Study On Improved Sludge Dewaterability Using Persulfate Activated With Humic Acid Supported Nanoscale Zero-valent Iron

With the rapid development of economy in China,the construction scale and service area of wastewater treatment plants?WWTPs?has been growing,and the amount of waste water treatment has also increased.However,waste activated sludge come into being inevitably in the waste water treatment.The massive increase in waste activated sludge production escalated the operational costs of sludge disposal in wastewater treatment plants,and the generated sewage sludge that is not disposed effectively poses a serious pollution threat in our country.Therefore,it is necessary to reduce the volume of sewage sludge by sludge conditioning method.Only in this way,can we reduce the sludge transportation cost,thereby controlling related environmental risks.Extracellular polymeric substances?EPS?are a key factor that sewage sludge dewaterability is difficult.Persulfate?PS?,as a strong oxidant,is easy to store,diffluent and inexpensive.It can destroy the sludge floc structure and dissolve the EPS component of sludge effectively.In this study,humic acid supported nanoscale zero valent iron?nZVI/HA?as a novel nanocomposite was synthesized.The nZVI/HA nanocomposite was used as persulfate?nZVI/HA-PS?activator to enhance sludge dewatering.The sludge sample used was harvested from Gongzhufu WWTP located in Hohhot,Inner Mongolia.The specific resistance to filterability?SRF?and water content?Wc?were used as the indicators of sludge dewaterability.The influencing factors such as mass ratios of nZVI to HA,initial pH,PS dosage and nZVI/HA nanocomposite dosage were investigated by batch experiments.The potential mechanism of nZVI/HA-PS combined with the optimized conditions of sludge was revealed,which provided theoretical support for the development of sludge dewatering technology in practice.The main research conclusions are as follows:1)nZVI/HA was synthesized by a classical liquid reduction method and characterized by field emission scanning electron microscope?FE-SEM?,energy dispersive spectrometry?EDS?,Fourier transform infrared?FTIR?,and Brunauer Emmett Teller method.Therefore,we are aware of the microscopic properties,surface structure,functional groups and elemental composition about nanomaterials.The results indicate that nanoscale zero valent iron particles are uniformly dispersed on humic acid,which solves the problems of easy aggregation and instability about nanoscale zero valent iron.This work provides theoretical basis for studying the mechanism that improved sludge dewaterability using persulfate activated with nZVI/HA.2)Based on the single factor experiment method,the optimal conditions for improving sludge dewaterability using persulfate activated with nZVI/HA were obtained.Under normal temperature and without pH adjustment,SRF reduction efficiency was 86.47% and moisture content sludge cake was 79.87% using initial concentrations of 1.2mmol/gVSS PS and 300 mg/L nZVI/HA(m_nZVI:m_HA=1:3).3)Variation of the protein and polysaccharide content in EPS under chemical conditioning was investigated concretely and the microscopic characteristics of the sludge particles were analyzed to reveal the reaction mechanisms.The results show that persulfate is activated by nZVI/HA to generate sulfate radicals?SO₄^-·?,which has a strong oxidation capacity could efficiently decompose the sludge floc.TB-EPS decomposition was the major mechanism of nZVI/HA-PS treatment,and the protein-like organic components in TB-EPS were converted into S-EPS.In addition,introducing of HA particles not only effectively prevented the aggregation of nZVI but contributed in decreased sludge compressibility by serving as skeleton builders during sludge dewatering.It is demonstrated that nZVI/HA-PS would become a promising economical method for improving sludge dewaterability.