Method for denitrification digestion of residual sludge from sewage treatment plant

Abstract

The application discloses a kind of sewage treatment plant residual sludge denitrification digestion methods, belong to sludge treatment technical field.The method is introduced into the sludge pool of sewage treatment plant with nitrate nitrogen material, and mix with residual sludge in pool;Denitrifying bacteria group in sludge is with organic matter carried by sludge itself as carbon source, nitrate nitrogen is reduced to nitrogen;Organic matter in sludge is oxidized and decomposed in the reaction process, realize the inorganic of sludge, stabilization and reduction.The application does not need to purchase carbon source and commercial bacterial agent, utilize existing sludge pool, low investment, low operating cost.Nitrate nitrogen material can be derived from in-plant nitrification liquid, external nitrate-containing waste liquid, NO2 generated by catalytic oxidation of ammonia-containing waste material etc..Sludge pool can be used as resource utilization workshop, and a variety of waste is treated in coordination, and the application method of concentrated residual sludge in denitrification treatment submitted on the same day forms technical complementation.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, specifically relating to a method for digesting residual sludge from wastewater treatment plants using denitrification reaction, thereby achieving the inorganicization, stabilization, and volume reduction of sludge, and can also co-treat various nitrate-containing wastes. Background Technology

[0002] Wastewater treatment plants generate a large amount of excess sludge during the biological treatment process. This excess sludge has a high water content, large volume, and high organic matter content, requiring treatment such as concentration, digestion, and dewatering before being transported for disposal. Sludge digestion is a crucial step in sludge reduction and stabilization. Traditional sludge digestion methods mainly include:

[0003] Anaerobic digestion: Under anaerobic conditions, anaerobic bacteria decompose organic matter in sludge into methane and carbon dioxide, thus reducing sludge volume. However, anaerobic digestion requires significant investment, is complex to operate, and has a long cycle (20-30 days), making it difficult for small and medium-sized wastewater treatment plants to apply.

[0004] • Aerobic digestion: Under aerobic conditions, microorganisms consume their own organic matter through endogenous respiration. However, aerobic digestion has high energy consumption and high operating costs.

[0005] • Lime stabilization: Adding lime increases the pH and inhibits microbial activity, but only achieves stabilization without reducing the amount of sludge, and increases the amount of dry solids in the sludge.

[0006] The methods described above all suffer from problems such as high investment, high energy consumption, complex operation, or limited effectiveness. Furthermore, these methods all achieve sludge reduction through microbial decomposition and metabolism (anaerobic or aerobic), and there are no reports of utilizing denitrification metabolism to digest excess sludge.

[0007] The applicant previously proposed a process for the co-treatment of multiple wastes using an anaerobic system (application number 202610435628.7), expanding the anaerobic system into a co-treatment center for multiple industrial wastes. Inspired by this, the applicant further discovered that denitrification not only removes nitrate nitrogen from water, but more importantly, denitrifying bacteria use nitrate nitrogen as an electron acceptor during metabolism to oxidize and decompose organic matter. This principle was applied to waste sludge treatment—nitrate-containing substances were introduced into the sludge tank, utilizing the existing denitrifying bacteria in the sludge and the organic matter carried by the sludge itself as a carbon source to carry out denitrification—the organic matter in the sludge was oxidized and decomposed, thereby achieving the inorganicization, stabilization, and volume reduction of the sludge. Summary of the Invention

[0008] Purpose of the invention

[0009] The purpose of this invention is to provide a method for denitrifying and digesting residual sludge from wastewater treatment plants. This method utilizes denitrification to oxidize and decompose organic matter in the sludge, thereby achieving the inorganicization, stabilization, and volume reduction of the sludge. It overcomes the shortcomings of traditional sludge digestion methods, such as high investment, high energy consumption, and complex operation.

[0010] Technical solution

[0011] A method for denitrification and digestion of excess sludge from a wastewater treatment plant includes the following steps:

[0012] S1. Prepare the sludge tank:

[0013] Existing sludge thickening tanks, sludge digestion tanks, sludge storage tanks, or sludge conditioning tanks in wastewater treatment plants are used as reaction tanks. The tanks already contain thickened excess sludge with a moisture content typically between 95% and 98% (thickening tank) or 97% and 99% (storage tank). The sludge is rich in facultative denitrifying bacteria and biodegradable organic matter.

