Understanding the impact of chemical conditioning with inorganic polymer flocculants on soluble extracellular polymeric substances in relation to the sludge dewaterability

• Waste sludge was conditioned with two inorganic polymer flocculants (IPFs).
• Influence of chemical conditioning on characteristics of soluble EPS was investigated.
• HPAC exhibited higher efficiency due to superior charge and bridging properties.
• The high MW biopolymers were easier to be removed by chemical coagulation.
• 3DEEM is an attractive way to evaluate the conditioning efficiency of IPFs.

Generally, sludge conditioned with inorganic coagulants exhibits rigid structure and is suitable for high pressure dewatering process. Sludge flocs possess multilayered structure, and the sludge dewaterability is mainly dependent on the properties of soluble extracellular polymeric substances (SEPS). However, few studies have focused on influence of chemical conditioning on the characteristics of SEPS. In this study, the surplus sludge obtained from wastewater treatment plant (WWTP) was conditioned with two inorganic polymer flocculants (IPFs), PACl and HPAC, for improving the sludge dewaterability which was measured using specific resistance to filtration (SRF). Meanwhile, the variation in SEPS properties was investigated with combined high performance size-exclusion chromatography (HPESC) and fluorescence excitation–emission matrix (EEM). According to the experimental results, HPAC showed better performance in improving sludge dewaterability due to higher charge density and better bridging properties. EEM coupled to fluorescence region integration (FRI) demonstrated that protein-like substances were dominant fraction of soluble EPS. HPSEC analysis indicated that most of the SEPS with high molecular weight (>2000 Da) were effectively removed from aqueous phase after conditioning, they might play more important roles in sludge dewatering. SRF correlated well with zeta potential, dissolved organic carbon (DOC) and EPS content located in all four EEM regions under chemical conditioning. This result revealed that EEM in conjunction with FRI was an attractive way to evaluate the sludge conditioning efficiency of IPFs.