Contribution of extracellular polymeric substances (EPS) to the sludge aggregation

The contribution of extracellular polymeric substances (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), to the aggregation of both aerobic and anaerobic sludge is explored using the extended DLVO theory. It is observed that the aggregation abilities of both sludge samples decrease with the extraction of LB-EPS and TB-EPS, implying the crucial roles of EPS in sludge aggregation. Furthermore, through analyzing the interaction energy curves of sludge before and after the EPS extraction using the extended DLVO theory, it is found that both LB-EPS and TB-EPS have a substantial contribution to the sludge aggregation. The interaction energy of LB-EPS is always negative, suggesting that the LB-EPS always display a positive effect on the sludge aggregation. On the other hand, the interaction energy of TB-EPS is not always negative, depending on the separation distance between sludge cells. These results imply that the LB-EPS and TB-EPS have different contributions to the sludge aggregation.