[0014] S2. Introduce substances containing nitrate nitrogen:

[0015] Nitrate-containing nitrogen substances are introduced into the sludge tank and mixed with the remaining sludge in the tank. The nitrate-containing nitrogen substances include:

[0016] • Effluent from the aerobic tank inside the wastewater treatment plant and nitrified liquid (nitrate nitrogen concentration 10-50 mg / L).

[0017] • High-concentration nitrate-containing wastewater (nitrate nitrogen concentration 1-100 g / L) in industrial parks.

[0018] • Nitrogen dioxide gas (dissolves in water to form nitric acid / nitrite after being introduced);

[0019] • Nitric acid or nitrite solution (such as a solution after absorbing NO2);

[0020] • Externally generated ammonia-containing waste (which is catalytically oxidized to NO2 and then introduced).

[0021] The amount introduced should be controlled at 50-500 mg / L based on the nitrate nitrogen concentration in the sludge tank mixed liquor to ensure that the denitrification reaction has sufficient electron acceptors.

[0022] S3. Denitrification digestion reaction:

[0023] The sludge tank is maintained in an anoxic state (dissolved oxygen <0.5 mg / L), and intermittent stirring or a circulating pump is used for mixing. The denitrifying bacteria in the tank use the organic matter carried by the sludge (including extracellular polymers and the bacteria's own biomass) as a carbon source and nitrate nitrogen as an electron acceptor, reducing it to nitrogen gas. During the reaction, the organic matter in the sludge is oxidized and decomposed, and the sludge gradually becomes inorganic, stabilized, and reduced in volume.

[0024] The reaction time is determined based on the sludge properties, nitrate nitrogen concentration, and target digestion level, and is typically 12-72 hours. Nitrogen bubbles can be seen escaping during the reaction.

[0025] S4. Sludge-water separation and subsequent treatment:

[0026] The resulting mixture undergoes sludge-water separation (using gravity thickening, mechanical dewatering, or pressure filtration). The separated supernatant has a significantly reduced nitrate nitrogen concentration and is returned to the equalization tank or biological treatment tank of the wastewater treatment system for further processing. The separated sludge has been inorganicated, stabilized, and reduced in volume, and can be directly dewatered and transported for disposal.

[0027] S5. Co-processing of external waste (optional):

[0028] Nitrate-containing waste liquid, nitrate-containing waste gas, or ammonia-containing waste (catalytically oxidized to NO2) generated externally are simultaneously introduced into the sludge tank and digested using the same denitrification system. At this time, the sludge tank also serves as a resource utilization workshop, disposing of various external wastes.

[0029] Beneficial effects

[0030] 1. Core Invention – Sludge Inorganization, Stabilization, and Volume Reduction: Utilizing denitrification to oxidize and decompose organic matter in sludge, MLVSS is reduced by 15%-30%, sludge volume is reduced, and organic matter content is lowered, achieving true “digestion”.

[0031] 2. No need to purchase carbon sources and microbial agents: The sludge itself provides carbon sources and microbial strains, and the denitrifying bacteria naturally exist in the residual sludge.

[0032] 3. Utilize existing facilities: Sludge ponds are standard equipment in wastewater treatment plants, eliminating the need for new pond construction and resulting in extremely low investment.

[0033] 4. Low operating cost: It only requires the introduction of nitrate nitrogen-containing substances and intermittent stirring, and its energy consumption is much lower than that of aerobic digestion, and its cycle is much shorter than that of anaerobic digestion.

[0034] 5. Improved dewatering performance: After the extracellular polymer is consumed, the sludge viscosity decreases and the dewatering speed increases by 20%-40%.

[0035] 6. Co-processing of multiple wastes: The sludge pond can serve as a resource utilization workshop to dispose of nitrate-containing waste liquid, nitrate-containing waste gas, and ammonia-containing waste (which are catalytically oxidized to NO2) from inside and outside the plant, thus achieving "waste treatment with waste and synergistic treatment of multiple wastes".

[0036] 7. Complementary to the application submitted on the same day: This method complements the application submitted on the same day, "Application Method of Concentrated Excess Sludge in Denitrification Treatment." The latter uses concentrated excess sludge as a product to treat external wastewater / waste gas containing nitrate nitrogen; this method introduces nitrate nitrogen-containing substances (including NO2 generated from the catalytic oxidation of waste ammonia) into a sludge tank to digest the excess sludge. Together, they form a two-way closed loop of "sludge leaving the plant for industrial denitrification" and "nitrate-containing waste entering the plant to digest sludge." Detailed Implementation

[0037] Example 1 (Digesting sludge from the concentration tank using nitrification liquor from the plant)

[0038] A municipal wastewater treatment plant has a daily treatment capacity of 100,000 tons and uses the AAO process. The sludge thickening tank produces approximately 500 m³ of thickened excess sludge (97% moisture content) daily, with an MLVSS of approximately 8000 mg / L.

