Microbial enhanced tail water purification process

Abstract

The invention discloses a microorganism-enhanced tail water purification process which comprises the following steps: S1, tail water of a sewage treatment plant is introduced into an ecological pond through a diversion pipe network, and the tail water is first-grade A standard effluent of a municipal sewage treatment plant; s2, floating plants and submerged plants are planted in the ecological pond, a first type of efficient compound microbial agent is added, and the first type of efficient compound microbial agent comprises acid-producing bacteria, ammonifying bacteria and phosphorus adsorption bacteria; s3, the tail water pretreated in S2 sequentially enters first-stage to eighth-stage vertical subsurface flow wetlands, the subsurface flow wetlands are filled with composite filler systems, emergent aquatic plants are planted, second-class efficient compound microbial agents are added, and the second-class efficient compound microbial agents comprise nitrifying bacteria, denitrifying bacteria and phosphorus-accumulating bacteria; s4, effluent of the subsurface flow wetland enters the surface flow wetland, and the effluent is discharged into a receiving water body after reaching the surface water class IV standard. Through pretreatment of the ecological pond, enhanced purification of the multi-stage subsurface flow wetland and deep purification of the surface flow wetland, efficient removal of tail water pollutants is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tail water purification, and particularly relates to a microbial reinforced tail water purification process. BACKGROUND

[0002] With the rapid development of social economy, the construction scale of urban sewage treatment plants is continuously expanded, but the water environment problems caused by the tail water discharge of sewage treatment plants are increasingly prominent. According to the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2018), the indexes of ammonia nitrogen, total phosphorus and COD in the tail water of the first A standard are not more than 5 mg / L, 0.5 mg / L and 50 mg / L respectively, which is equivalent to the level of surface water of inferior V class, while the water function zoning of many receiving water bodies requires to reach the surface water of class III or even higher standards, resulting in that the tail water still causes great pollution pressure to the water body after being discharged.

[0003] At present, the tail water advanced purification technology mainly includes artificial wetland method, advanced filtration method, advanced oxidation method and the like. Among them, the artificial wetland method is widely applied due to low cost and good ecological benefits, but the traditional artificial wetland has obvious defects: first, the purification efficiency is limited, the removal rate of low concentration pollutants is insufficient, and it is difficult to improve the tail water of the first A standard to the surface water of class IV and above; second, the anti-shock load capacity is weak, and is greatly affected by the water quality fluctuation of the influent; third, the microbial community structure is unstable, and the naturally domesticated microorganisms have poor targeting for the degradation of specific pollutants; fourth, the adsorption capacity of the filler is limited, and saturation is easy to occur after long-term operation, resulting in the attenuation of the treatment effect. Although the advanced filtration method and the advanced oxidation method can realize efficient purification, they have problems of high investment cost, large operation energy consumption and complex maintenance, and are not suitable for small towns and basin tail water treatment projects.

[0004] Therefore, it is an urgent need to develop a tail water advanced purification technology with high purification efficiency, strong anti-shock capacity and low operation cost to solve the tail water pollution problem of sewage treatment plants. SUMMARY

[0005] The present application aims to provide a microbial reinforced tail water purification process, which realizes efficient removal of tail water pollutants by combining the synergistic effect of microbial inoculants and composite fillers through ecological pond pretreatment, multi-stage subsurface flow wetland reinforced purification and surface flow wetland advanced purification.

[0006] In order to achieve the above purpose, the present application provides the following technical scheme: A microbial reinforced tail water purification process, S1, tail water diversion: introducing the tail water of a sewage treatment plant into an ecological pond through a diversion pipe network, wherein the tail water is the first A standard effluent of an urban sewage treatment plant; S2, ecological pond pretreatment: aquatic plants and submerged plants are planted in the ecological pond, and a first type of high-efficiency composite microbial agent is added, the first type of high-efficiency composite microbial agent comprising acid-producing bacteria, ammonifying bacteria and phosphorus adsorption bacteria; S3, multi-stage subsurface flow wetland purification: the tail water after S2 pretreatment enters a first-stage to an eighth-stage vertical subsurface flow wetland in turn, the subsurface flow wetland is filled with a composite filler system and planted with emergent plants, and a second type of high-efficiency composite microbial agent is added, the second type of high-efficiency composite microbial agent comprising nitrifying bacteria, denitrifying bacteria and phosphorus accumulating bacteria; S4, surface flow wetland deep purification: the effluent of the subsurface flow wetland enters the surface flow wetland, and the effluent reaches the Class IV standard of surface water and is discharged into a receiving water body.

