A novel conditioning process for enhancing dewaterability of waste activated sludge by combination of zero-valent iron and persulfate

• Combined conditioning by ZVI and persulfate enhanced sludge dewaterability effectively.
• The improvement of sludge dewaterability was over 50%.
• Cost saving was up to 29% with ZVI–persulfate conditioning in comparison to classical method.

Improvement of sludge dewaterability is crucial for reducing the costs of sludge disposal in wastewater treatment plants. This study presents a novel conditioning method for improving waste activated sludge dewaterability by combination of persulfate and zero-valent iron. The combination of zero-valent iron (0–30 g/L) and persulfate (0–6 g/L) under neutral pH substantially enhanced the sludge dewaterability due to the advanced oxidization reactions. The highest enhancement of sludge dewaterability was achieved at 4 g persulfate/L and 15 g zero-valent iron/L, with which the capillary suction time was reduced by over 50%. The release of soluble chemical oxygen demand during the conditioning process implied the decomposition of sludge structure and microorganisms, which facilitated the improvement of dewaterability due to the release of bound water that was included in sludge structure and microorganism. Economic analysis showed that the proposed conditioning process with persulfate and ZVI is more economically favorable for improving WAS dewaterability than classical Fenton reagent.