Method for promoting anaerobic fermentation phosphorus release and short-chain fatty acid production of excess sludge

Abstract

The invention discloses a method for promoting anaerobic fermentation phosphorus release and short-chain fatty acid production of excess sludge, relates to the technical field of sludge treatment and resource utilization, and particularly relates to a method for promoting anaerobic fermentation phosphorus release and short-chain fatty acid production of excess sludge by utilizing thermal activation potassium persulfate (PMS, K2S2O8). The method comprises the following steps: mixing PMS with excess sludge, putting the mixture into a sludge pyrolysis device, carrying out thermal activation at 80 DEG C for 2 hours, then carrying out anaerobic fermentation in a sealed reactor, and filtering the fermented sludge mixed solution to obtain a phosphorus-rich supernatant. According to the method, the residual sludge is pretreated by utilizing the thermal activation PMS, so that phosphorus in the residual sludge can be enriched from a solid phase to a liquid phase, and the release efficiency of the phosphorus in the residual sludge is improved; meanwhile, organic matters in the excess sludge are decomposed and released into supernate along with the rupture of microbial cells in the excess sludge in the pretreatment process, so that the microbial acid production fermentation rate in the anaerobic fermentation process is increased, and the resource and reduction utilization of the sludge is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge biochemical treatment, and relates to a method for promoting the anaerobic fermentation of excess sludge to release phosphorus and produce short-chain fatty acids. The present invention uses the excess sludge produced by the sludge sedimentation tank of a municipal sewage treatment plant as a fermentation substrate, and the short-chain fatty acids produced by the fermentation are used as electron donors for sulfate-reducing bacteria to achieve sludge treatment and energy recycling, thereby solving the problems of difficulty in releasing sludge phosphorus and slow acid production efficiency. Background Art

[0002] Phosphorus is widely used in industry and agriculture. At the current rate of mining and consumption, global phosphate rock reserves will be exhausted in the next 50 to 100 years. Therefore, it is urgent to explore methods to recover phosphorus from phosphorus-containing waste streams to achieve sustainable global phosphorus utilization. Sludge produced by sewage treatment plants usually contains phosphorus by mass between 1% and 9%, so it is suitable for phosphorus recovery.

[0003] In recent years, people have developed various methods to improve the release efficiency of phosphorus in sludge. Such as ultrasonic pretreatment, acidification, co-fermentation of kitchen waste and sludge, etc., but these methods not only require a large amount of energy input, but also require considerable economic costs. Thermally activated PMS has a strong oxidizing ability and is relatively simple to use. It can destroy sludge through the persulfate ions produced by persulfate oxidation, and release nitrogen, phosphorus, organic matter, etc. into the supernatant. This method is simple to operate, has significant treatment effects, has little impact on the environment, and is economically feasible.

[0004] PMS activation will produce sulfate free radicals for decomposing sludge and degrading difficult-to-biodegrade organic components, which improves the biodegradability of organic matter in sludge and promotes further metabolism and acid production of microorganisms. In addition, sulfate free radicals will produce sulfate after oxidation, and sulfate can be reduced to sulfide by sulfate-reducing bacteria (SRB) during anaerobic fermentation. The sulfide produced by SRB will react with the remaining sludge to form FeS, thereby promoting the release of Fe-P; in addition, the PMS activation pretreatment process of decomposing sludge will also promote the release of other forms of phosphorus, thereby improving the overall release efficiency of phosphorus.

[0005] Therefore, the present invention utilizes heat-activated PMS to pre-treat excess sludge and then conducts anaerobic fermentation, thereby promoting the excess sludge to release phosphorus and produce short-chain fatty acids during the anaerobic fermentation process. The combination of heat-activated PMS pre-treatment and anaerobic fermentation process is intended to provide a reference for the development of simple and environmentally friendly technologies, thereby optimizing the recovery efficiency of phosphorus in excess sludge. Summary of the invention

[0006] The purpose of the present invention is to provide a method for strengthening the anaerobic fermentation of excess sludge to release phosphorus and produce short-chain fatty acids, which belongs to the technical field of sludge biochemical treatment and can solve the problems of difficult sludge phosphorus release and slow acid production efficiency.

