Biofilm Succession On The Support Materials Of Dynamic Membrane Bioreactor And Its Effect On Filtration Behavior

Dynamic membrane bioreactor(DMBR)is a kind of membrane bioreactor which uses the dynamic biofilm layer formed on the large pore support materials to achieve the solid-liquid separation.Unlike polymer membranes,the biofilm layer on the support material is mainly composed of microorganisms and its extracellular polymer substances(EPS),which is a"living"membrane,and its microbial community can change with operating conditions.In turn,it will affect the filtration behavior of DMBR,such as the effect on solid-liquid separation,flux and hydraulic resistance.This study analyzes the filtration performance,composition and structure of the biofilms on the surface of the support materials,and then reveals the affect of biofilm succession on the filtration behavior.Firstly,during the start-up experiment,nylon mesh with a pore size of 25?m was used as support materials,DMBR was operated to treat synthetic wastewater.Then the DMBR was used to treat the actual domestic wastewater for long-term experiment to further study the biofilm succession process and its effect on the filtration behavior.Finally,the DMBR was used to treat the actual domestic wastewater steadily,and the effluent water quality of the dynamic membrane and the microfiltration membrane was compared in the same reactor.The main findings of study are as follows:(1)During the start-up period,the composition and structure of the biofilm microbial community on the support materials in DMBR will change,which will further affect the filtration resistance.When DMBR was started to treat simulated domestic wastewater,the filtration resistance increased rapidly at the first and decreased to a lower level without any cleaning spontaneously.With the operation and the decrease of the F/M ratio of reactor,the microbial community of the biofilm had changed significantly,and the permeability of the biofilm was higher.As a result,the DMBR was operated with a high flux of 42 L/m~2·h and a low pressure of 0.1 k Pa.The low EPS content in the biofilm reduced the filtration resistance of the biofilm,and the lower F/M ratio could form a looser and porous biofilm.The succession of the dominant bacteria in different periods made the biofilms change in composition and structure,these all affected the filtration resistance of the biofilms.(2)Due to the change of operating conditions,the biofilms on the support materials in the DMBR will evolve during the long-term experiment,which affected the filtration resistance.The same phenomenon was observed repeatedly when the DMBR was started to treat actual domestic wastewater:the filtration resistance increased rapidly at first and decreased to a lower level without any cleaning spontaneously.As a result,the DMBR was operated with a high flux of 26 L/m~2·h and a low pressure of 0.1 k Pa.F/M,EPS content of biofilms,protein/polysaccharide(PN/PS),ratio of live to dead cells(L/D),and the succession of microbial community affected the filtration resistance of biofilms.It is feasible to control the growth of microbial communities in biofilms to form loose and porous biofilms for long-term operation of DMBR in a high flux,low-pressure and clean-free manner.(3)Comparing the dynamic membrane formed by nylon mesh(25?m)and the microfiltration membrane(0.1?m),it was found that the dynamic membrane could achieve the similar filtration effect as the microfiltration membrane,and retained suspended particles effectively and achieved good water quality under the stable operation.