The cooling extraction method, which was described as follows, was applied for the extraction of the extracellular polymeric substances (EPSs) from the sludge. Firstly, 2 mL of sludge was centrifuged. Secondly, the supernatant was removed. Thirdly, 10 mL of NaCl solution (0.85 %) and 60 mL formalin were added.