Enhanced paper sludge dewatering and in-depth mechanism by oxalic acid/Fe2+/persulfate process

As a typical advanced oxidation process, Fe2+-persulfate (PDS) oxidation technology has been widely and effi-ciently reported for enhancing sludge dewaterability. However, higher dosage of Fe2+ must be added, which will restrain the oxidation efficiency of Fe2+-PDS process. In this work, the oxalic acid (OA)/Fe2+-PDS process was studied to improve paper sludge dewatering. With the OA dosage of 6 mu mol (g total solid (TS))-1, Fe2+ dosage of 0.3 mmol (g TS)-1, and PDS dosage of 0.6 mmol (g TS)-1, sludge dewaterability was improved more efficiently. The specific resistance to filtration and water content of sludge cake were decreased by 70.7% and 8.0%, respectively. In comparison with Fe2+-PDS process, the viscosities of sludge suspension and supernatant were further reduced by 3.73% and 51.77%, respectively, and the contents of extracellular polymeric substances fractions were increased. The improved sludge dewaterability in OA/Fe2+-PDS process was mainly contributed by the synergistic effect of oxidative disintegration by free radicals and flocs re-flocculation, the contributions of which were the orders: metal cations > sulfate radical > hydroxyl radical. OA enhanced the efficient disinte-gration of sludge flocs, released more bound water, generated more Fe3+-oxalate complexes, and finally increased the sludge particle size significantly, forming a larger aggregation and obvious cracks. Additionally, the stabilization of several heavy metals was improved due to the chelating capacity of OA. These works will provide a novel approach for sludge dewatering in the PDS oxidation process.

Automated summary

In this study, the combination of oxalic acid (OA) and Fe2+-persulfate (PDS) was used to improve the dewatering efficiency of paper sludge. The OA/Fe2+-PDS process effectively reduced the viscosity of sludge suspension and supernatant, increased the content of extracellular polymeric substances fractions, and improved the stability of heavy metals. These findings provide a novel approach for sludge dewatering in the PDS oxidation process.