[0007] The method of the present invention can be implemented by the following technical solutions:

[0008] A method for promoting the anaerobic fermentation of excess sludge to release phosphorus and produce short-chain fatty acids. The device used in the method comprises a dosing water tank (1), a sludge storage tank (4), a sludge anaerobic fermentation system (5), a water outlet tank (10), a sludge discharge tank (14), a computer (15), and a programmable control system (16); the dosing water tank (1) is connected to the sludge anaerobic fermentation system (5) through a water inlet pump (2); the sludge storage tank (4) is connected to the sludge anaerobic fermentation system (5) through a sludge inlet pump (3); the sludge anaerobic fermentation system (5) is a closed reactor, equipped with a drain valve (17), a sludge discharge valve (18), an inlet / exhaust valve (20), a sampling port (6), a stirring device (17), and a stirring device (18). The anaerobic sludge fermentation system (5) is connected to the effluent tank (10) through the effluent pump (12), and is connected to the sludge discharge tank (14) through the sludge discharge pump (13); the built-in interface of the programmable control system (PLC) (16) is respectively connected to the raw water inlet pump (2), the sludge inlet pump (3), the gas flow meter (9), the pH probe (11), the ORP probe (8), the effluent pump (12), the sludge discharge pump (13), and the computer (15), and the entire operation cycle is controlled by the PLC system;

[0009] It is characterized by comprising the following steps:

[0010] The residual sludge discharged from the sludge sedimentation tank of the actual urban sewage treatment plant was injected into the sludge anaerobic fermentation system as the fermentation substrate, and the residual sludge concentration was 15500-19500 mg / L; it was operated under anoxic conditions, and each cycle went through five stages: sludge addition, pretreatment, air intake, anoxic stirring, and sedimentation;

[0011] Ⅰ Adding mud: The fermentation substrate in the mud storage tank (4) is taken from the residual sludge in the sludge sedimentation tank of the urban sewage treatment plant, and the supernatant is removed after being allowed to settle at 4°C for 24 to 48 hours to obtain a sludge sample; the total suspended solid concentration of the sludge in the anaerobic fermentation system (5) is controlled to be 15500 to 19500 mg / L;

[0012] II. Pretreatment: The dosing water tank (1) contains PMS solution, and the concentration of the PMS solution in the anaerobic sludge fermentation system (5) is controlled to be 0.2-0.8 mmol / g VSS by controlling the raw water inlet pump (2), and thermal activation is performed in the sludge pyrolysis device at 80°C for 2 hours; the PMS solution is K2S2O8 solution;

[0013] III. Air intake: N2 is charged into the anaerobic fermentation system (5) for 3 to 5 minutes through the air intake valve (20) to remove oxygen in the reactor;

[0014] IV. Anoxic stirring: Keep the sludge anaerobic fermentation system (5) in a closed state, and do not adjust the pH value during the whole process; turn on the stirrer (7), the stirring rate is 200-400 r / min, the fermentation temperature is 35±2°C, and the fermentation time is 7 days;

[0015] Ⅴ Sedimentation: Set the sedimentation time to 20 to 30 minutes. This stage completes the mud-water separation process.

[0016] The invention realizes the treatment of sludge and the recycling of energy, and solves the problems of difficulty in releasing sludge phosphorus and slow acid production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the device of the present invention.

[0018] Figure 2 is SO4 at different PMS solution concentrations 2- The concentration change trend diagram.

[0019] Figure 3 is PO4 at different PMS solution concentrations 3- -P concentration change trend chart.

