Conditioning Mechanism Of Municipal Sludge Deep Dewatering And The Establishment Of The Evaluation System For Sludge Dewatering Potential

Along with the increasing improvement of environment consciousness and the deepening strict of national environmental requirements,the ratio of sewage disposal and level of advanced treatment are also increasing.Subsequently the sludge production increases sharply,as the inevitable outcome of sewage treatment.The deep dewatering of sludge can not only realize sludge reducetion,but also lower its follow-up treatment cost.In order to improve the dewatering performance of sludge,PAM and lysozyme as separate or joint conditioner were applied in this study.Then the effect sludge dewatering performances as well as the conditioning mechanism was investigated thoroughly.In addition,it was discussed the resource utilization potential of dewatered municipal sludge briefly.Finally,the correlation between sludge components,characteristics and other performance indicators and sludge dewatering performance?the moisture content of dewatered sludge?,with the experimental data collected during above conditioning process,were analyzed and modelled.Eventually an evaluation system for sludge deep dewatering potential was established by the means of PLS regression.The municipal sludge was yellow-brown,with good fluidity and the water content was found to be about 97.1%⁹7.6%.The CST,SRF and the content of organic matter was 59.2s,7.67×10¹²m/kg and 60.2%,respectively.The CST,SRF,SVI and W was used as indiactor of sludge the dewatering performance to explore the conditioning effect of several PAM.CPAM with molecular weight of 10-12 million and charge density of 60%exhibited the best conditioning effect.With the optimum CPAM dosage of 2.5mg/g DS,the sludge CST,SRF,SVI reduced by 88.4%,96.0%and 26.3%,respectively.However,the W decreased by only7.76%.For purpose of exploring the changes of EPS content and distribution,surface contact angle,zeta potential,bound water content,fractal dimension,aperture analysis and microstructure of sludge during the conditioning process were analyzed separately,which was aiming to investigate the conditioning mechanisms of lysozyme.The results indicated that the ratio of PN/PS in S-EPS rose to 4.21 from 0.972,with CPAM dosage of 2.5mg/g DS.Because the amino of PN carried positive charge and some amino acids possessed hydrophobic side chains,the bound water content reduced by 16.4%,and zeta potential increased from-16.2mV to-10.9mV.The release of intracellular organic matter increased the surface porosity of the flocs,and the median pore diameter decreased,while D2 and flocs size had little change,which indicated that the flocculation effect was not obvious.Joint conditioning with the optimum CPAM above and lysozyme could improve the dewatering performance of municipal sludge by means of increasing its dewatering rate and level.Under the optimum condition with 2.4×10⁶U/g DS lysozyme and 2.5mg/g DS CPAM,the sludge CST,SRF and bond water content reduced by 69.6%,92.3%and 20.2%respectively,and W dropped to 60.0%.Further research was foused on the differences of floc structure of municipal sludge.Compared to the results after conditioning sludge with CPAM alone,the pore diameter was smaller,and the floc became tighter on account of the increase of D2.On basis of data analysis and mathematical modeling,a prediction model was established based on PLS regression,which was W=70.30+0.12 NCST-0.32×10^?-12?SRF-0.60 PNS-0.87 PNL+4.28 PSS+0.44 PSL-0.99 PST.The model obtained could accurately predict the solid content of municipal sludge treated by high-pressure deep dewatering,which was applicable for the conditioning system of CPAM and lysozyme separate or joint conditioning.PCA method was also used to explore the core factors that influenced the sludge deep dewatering performance.It was concluded that PC1 accounted for62.9%of the total Y variation and PC2 accounted for 11.9%.Each component of EPS displayed higher eigenvector projection values than NCST and SRF in PC1.Furthermore,the VIP values of PNS and PST were greater than1,which proved that both PNS and PST were of great significance for sludge deep dewatering performance.