Modification Method of Polyethylene Suspended Packing for Moving Bed Biofilm Reactor

Abstract

The present invention discloses a modification method for polyethylene suspension fillers used in a moving bed biofilm reactor. This method uses polyethylene fillers as the matrix. After treating the surface of the fillers with an acidic potassium dichromate mixed solution, it is immersed in an aqueous solution of a coupling agent (silane coupling agent KH-560, silane coupling agent KH-570, titanate coupling agent CS-311), and activated carbon powder and gelatin protein as modifiers are added, successfully loading activated carbon and gelatin protein onto the surface of the fillers. Based on conventional polyethylene fillers, after treating the surface with an acidic potassium dichromate mixed solution, the present invention utilizes the cross-linking reaction of the coupling agent with macromolecular compounds to make the surface of the fillers carry hydrophilic groups such as hydroxyl and carbonyl groups, providing favorable conditions for the rapid growth of microorganisms on the surface of the fillers and enhancing the film-forming effect of the fillers. During the sewage treatment process, it is superior to conventional fillers in terms of the film-forming speed of the fillers, the amount of biofilm, the tightness between the biofilm and the carrier, and the microbial activity, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage biological treatment and relates to a modification method of a polyethylene suspended filler used in a moving bed biofilm reactor (MBBR). Background Art

[0002] At present, among the traditional sewage treatment technologies in my country, the biochemical method mainly includes two types: activated sludge method and biofilm method. Compared with the traditional activated sludge method, the biofilm method has the advantages of less residual sludge and higher treatment efficiency; the MBBR process has the advantages of both traditional fluidized bed and biological contact oxidation method, becoming a new and efficient sewage treatment method. By adding a certain amount of suspended carriers to the reactor, the carriers are fluidized by aeration and water flow in the reaction tank, and then suspended activated sludge and attached biofilm are formed. This allows the moving bed biofilm to use the entire reactor space, giving full play to the advantages of both attached and suspended phase organisms, making them complement each other.

[0003] The key to the MBBR process is the suspended filler whose specific gravity is close to that of water and which can move freely with water under slight stirring. It has the advantages of large effective specific surface area, suitable for microbial adsorption and growth, strong applicability, and wide application range. It can be used for both organic matter removal and nitrogen and phosphorus removal. In addition, it has high processing load, small footprint, no sludge swelling and sludge reflux problems, and is resistant to shock loads, and has broader application prospects in industrial wastewater treatment.

[0004] At present, there are many types of suspended fillers produced on the market. The differences in filler materials, structures, and performances directly affect their treatment effects and also affect the investment cost of sewage treatment to a certain extent.

[0005] Polyethylene suspended filler is a common suspended filler on the market. It has a large specific surface area, no toxicity to microorganisms, long service life, and low price, which makes it have certain applications in the field of water treatment. However, its hydrophilicity and biocompatibility are poor, and the performance of biofilm carrier is poor. There are problems such as slow biofilm formation speed, small biofilm formation amount, low degree of close contact between biofilm and carrier, and poor microbial activity, which greatly limit the wide application of polyethylene filler in sewage treatment. Therefore, it is of great significance to develop hydrophilic polyethylene suspended filler with better microbial fixation effect and high pollutant treatment efficiency through modification. Summary of the invention

[0006] The present invention provides a method for modifying polyethylene suspension packing for a moving bed biofilm reactor. The conventional polyethylene packing on the market is modified by bonding macromolecules with a coupling agent. After modification, the surface of the packing has a certain amount of hydrophilic groups such as hydroxyl and carbonyl groups, and its hydrophilicity is significantly improved. Microorganisms are negatively charged, and the surface of ordinary packing is mostly negatively charged, resulting in a repulsive force between the microorganisms and the packing. By bonding macromolecules with a silane coupling agent, the surface of the modified packing is mostly positively charged, and the microorganisms and the packing attract each other due to opposite charges, thus improving the film-forming speed.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for modifying polyethylene suspension packing for a moving bed biofilm reactor, specifically including the following steps:

[0008] S1. At a temperature of 40°C - 60°C, soak the polyethylene packing in an acidic potassium dichromate solution for 2 - 4 h, then take it out, rinse the surface with water to remove the brown layer, and drain it.

