochloric acid to adjust the isoelectric point of the primary sludge produced in the primary sedimentation tank of the sewage treatment plant.

[0044] Add sodium nitrite to the sludge for pretreatment. In the example, the addition of sodium nitrite makes the NO2 - -N concentration in the sludge mixture system is 300 mg / L (the amount of sodium nitrite added is determined accordingly). The pretreatment time is 2h, and the pretreatment conditions are: 35℃, anaerobic environment, and 140 rpm stirring.

[0045] 2) Dehydrate the sludge treated by step 1), and retain the solid sludge. Add pure water to resuspend the solid sludge, and in the example, the volume of the resuspended sludge is the same as the initial volume (the amount of pure water added is determined accordingly).

[0046] 3) Resuspend the sludge and perform anaerobic fermentation: add hydrochloric acid / sodium hydroxide to adjust the initial pH to 5, and the anaerobic fermentation conditions are: 35℃, 140 rpm stirring. The anaerobic fermentation time is 5 days.

[0047] In this embodiment, the anaerobic environment should use nitrogen or helium to blow gas into the reaction system to discharge oxygen, so as to achieve anaerobic conditions.

[0048] In the sewage treatment process, the product of the above anaerobic fermentation can be added as a carbon source into the water at the anaerobic tank section.

[0049] The application example of denitrification and phosphorus removal of acidified sludge from primary sludge adopts inverted A 2The / O reactor, the reactor and the high are respectively 25 cm, 27.5 cm and 25 cm, the effective water depth is 15 cm, the effective volume is 13.12 L, the water inlet is Q, the internal reflux ratio is 180%, the external reflux ratio is 80%, the secondary sedimentation tank is a vertical flow sedimentation tank, the volume is 3 L, and the residence time is 4 h. The raw water to be treated is tap water in Chongqing, sodium acetate is added to adjust the COD concentration to 200 mg / L, ammonium chloride is added to adjust the NH4 + -N concentration is 50 mg / L, potassium dihydrogen phosphate is added to adjust the PO4 3- -P concentration is 5 mg / L, the influent C / N is 4:1, and the specific process is as follows:

[0050] (1) Domestication of activated sludge: the inverted activated sludge is taken from residual sludge of a sewage plant in Chongqing, daily aeration is carried out according to DO=2 mg / L, and microorganisms such as clockworms and branchworms are observed under a microscope until the activated sludge is successfully domesticated;

[0051] (2) Start-up of the inverted A 2 / O reactor: normal water inlet every day, the influent C / N is 4:1, and the N and P indexes of the effluent are determined to be stably up to the first level A standard to determine that the inverted A 2 / O reactor is successfully started up;

[0052] (3) Comparison of denitrification and phosphorus removal effects: the influent C / N is increased to 6:1 by adding sodium acetate, glucose and primary sludge fermentation liquor respectively, the reactor is started up normally, the DO in the aerobic zone is 2-3 mg / L; the NH4 + -N is removed through the nitrification and denitrification processes of microorganisms, and finally removed through the overflow of the top of the secondary sedimentation tank.

[0053] The denitrification and phosphorus removal effects after the addition of the three carbon sources are shown in Table 1:

[0054] Table 1 Denitrification and phosphorus removal effects of the device

[0055]

Claims

1. A method for carbon source mining and preparation in a low carbon-to-nitrogen ratio sewage plant, characterized in that, Comprising the following steps: 1) Adjusting the sludge to be treated to isoelectric point by hydrochloric acid adjustment; after adjusting to isoelectric point, adding nitrite for pretreatment; The addition of nitrite effectively reduces the dissolution of ammonia and phosphorus elements, improves the recycling rate of organic matter and nitrogen and phosphorus elements in sludge, and the dosage is 300 mg / L NO2 - -N, the pretreatment time is 1 h; After the addition of nitrite, the NO2 - - N concentration is 100-300 mg / L; 2) Dehydrating the sludge treated by step 1, retaining the solid-phase sludge, and adding pure water to resuspend the solid-phase sludge; The pure water is added to make the volume of the resuspended sludge the same as that of the sludge to be treated in step 1); 3) Anaerobic fermentation of the resuspended sludge to obtain an acidified liquid thereof as a high-quality supplemental carbon source; the initial pH of the anaerobic fermentation is 5; the anaerobic fermentation environmental conditions are: stirring the sludge mixture under anaerobic conditions at 35 DEG C.

2. The method according to claim 1, characterized in that: In step 1), the sludge is primary sludge generated by a primary sedimentation tank of a sewage treatment plant.

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