Characterization of key organic compounds affecting sludge dewaterability during ultrasonication and acidification treatments

This study investigated the mechanism and effects of ultrasonic pretreatment followed by acidification on sludge dewaterability through looking at the changes of extracellular polymeric substances (EPS) content, composition and stratification. The results suggested sludge filterability was closely correlated with quantity of protein (R = 0.94, p < 0.01) and polysaccharide (R = 0.97, p < 0.01) present in loosely bound EPS rather than in soluble and tightly bound EPS. The fractions of polymers, especially tryptophan-like proteins and microbial by-product like material at molecular weight of 10⁶–5 × 10⁷ Da, were the key compounds related to sludge filterability. Ultrasonication may increase biopolymers concentrations that in turn deteriorate sludge filterability as evidenced at high ultrasonic power conditions. However, the subsequent acidification can reduce the concentrations of these organic compounds, reduce negative zeta potential, and increase floc size, thus increase sludge filterability. Combined ultrasonic-acid pretreamtent was more effective than the acidification treatment alone in reducing the concentrations of macromolecular compounds that may deteriorate sludge filterability.