Enhancing the dewaterability of waste activated sludge by the combined ascorbic acid and zero-valent iron/persulfate system

In this work, a reducing/chelating agent, ascorbic acid (H(2)A) was introduced to the traditional zero-valent iron (Fe-0)/persulfate (PS) process for waste activated sludge dewatering. The experimental data indicated that H(2)A-Fe-0/PS process significantly enhanced the dewatering performance of sludge and enhanced the oxidation efficiency of Fe-0-PS treatment. Under optimal conditions, the capillary suction time ratio before and after treatment (CST0/CST) of H(2)A-Fe-0/PS treated sludge increased by 118% and 31.3% compared with untreated sludge and Fe-0-PS treated sludge, respectively. The mechanism investigations revealed that the H(2)A-Fe-0/PS induced excellent enhancement for sludge dewaterability could be credited to the reduction and chelating capacity of ascorbic acid. Free radicals including SO4 center dot-, O-2(center dot-) and center dot OH produced in the H(2)A-Fe-0/PS process destroyed proteinaceous components and humic substances in sludge extracellular polymeric substances (EPS), thus reducing the negative charge and water holding capacity of sludge, improving the sludge rheological properties. As a result, the dewatering performance of sludge has been significantly improved.