METAPROTEOMIC APPROACH TO MBR BIOMASS CHARACTERIZATION

Membrane bioreactors (MBR) are a relatively new and promising technology in the sector of advanced wastewater treatment (Yang et al., 2006). The combination of a bioreactor with a set of membrane modules enables the straightforward separation of treated sewage from activated sludge. MBRs compete by many advantages to conventional activated sludge processes (CAS), but its greatest feature leads to the support of both non-flocculating and flocculating bacteria. Therefore MBRs can be operated on higher loading rates and provide very high effluent quality. Nevertheless, MBRs still tend to membrane biofouling that impedes further process optimization. Biofouling is mainly caused by extracellular polymeric substances (EPS) and soluble microbial products (SMP) that accumulates onto and into the membrane. Consequently the permeate flux declines while simultaneously the pressure on the membrane (transmembrane pressure - TMP) inclines. Until recently, much research has been carried out to minimize biofouling effects. Engineering tools were mainly applied with regard to process optimization and monitoring. In contrast, biological tools to were rarely applied due to the fact that biofouling have been strongly related to the occurrence of EPS and SMP that consist mainly of polysaccharides and proteins. Thus, studies on DNA and/or RNA have become impractical in studying biofouling phenomena. Both engineering and biological tools did not reveal sufficient inside to the linkage between biofouling and biomass dynamics. There still exists a lack of knowledge about enzymatic activities and microbial dynamics of the MBR bioconsortium. However, a novel approach called "metaproteomics" has been recently proposed to explore environmental samples and activated sludge (Wilmes and Bond, 2004; Kan et al., 2005). This approach can deliver important information about the microbial enzymatic activity and can reflect reaction/adaptation of a biocommunity to its environment. It is for this the reason that metaproteomics will gain the understanding about biofouling in MBR. Here we present the first application of metaproteomic approach to MBR sludge, an extremely heterogeneous sample often found in environmental systems. We have developed a novel extraction and purification method based on phenol, especially for environmental samples (Benndorf et al., 2007). First studies were carried out on steady stage development of the MBR biomass and its specific reactions to a punctual salt shock load. It could be demonstrated that conventional engineering tools to monitor the reactor performance were not as sensitive as proteomic tools to reveal reactions and adaptations of the MBR biomass. Important protein-protein interactions could be detected by 2D-PAGE application only and provided a new inside into the complex nature of the MBR bioconsortium.