Effects of sludge particles on performance of enhanced backwash for fouling reduction in anaerobic membrane bioreactors

The objectives of this research are to investigate effects of sludge properties in terms of particle size composition on performance of physical and chemical cleaning and to understand fouling mechanisms of the specific feed solutions. The sludge was centrifuged at three rotational speeds to differentiate particle size distributions, and the supernatant and residual flocs were used for microfiltration and cleaning processes. The filtration flux with the flocs was greater than those of the three supernatants, which indicates that fouling was greater with supernatants. Taking into account that the solid concentrations of the raw sludge and the residual flocs were 10 times greater than those of the supernatants, the reduction in flux for the supernatants is significant. The flux was recovered to 64% of the clean water flux at the maximum efficiency by two cleaning of membrane fouled with supernatant treated at 1,000rpm. In addition, increasing removal of coarse particles by applying higher centrifugal speed (i.e. 1,000 and 1,500rpm) yielded greater recovery performance by chemical cleaning. Particle composition such as the fine particle concentration played a significant role in fouling and the enhanced backwash cleaning efficiency.