Enhanced Dewaterability Of Waste Activated Sludge With Fe(?)-activated Hypochlorite Treatment

Biological wastewater treatments are widespread in the world,but it is inevitable to generate a by-product,waste activated sludge?WAS?.Large amount of sludge containing orgaics,pathogenic bacteria and heavy metal can cause a great threat to human beings and environment if without properly disposal.In general,the treatment/disposal cost of WAS accounts for 35-60%of the total operating expense in wastewater treatment plants.Sludge dewatering is a promising approach in reducing the volume of WAS and the cost of sludge transport.WAS has a high water content over 99 wt%and strong hydrophily,and the floc stability is strong.Thus,how to improve sludge dewatering performance and efficiency becomes a challenge in wastewater and sludge treatments.Formerly,flocculation is the most used to condition sludge before mechanical dewatering,and it is difficult to release bound water from slude flocs.Advanced oxidation processes?AOPs?have attracted great attention on sludge dewatering because it can cause destroy the sludge flocs enhanced by extracellular polymeric substances?EPS?,and then promote the release of bound water.In this study,a novel AOPs Fe???-activated hypochlorite oxidation on WAS dewatering and its mechanism were investigated.Capillary suction time?CST?,specific resistance to filtration?SRF?of sludge and water content?W_C?of dewatered sludge cake were selected as the factors to evaluate the sludge dewaterability.Meanwhile,the effect of individual Ca?ClO?₂ dosage,initial pH value and the molar ratio of Fe???/Ca?ClO?₂ were investigated and analyzed respectively.The maximum reduction of W_C?30.76%?was achieved under the optimal conditions of Ca?ClO?₂ 0.04 g/g total suspended solids?TSS?,FeSO₄·7H₂O 0.097 g/g TSS and pH 7.3,while the reduction of CST and SRF reached 91.24%,99.47%respectively.Scanning electron microscope?SEM?,protein and polysaccharide content in EPS and three-dimensional excitation-emission matrix?3D-EEM?fluorescence spectroscopy and live/dead bacterial viability before and after Fe???-Ca?ClO?₂ oxidation were determined to explain the enhanced dewatering mechanism.The cell lysis in sludge,bound water release and the small fragment re-flocculation were the primary reason for the improvement of sludge dewaterability during Fe???-activated hypochlorite oxidation.