[0020] Figure 4 It is the concentration change trend diagram of VFAs under different PMS solution concentrations. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] A method for promoting the anaerobic fermentation of excess sludge to release phosphorus and produce short-chain fatty acids, the device includes 1-dosing water tank, 4-sludge storage tank, 5-sludge anaerobic fermentation system, 10-outlet tank, 14-sludge discharge tank, 15-computer, 16-programmable control system. The effective volume of the dosing water tank and the outlet tank is 25L, and the material is organic plastic. The effective volume of the sludge storage tank and the sludge discharge tank is 5L, and the material is organic glass. The sludge anaerobic fermentation system is made of cylindrical organic glass, and the effective working volume is 4L.

[0023] The connection sequence of the device is as follows: the dosing water tank (1) is connected to the anaerobic sludge fermentation system (5) through the raw water inlet pump (2); the sludge storage tank (4) is connected to the anaerobic sludge fermentation system (5) through the sludge inlet pump (3); the anaerobic sludge fermentation system (5) is a closed reactor, equipped with a drain valve (17), a sludge discharge valve (18), an inlet / exhaust valve (20), a sampling port (6), an agitator (7), a pH probe (11), and an ORP probe (8); the data of the pH probe (11) and the ORP probe (8) Feedback is in WTW (19); and the sludge anaerobic fermentation system (5) is connected to the water outlet tank (10) through the water outlet pump (12), and is connected to the sludge discharge tank (14) through the sludge discharge pump (13); the built-in interface of the programmable control system (PLC) (16) is respectively connected to the raw water inlet pump (2), the sludge inlet pump (3), the gas flow meter (9), the pH probe (11), the ORP probe (8), the water outlet pump (12), the sludge discharge pump (13), and the computer (15), and the entire operation cycle is controlled by the PLC system.

[0024] The specific implementation cases are as follows:

[0025] The residual sludge discharged from the sludge sedimentation tank of an actual urban sewage treatment plant was injected into the sludge anaerobic fermentation system as the fermentation substrate (5). The initial characteristics of the sludge were as follows: suspended solid concentration (TSS) 19300±300mg / L, volatile solid concentration (VSS) 11600±200mg / L, TCOD 34700±400mg / L, SCOD 76.2±0.8mg / L, TP 33.5±0.2mg / gTS, phosphate 0.8±0.1mg / L. The system was operated under anoxic conditions, and each cycle went through five stages: sludge addition, pretreatment, aeration, anoxic stirring, and sedimentation.

[0026] Comparative Example:

[0027] Ⅰ Adding mud: The fermentation substrate in the mud storage tank (4) is taken from the residual sludge in the sludge sedimentation tank of the urban sewage treatment plant, and the supernatant is removed after being allowed to settle at 4°C for 24 hours to obtain a sludge sample; the total suspended solid concentration of the sludge in the anaerobic fermentation system (5) is controlled to be 15500-19500 mg / L;

[0028] II. Pretreatment: The dosing water tank (1) contains PMS solution. The concentration of PMS solution in the anaerobic sludge fermentation system (5) is made 0 mmol / g VSS by controlling the raw water inlet pump (2). The sludge is thermally activated in the sludge pyrolysis device at 80°C for 2 hours.

[0029] III. Air intake: N2 is charged into the anaerobic fermentation system (5) for 3 min through the air intake valve (20) to remove oxygen in the reactor;

[0030] IV. Anoxic stirring: Keep the sludge anaerobic fermentation system (5) in a closed state, and do not adjust the pH value during the whole process; turn on the stirrer (7), the stirring rate is 200 r / min, the fermentation temperature is 35±2°C, and the fermentation time is 7 days;

[0031] Ⅴ Sedimentation: Set the sedimentation time to 20 minutes. This stage completes the mud-water separation process.

[0032] The comparative example was subjected to 5 cycles, with an average soluble phosphate release of 10.1 mg / L and an average short-chain fatty acid production of 1924 mgCOD / L.

