Performance Of MBBR-MBR Integrated Reactor In Treating Domestic Sewage

With the proposal of carbon peaking and carbon neutrality goals,our country pays more and more attention to the protection of ecological environment,and the effluent control of domestic sewage treatment is more stringent,whether it is large-scale urban sewage treatment plant or small rural decentralized domestic sewage treatment.Scholars are exploring more space-saving and effective treatment processes.Moving bed biofilm reactor（MBBR）has the advantages of small size,strong adaptability,stable and reliable operation,strong resistance to impact load,small production of excess sludge and so on.Membrane bioreactor（MBR）has many advantages,such as high treatment efficiency,stable effluent,strong resistance to impact load,low sludge output and so on.The two are combined to form the MBBR-MBR coupling process,which has the advantages of good treatment performance for pollutants,simple operation and installation and space saving,which are widely used in rural domestic sewage treatment.In this experiment,with common black polyurethane sponge（PU）and white porous polymer carriers（PPC）as fillers and flat ceramic membrane as membrane module,MBBR and flat ceramic membrane were combined in a reactor to form a new type of flat ceramic membrane-MBBR integrated reactor.The fluidization of the suspended filler can friction with the ceramic membrane under the action of aeration,and the friction process can make part of the unstable filter cake layer fall off and reduce the pollution.At the same time,friction will also accelerate the renewal of biofilm and play a screening role for microorganisms,while polyvinylidene fluoride film with lower strength may be deformed or damaged in the process of impact and friction.Through the start-up and commissioning of the reactor,the treatment effect and reaction mechanism of simulated domestic wastewater were explored,and the effects of filling rate（FR）,hydraulic retention time（HRT）and temperature on the treatment efficiency of integrated reactor and flat ceramic membrane fouling were explored.When other conditions remain the same,the comprehensive treatment effect is the best when the filling rate is 15%.When the filling rate is stable,the removal rates of COD,NH₄⁺-N and TN are 95.1%,89.5%and 60.7%,respectively.COD and NH₄⁺-N effluent meet the corresponding requirements of Grade An effluent standard of"Urban sewage treatment Plant Pollutant discharge Standard"（GB18918-2002）.The optimal filling rate is determined to be15%.Under the condition of 15%FR,the domestic sewage treatment effect of the new flat ceramic membrane-MBBR integrated reactor and the changes of parameters in the reactor were studied when the HRT was 12 h and 24 h respectively.The results showed that the COD removal rate,TN removal rate and SND performance of the reactor in HRT=24 h were higher than those in HRT=12 h.Under the condition of 15%HRT=24 h and 15%FR,the treatment effect of the new flat ceramic membrane-MBBR integrated reactor on domestic sewage at different temperatures（20℃,25℃and 30℃）was studied.It was found that it had no significant effect on the removal efficiency of COD,NH₄⁺-N and TN.After comprehensive comparison,the optimum temperature was determined to be 25℃.The fouling rate of flat ceramic membrane and the content of extracellular polymeric substances（EPS）and soluble microbial products（SMP）in the reactor were compared under different filling rates.It was found that the filler FR had a great influence on the transmembrane pressure difference of the membrane module,and the slowest membrane fouling rate reached the transmembrane pressure（TMP）difference 30k Pa in 22 days with filler FR=15%,which significantly alleviated the membrane fouling rate.The concentration of EPS and SMP in the mixture of each reactor increased with the increase of transmembrane pressure difference,and the value of SMPp/SMPc decreased with the increase of transmembrane pressure difference,but the concentrations of EPS and SMP were different among different reactors.Combined with the effect of filling rate on membrane fouling rate,it is inferred that EPS concentration and SMP concentration in the reactor are two important factors causing membrane fouling.Through the Fourier transform infrared spectrum analysis of the surface of the flat ceramic membrane before and after fouling,the composition and structure of the filter cake layer was determined,and it was verified that EPS and SMP in the reactor were the important factors causing membrane fouling.The difference of microbial community structure between activated sludge and suspended filler biofilm under different filling rates was compared to explore the reaction mechanism.At the gate level,it was found that the suspended sludge in the three reactors was similar to the main dominant bacteria on the biofilm.In addition,due to different types of microbial metabolism,the relative abundance of dominant bacteria in them is different,for example,the relative abundance of proteobacteria in suspended sludge microorganisms is higher than that in biofilm microorganisms,and the relative abundance of chloroflexi on biofilm is higher than that in suspended sludge.Different microflora have different functions,such as chloroflexi may help to degrade SMP,polysaccharides and cellular substances,and their increase may reduce membrane fouling.The same is true at the class level.The structure of microflora in different reactors is also different.It is the analysis and comparison of these microflora that explains part of the reason why the treatment efficiency of the reactor is different under different FR.A new type of flat ceramic membrane-MBBR integrated reactor is constructed.Through the start-up of the reactor and the debugging of three parameters,it is verified that the integrated reactor is feasible and scientific for simulating domestic sewage treatment,in order to provide useful reference for domestic sewage treatment.