Understanding and Controlling Fouling in Membrane Bioreactors

Membrane bioreactors (MBRs) are an activated sludge process in which the conventional secondary clarifier is replaced by a membrane separation process (either microfiltration or ultrafiltration). As with other membrane systems, the most important characteristics are the membrane flux and the membrane permeability both of which are highly dependent upon temperature and degree of fouling. Like other membrane systems but to a greater degree, MBRs are susceptible to biofouling. Biofouling is not well understood but does increase operating pressure, reduce maximum flux, increase recovery cleaning requirements, and possibly reduce total membrane life. All of these effects of biofouling have adverse effects on either initial capital cost or ongoing operation and maintenance costs for MBRs. The overall goal of this research is to obtain a better understanding of biofouling in MBRs and methods to control said fouling in order to improve the economics of water recycling. The conclusions thus far from the pilot and bench-scale studies are that SMP and EPS are very important relative to biofouling in MBRs and that several tools are useful to examine biofouling trends. These tools include the critical flux test, resistance in series component analysis, and measurement of different fractions of EPS and SMP.