[0033] Implementation Case 1:

[0034] Ⅰ Adding mud: The fermentation substrate in the mud storage tank (4) is taken from the residual sludge in the sludge sedimentation tank of the urban sewage treatment plant, and the supernatant is removed after being allowed to settle at 4°C for 24 hours to obtain a sludge sample; the total suspended solid concentration of the sludge in the anaerobic fermentation system (5) is controlled to be 15500-19500 mg / L;

[0035] II. Pretreatment: The dosing water tank (1) contains PMS solution. The concentration of PMS solution in the sludge anaerobic fermentation system (5) is adjusted to 0.2 mmol / g VSS by controlling the raw water inlet pump (2). The sludge is thermally activated in a sludge pyrolysis device at 80°C for 2 hours.

[0036] III. Air intake: N2 is charged into the anaerobic fermentation system (5) for 3 min through the air intake valve (20) to remove oxygen in the reactor;

[0037] IV. Anoxic stirring: Keep the sludge anaerobic fermentation system (5) in a closed state, and do not adjust the pH value during the whole process; turn on the stirrer (7), the stirring rate is 200 r / min, the fermentation temperature is 35±2°C, and the fermentation time is 7 days;

[0038] Ⅴ Sedimentation: Set the sedimentation time to 20 minutes. This stage completes the mud-water separation process.

[0039] Implementation Case 1 was carried out for 5 cycles, with an average soluble phosphate release of 110.7 mg / L and an average short-chain fatty acid production of 2285 mgCOD / L.

[0040] Implementation Case 2:

[0041] Ⅰ Adding mud: The fermentation substrate in the mud storage tank (4) is taken from the residual sludge in the sludge sedimentation tank of the urban sewage treatment plant, and the supernatant is removed after being allowed to settle at 4°C for 48 hours to obtain a sludge sample; the total suspended solid concentration of the sludge in the anaerobic fermentation system (5) is controlled to be 15500-19500 mg / L;

[0042] II. Pretreatment: The dosing water tank (1) contains PMS solution. The concentration of PMS solution in the sludge anaerobic fermentation system (5) is adjusted to 0.4 mmol / g VSS by controlling the raw water inlet pump (2). The sludge is thermally activated in a sludge pyrolysis device at 80°C for 2 hours.

[0043] III. Air intake: N2 is charged into the anaerobic fermentation system (5) for 5 min through the air intake valve (20) to remove oxygen in the reactor;

[0044] IV. Anoxic stirring: Keep the sludge anaerobic fermentation system (5) in a closed state, and do not adjust the pH value during the whole process; turn on the stirrer (7), the stirring rate is 400 r / min, the fermentation temperature is 35±2°C, and the fermentation time is 7 days;

[0045] Ⅴ Sedimentation: Set the sedimentation time to 30 minutes. This stage completes the mud-water separation process.

[0046] Implementation Case 2 was carried out for 5 cycles, with an average soluble phosphate release of 157.1 mg / L and an average short-chain fatty acid production of 2773 mgCOD / L.

[0047] Implementation Case 3:

[0048] Ⅰ Adding mud: The fermentation substrate in the mud storage tank (4) is taken from the residual sludge in the sludge sedimentation tank of the urban sewage treatment plant, and the supernatant is removed after being allowed to settle at 4°C for 36 hours to obtain a sludge sample; the total suspended solid concentration of the sludge in the anaerobic fermentation system (5) is controlled to be 15500-19500 mg / L;

[0049] II. Pretreatment: The dosing water tank (1) contains PMS solution. The concentration of PMS solution in the anaerobic sludge fermentation system (5) is adjusted to 0.8 mmol / g VSS by controlling the raw water inlet pump (2). The sludge is thermally activated in a sludge pyrolysis device at 80°C for 2 hours.

