Unraveling the Bound-Water Removal Mystery: Preoxidation Enhances Sludge Dewatering via Cell Permeabilization and Transformation of Intracellular Polymeric Substances to Extracellular Polymeric Substances

Abstract

The effect of oxidation degree on sludge dewaterability during oxone-induced preoxidation was investigated. The optimal oxone concentration increased free cells and membrane permeabilization while limiting cell lysis, releasing bound water, and producing a drier sludge cake without reducing the filtrate volume. Dewaterability enhancement was mainly driven by the shift of low-molecular-weight proteins and polysaccharides (<20 kDa) from intracellular polymeric substances (IPS) to extracellular polymeric substances (EPS), along with selective degradation of hydrophilic glucose and peptidoglycan in EPS. Organic matter transferred to the outer EPS layer was mainly derived from the cellular constituents of Gram-negative bacteria in sludge. Importantly, IPS was found to exert a distinct and non-negligible influence on sludge dewatering with its oxidative response fundamentally differing from that of EPS. As the oxidation intensity increased, the ratio of protein to polysaccharide rose in loosely bound EPS but declined in IPS, whereas carboxyl and lactone groups decreased in both soluble and loosely bound EPS fractions, while carboxyl groups concurrently increased within IPS. IPS contained more hydrophobic components than did EPS at all oxone concentrations. Excessive oxidation induced cell disruption and hydrophilic debris, impairing sludge dewaterability. Cell membrane permeabilization, rather than cell lysis, was the key factor affecting sludge dewaterability.