Combining submerged membrane technology with anaerobic and ...

Impact of a methanogenic pre-treatment on the performance of an aerobic MBR systemreuse both in agriculture and as heating or cooling water or for cleaning purposes,depending on the quality standards.The methanogenic treatment could affect results obtained in aerobic MBRs. Partialdegradation products coming from the treatment of complex substrates in themethanogenic stage might have a negative impact on membrane performance. Wilén et al.(2000) observed that a complex substrate as activated sludge flocs deflocculated underanaerobic conditions. The deflocculated particles were mainly bacteria and floc fragments,although some soluble polymeric substances were also released. Therefore, the hydrolysisof complex substrates such as aerobic sludge (for instance coming from the recirculationbetween aerobic and methanogenic stages) could lead to a release of biopolymers,affecting membrane fouling.The fraction of biopolymers most frequently mentioned in relation with membranefouling is the group of soluble microbial products (SMP). This group contains soluble andcolloidal biopolymers, mostly carbohydrates (SMPc) and proteins (SMPp) (Drews, 2010).SMPc has been widely considered as the most important parameter regarding membranefouling (Rosenberger et al., 2006; Drews, 2010). Nevertheless, recent studies haveintroduced a more general approach to the biopolymers responsible for membrane foulingby defining biopolymer cluster (BPC) and transparent exopolymer particles (TEP) asimportant factors in the formation of the sludge fouling layer on the membrane surface andthe increase of fouling potential (Sun et al., 2008; de la Torre et al., 2008). BPC have beendefined as a pool of non-filterable organic matter in the liquid phase of the MBR sludgemixture much larger than SMP (Sun et al., 2008) whereas TEP are very sticky particlesthat exhibit the characteristics of gels, and consist predominantly of acidic polysaccharides(Passow, 2002). Depending on the applied assays, these groups are not distinct butoverlap (Drews, 2010).Different post-treatment systems for UASB effluents have been widely studied,among them aerobic MBRs being one of the most recent and not yet understoodpossibilities (Chong et al., 2012). Therefore, it is of prime importance to identify andunderstand the causes responsible for membrane fouling in these systems.5.2. ObjectivesThe objective of this work was to study membrane fouling in an aerobic MBR after amethanogenic pre-treatment of low-strength wastewater at ambient temperatures.131