[0007] The working principle and beneficial effects of the present application are as follows: S1, the guide pipe network provides a stable conveying channel for the tail water, avoiding the influence of hydraulic impact on the subsequent treatment effect; in S2, the aquatic plants and submerged plants absorb the nitrogen and phosphorus nutrients in the tail water through the root system, and at the same time, they secrete coagulation aids to promote the sedimentation of colloidal pollutants; in the first type of high-efficiency composite microbial agent, the acid-producing bacteria decompose macromolecular organic matter into small-molecular organic acids to provide carbon sources, the ammonifying bacteria convert organic nitrogen into inorganic ammonia nitrogen, and the phosphorus adsorption bacteria convert soluble phosphorus into solid phosphorus through metabolic action, thereby achieving the pretreatment cooperatively; in S3, in the multi-stage subsurface flow wetland, the composite filler system adsorbs ammonia nitrogen and phosphorus through ion exchange and chemical precipitation, the root system of the emergent plants supplies oxygen to form anoxic, anoxic and anaerobic alternating regions, and in the second type of high-efficiency composite microbial agent, the nitrifying bacteria convert ammonia nitrogen into nitrate nitrogen, the denitrifying bacteria reduce the nitrate nitrogen to nitrogen gas for release, and the phosphorus accumulating bacteria complete the absorption and release of phosphorus in the anoxic and aerobic alternating environment, thereby achieving efficient removal of pollutants; in S4, the surface flow wetland cooperates with the water plants and microorganisms to achieve deep purification of residual pollutants, and finally the effluent reaches the Class IV standard of surface water.

[0008] As a preferred embodiment, the composite filler system comprises, from top to bottom, a planting soil layer, a 2-5mm gravel main layer, a 5-10mm gravel transition layer and a 10-15mm gravel drainage layer, and the total height of the filler is 1.75-1.8m, wherein the gravel main layer is added with calcium-based modified zeolite and iron oxide modified ceramsite, and the mass ratio is 20%-30% and 15%-25%, respectively.

[0009] As a preferred embodiment, the adding concentration of the first type of high-efficiency composite microbial agent is 10 6 -10 7 CFU / L, and the adding concentration of the second type of high-efficiency composite microbial agent is 10 7 -10 8 CFU / L, the microbial agent is added continuously and intermittently, and the intermittent adding period is 7-10 days.

[0010] As a preferred, the floating plants in the ecological pond include Eichhornia crassipes and Nymphaea, and the planting density is 3-5 plants / m 2 ; the submerged plants include Elodea and Ceratophyllum, and the planting density is 8-10 plants / m 2 ; the emergent plants in the subsurface flow wetland include Typha latifolia, Acorus, Iris, and Canna, and the planting density is 9-12 plants / m 2 ; the aquatic plants in the surface flow wetland include Sagittaria and Phragmites, and the planting density is 3-4 plants / m 2 .

[0011] As a preferred, the hydraulic retention time of the ecological pond is 5-8 days, the total hydraulic retention time of the multi-stage subsurface flow wetland is 2-3 days, and the hydraulic retention time of the surface flow wetland is 2-3 days.

[0012] As a preferred, in the second type of high-efficiency composite microbial agent, the mass ratio of nitrifying bacteria, denitrifying bacteria and phosphorus accumulating bacteria is 3:4:3, wherein the nitrifying bacteria include Nitrosomonas and Nitrobacter, the denitrifying bacteria include Pseudomonas and Denitrifying bacteria, and the phosphorus accumulating bacteria include Acinetobacter and Aeromonas.