[0009] S2. Put the drained polyethylene packing into a phosphate buffer solution and soak it for a period of time. Take it out and rinse it with water until the eluent is neutral, and then air-dry it naturally.

[0010] S3. Soak the air-dried polyethylene packing in a coupling agent hydrolysis solution at 25°C - 40°C and stir for 6 - 12 h. Then take out the packing and drain it, add it to a mixed solution of powdered activated carbon and gelatin protein, heat it to 25°C - 40°C, and stir for 18 - 36 h.

[0011] S4. Take out the packing, rinse it with water, and air-dry it naturally to obtain the polyethylene suspension packing for a moving bed biofilm reactor.

[0012] As a further improvement to the preparation method of the modified polyethylene MBBR suspension packing:

[0013] Preferably, the acidic potassium dichromate mixture is a mixed solution of sulfuric acid and potassium dichromate.

[0014] Preferably, the concentration of potassium dichromate contained in the acidic potassium dichromate mixture is 6 - 8 mol / L, and the concentration of sulfuric acid contained is 2 - 4 mol / L.

[0015] Preferably, the coupling agent in the coupling agent aqueous solution is one or a combination of two or more of silane coupling agent KH-560, silane coupling agent KH-570, and titanate coupling agent CS-311.

[0016] Preferably, the preparation method of the coupling agent hydrolysis solution is as follows: Mix the coupling agent: ethanol: water according to a mass ratio of 20:72:8, adjust the pH to 5.5 - 6.5, and hydrolyze for 10 - 20 min for later use.

[0017] Preferably, in the phosphate buffer solution in step S2, the concentration of phosphoric acid is 0.01 - 0.02 mol / L, and the soaking time of the polyethylene filler in it is 2 - 3 h.

[0018] Preferably, in the mixed solution of powdered activated carbon and gelatin protein in step S3, it contains 16 - 32 g / L of activated carbon and 2 - 4 g / L of gelatin protein.

[0019] The beneficial effects of the present invention compared with the prior art are as follows:

[0020] 1) The present invention provides a method for modifying a polyethylene MBBR (Moving Bed Biofilm Reactor) suspension filler, including the following steps:

[0021] Using a polyethylene filler as the matrix, treating the surface of the filler with an acidic potassium dichromate mixed solution, aiming to hydroxylate the surface of the filler, forming multiple hydroxyl groups on the surface of the polyethylene matrix, so as to perform dehydration condensation with the silane coupling agent;

[0022] Soaking the treated polyethylene filler in a phosphate buffer solution, aiming to adjust the pH of the polyethylene filler to neutral, avoiding excessive hydrolysis of the silane coupling agent when adding the modified filler to the silane coupling agent solution.

[0023] Soaking the polyethylene filler treated with the phosphate buffer solution in a coupling agent hydrolysis solution, and the coupling agent undergoes a surface dehydration reaction with the filler, increasing hydrophilic groups such as hydroxyl and carbonyl groups.

[0024] Then adding the polyethylene filler to the mixed solution of activated carbon powder and gelatin protein, successfully loading the activated carbon and gelatin protein on the surface of the filler. The increase in hydrophilic groups such as surface hydroxyl and carboxyl groups improves the hydrophilicity of the carrier, and due to the change in surface roughness and the number of charged groups, a large number of attachment sites are provided for microbial attachment. And according to the principle of opposite-sex attraction, microorganisms represented by nitrifying bacteria are more likely to adhere to the surface of the carrier, thus accelerating the formation of the biofilm and increasing the film-forming speed. Through the adsorption of pollutants by activated carbon, the adhesion of microorganisms on the surface of the filler is accelerated, and gelatin protein provides a carbon source for the nitrification and denitrification reactions inside the individual filler, better promoting the growth and reproduction of microorganisms.

