Effect And Regulation Of Hydrophobic/Hydrophilic Composition Of EPS In The Process Of Fe²⁺-activated Persulfate Conditioning Sludge

As a pre-treatment sludge dewatering,sludge conditioning is attracted more and more attention in recent years.At present,common sludge conditioning technologies mainly include ultrasonic,microwave,Fenton and advanced oxidation technologies,etc.The activated persulfate oxidation technology as a kind of advanced oxidation technologies,which can destroy and decompose organic matter because of the produced a large amount of high sulfate radical,is used by some researchers at home and abroad to undertake recuperating sludge dehydration to improve the sludge dewatering performance.They preliminary confirmed that activation persulfate extracellular polymers in the sludge mixture can be effective damage effect,make the parts of the sludge combined water release,so as to improve sludge dewatering properties.Therefore,the activated persulfate oxidation technology will be applied to the sludge conditioning in this paper,the aim of which is to understand the improvement efficiency of activated persulfate oxidation system on sludge dehydration performance and the influence of EPS composition and hydrophilic and hydrophobic properties on its dehydration performance in this process.In this paper,the effect of initial pH condition,persulfate concentration(n(S₂O₈^2-))and the molar ratio of persulfate/ferroite(n(S₂O₈^2-)/n(Fe²⁺))on sludge dewatering performance were observed by using CST and Water content（Wc）as main indexes for evaluating sludge dewatering performance.The results show that the ferric salt-persulfate oxidation system could effectively crack the EPS structure and improve the sludge dewatering performance.At the same time,under the original sludge pH condition,when n(S²O8^2-)=1.2 mmol/gVSS,S₂O₈^2-/Fe²⁺=0.9,the highest CST reduction rate was 56.15%and Wc reduction rate was 40.19%.At the same time,the reduction rate of CST of sludge samples fed on sodium acetate can be up to 70%after Fe²⁺-S₂O₈^2-oxidation treatment,which was significantly higher than that of sludge samples fed on glucose.The characteristics of EPS hydrophilic/hydrophobic were inseparable from the sludge dewatering performance.A series of Fe²⁺-activated persulfate oxidation process was carried out on the sludge in the laboratory.Sludge samples fed on sodium acetate（similar to hydrophobic sludge）had higher EPS content,while those fed on glucose（similar to hydrophilic sludge）had lower EPS content.There was a significant linear positive correlation between the proportion of hydrophobic components and the water content（Wc）of sludge filter cake,indicating that the increase in the proportion of hydrophobic organic matter in EPS would directly worsen the sludge dewatering performance.In addition,different types of carbon sources and SRT also had certain influence on the composition and properties of sludge EPS.With the concentration of protein in LB-EPS and TB-EPS showed a gradual decline trend for both the acetate and glucose sludge samples,while the polysaccharide content in LB-EPS and TB-EPS was in a random variation,which indicating that the distribution and concentration of protein in EPS would directly influence the performance of sludge dewatering,mainly as the increase of protein content in the TB-EPS would deteriorate sludge dewatering performance.Through a series of index determination and characterization experiments,the protein content,polysaccharide concentration,UV-254 and TOC of each component of sludge EPS before and after the treatment of Fe²⁺-activated persulfate oxidation were estimated.And the results showed that the The sulfate radicals generated from the Fe²⁺-S₂O₈^2-system mainly attacked the EPS and microbial cells in the initial stage of the reaction,and destroyed and degraded the hydrophobic organic compounds with benzene or conjugated system in EPS,namely hydrophobic tryptophan large molecules such as proteins,humic acid and polysaccharide skeleton structure compounds,and the binding water inside the sludge flocs was initially released.As the reaction progresses,sulfate radical would further react with the dissolved hydrophobic organic matter and prompted them to degrade into small monomer material and release the EPS-bound water,and eventually improve the performance of sludge dewatering and effectively reduce the filter cake moisture content.