[0013] As a preferred, in the first type of high-efficiency composite microbial agent, the mass ratio of acid-producing bacteria, ammonifying bacteria and phosphorus adsorbing bacteria is 4:3:3, wherein the acid-producing bacteria include Lactobacillus and Acetobacter, the ammonifying bacteria include Bacillus and Proteobacteria, and the phosphorus adsorbing bacteria include Pseudomonas and Arthrobacter. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a flow chart of the microbial enhanced tail water purification process of the application. DETAILED DESCRIPTION

[0015] The following will be further described in detail through specific embodiments: Reference Figure 1 , Embodiment: A microbial enhanced tail water purification process, comprising the following steps: S1, tail water diversion: introducing the tail water of a sewage treatment plant into an ecological pond through a diversion pipe network, and the tail water is the first level A standard effluent of a municipal sewage treatment plant; S2, ecological pond pretreatment: planting floating plants and submerged plants in the ecological pond, and adding a first type of high-efficiency composite microbial agent, which contains acid-producing bacteria, ammonifying bacteria and phosphorus adsorbing bacteria; the floating plants in the ecological pond include Eichhornia crassipes and Nymphaea, and the planting density is 3-5 plants / m 2 ; the submerged plants include Elodea and Ceratophyllum, and the planting density is 8-10 plants / m 2, the mass ratio of the first type of high-efficiency composite microbial agent, acid-producing bacteria, ammonifying bacteria and phosphorus adsorption bacteria is 4:3:3, wherein the acid-producing bacteria include Lactobacillus and Acetobacter, the ammonifying bacteria include Bacillus and Proteus, and the phosphorus adsorption bacteria include Pseudomonas and Arthrobacter, and the dosing concentration is 10 6 ~ 10 7 CFU / L, and the dosing mode is a combination of continuous dosing and intermittent dosing, and the intermittent dosing period is 7-10 days. S3, multi-stage subsurface flow wetland purification: the tail water after S2 pretreatment enters the first to eighth vertical subsurface flow wetlands in turn, the subsurface flow wetland is filled with a composite filler system, emergent plants are planted, and the second type of high-efficiency composite microbial agent is added, and the second type of high-efficiency composite microbial agent includes nitrifying bacteria, denitrifying bacteria and phosphorus accumulating bacteria. The composite filler system is composed of, from top to bottom, a planting soil layer, a 3mm gravel main layer, a 7mm gravel transition layer and a 12mm gravel drainage layer, and the total height of the filler is 1.8m, wherein the calcium-based modified zeolite and the iron oxide modified ceramsite are added to the gravel main layer, and the mass ratio is 25% and 20% respectively.

[0016] The emergent plants in the subsurface flow wetland include Cyperus alternifolius, Acorus gramineus, Iris, and Canna indica, and the planting density is 9-12 plants / m 2 . In the second type of high-efficiency composite microbial agent, the mass ratio of nitrifying bacteria, denitrifying bacteria and phosphorus accumulating bacteria is 3:4:3, wherein the nitrifying bacteria include Nitrosomonas and Nitrobacter, the denitrifying bacteria include Pseudomonas and Denitrifying bacteria, and the phosphorus accumulating bacteria include Acinetobacter and Aeromonas, and the dosing concentration of the second type of high-efficiency composite microbial agent is 10 7 ~ 10 8 CFU / L, and the dosing mode is a combination of continuous dosing and intermittent dosing, and the intermittent dosing period is 7-10 days. S4, surface flow wetland deep purification: the effluent of the subsurface flow wetland enters the surface flow wetland, and the effluent reaches the Class IV standard of surface water before being discharged into the receiving water body, and the surface flow wetland is planted with aquatic plants including Alocasia, and the planting density is 3-4 plants / m 2 .

[0017] In a preferred scheme, the hydraulic retention time of the ecological pond is 7 days, the total hydraulic retention time of the multi-stage subsurface flow wetland is 3 days, and the hydraulic retention time of the surface flow wetland is 2 days.