[0025] 2) The present invention modifies conventional polyethylene fillers using a coupling agent. After modification, the filler surface is provided with a certain amount of hydrophilic groups such as hydroxyl and carbonyl groups, and the positive charge number on the surface increases significantly, and its hydrophilicity is significantly improved. Through the synergistic mechanism of the adsorption of activated carbon attached to the filler surface and the biodegradation of microorganisms, the degradation performance of the filler for pollutants in water can be effectively improved, thereby improving the sewage treatment effect. A large number of micropores in the activated carbon adsorb organic matter and oxygen in the wastewater, providing a high-concentration nutrient source for the growth and reproduction of the microbial community. Enzymes and coenzymes produced during the microbial metabolism process are adsorbed and enriched in the micropores of the activated carbon. In addition, due to the long contact time between the microorganisms and organic matter on the activated carbon, it is possible for the difficult-to-degrade organic matter to be decomposed by biological oxidation. In addition, with the help of the adsorption of activated carbon, gelatin protein is used as a carbon source supplement, and a large amount of organic matter is attached to the filler surface, providing favorable conditions for the rapid growth of microorganisms on the filler surface, thereby improving the film-forming speed and enhancing the film-forming effect. Detailed implementation mode

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail in conjunction with embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment provides a modification method for polyethylene suspension fillers used in MBBR (Moving Bed Biofilm Reactor), which specifically includes the following steps:

[0029] S1. Immerse the cake-shaped polyethylene filler (25×10mm) in an acidic potassium dichromate solution at 60°C for 3h. The acidic potassium dichromate solution is a mixed solution of sulfuric acid and potassium dichromate. The concentration of potassium dichromate in the mixed solution is 8mol / L, and the concentration of sulfuric acid is 3mol / L. Then take out the polyethylene filler and rinse the surface brown layer with water and drain it;

[0030] S2. Immerse the drained polyethylene filler in a 0.01mol / L phosphate buffer solution for 2h, and take it out and air-dry it naturally after the solution becomes neutral;

[0031] S3. Mix silane coupling agent KH-560, ethanol and water according to a mass ratio of 20:72:8 to prepare a coupling agent hydrolysis solution with a pH of 6.0. After hydrolysis for 15min, it is ready for use; Immerse the air-dried polyethylene filler in step S2 in the coupling agent hydrolysis solution at 40°C and stir for 12h, then take out the filler and drain it, and add it to a mixed solution of powdered activated carbon (concentration in the mixed solution is 24g / L) and gelatin protein (concentration in the mixed solution is 2g / L), heat to 37°C and stir for 24h;

[0032] S4. Take out the packing, rinse it with water and dry it naturally to obtain the modified packing for sewage treatment.

[0033] Take the unmodified packing as a control, and conduct the following tests on the modified packing and the unmodified packing respectively:

[0034] 1) After testing, the surface potential of the polyethylene packing changed from -20 mV before modification to 140 mV after modification.

[0035] 2) Place the modified packing in the MBBR reactor for the biofilm formation experiment. Rotifers, Vorticellas, etc. appeared in the modified packing after 7 days, indicating the completion of biofilm formation, while it took 14 days for the unmodified packing to complete biofilm formation.

[0036] Analysis of the immobilized biomass of the modified polyethylene packing and the unmodified polyethylene showed that the immobilized biomass after modification could be increased by 18%, and the biofilm formation amount increased significantly.

[0037] 3) Use the above-prepared modified packing in the MBBR reactor. The hydraulic retention time (HRT) is set at 4 h. The concentrations of COD and ammonia nitrogen in the sewage are reduced from 397.4 and 48.6 mg / L to 23.5 and 4.3 mg / L respectively, and the removal rates of COD and ammonia nitrogen are 94.08% and 91.2% respectively.

[0038] Under the same conditions, the removal rates of COD and ammonia nitrogen using the unmodified polyethylene packing are 85.08% and 80.32% respectively. It can be seen that the removal rates of COD and ammonia nitrogen of the modified polyethylene packing are significantly improved.

