Study On The Dewatering Performance And Mechanism Of Sewage Sludge Conditioned By Activated Persulfate And Biomass

According to the statistics of "China's ecological environment bulletin in 2017",the national urban sewage treatment capacity had reached to 157 million m' per day.Generally,ten thousand m3 sewage could generated 1.0-2.0 tons dry sewage.This means there are 5.73-11.46 million tons dry sludge generated in 2017.The total amount is 28.65-57.30 million tons per year if the water content of sewage sludge is 80%and the data would continue to increase and reach to 60 million tons per year in 2020.Such a large amount of sludge will cause serious environment pollution without proper treatment and disposal.Conditioning of sewage sludge to make it easily dewatering is a vital step before disposal in terms of reducing the volume of the sludge and saving treatment cost.Activated persulfate is an advanced oxidation process which can generate strong oxidant sulfate radical(SO4·-),could degrade sludge flocs and improve the dewatering performance finally.Meanwhile,the skeleton builders were used widely to improve the dewaterability of sludge because they can decrease the sludge compressibility.Rice husk or wood flour is a typical farming and forestry disposables,as a novel skeleton builder,it can save conditioning cost and realize the resource utilization of waste.In this study,activated persulfate combined biomass were used to condition sludge.The effect of composite conditioner on sludge dewaterability were studied.The mechanism of composite conditioner for improving sludge dewaterability were investigated.The migration and transfer of heavy metals during conditioning process were discussed.And correlation analysis among characteristics of the sludge were carried.The main research content and results of this paper are as follows:(1)The activated persulfate combined biomass can significantly improve the sludge dewaterability.Either of the constituents of composite conditioner solely used cannot achieve good effect.We mainly studied the activated persulfate combined rice husk flour(SPS/Fe2+-RH).Using response surface methodology(RSM),the optimal composite conditioner concentrations were 151.5 mg/g dry solid(DS)of SPS,46 mg/g DS of Fe2+ and 333 mg/g DS of RH.When conditioned by SPS/Fe2+,the CST and SRF reduction efficiency were 77.2%and 79.6%.respectively.After the addition of RH as skeleton builder,the CST and SRF reduction efficiency increased to 92.8%and 94.6%,respectively.And the water content of sludge cake decreased from 95%for raw sludge to 68%for conditioned sludge.The effect of pH and temperature on composite conditioning process were studied.The results illustrated that SPS/Fe2+-RH has a good adaptation at pH 5-11 and temperature 25 ?-70?.(2)The mechanism of activated persulfate combined rice husk flour for improving sludge dewaterability was investigated.The results show that the activated persulfate and rice husk flour have synergistic effect on sludge dewaterability.The sludge net yield increased by 1.93 times and the compressible coefficient of sludge cake was reduced by 32.6%after conditioned by SPS/Fe2+-RH.SEM results show that the raw sludge is plate-like structure,after conditioning,the sludge flocs degraded and obtained a porous structure which is favor of water to pass through.Zeta potential was nearly 0 mV after conditioning which illustrated that the sludge is unstable and easy to agglomerate for setting,the internal water was released.The protein and polysaccharide content in extracellular polymeric substances(EPS)changed and the content of bound water reduced by 66.2%.The FI-TR results show that the functional group related to EPS changed after conditioning process.According to the effect of rice husk flour size on sludge dewaterability,when the rice husk flour size is 0.075-0.15 mm,the sludge dewaterability is preferable.Meanwhile,the rice husk flour combined with different size is a better skeleton builder,the mass distribution of less than 0.075 mm,0.075-0.15 mm and 0.15-1.25 mm is 19.2%,75%and 5.8%,respectively.(3)The migration and transfer of heavy metals(HMs)during conditioning process were discussed.The results showed that the distribution of HMs in filtrate and sludge cakes changed significantly after conditioning.The concentrations of object HMs in filtrate increased and in sludge cakes decreased.The leaching value and rate of HMs obviously decreased after conditioned by activated persulfate.The leaching toxicity continue to reduce with the addition of rice husk flour.The leaching value of Pb in sludge cake decreased to zero.The chemical species distribution of HMs showed that HMs in the residual increased and the exchangeable decreased which indicated that the mobility of HMs decreased after composite conditioned by SPS/Fe2+-RH.The leaching rate of HMs have positive correlation with the fraction of exchangeable and negative correlation with the fraction of residual.According to the risk assessment code(RAC)values of HMs,Cu posed low risk,Cd and Zn were at medium risk,Cr and Pb posed no risk in sludge cake after conditioned by composite conditioner.(4)According to the correlation analysis among characteristics of the sludge,there are no remarkable correlation exist between pH/temperature and sludge dewaterability.CST reduction efficiency,interface position and water content of sludge cake have a linear regression model.CST reduction efficiency have negative correlation with SRF,interface position and water content of sludge cake.Using principal component analysis to illustrate the relationship of sludge characteristics during sludge dewatering,such as Zeta potential,sludge particle,bound water content.The results showed there are two principal components,one related to CST reduction efficiency,another related to B-EPS,which can respond the relationship of all indexes.The indexes of the sludge dewatering performance were simplified.