[0018] The preparation of calcium-based modified zeolite is as follows: Take 200g of calcium chloride with an electronic balance, add 1000mL of deionized water, put it in a constant temperature water bath, set the temperature to 60℃, start the electric stirrer (speed 500r / min) and stir for 30min until the calcium chloride is completely dissolved, get a modified calcium chloride solution with a mass concentration of 20%, keep it warm for later use. Take 500g of pretreated natural zeolite, slowly add the above modified calcium chloride solution, make sure the zeolite is completely immersed. Adjust the stirring speed to 300r / min, continue stirring at 60℃ for 2h, observe the mixing state every 30min to avoid the zeolite from settling. After stopping stirring, keep it at 60℃ for 4h to allow the calcium ions to fully exchange with the sodium ions and potassium ions on the surface of the zeolite, enhancing the selective adsorption sites of the zeolite for ammonia nitrogen. Take out the aged zeolite, rinse it repeatedly with deionized water until the conductivity of the rinse water is ≤50μS / cm (measured by conductivity meter), remove the residual calcium chloride solution on the surface. Put the washed zeolite into a vacuum drying oven, set the temperature to 110℃ and the vacuum degree to-0.08MPa, dry for 6h to stabilize the internal pore structure of the zeolite. Take it out after drying, cool it to room temperature naturally, and screen out the 2-5mm particles with a sieve machine, you get the calcium-based modified zeolite.

[0019] The preparation of iron oxide modified ceramsite is as follows: Take 600g of clay, 300g of fly ash and 100g of coal powder according to the mass ratio of 6:3:1, put them into a planetary ball mill, add 200mL of deionized water, ball mill for 30min until the mixture is uniform, get a fine base material slurry. Take 150g of ferrous sulfate and dissolve it in 500mL of deionized water, stir and dissolve, then transfer it into a constant temperature water bath, heat to 50℃; slowly add 80g of sodium hydroxide, stir (speed 400r / min) while adding, adjust the pH value to 10, continue stirring for 1h, generate ferrous hydroxide suspension, then keep it warm for 3h until the suspension turns reddish brown, get the iron oxide (mainly iron hydroxide) modified solution. Transfer the base material slurry into a kneader, slowly add the iron oxide modified solution, knead for 40min to make the iron oxide evenly dispersed in the base material, form a plastic mud with water content of about 35% (it should be easy to form a ball and not to scatter when dropped). Put the plastic mud into an extrusion granulator, extrude and granulate through a 2-5mm aperture die, get cylindrical particles, place them in the air for 24h to dry, remove the surface moisture. Put the dried particles into a muffle furnace, set the temperature program: from room temperature to 300℃ (heating rate 5℃ / min), keep it at 300℃ for 1h to remove organic matter; continue to heat to 850℃ (heating rate 10℃ / min), keep it at 850℃ for 2h to sinter the particles and make the iron oxide firmly combined with the base material; then cool it to room temperature naturally, you get the iron oxide modified ceramsite.

[0020] The water quality indexes of the influent are shown in Table 1 below:

[0021] The following groups are set: Experimental group (G1): complete process, i.e. ecological pond (adding first type of bacterial agent + specified plants) + 8-stage subsurface flow wetland (composite filler + specified emergent plants + second type of bacterial agent) + surface flow wetland (specified plants), hydraulic retention time: ecological pond 7 days, subsurface flow wetland total 3 days, surface flow wetland 2 days.

[0022] Control group 1 (G2): process same as G1, no first type of bacterial agent added to ecological pond, no second type of bacterial agent added to subsurface flow wetland.

[0023] Control group 2 (G3): common filler group, process same as G1, but filler of subsurface flow wetland is single 3mm gravel (without adding calcium-based modified zeolite and iron oxide modified ceramsite).

[0024] Control group 3 (G4): single wetland group, process is ecological pond + 1-stage subsurface flow wetland + surface flow wetland, other parameters same as G1.

[0025] Water samples are collected daily at the influent inlet (S0), outlet (S1) of the ecological pond, outlet (S2) of the subsurface flow wetland and outlet (S3) of the surface flow wetland of each device, and the concentrations of COD, ammonia nitrogen and total phosphorus are determined; microbial amount on the surface of the filler of the subsurface flow wetland of each group is determined every 10 days (using the spread plate method); and the biomass (fresh weight) of the plants is determined after the experiment. The average values of the water quality indexes at S0 (influent), S1 (outlet of the ecological pond), S2 (outlet of the subsurface flow wetland) and S3 (outlet of the surface flow wetland) of each group are shown in Table 2 (unit: mg / L):

[0026] As can be seen from Table 2, through pretreatment by the ecological pond, enhanced purification by the multi-stage subsurface flow wetland and advanced purification by the surface flow wetland, combined with the synergistic effect of the microbial bacterial agent and the composite filler, efficient removal of pollutants in the tail water is achieved.

