Optimization of extracellular polymeric substance extraction method and its role in the dewaterability of sludge

Seven commonly adopted extraction schemes were selected to extract extracellular polymeric substance (EPS) from the sludge, and the dewaterability of sludge was also investigated before and after extracting EPS. Results showed that Formaldehyde+NaOH and 2% EDTA methods were proved to be effective in extracting EPS from the sludge, and the total EPS production of the total suspend solid was 128.86 mg·g^-1 and 42.38 mg·g^-1, respectively. However, the cell destructed seriously after extracted by Formaldehyde+NaOH and 2% EDTA methods. Heating method was a gentle and efficient method, and the total EPS production was 21.97 mg·g^-1. Sludge dewaterability was largely improved after extracted slime, loosely bound EPS and tightly bound EPS from the sludge flocs. It was also found that the higher content of EPS in slime, the worse dewaterability of sludge, and sludge dewaterability would be deteriorated when EPS was released from other layers to slime. Capillary suction time (CST) values of sludge from the ShekWuHui and Stonecutters Island Treatment works were 132.9 s and 229.9 s compared to 80.8 s and 79.4 s, separately after extracted Slime from sludge flocs, and the dewaterability of sludge was greatly improved.