[0039] Example 2

[0040] This example provides a modification method for polyethylene suspension packing used in MBBR (Moving Bed Biofilm Reactor), which specifically includes the following steps:

[0041] S1. Immerse the cake-shaped polyethylene packing (25×10 mm) in a 60°C acidic potassium dichromate solution for 2 h. The acidic potassium dichromate solution is a mixed solution of sulfuric acid and potassium dichromate. The concentration of potassium dichromate in the mixed solution is 6 mol / L, and the concentration of sulfuric acid is 3 mol / L. Then take out the polyethylene packing, rinse off the brown layer on the surface with water and drain it;

[0042] S2. Immerse the drained polyethylene packing in a 0.01 mol / L phosphate buffer solution for 2.5 h, and take it out and dry it naturally after the solution becomes neutral;

[0043] S3. Mix silane coupling agent KH-570, ethanol and water in a mass ratio of 20:72:8 to prepare a coupling agent hydrolysis solution with a pH of 6.0. Let it stand for 15 minutes after hydrolysis and then use it. Immerse the air-dried polyethylene filler in the coupling agent hydrolysis solution at 40°C and stir for 12 hours. Take out the filler, drain it, and add it to a mixed solution of powdered activated carbon (concentration in the mixed solution is 8 g / L) and gelatin protein (concentration in the mixed solution is 2 g / L). Heat to 37°C and stir for 18 hours.

[0044] S4. Take out the filler, rinse it with water, and let it air-dry naturally to obtain a modified filler for sewage treatment.

[0045] Take the unmodified filler as a control and conduct the following tests on the modified filler and the unmodified filler respectively:

[0046] 1) After testing, the surface potential of the polyethylene filler changed from -20 mV before modification to 1168 mV after modification.

[0047] 2) Place the filler in the reactor for a biofilm formation experiment. Rotifers and Vorticella appeared on the modified filler on the 11th day, indicating the completion of biofilm formation, while the unmodified filler took 14 days to complete biofilm formation.

[0048] Analysis of the immobilized biomass of the modified polyethylene filler and the unmodified polyethylene found that the immobilized biomass after modification could be increased by 22%, and the biofilm formation amount increased significantly.

[0049] 3) Use the modified filler prepared above in the MBBR reactor. Set the HRT to 6 h. The concentrations of COD and ammonia nitrogen in the sewage decreased from 600 and 65.4 mg / L to 45.12 and 6.3 mg / L respectively. The removal rates of COD and ammonia nitrogen were 92.48% and 90.4% respectively.

[0050] Under the same conditions, the removal rates of COD and ammonia nitrogen using the unmodified polyethylene filler were 88.65% and 82.38% respectively. It can be seen that the removal rates of COD and ammonia nitrogen of the modified polyethylene filler were significantly improved.

[0051] Example 3

[0052] This example provides a method for modifying a polyethylene suspension filler for MBBR (Moving Bed Biofilm Reactor), which specifically includes the following steps:

[0053] S1. Immerse the cake-shaped polyethylene filler (25×10 mm) in an acidic potassium dichromate solution at 50°C for 4 hours. The acidic potassium dichromate solution is a mixed solution of sulfuric acid and potassium dichromate. The concentration of potassium dichromate in the mixed solution is 8 mol / L, and the concentration of sulfuric acid is 3 mol / L. Then take out the polyethylene filler, rinse off the brown layer on the surface with water, and drain it.

[0054] S2. Immerse the drained filler in a 0.01 mol / L phosphate buffer solution for 3 h, take it out and air-dry it naturally after the solution becomes neutral.

[0055] S3. Mix silane coupling agent CS-311, ethanol and water in a mass ratio of 20:72:8 to prepare a coupling agent hydrolysis solution with a pH of 6.0. After hydrolysis for 15 min, it is ready for use. Immerse the air-dried polyethylene filler in the coupling agent hydrolysis solution at 40 °C and stir for 12 h. Take out the filler and drain it, then add it to a mixed solution of powdered activated carbon (with a concentration of 24 g / L in the mixed solution) and gelatin protein (with a concentration of 2 g / L in the mixed solution), heat to 37 °C and stir for 24 h.

