Novel methodologies for determining a suitable polymer for effective sludge dewatering

Abstract

Understanding the interactions between sludge particles and polymers during sludge dewatering is necessary to: firstly, maximize dewatered cake solids content; and secondly, minimize polymer demand. In this study, two scientific methodologies, namely the 'yintercept' concept and Higgins modified centrifugal technique (Higgins MCT) were used to identify the optimum polymer demand and type for effective conditioning and dewatering.Results from the 'y-intercept' concept show that a large amount of polymer required during conditioning of anaerobically digested sludge (ADS) is mainly due to neutralization of soluble biopolymers. In contrast, conditioning of aerobically digested sludge (AEDS) and waste activated sludge (WAS) is mostly controlled by a polymer bridging mechanism. The results indicated that, in order to achieve maximum dewatering performance with minimum conditioning polymer requirement, high charge density polymers are suitable for ADS while branched (or cross-linked) polymers can be used for AEDS and WAS. The new lab-scale technique, Higgins MCT, was successfully implemented for measuring cake solids content achievable by centrifuge and determining the optimum polymer demand (OPD). The Higgins MCT also helped to understand the relationship between digestion, conditioning and dewatering.

Deleterious effects of soluble extracellular polymeric substances on polyacrylamide demand for conditioning of anaerobically digested sludge

“…TB-PN is believed to help enhance sludge dewaterability and settleability because of its hydrophobic characteristics [42,45,46]. In the meantime, soluble PN contents have been demonstrated to contribute to polymer demand for conditioning [19,20,30]. In this study, soluble PN content was the second largest amount, accounting for 17 wt% of total EPS (or 47.9 ± 8.3 mg/g TS -Figure 3).…”

“…Recent studies have proved that the high polymer demand for conditioning of digested sludge is attributed to the increase in soluble EPS released during digestion, especially when anaerobic digestion is used [19,20,30]. However, how soluble EPS in ADS interact with the conditioning polymer and how much of this EPS fraction contributes to the polymer demand for dewatering are not yet well understood.…”

Enhancing sludge dewaterability and phosphate removal through a novel chemical dosing strategy using ferric chloride and hydrogen peroxide

“…Dewaterability rate is the focal point of conventional dewatering indices, including specific resistance to filtration (SRF) and capillary suction time (CST) (Novak, 2006; To, Nguyen, Vigneswaran, & Ngo, 2016). Although SRF is able to predict the cake solid content for sludge with suspended solids concentration higher than 0.5%, its complexity and laborious nature hinder its widespread utilization (To et al, 2018). On the other hand, CST is a straightforward and hence popular technique which is most beneficial when conducted to ascertain the best flocculation condition.…”

“…Considerable efforts have been made to pinpoint the decisive parameters in sludge dewaterability by centrifuge. However, no method was comprehensive enough to incorporate all contributory factors (To et al, 2018; To, Nguyen, Vigneswaran, Duc Nghiem, et al, 2016). Higgins et al introduced a modified centrifuge technique (Higgins MCT) that allows for solid–liquid separation in the sludge suspension and addresses the complications correlated with evaluating sludge dewaterability by a centrifuge (To et al, 2016, 2018).…”

“…The technique has proven to be an effective laboratory‐scale dewatering device that could overcome the drawbacks of traditional dewatering indices. Higgins MCT enables mimicking the full‐scale centrifuge process, anticipating maximum cake solid content, and determining OPD for sludge dewatering (To et al, 2018; To, Nguyen, Vigneswaran, Duc Nghiem, et al, 2016).…”