Research On Distribution Characteristics Of Extracellular Polymer Substance (EPS) Extracted From Thermal Pressed Sludge

As the inevitable product of the sewage treatment, high moisture content is the bottleneck of the Mechanical dewatered sludge disposal. Extracellular Polymeric Substances(EPS)is complex polymer secreted by cell lysis, which has significant relationship with sludge moisture content. EPS largely affects the sludge floc structure, the sludge sedimentation and dehydration performance. To date, no standard EPS extraction has been established in academia because different methods have different efficiency.In order to find a suitable EPS extraction method for mechanical dewatered sludge, four different methods including EDTA extraction, alkali extraction, acid extraction, ultrasonic extraction method have been used in extracting EPS from belt filter dewatered sludge. The contents of polysaccharide and proteins extracted from the dewatered sludge by different extraction methods are also analyzed. The results indicated that EDTA method and alkali extraction method are more suitable for dewatered sludge with more EPS content and less cell damage, while sulfuric acid extraction and ultrasonic extraction were poorer with obvious cell lysis shown by higher DNA content in extracted EPS. For the mechanical dewatered sludge, the protein concentration of four different EPS extraction methods was: alkali extraction method> EDTA method > ultrasonic extraction method> sulfuric acid extraction method.As a anionic surfactant, Sodium Dodecyl Sulfate(SDS) might improve significantly of the EPS contents extracted from sludge, especially the protein contents, it can also release the bound water of sludge and reduce the moisture content of sludge. The contents of slime EPS(SEPS)is more than that of loosely bound EPS(LB-EPS)and tightly bound EPS(TB-EPS) was found by extraction of different EPS fractions from 4 kinds of sludges. bound water proportion in four different sludge samples can be ranged in values as U(sludge from thickening tank)>US(sample U+SDS)>D(mechanical dewatered sludge)>DS(sample D+SDS). Results from other analytical techniques such as FTIR and NMR were also given the supported proof for the above conclusions.For further reducing the moisture content of mechanical dewatering sludge, sludge deep dewatering can lessen the difficult degree of sludge treatment and disposal. By exploring the index such as the component distribution in each layer of extracellular polymeric substances(EPS), bound water content and organic-functional groups of sludge under different thermal press treated conditions, this study tries to discuss the characteristic of dewatering sludge influenced by thermal pressure treatment. The results indicate that the layers distribution of EPS extracted from dewatering sludge is different from the activated sludge; the total EPS contents of treated sludge is lower than that of original sludge; and changes of EPS contents are the coupled effect of pressure and temperature; The proteins in TB-EPS have significant positive correlation with the bound water in dewatering & treated sludge; FTIR shows that the organic-functional groups in TB-EPS changed obviously after thermal pressure.