Biomass characteristics and membrane aeration: toward a better understanding of membrane fouling in submerged membrane bioreactors (MBRs).

Fouling in submerged membrane bioreactors (MBRs) was studied under different operating conditions and with varying biomass characteristics. Fouling rates were determined using a flux-step method for seven biomass conditions with mixed liquor solids concentrations ranging from 4.3 to 13.5 g x l(-1), six permeate fluxes (5.5, 11.0, 16.5, 22.0, 27.5, and 33.0 l x m(-2) x h(-1)), and three membrane airflow velocities (0.07, 0.10, and 0.13 m x s(-1)). Statistical analysis was used to specify the degree of influence of each of the biomass characteristics (solids concentration, dewaterability, viscosity, particle size distribution, concentrations of protein and carbohydrate in the soluble microbial products, SMP, and extracellular polymer substances, EPS), the permeate flux and the membrane aeration velocity on the membrane fouling rate. Among all these variables, only the permeate flux, the solids concentration (correlated to the viscosity and the dewaterability), the carbohydrate concentration in the EPS, and the membrane aeration velocity were found to affect the fouling rate. The permeate flux had the greatest effect. A transitional permeate flux was observed between 16.5 and 33 l x m(-2) x h(-1), below which no significant fouling was observed regardless of the biomass characteristics, the permeate flux, and the membrane aeration velocity.