[0039] Using the method of this invention:

[0040] The effluent from the aerobic tank (nitrate nitrogen concentration approximately 15-20 mg / L) is introduced into the sludge thickening tank through a return pipe, controlling the nitrate nitrogen concentration in the thickening tank mixture to approximately 80-120 mg / L. The thickening tank is maintained in anoxic conditions (dissolved oxygen <0.3 mg / L), and intermittently stirred 4-6 times daily for 30 minutes each time. The retention time is approximately 48 hours. During the reaction, nitrogen bubbles can be seen escaping from the surface of the thickening tank.

[0041] Execution result:

[0042] • The MLVSS of the sludge in the thickening tank was reduced from 8000 mg / L to about 6000 mg / L, a reduction of 25%, achieving inorganicization and stabilization;

[0043] • Improved sludge dewatering performance, reduced specific resistance by approximately 35%, and shortened filter press cycle by 30%;

[0044] • When the nitrate nitrogen concentration in the supernatant of the thickener is reduced to <5 mg / L, the external carbon source is reduced by approximately 40% after being returned to the system;

[0045] • No external carbon source or commercial bacterial agent needs to be purchased throughout the entire process.

[0046] Example 2 (Using NO2 generated from the catalytic oxidation of waste ammonia to digest excess sludge)

[0047] A municipal wastewater treatment plant has a daily treatment capacity of 100,000 tons. The plant's sludge thickening tank produces approximately 500 m³ of thickened waste sludge daily. Simultaneously, the plant's sludge dewatering room generates ammonia-containing waste gas (ammonia concentration approximately 500-1000 ppm), which was originally treated using a biological deodorization system.

[0048] Using the method of this invention:

[0049] A small-scale catalytic oxidation device (Cr2O3 catalyst, reaction temperature 600℃) is set up. Ammonia-containing waste gas is mixed with air and then introduced into the device for catalytic oxidation to produce NO2. The reaction equations are: 4NH3 + 5O2 → 4NO + 6H2O, 2NO + O2 → 2NO2. The NO2 gas is then introduced into the bottom of the sludge thickening tank through a gas distribution pipe. The NO2 is absorbed by the water in the sludge to produce nitric acid and nitrite: 2NO2 + H2O → HNO3 + HNO2. The dosage is controlled to maintain the nitrate nitrogen concentration in the thickening tank mixture at approximately 100-200 mg / L. The thickening tank is kept in an anoxic state (dissolved oxygen <0.3 mg / L), with intermittent stirring daily and a residence time of approximately 48 hours.

[0050] Execution result:

[0051] • The MLVSS of the sludge in the thickening tank decreased from 8000 mg / L to approximately 5800 mg / L, a reduction of 27.5%;

[0052] • Improved sludge dewatering performance, with a specific resistance reduction of approximately 40%;

[0053] • Ammonia removal rate in ammonia-containing waste gas >95%, converted into nitrogen gas;

[0054] • The nitrate nitrogen concentration in the supernatant of the thickener is <5 mg / L;

[0055] • Waste gas treatment and sludge digestion are completed simultaneously, eliminating the need to purchase external carbon sources and microbial agents.

[0056] Example 3 (Co-processing of external nitrate-containing waste – sludge pond as a resource utilization workshop)

[0057] A wastewater treatment plant in a chemical industrial park produces approximately 20 tons of residual sludge (85% moisture content) daily. Several companies within the park generate nitrate-containing waste liquid (nitrate nitrogen concentration 10-50 g / L) and ammonia-containing waste gas.

[0058] Using the method of this invention:

[0059] The nitrate-containing wastewater generated by the enterprise is pumped into a sludge conditioning tank in batches, controlling the nitrate nitrogen concentration in the mixed liquor to approximately 300-500 mg / L. Simultaneously, a catalytic oxidation device is installed to treat ammonia-containing waste gas from the industrial park, with the generated NO2 being introduced into the same conditioning tank. The conditioning tank is maintained in an anoxic state with intermittent stirring for 48 hours. After the reaction is complete, the mixed liquor is dewatered using a plate and frame filter press.

