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

Abstract

a b s t r a c tGenerally, 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.

Enhancement of waste activated sludge dewaterability using calcium peroxide pre-oxidation and chemical re-flocculation

“…It reached the minimum of 86.31 wt% when the dosage of CaO 2 was 20 mg/gTSS and the SRF was 1.28 Â 10 13 m/kg. According to the value of SRF, sludge can be classified into poor dewaterability (>1 Â 10 13 m/kg), medium dewaterability, (0.5e0.9 Â 10 13 m/kg) and good dewaterability (<0.4 Â 10 13 m/kg) (Zhang et al, 2014). By comparison, although addition of CaO 2 can improve sludge dewatering performance, the minimum SRF value can not reach the sludge with good dewaterability.…”

“…For example, addition of inorganic or organic flocculants can agglomerate fine sludge colloids to form large flocs through charge neutralization and bridging, which can be more easily separated from the water (Niu et al, 2013;Zhang et al, 2014). EPS fraction in activated sludge was highly hydrated, and the traditional chemical flocculants was ineffective to destroy EPS structure and convert bound water into free water (Neyens et al, 2004).…”

Improvement of wastewater sludge dewatering performance using titanium salt coagulants (TSCs) in combination with magnetic nano-particles: Significance of titanium speciation

“…(Zhang et al, 2015b). Many studies have demonstrated that sludge filtration property was mainly dependent on properties of soluble EPS fraction, and the high content of protein in soluble EPS was always detrimental to sludge filterability (Zhang et al, 2014b(Zhang et al, , 2015c(Zhang et al, , 2015d. In addition, reduction of soluble EPS concentration contributed to improvement of sludge filterability, it was obvious that TSC 0.5 was more effective in removal of soluble EPS fraction.…”

“…Addition of traditional chemical conditioners (inorganic salt coagulants and organic polymers) can agglomerate fine sludge colloids to form large flocs through charge neutralization and bridging, which can be more easily separated from the water (Niu et al, 2013;Zhang et al, 2014a). TiCl 4 is novel environmentally friendly inorganic coagulants and has attracted much attention in water and wastewater treatment (Shon et al, 2007;Zhao et al, 2011).…”

Wastewater sludge dewaterability enhancement using hydroxyl aluminum conditioning: Role of aluminum speciation

“…5 can see that the TB-EPS concentrations conditioned by Al 13 and PAC 2.5 increased again comparing to other aluminum salt coagulants, this also indicated that Al b and Al c showed better performance in compressing EPS structure than Al a , which made SEPS and LB-EPS transfer into TB-EPS, so TP-EPS conditioned by Al 13 and PAC 2.5 increased when SEPS and LB-EPS concentration conditioned by Al 13 and PAC 2.5 decrease, so their TB-EPS concentration was increased. Many studies have demonstrated that sludge filtration property was mainly dependent on properties of SEPS fraction, and the high content of protein in SEPS was always detrimental to sludge filterability (Zhang et al, 2014a(Zhang et al, , 2014b(Zhang et al, , 2015b. In addition, reduction of SEPS concentration contributed to improvement of sludge filterability, it was obvious that PAC with high alkalinity and Al 13 were more effective in removal of SEPS.…”