Production Of Extracellular Polymeric Substances From Aerobic Granular Sludge And Its Distribution

Biogranulation is a process of cell-to-cell aggregation and is a promising biotechnology developed for wastewater treatment. Current studies focus on granule cultivation; however, its formation mechanism is unclear. Accordant viewpoint is that the formation of granule is related to extracellular polymeric substances (EPS).EPS are sticky materials secreted by cells. They can be noticed in all kinds of microbe aggregation, forming a three-dimensional matrix in which bacteria and other particles are embedded. The spatial position and content indicates that EPS could play a central role in the biogranulation process.This study investigated the effect of operating and nutritional conditions on the mass of EPS produced by aerobic granular sludge and its distribution between sludge and supernatant. In addition the influence of EPS on configuration of granular sludge, effluent quality of reactor system through comparing characteristics of EPS and its distribution between sludge and supernatant with different kinds of sludge under similar or different culture conditions were investigated. The study is not only a complementary to current studies about EPS in wastewater treatment process, and optimizing the efficiency of treatment process and quality of effluent, but also provide a deeper insight into formation and cultivation of aerobic granular sludge. The results are shown as follows:(1) The changes of EPS content produced and its distribution were regular with the operating and nutritional conditions. The amount of EPS in sludge was relatively stable and the excessive EPS appeared to be released into the supernatant. Moreover, a large amount of EPS was produced only when the aerobic sludge granules are disintegrated. Low pH, high organic load and improper C/N ratio badly effected to the granulation of sludge leading to poor effluent quality.(2) The good configuration of granular sludge was observed under the conditions of 4.5 mg/L DO, 7.0 pH, 0.37 kgCOD/kgMLSS·d sludge loading and 20:1 C/N ratio and the content of EPS in aerobic granular sludge was around 9 ~ 12 %, which changed into 0.6 ~ 20 % in anaerobic granular sludge, and the concentration of EPS in supernatant amounted to the lowest with 14 ~ 26 mg/L.(3) The major component in EPS was polysaccharide in aerobic granular sludge and it account for 52.6 % of total amount whereas protein was dominant component amounting 60.9 ~ 78.1 % of total EPS in sludge under other conditions. Protein had great influence on granulation and the maintaining of granule configuration. The granule disintegration happened when amount of protein reduced in sludge EPS.(4) Total amounts of EPS in aerobic granular sludge, biofilm, floc sludge and anaerobic granular sludge were 130.8, 106.5, 102.1 and 64.2 mg/gVSS, respectively. Polysaccharides were...