[0060] Execution result:

[0061] • Excess sludge MLVSS was reduced by approximately 28%, demonstrating a significant reduction effect;

[0062] • The moisture content of the filter cake was reduced from 75% to 68%, improving the dehydration performance;

[0063] • Outsourcing costs for nitrate-containing wastewater have been completely eliminated;

[0064] • Ammonia-containing waste gas treatment costs reduced by 60%;

[0065] • One pool serves three purposes: it treats nitrate-containing waste liquid, ammonia-containing waste gas, and excess sludge, turning the sludge pool into a resource utilization workshop.

[0066] Example 4 (Direct digestion of high-concentration nitrate-containing wastewater)

[0067] A plating plant's wastewater treatment plant generates approximately 10 tons of residual sludge per month, along with high-concentration aging tank solution containing nitrates (approximately 80 g / L of NO3⁻-N). Previously, the solution was outsourced for disposal (costing 6000 yuan / month), and the sludge was transported for landfill.

[0068] Using the method of this invention:

[0069] The nitrate-containing aging tank liquid is pumped into the sludge thickening tank in batches, and the nitrate nitrogen concentration of the mixed liquid is controlled at about 200-300 mg / L. The reaction time is 48 hours.

[0070] Execution result:

[0071] • Sludge MLVSS decreased by approximately 22%;

[0072] • Outsourcing costs for bath solutions have been completely eliminated;

[0073] • Improved sludge dewatering performance;

[0074] • Waste-to-waste treatment: Use the tank solution to digest the sludge, and use the sludge to treat the tank solution.

[0075] Industrial applicability

[0076] This invention is applicable to urban wastewater treatment plants, industrial park wastewater treatment plants, and industrial enterprises. It utilizes denitrification to digest excess sludge, achieving sludge inorganization, stabilization, and volume reduction. This method utilizes existing sludge ponds, eliminating the need for new construction, external carbon sources, and commercial microbial agents, resulting in low investment and operating costs. Simultaneously, the sludge ponds can serve as resource utilization workshops, co-treating nitrifying waste liquids, nitrifying waste gases, and ammonia-containing wastes (catalytically oxidized to NO2) from both within and outside the plant, achieving "waste treatment with waste, and synergistic multi-waste treatment." This method complements the "Application Method of Concentrated Excess Sludge in Denitrification Treatment" submitted on the same day.

Claims

1. A method for denitrification and digestion of excess sludge from a wastewater treatment plant, characterized in that: Nitrate-containing substances are introduced into the sludge tank of the wastewater treatment plant and mixed with the remaining sludge in the tank. The denitrifying bacteria in the sludge use the organic matter carried by the sludge as a carbon source to reduce nitrate nitrogen to nitrogen gas. During the reaction, the organic matter in the sludge is oxidized and decomposed, realizing the inorganicization, stabilization and volume reduction of the sludge.

2. The method according to claim 1, characterized in that: The nitrate-containing nitrogen substances include one or more of the following: nitrate-containing wastewater, waste acid liquid, nitrogen dioxide gas, nitric acid or nitrite solution.

3. The method according to claim 2, characterized in that: The nitrogen dioxide gas is prepared by catalytic oxidation of ammonia-containing waste, or it may be derived from industrial waste gas or gas cylinders.

4. The method according to claim 1, characterized in that: The sludge tank is one or more of the following: sludge thickening tank, sludge digestion tank, sludge storage tank, or sludge conditioning tank.

5. The method according to claim 1, characterized in that: The amount of nitrate-containing nitrogen substances introduced is controlled at 50-500 mg / L based on the nitrate nitrogen concentration in the sludge tank mixed liquor.

6. The method according to claim 1, characterized in that: During the denitrification process, the sludge tank is kept in an anoxic state with dissolved oxygen below 0.5 mg / L, and intermittent stirring or circulating pump mixing is used.

7. The method according to claim 1, characterized in that: In the method described, no additional purchased carbon source or commercial denitrifying bacteria agent is added.

8. The method according to claim 1, characterized in that: The method is also used for the co-treatment of external nitrate-containing waste, by simultaneously introducing external nitrate-containing waste liquid, nitrate-containing waste gas, or ammonia-containing waste (which is catalytically oxidized to NO2) into the sludge tank.

9. The method according to claim 1, characterized in that: During the denitrification process, volatile suspended solids (MLVSS) in the sludge are reduced by 15%-30%, and the sludge dewatering performance is improved.

10. The method according to claim 1, characterized in that: The sludge pond serves as a resource utilization workshop during the denitrification and digestion process, absorbing nitrate-containing nitrogenous substances from both inside and outside the plant.