Sewage defluorination method for enhancing coagulative precipitation by using residual activated sludge microorganisms

Abstract

The invention relates to the technical field of sewage defluorination, and discloses a sewage defluorination method for enhancing coagulative precipitation by using residual activated sludge microorganisms, which comprises the following steps: (1) activated sludge microorganism adsorption; (2) removing fluorine by coagulating sedimentation and microbial flocculation; the method comprises the following steps: (1) a polymerization stage: adding a fluorine removal agent into a coagulative precipitation tank, and carrying out mixed reaction on the fluorine removal agent and fluoride, phosphate ions and the like in sewage to form a polymer; (2) a flocculation stage: adding cation PAM and activated sludge microorganisms into a coagulative precipitation tank, and further performing chemical flocculation and microbial flocculation; (3) a precipitation stage: chemical sludge and biological sludge generated in the coagulative precipitation tank are precipitated to realize sludge-water separation, and the sludge is discharged to a sludge storage tank; and (3) sludge dewatering. According to the method, the reutilization of residual activated sludge microorganisms of a sewage plant is realized, and the fluorine removal effect of a conventional coagulating sedimentation method is enhanced through adsorption of the activated sludge microorganisms on fluorides and microbial flocculation.

Description

Technical Field

[0001] The invention relates to a method for removing fluorine from sewage, in particular to a method for removing fluorine from sewage by utilizing residual activated sludge microorganisms to strengthen coagulation and sedimentation, and belongs to the technical field of sewage defluorine removal. Background Art

[0002] Fluoride-containing wastewater must be properly treated before it can be discharged, otherwise it will cause great harm to the natural environment and human health.

[0003] At present, the main fluorine removal technologies widely used in engineering are: chemical precipitation, coagulation sedimentation, adsorption, electrochemical method and ion exchange resin; as well as composite fluorine removal technology that combines the above processes.

[0004] Fluoride removal by coagulation and sedimentation is currently the most widely used defluoridation process. The coagulation and sedimentation method mainly involves adding aluminum salts and iron salts as coagulants to the fluoride-containing wastewater to hydrolyze it in the water, and then destabilizing it from fluoride ions by means of netting, sweeping, adsorption bridging, and electrical neutralization, and forming floccules for sedimentation, and then removing fluoride by solid-liquid separation. Compared with other process technologies, the coagulation and sedimentation method has a lower cost in the treatment of low-concentration fluoride-containing wastewater.

[0005] The adsorption method is to separate fluoride ions from water by adsorbing them through electrostatic action, complexation, ion exchange, etc. At present, the commonly used adsorbents mainly include various metal-based substances, minerals, industrial waste, biomass (activated carbon) and high molecular organic matter, and the adsorption capacity and suitable pH of different adsorbents vary significantly.

[0006] The above-mentioned defluorination method has a relatively high defluorination cost. Summary of the invention

[0007] In view of the shortcomings of existing sewage defluorination technologies, the present invention proposes a sewage defluorination method using excess activated sludge microorganisms to enhance coagulation and sedimentation, so as to reduce the load of the coagulation and sedimentation method, realize the resource utilization of excess activated sludge, and effectively reduce the defluorination cost.

[0008] The method for removing fluoride from sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation comprises the following steps:

[0009] (1) Activated sludge microbial adsorption:

[0010] ① Continuously put the activated sludge into the clarifier, add sodium acetate solution, adjust the pH of the solution in the clarifier to 7.7-7.9 or 8.0-8.1, and perform microbial adsorption of fluoride in the sewage;

[0011] ② Continuously discharge the adsorbed activated sludge microorganisms from the clarification tank to the sludge storage tank; the effluent from the clarification tank enters the coagulation sedimentation tank;

[0012] (2) Fluoride removal by coagulation and sedimentation combined with microbial flocculation:

[0013] ① In the polymerization stage, a defluoridating agent is added to the coagulation sedimentation tank, and the defluoridating agent reacts with fluoride, phosphate ions, etc. in the sewage to form a polymer;

[0014] ② In the flocculation stage, cationic PAM and activated sludge microorganisms are added to the coagulation sedimentation tank to further carry out chemical flocculation and microbial flocculation;

[0015] ③ In the sedimentation stage, the chemical sludge and biological sludge produced in the coagulation sedimentation tank are precipitated to achieve mud-water separation, and the sludge is discharged into the sludge storage tank.

[0016] (3) Sludge dewatering:

[0017] Cationic PAM is added to the sludge discharged into the sludge storage tank in steps (1) and (2), stirred to adjust the pH, and then dehydrated.

[0018] The activated sludge microorganisms in step (1)① are in liquid form and come from the residual activated sludge in the aerobic tank of the sewage treatment plant. The concentration is 30000mg / L to 34000mg / L or 35000mg / L to 39000mg / L, and the flow ratio of the activated sludge to the sewage is 3% when added.

