MEMBRANE ATTACHED BIOFILMS FOR WASTE TREATMENT - FUNDAMENTALS AND APPLICATIONS

Membrane Attached Biofilms (MABs) are being used in an increasing vari ety of bioreactors. Extractive Membrane Bioreactors (EMB) have been de veloped at Imperial College (1,2) for the aerobic biotreatment of toxi c organics which employ MABs for treating Volatile Organic Compounds ( VOCs)-containing wastewaters without incurring air-stripping problems. Investigations of the key factors controlling the optimal operating c onditions for the EMB system have shown that process efficiency is hig hly dependent on the development of these MABs. Therefore MAB developm ent and its influence on the flux across the membrane over time has be en studied and is presented here. Two MAB model systems have been stud ied; Xanthobacter autotrophicus GJ10 growing on 1,2-Dichloroethane (DC E) and Pseudomonas JS150 growing on Monochlorobenzene (MCB). The resul ts show that there is a problem in this system with excess biofilm gro wth on the membrane surface, resulting in reduced flux of organic subs trate across the membrane. At the same time, a diffusion-reaction mode l has been developed to explain the experimental results, and to descr ibe the behaviour of the EMB. It was theoretically concluded that an o ptimal biofilm thickness could be found from a compromise between the level of air-stripping and flux of pollutant across the membrane, and that cell endogenous decay could be used to manipulate the biofilm thi ckness. Methods of controlling excessive growth of biomass have been i nvestigated, and the addition of sodium chloride to the biomedium to c ontrol excessive biofilm development has been shown to be effective.