Improvement Of Waste Activated Sludge Dewaterability By Fe⁰/H₂O₂ Fenton-like Process And Its Mechanism Analysis

Waste active sludge is the byproduct of waste water biological treatment which has large amount and high moisture.Dewatering is an important part of sludge treatment and disposal,so improving sludge dewatering performance is essential to recycle sludge and reduce sludge disposal cost.Fenton technology is widely used to improve sludge dewaterability,but the conversion of Fe³⁺to Fe²⁺is so slow that a great deal of ferrous salt is required to maintain the concentration of Fe²⁺and catalyst cannot be recycled and so on.To overcome these drawbacks,the Fe⁰/H₂O₂ Fenton-like method was used to improve the sludge dewaterability in this study.The aim of this study was to investigate the effects of initial pH value,dosage of Fe⁰ and H₂O₂,and reaction time on sludge dewatering performance and explore the optimum conditioning parameters.The law of the sludge disintegration,the recycling efficiency of Fe⁰and the mechanism of dewatering were also studied in this study.The main conclusions are as follows:The optimized dehydration performance was achieved when the initial pH,dosage of Fe⁰and H₂O₂ were 2.5,750 mg/g TS,20 mg/g TS respectively.After 60min reaction,the SRF of sludge reduced to 1.35×10¹²m/kg from 19.7×10¹² m/kg,SRF reduction rate decreased by 93.1%and the water content of sludge cake reduced from 91.6%of raw sludge to 73.6%under the optimal conditions.The concentration of SCOD,protein,polysaccharide,NH₄⁺-N and PO₄^3--P were 720mg/l,82.6mg/l,157.7mg/l,191.9 mg/l and 6.6 mg/l in the supernatant respectively after sludge conditioned by Fe⁰/H₂O₂ Fenton-like method.Under the optimal conditioning,the recovery rate of Fe⁰ was 98.3%and actual consumption of Fe⁰ was 12.75mg/g TS.After10 times recyclinge of Fe⁰,the sludge dewatering performance still maintained in effective states.The sludge specific resistance was reduced to 1.75×10¹²m/kg,compared with the original sludge,SRF reduction rate was 91.1%,and the water content of sludge cake reduced to 74.3%.The EPS composition,particle size distribution,bound water content,and Zeta potential of the original sludge and the Fenton-treated sludge were compared with the control.The experimental results showed that the concentration of polysaccharide and protein in soluble EPS?S-EPS?increased and the concentration of polysaccharide and protein in tightly bound EPS?TB-EPS?and loosely bound EPS?LB-EPS?decreased after Fenton-like technology conditioning.TB-EPS and LB-EPS converted to S-EPS.The average particle size,the zeta potential and bound water content all decreased.Based on the aforementioned results,the Fe⁰/H₂O₂ Fenton-like method could effectively improve the dewatering property of the sludge.The mechanisms of dehydration mainly included that hydroxyl radical which produced by Fe⁰ reaction with H₂O₂ under acidic conditions oxidize sludge extracellular polymers.The floc structure was destroyed,resulting in a reduction of sludge particle size,the release of organic substances such as proteins and polysaccharides,and the conversion of bound water into free water.At the same time,the sludge surface charge was neutralized,which is conducive to sludge particle condensation.All of these can improve sludge dewatering performance effectively.