[0019] The concentration of the sodium acetate solution in step (1) ① is 25% to 26%, and the addition ratio in the sewage is 20 mL / L.

[0020] The hydraulic retention time in step (1)① is 15 minutes.

[0021] The defluoridating agent in step (2) is a composite defluoridating agent of aluminum salt, and the aluminum salt content is 31-33%.

[0022] In step (2) ②, the cationic PAM is in liquid form (tap water is used for preparation), with a concentration of 0.25-0.28%, and a flow ratio of 0.33-0.36% to the sewage.

[0023] The flow ratio of activated sludge microorganisms to sewage in step (2) ② is 0.4%.

[0024] In the step (2), the polymerization reaction time of the defluoridating agent and the fluoride in the sewage is 5 to 7 minutes, the flocculation reaction time is 4 to 5 minutes, and the precipitation reaction time is 15 to 20 minutes.

[0025] The stirring and conditioning in step (3) refers to mechanical stirring and aeration stirring, and adjusting the pH to 7.6-8.0.

[0026] In the step (3), the storage time of the sludge in the sludge storage tank is less than 24 hours.

[0027] The present invention realizes the reuse of the residual activated sludge microorganisms in the sewage plant, strengthens the defluorination effect of the conventional coagulation and sedimentation method through the adsorption of fluoride by activated sludge microorganisms and microbial flocculation, reduces the use of defluoridation agents, and reduces production costs. And by strengthening the control measures of the sludge dehydration link, the endogenous release of fluoride in the sludge is avoided. While removing fluoride in sewage, the present invention has a synchronous removal effect on phosphate, heavy metal ions and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a schematic flow diagram of a method for removing fluoride from sewage by utilizing residual activated sludge microorganisms to enhance coagulation and sedimentation. DETAILED DESCRIPTION

[0029] like Figure 1 As shown, the method for defluoridating sewage by utilizing residual activated sludge microorganisms to enhance coagulation and sedimentation is as follows: residual activated sludge in an aerobic tank of a sewage treatment plant is added to a clarification tank, and fluoride in the sewage is adsorbed by microorganisms in the residual activated sludge; the sewage is then sequentially subjected to three stages of polymerization, flocculation and sedimentation for chemical defluoridation, a portion of residual activated sludge is added in the flocculation stage, and the flocculation effect is enhanced by biological synergistic flocculation; finally, the fluoride-containing sludge produced in the clarification tank and the sedimentation tank is dehydrated, and the sludge conditioning and dehydration process are controlled to prevent endogenous release of fluoride.

[0030] The specific process of defluorination of the present invention comprises the following steps.

[0031] 1. Activated sludge microbial adsorption

[0032] The residual activated sludge in the aerobic tank of the sewage treatment plant is continuously added to the clarifier at a concentration of 30000mg / L~34000mg / L or 35000mg / L~39000mg / L, and the ratio of the flow rate of sewage entering the clarifier is 3%. In this process, a sodium acetate solution with a concentration of 25%~26% is added to improve the activity of microorganisms. The amount of sodium acetate added relative to the amount of sewage treated is 20mL / L. At the same time, NaOH is added to adjust the pH of the solution in the clarifier to 7.7~7.9 or 8.0~8.1. The pH value of 8.0~8.1 can obtain the best fluoride adsorption capacity.

[0033] The hydraulic retention time in the clarifier is 15 minutes. After the activated sludge is saturated with adsorption, it is continuously discharged from the clarifier to the sludge storage tank; the effluent from the clarifier enters the coagulation sedimentation tank.

[0034] The floc structure of the activated sludge microbial flora and the rich functional groups carried by the flora have a strong adsorption capacity for fluoride. Fluoride-containing sewage is fully mixed with the activated sludge microorganisms in the clarification tank, adsorption occurs, and mud and water are separated in the sedimentation area of ​​the clarification tank. The fluoride concentration in the sewage is effectively reduced, and the fluoride enters the activated sludge microbial flora.

[0035] 2. Fluoride removal by coagulation and sedimentation combined with microbial flocculation

[0036] In the coagulation sedimentation tank, three stages of polymerization, flocculation and sedimentation are carried out. Fluoride in the sewage and the defluoridation agent first undergo polymerization reaction, and then chemical flocculation occurs in the flocculation stage. At the same time, the microbial flora contains a large amount of extracellular polymers that can synergistically produce microbial flocculation. In the sedimentation stage, mud and water are separated under the action of gravity, and the treated sewage is discharged.

[0037] (1) Aggregation stage

[0038] Add defluoridation agent to the coagulation sedimentation tank. The defluoridation agent is a composite defluoridation agent with aluminum salt content of 31-33%. The defluoridation agent reacts with fluoride and phosphate ions in the sewage to form a polymer. The polymerization reaction time of the defluoridation agent and the fluoride in the sewage is 5-7 minutes.

