A novel Fe 2+ /persulfate/tannic acid process with strengthened efficacy on enhancing waste activated sludge dewaterability and mechanism insight.

As an essential section before final sludge disposal, sludge dewatering has currently been one of the focus issues. In this study, an innovative Fe ²⁺ /persulfate/tannic acid (TA) process was verified to further strengthen systemic efficacy on enhancing sludge dewaterability, compared with the conventional Fe ²⁺ /persulfate process. With the efficient TA/Fe ²⁺ (molar ratio) of 0.25 added in Fe ²⁺ (0.3 mmol/gTS (total solid))/persulfate (0.6 mmol/gTS) process, sludge dewaterability was enhanced remarkably. Capillary suction time, specific resistance to filtration, and water content of dewatered sludge cake were further reduced by 61.5%, 35.3%, and 6.4% than these in Fe ²⁺ /persulfate. Sludge supernatant viscosity was further reduced by 86.7% due to the more removal of extracellular polymeric substances (EPS). The secondary structure of EPS protein changed apparently and fluorescent components of EPS decreased distinctly. Sludge functional group contents were observed to be lower. TA effectually increased sludge particle size and heightened sludge flocculability, rendering the large and compact aggregations. Moreover, TA accelerated the recovery of Fe ²⁺ , facilitating persulfate activation to generate more SO ₄ ^·- and ^· OH for EPS disruption and cell lysis in the conditioning system. These findings provided a novel approach based on the Fe ²⁺ /persulfate process in sludge treatment for desirable dewaterability.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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