Study on the Function of the Biofilm Attached to Membrane on Effluent Quality in MBR

Abstract

Combined membrane separation processes with biological treatment technology; membrane bioreactor (MBR) is a new efficient wastewater treatment technique for the advantage of high removal rate, high quality effluent and stable treatment effect etc. However, being conventionally identified that the removals of contaminants is dependent on suspended growth activated sludge system and micro porous membranes in the MBR. In this paper, a Laboratory MBR using a submerged polyethylene hollow-fribre membrane module with a pore size of 0.45nm and a total surface area of 0.1m was used for treating raw water from artificial water. The actual operation indicated that membrane separation achieved to not only solid-liquid in the intermixture, but also the separation of soluble organics from water. A comparison of the effluents between a new film and an old film was carried out under soluble microbial product (SMP) accumulated in MBR. Experiment result shows that the effluent quality of the old film is more stable and excellent than the new film. The feeding influent had a total organic carbon (TOC) level of 437mg/L. The effluent TOC concentration of the old film is 12.9mg/L, on average, much lower than the new film (36.9 mg/L), which indicates the intensified interception of SMP by the biofilm attached membrane. In the MBR supernatant, both macromolecules with molecular weight (MW)>10ku and small molecules with MW<3ku are dominant and have a much larger occupation. The old film interception for all molecules with different MW is more effective than the new film. After the cleaning of the old film, with the falling of membrane specific flux, its effluent TOC concentration will decline. These results indicate that the biofilm attached to membrane in the MBR could obtain the separation of soluble organics from water, consequently improve the quality of the effluent.