Study On The Improvement Of Sludge Dewatering Performance By Bioleaching-skeleton Builder Compound Conditioning

Dewatering treatment is an essential part of the disposal of municipal sludge.Sludge contains a large amount of hydrophilic extracellular polymeric substances(EPS)and sludge flocs,which hinder the release of bound water in sludge.In addition,sludge with high content of organic matter is easy to be compressed during the stage of mechanical pressure filtration,leading to the blockage of drainage channels and the reduction of permeability in the sludge,and finally affecting the degree of dehydration and filtration performance of the sludge.Bioleaching could acidify sludge,thereby releasing bound water from EPS and sludge flocs,and skeleton builder could improve the incompressibility of sludge.Based on this,in this study,industrial waste coal fly ash(CFA)was used as the skeleton builder,and the effects of conditioning on sludge dewatering performance were explored by bioleaching combined with coal fly ash(BL-CFA).The optimal operating parameters,reaction mechanism,and operating economy of the compound conditioning were analyzed in this study.The optimal operation parameters of the BL-CFA process were optimized by response surface methodology,that is,the inoculum size was 5.25%,the dosage of sulfur powder was 5.23 g/L,and the dosage of coal fly ash was 434.34 mg/g DS(Dry solid).At this time,the capillary suction time(CST)and water content(WC)of the sludge were 27.3 s and 59.20%,respectively.After the compound conditioning,the CST and WC of the sludge were reduced by 52.27% and 38.91%compared with the raw sludge,and the compound conditioning treatment effect was better than the single bioleaching treatment effect.After conditioning by the BL-CFA process,the heavy metal content of Zn,Cu,and Cr was dramatically decreased by 66.33%,41.17%,and 38.57% respectively,which effectively reduced the pollution risk of heavy metals in the subsequent resource utilization of sludge.The analysis of scanning electron microscopy demonstrated that the BL-CFA process could effectively crack the EPS and flocs of sludge,forming a skeleton supporting structure in sludge,thus improving the incompressibility of sludge.The indicators such as total nitrogen,total phosphorus,soluble chemical oxygen demand,and the analysis of fourier infrared spectroscopy further confirmed that the compound conditioning could crack the EPS and flocs of sludge,releasing the bound water in sludge.The analysis of laser particle size indicated that the compound conditioning could promote the agglomeration and flocculation of sludge particles.The results of the three-dimensional fluorescence spectrum analysis showed a decrease in the fluorescence region of proteins and soluble microbial by-products in LB-EPS and TB-EPS,and the hydrophilic proteins in EPS were released into the supernatant of sludge,which was conducive to the improvement of sludge dehydration performance.The mechanism of the BL-CFA process to improve sludge dewatering performance could be described as cracking,flocculation,and skeleton builder.Firstly,bioleaching cracks the EPS and flocs of the sludge through biological oxidation and acidification,releasing the bound water.Secondly,the aluminum ions released from coal fly ash during bioleaching acidification could further neutralize the negative charges on the surface of sludge particles and reduce the electrostatic repulsion between sludge particles,contributing to the agglomeration and flocculation of sludge particles.Finally,the silica particles in coal fly ash are insoluble in the acid,and it plays a skeleton supporting role in the sludge,which improves the incompressibility and porosity of the sludge and promotes the deep dehydration of the sludge.Pearson correlation analysis revealed that the WC of sludge filter cake had a significant positive correlation with the protein content in LB-EPS and the polysaccharide content in TB-EPS,while a high negative correlation with the protein content in S-EPS.The CST of sludge was highly positively correlated with the protein content of TB-EPS and the polysaccharide content of LB-EPS,while highly negatively correlated with the protein content and polysaccharide content of S-EPS.The results of the economic analysis showed that the cost of the BL-CFA process is 298 RMB/T of dry sludge,and the WC of sludge could be reduced to less than 60% after the treatment of the BL-CFA process.