[0039] (2) Flocculation stage

[0040] Cationic PAM and activated sludge are added to the coagulation sedimentation tank for further chemical flocculation and microbial flocculation. Cationic PAM is in liquid form and is prepared with tap water at a concentration of 0.25-0.28%. The ratio of the flow rate of liquid cationic PAM added to the coagulation sedimentation tank to the flow rate of sewage entering the coagulation sedimentation tank through the clarification tank is 0.33-0.36%. The activated sludge is the same as the activated sludge and its concentration used in step 1, and the ratio of its addition flow rate to the flow rate of sewage entering the coagulation sedimentation tank through the clarification tank is 0.4%.

[0041] The flocculation reaction time in this stage is 4 to 5 minutes.

[0042] (3) Sedimentation stage

[0043] After the flocculation reaction, the sludge produced by the chemical reaction and biological reaction in the coagulation sedimentation tank is precipitated. The precipitation reaction time is 15 to 20 minutes. After the mud and water are separated, the sludge is discharged to the sludge storage tank.

[0044] 3. Sludge dewatering

[0045] The sludge produced in the clarification tank and sedimentation tank is first discharged into the sludge storage tank for less than 24 hours. Then NaOH is added to the sludge to adjust the pH to 7.6-8.0, and stirring and oxygenation measures are taken to prevent endogenous release of fluoride.

[0046] The dehydration is carried out using a dehydrator, and the fluoride is finally transferred to the dehydrated sludge for disposal. The dehydrator filtrate is returned to the water inlet for treatment.

[0047] When the defluoridation agent is used at a dosage of 0.25 ml / L (the defluoridation agent is a liquid with an aluminum salt content of 31% to 33%), the fluoride concentration in the effluent can be reduced to below 0.75 mg / L. At the same time, it also has a good removal effect on total phosphorus and heavy metals. The main components of the sewage before and after treatment are shown in Table 1.

[0048] Table 1 Main components of sewage before and after treatment

[0049]

Claims

1. A method for defluoridating sewage by using excess activated sludge microorganisms to enhance coagulation and sedimentation, characterized in that: The following steps are involved: (1) Activated sludge microbial adsorption: ① Continuously put the activated sludge into the clarifier, add sodium acetate solution, adjust the pH of the solution in the clarifier to 7.7-7.9 or 8.0-8.1, and perform microbial adsorption of fluoride in the sewage; ② Continuously discharge the adsorbed saturated activated sludge microorganisms from the clarification tank to the sludge storage tank; The effluent from the clarifier tank enters the coagulation sedimentation tank; (2) Fluoride removal by coagulation and sedimentation combined with microbial flocculation: ① In the polymerization stage, a defluoridating agent is added to the coagulation sedimentation tank, and the defluoridating agent reacts with the fluoride and phosphate ions in the sewage to form a polymer; ② In the flocculation stage, cationic PAM and activated sludge microorganisms are added to the coagulation sedimentation tank to further carry out chemical flocculation and microbial flocculation; ③ In the sedimentation stage, the chemical sludge and biological sludge produced in the coagulation sedimentation tank are precipitated to achieve mud-water separation, and the sludge is discharged to the sludge storage tank; (3) Sludge dewatering: Cationic PAM is added to the sludge discharged into the sludge storage tank in steps (1) and (2), stirred to adjust the pH, and then dehydrated.

2. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: The activated sludge microorganisms in step (1) ① are in liquid form, with a concentration of 30,000 mg / L to 34,000 mg / L or 35,000 mg / L to 39,000 mg / L, and the flow ratio of the activated sludge microorganisms to the sewage is 3% when added.

3. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: The concentration of the sodium acetate solution in step (1) ① is 25% to 26%, and the addition ratio in the sewage is 20 mL / L.

4. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: The hydraulic retention time in step (1)① is 15 minutes.

5. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: The defluoridating agent in step (2) is a composite defluoridating agent of aluminum salt, and the aluminum salt content is 31-33%.

6. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: In step (2)②, the cationic PAM is in liquid state, with a concentration of 0.25-0.28%, and a flow ratio of 0.33-0.36% to the sewage.

7. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: The flow ratio of activated sludge microorganisms to sewage in step (2) ② is 0.4%.

8. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: In the step (2), the polymerization reaction time of the defluoridating agent and the fluoride in the sewage is 5 to 7 minutes, the flocculation reaction time is 4 to 5 minutes, and the precipitation reaction time is 15 to 20 minutes.

9. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: The stirring and conditioning in step (3) refers to mechanical stirring and aeration stirring, and the pH is adjusted to 7.6-8.

0.

10. The method for defluoridating sewage by utilizing excess activated sludge microorganisms to enhance coagulation and sedimentation according to claim 1, characterized in that: In the step (3), the storage time of the sludge in the sludge storage tank is less than 24 hours.

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