[0056] S4. Take out the filler, rinse it with water and air-dry it naturally to obtain a modified filler for sewage treatment.

[0057] Take the unmodified filler as a control, and conduct the following tests on the modified filler and the unmodified filler respectively:

[0058] 1) After testing, the surface potential of the polyethylene filler changed from -20 mV before modification to 200 mV after modification.

[0059] 2) Place the filler in the reactor for a biofilm formation experiment. Rotifers and Vorticellas appeared on the modified filler after 10 d, indicating the completion of biofilm formation, while the unmodified filler took 14 d to complete biofilm formation.

[0060] Analysis of the fixed biomass of the modified polyethylene filler and the unmodified polyethylene found that the fixed biomass after modification could be increased by 20%, and the biofilm formation amount increased significantly.

[0061] 4) Use the above-prepared modified filler in the MBBR reactor, set the HRT to 4 h, and the concentrations of COD and ammonia nitrogen in the sewage decreased from 226 and 25.44 mg / L to 11.11 and 0.88 mg / L respectively. The removal rates of COD and ammonia nitrogen were 95.08% and 96.55% respectively.

[0062] Under the same conditions, the removal rates of COD and ammonia nitrogen using the unmodified polyethylene filler were 83.2% and 84.32% respectively. It can be seen that the removal rates of COD and ammonia nitrogen of the modified polyethylene filler are significantly improved.

[0063] Those skilled in the art should understand that the above are only several specific embodiments of the present invention, rather than all embodiments. It should be noted that many variations and improvements can be made for those of ordinary skill in the art. All variations or improvements that do not exceed the scope of the claims should be regarded as the protection scope of the present invention.

Claims

1. A method for modifying a polyethylene suspension packing for a moving bed biofilm reactor, characterized in that, it comprises the following steps: S1. At a temperature of 40°C - 60°C, soak the polyethylene packing in an acidic potassium dichromate solution for 2 - 4 h for treatment, then take it out, rinse the surface brown layer with water and drain it; S2. Put the drained polyethylene packing into a phosphate buffer solution and soak it for a period of time, take it out, rinse it with water until the eluent is neutral, and then air-dry it naturally; S3. Soak the air-dried polyethylene packing in a coupling agent hydrolysis solution at 25°C - 40°C and stir for 6 - 12 h, then take out the packing and drain it, add it to a mixed solution of powdered activated carbon and gelatin protein, heat it to 25°C - 40°C and stir for 18 - 36 h; The preparation method of the coupling agent hydrolysis solution is as follows: Mix the coupling agent: ethanol: water in a mass ratio of 20:72:8, adjust the pH to 5.5 - 6.5, hydrolyze for 10 - 20 min and then use it. The coupling agent is one or a combination of two or more of silane coupling agent KH-560, silane coupling agent KH-570, and titanate coupling agent CS-311; The mixed solution of powdered activated carbon and gelatin protein contains 16 - 32 g / L of activated carbon and 2 - 4 g / L of gelatin protein; S4. Take out the packing, rinse it with water and then air-dry it naturally to obtain the polyethylene suspension packing for the moving bed biofilm reactor.

2. The method for modifying a polyethylene suspension packing for a moving bed biofilm reactor according to claim 1, characterized in that, the acidic potassium dichromate solution is a mixed solution of sulfuric acid and potassium dichromate.

3. The method for modifying a polyethylene suspension packing for a moving bed biofilm reactor according to claim 2, characterized in that, the concentration of potassium dichromate contained in the acidic potassium dichromate solution is 6 - 8 mol / L, and the concentration of sulfuric acid contained is 2 - 4 mol / L.

4. The method for modifying a polyethylene suspension packing for a moving bed biofilm reactor according to claim 1, characterized in that, in step S2, the concentration of phosphoric acid in the phosphate buffer solution is 0.01 - 0.02 mol / L, and the soaking time of the polyethylene packing in it is 2 - 3 h.