| This study investigated (1) the volatilization and biodegradation removal rates of volatile organic compounds (VOCs) in a membrane bioreactor (MBR), and (2) impacts of biomass and soluble organics characteristics on membrane fouling. A laboratory-scale MBR was operated to treat synthetic wastewater containing acetaldehyde, butyraldehyde and vinyl acetate. In Phase I, the organic loading rates were varied from 1.06 to 2.98 kg chemical oxygen demand (COD) m-3 d-1. In Phase II, the dissolved oxygen (DO) concentrations were varied from 0.2 to 5.4 mg L-1.; Total VOC removal rates were greater than 99.75 percent at all organic loading rates. Volatilization removal rates were achieved as low as 0.78 percent for acetaldehdyde, 1.27 percent for butyraldehyde, and 0.59 percent for vinyl acetate. Biomass stabilization status had a significant effect on volatilization. Under unstable conditions, 85 percent of vinyl acetate was volatilized. Regardless of the DO concentrations, total and biodegradation removal rates were greater than 99.7 and 95.9 percent. When the DO concentrations were increased, the volatilization rate increased. The experimental data were close to VOC emission modeling results using an analytical model and TOXCHEM+.; The biomass showed a non-Newtonian and pseudoplastic flow behavior. The average particle diameter was less than 10 microm. Few filamentous bacteria were observed, leading to weak and fragile microbial flocs. The microorganisms were dispersed freely as small clumps or individual cells. The total organic carbon (TOC) and COD concentration in the bound extracellular polymeric substances (EPS) increased linearly with viscosity. The membrane permeate flux was inversely proportional to mixed liquor volatile suspended solids (MLVSS) concentration, viscosity, and total bound EPS concentration.; The cake resistances were approximately 95 percent of the total membrane resistances. Soluble organics had a greater impact on cake layer formation under DO limited conditions, when soluble organics contained a larger amount of high molecular weight compounds. The bound EPS concentration had a greater influence on membrane filtering resistance than the molecular weight fraction of EPS. It is confirmed that confocal laser scanning microscopy (CLSM) could be a promising tool to visualize and map the biofouled membrane. |