[0027] It should be noted that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect of the implementation and the practicality of the patent. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation modes and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A microbial-enhanced wastewater purification process, characterized in that, Includes the following steps: S1. Tailwater diversion: The effluent from the sewage treatment plant is introduced into the ecological pond through a diversion pipeline network. The effluent is Class A standard effluent from the urban sewage treatment plant. S2. Ecological pond pretreatment: Plant floating and submerged plants in the ecological pond and add the first type of high-efficiency compound microbial agent, which includes acid-producing bacteria, ammonifying bacteria and phosphorus-adsorbing bacteria. S3, Multi-stage Subsurface Flow Wetland Purification: The effluent after S2 pretreatment enters the first to eighth stage vertical subsurface flow wetlands in sequence. The subsurface flow wetlands are filled with a composite filler system, planted with emergent plants, and dosed with a second type of high-efficiency composite microbial agent, which includes nitrifying bacteria, denitrifying bacteria and polyphosphate-accumulating bacteria. S4. Deep purification of surface flow wetlands: The effluent from the subsurface flow wetland enters the surface flow wetland, and the effluent is discharged into the receiving water body after meeting the Class IV standard for surface water.

2. The microbial enhanced effluent purification process according to claim 1, characterized in that, The composite filler system consists of a planting soil layer, a 2-5mm gravel main layer, a 5-10mm gravel transition layer, and a 10-15mm gravel drainage layer, from top to bottom. The total height of the filler is 1.75-1.8m. Calcium-modified zeolite and iron oxide-modified ceramsite are added to the gravel main layer, with a mass ratio of 20%-30% and 15%-25%, respectively.

3. The microbial enhanced effluent purification process according to claim 2, characterized in that, The dosage concentration of the first type of high-efficiency compound microbial agent is 10. 6 ~10 7 CFU / L, the dosage concentration of the second type of high-efficiency compound microbial agent is 10. 7 ~10 8 The concentration of CFU / L and the inoculant dosage method is a combination of continuous and intermittent dosing, with the intermittent dosing cycle being 7 to 10 days.

4. The microbial enhanced effluent purification process according to claim 3, characterized in that, The floating plants in the ecological pond include water hyacinth and water lily, with a planting density of 3-5 plants / m². 2 Submerged plants include Elodea nuttallii and Ceratophyllum demersum, with a planting density of 8–10 plants / m². 2 Emergent plants in the subsurface flow wetland include umbrella sedge, sweet flag, iris, and canna, with a planting density of 9–12 plants / m². 2 The aquatic plants in the surface flow wetland include arrowhead and reed, with a planting density of 3-4 plants / m². 2 .

5. The microbial enhanced effluent purification process according to claim 4, characterized in that, The hydraulic retention time of the ecological pond is 5 to 8 days, the total hydraulic retention time of the multi-stage subsurface flow wetland is 2 to 3 days, and the hydraulic retention time of the surface flow wetland is 2 to 3 days.

6. The microbial enhanced effluent purification process according to claim 5, characterized in that, In the second type of high-efficiency compound microbial agent, the mass ratio of nitrifying bacteria, denitrifying bacteria and polyphosphate-accumulating bacteria is 3:4:

3. The nitrifying bacteria include Nitrosomonas and Nitrobacterium, the denitrifying bacteria include Pseudomonas and Denitrifying Bacteria, and the polyphosphate-accumulating bacteria include Acinetobacter and Aeromonas.

7. The microbial enhanced effluent purification process according to claim 6, characterized in that, In the first type of high-efficiency compound microbial agent, the mass ratio of acid-producing bacteria, ammonifying bacteria and phosphorus-adsorbing bacteria is 4:3:

3. The acid-producing bacteria include Lactobacillus and Acetobacter, the ammonifying bacteria include Bacillus and Proteus, and the phosphorus-adsorbing bacteria include Pseudomonas and Arthrobacter.

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