[0050] III. Air intake: N2 is charged into the anaerobic fermentation system (5) for 5 min through the air intake valve (20) to remove oxygen in the reactor;

[0051] IV. Anoxic stirring: Keep the sludge anaerobic fermentation system (5) in a closed state, and do not adjust the pH value during the whole process; turn on the stirrer (7), the stirring rate is 300 r / min, the fermentation temperature is 35±2°C, and the fermentation time is 7 days;

[0052] Ⅴ Sedimentation: Set the sedimentation time to 25 minutes. This stage completes the mud-water separation process.

[0053] Implementation case 3 was carried out for 5 cycles, with an average soluble phosphate release of 245.9 mg / L and an average short-chain fatty acid production of 2269 mgCOD / L.

[0054] The results showed that thermally activated PMS pretreatment could enhance the phosphorus release and short-chain fatty acid production during the anaerobic fermentation of residual sludge, realize the sludge treatment and energy recycling, and solve the problems of difficult sludge phosphorus release and slow acid production efficiency.

Claims

1. A method for promoting the anaerobic fermentation of excess sludge to release phosphorus and produce short-chain fatty acids, the device used in the method comprising a dosing water tank (1), a sludge storage tank (4), a sludge anaerobic fermentation system (5), a water outlet tank (10), a sludge discharge tank (14), a computer (15), and a programmable control system (16); the dosing water tank (1) is connected to the sludge anaerobic fermentation system (5) through a water inlet pump (2); the sludge storage tank (4) is connected to the sludge anaerobic fermentation system (5) through a sludge inlet pump (3); the sludge anaerobic fermentation system (5) is a closed reactor, equipped with a drain valve (17), a sludge discharge valve (18), an inlet / exhaust valve (20), a sampling port (6), a stirring device (16), and a stirring device (17). agitator (7), pH probe (11), ORP probe (8), and data of pH probe (11) and ORP probe (8) are fed back to WTW (19); and the sludge anaerobic fermentation system (5) is connected to the water outlet tank (10) through the water outlet pump (12), and is connected to the sludge discharge tank (14) through the sludge discharge pump (13); the built-in interface of the programmable control system (PLC) (16) is respectively connected to the raw water inlet pump (2), the sludge inlet pump (3), the gas flow meter (9), the pH probe (11), the ORP probe (8), the water outlet pump (12), the sludge discharge pump (13), and the computer (15), and the entire operation cycle is controlled by the PLC system; It is characterized in that The following steps are involved: The residual sludge discharged from the sludge sedimentation tank of the actual urban sewage treatment plant was injected into the sludge anaerobic fermentation system as the fermentation substrate, and the residual sludge concentration was 15500-19500 mg / L; it was operated under anaerobic conditions, and each cycle went through five stages: sludge addition, pretreatment, air intake, anoxic stirring, and sedimentation; Ⅰ Adding mud: The fermentation substrate in the mud storage tank (4) is taken from the residual sludge in the sludge sedimentation tank of the urban sewage treatment plant, and the supernatant is removed after being allowed to settle at 4°C for 24 to 48 hours to obtain a sludge sample; the total suspended solid concentration of the sludge in the anaerobic fermentation system (5) is controlled to be 15500 to 19500 mg / L; II. Pretreatment: The dosing water tank (1) contains PMS solution, and the concentration of the PMS solution in the sludge anaerobic fermentation system (5) is adjusted to 0.2-0.8 mmol / g VSS by controlling the raw water inlet pump (2), and thermal activation is performed in the sludge pyrolysis device at 80°C for 2 hours; III. Air intake: N2 is charged into the anaerobic fermentation system (5) for 3 to 5 minutes through the air intake valve (20) to remove oxygen in the reactor; IV. Anoxic stirring: Keep the sludge anaerobic fermentation system (5) in a closed state, and do not adjust the pH value during the whole process; turn on the stirrer (7), the stirring rate is 200-400 r / min, the fermentation temperature is 35±2°C, and the fermentation time is 7 days; Ⅴ Sedimentation: Set the sedimentation time to 20 to 30 minutes. This stage completes the mud-water separation process.

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