Study On Hydrophilic And Electrophilic Modification Of Suspended Carriers And Their Enhanced Nitrogen And Phosphorus Removal Performance Of MBBR

The rapid development of industrialization in our country has brought about the takeoff of economic strength,and has also led to increasingly serious environmental pollution problems.Water resources are indispensable for human survival,and water environmental pollution can seriously affect human health.How to treat wastewater more timely and efficiently is an important environmental issue that urgently needs attention.Mobile bed biofilm reactor（MBBR）is a new and efficient sewage treatment technology,with carriers being the core of MBBR.Traditional carriers are mostly prepared from polymer materials such as polyethylene and polypropylene,which have obvious advantages in density and strength.However,the poor hydrophilicity and biological affinity of polyethylene materials on the surface make it difficult for microorganisms to adhere to the surface of the carriers,resulting in slow film formation during MBBR startup The sewage treatment effect is poor,and the nature of the carriers themself restricts their application in sewage treatment.Therefore,appropriate modification of the surface of the carriers to improve their hydrophilicity and electrophilicity can better meet the needs of sewage treatment.This article focuses on the issues of poor hydrophilicity,poor electrophilicity,and slow film formation speed of high-density polyethylene（HDPE）carriers.The carriers were successively modified with hydrophilicity and electrophilicity to improve their film formation performance and application effect in MBBR.Finally,an MBBR start-up optimization experiment was conducted to further improve the wastewater treatment efficiency of MBBR.Hydrophilic modification is the coating of nano Si O₂,polyvinyl alcohol（PVA）,polydopamine（PDA）and other materials on the surface of HDPE carriers by immersion coating to form a hydrophilic coating.Electrophilic modification is the coating of cationic polyacrylamide（CPAM）on the surface of the carriers based on the hydrophilic modified carriers,bringing a positive charge to the surface of the carriers to improve their electrophilicity.The single factor experiment was used to explore the optimal preparation conditions of hydrophilic and electrophilic modified carriers,and the contact angle,solid surface Zeta potential,SEM,FT-IR and XPS characterization of the modified carriers,as well as MBBR membrane formation startup experiment were carried out.The removal effect of the modified carriers on chemical oxygen demand（COD）,ammonia nitrogen（NH₃-N）,total nitrogen（TN）,total phosphorus（TP）in MBBR,as well as the membrane formation time,biofilm amount Changes in protein and polysaccharide content.The main conclusions are as follows:（1）Single factor experiments were conducted to explore the optimal preparation conditions for hydrophilic modified carriers by selecting four factors:the mass fraction of nano Si O₂,PVA/C₈H₁₁NO₂·HCl,reaction time,and reaction temperature.The hydrophilic modified carriers were characterized by SEM,FT-IR,and XPS.The SEM results showed that the surface of the modified carriers exhibited wrinkles,increased roughness,and enhanced hydrophilicity;The FT-IR and XPS results showed that the surface coating successfully coated nano Si O₂,PVA,PDA and other materials on the surface of HDPE carriers,introducing a C=O peak and increasing the peak area of O—H and C—O peaks,increasing the hydrophilic functional groups,and not changing the basic structure of the carriers.（2）The experimental results show that the optimal preparation conditions for hydrophilic modified carriers are 0.2%mass fraction of nano Si O₂,4:1PVA/C₈H₁₁NO₂·HCl,6 hours reaction time,and 50℃reaction temperature.The contact angle of the modified carriers decreased from 94.6°to 60.1°,and the coating time was advanced from 25 days to 16 days.The biomass,protein,and polysaccharide content were 42.8,8.8,and 5.8 mg·g^-1,respectively,which were 15.5,2.4,and 2.4 mg·g^-1higher than before the modification.The removal rates of COD,NH₃-N,TN,and TP were 94.9%,95.4%,83.5%,and 71.6%,respectively,which were9.3%,6.7%,13.7%,and 11.5%higher than before the modification.（3）Three factors,namely the mass fraction of CPAM,reaction time,and reaction temperature,were selected for single factor experiments to explore the optimal preparation conditions for hydrophilic and electrophilic modified carriers.FT-IR and XPS characterization were performed on hydrophilic and electrophilic modified carriers.The FT-IR characterization results showed that the basic structure of the modified carriers did not change and CPAM was successfully loaded on the surface of the carriers.XPS characterization results showed that the peak areas of C—OH and C—O on the surface of the modified carriers decreased,while the peak areas of C=O increased,further indicating that CPAM was successfully loaded on the surface of the carriers.（4）The experimental results show that the optimal preparation conditions for hydrophilic and electrophilic modified carriers are CPAM mass fraction of 0.2%,reaction time of 2 hours,and reaction temperature of 70℃.The surface Zeta potential of the modified carriers changed from-35.1 m V to+12.56 m V,and the coating time was advanced from 16 days to 12 days.The biofilm mass,protein,and polysaccharide content were 52.2,16.5,and 9.6 mg·g^-1,respectively,which were 9.4,6.8,and 3.8mg·g^-1higher than the hydrophilic modified carriers.The removal rates of COD,NH₃-N,TN,and TP were 95.7%,98.1%,85.1%,and 75.8%,respectively,which were0.8%,2.7%,1.6%,and 3.8%higher than before the modification.（5）Using a combination of single factor and orthogonal experiments,the effects of four factors,C/N,DO,HRT,and filling rate,on the wastewater treatment efficiency of MBBR start-up process were studied,and the optimal operating parameters for MBBR start-up were explored.The experimental results show that C/N,DO,HRT,and filling rate all have varying degrees of influence on the treatment efficiency of MBBR wastewater.After comprehensive consideration,the optimal parameter conditions are:C/N 20:1,DO 2～3 mg·L^-1,HRT 8 hours,and filling rate of 40%.