Evaluation of acidification and oxidation of sludge to improve the effect of a starch-based flocculant on the dewaterability of sewage sludge.

Conditioning is essential for achieving effective sludge dewatering and easier disposal. In this study, a combined pretreatment of acidification and oxidation using potassium permanganate (KMnO) as oxidant was conducted to improve the effect of a cationic starch-based flocculant (St-WH) on the dewaterability of sewage sludge. Synergetic dewatering mechanisms by acidification, oxidation, and flocculation are discussed in detail according to the analysis of the changes in bound water content, extracellular polymeric substances (EPS) fractions and components, zeta potentials, floc size, and surface microstructures of sludge cakes in the dewatering process. Acidification and oxidation could destroy the sludge flocs, thereby causing the degradation of EPS and formation of fine particles. Original loosely and tightly bound EPS partially converted to soluble EPS, resulting in release of trapped water, which can be reflected by the significant correlation between loosely bound EPS and filter cake moisture content (FCMC) (R = 0.83, P < 0.05). Those fine particles, simultaneously produced, were adverse to filtration efficiency. In addition to enhancing the oxidation effect of KMnO, acidification treatment could still compress the protein-like materials in soluble EPS due to protonation effect, which was positively related to specific resistance to filtration (SRF) (R = 0.74, P < 0.05). The following flocculation using St-WH efficiently aggregated those fine particles and restrained the released EPS to bind with free water through charge neutralization and bridging effects, thereby resulting in improved filtration performance and enhanced removal of bound water (R = 0.88, P < 0.01). Response surface methodology was also applied to achieve an optimal condition and evaluate the effects of various environmental factors.