Study On Sludge Dewaterability And Utilization By Combination Of Biochar And Fenton Oxidation

The increasing scale of sewage has led to large amount of sludge.Dewaterability constrains sludge treatment mainly.Also the large amount of harmful substances in sludge affects its utilization,therefore,demanding an efficient treatment method that can not only enhance sludge dewaterability but also reduce the contamination.This research focuses on the feasibility of using biochar as a supplemental framework for Fenton conditioning.The optimum ratio of Fenton oxidation reagents was selected by orthogonal test.Based on this,biochars with different concentrations were added in order to investigate the effects of combination,and meanwhile the mechanism was explored.Finally,a pilot-scale bio-drying experiment was conducted.The main research contents and results are as follows:?1?The orthogonal test results show that Fenton oxidation can enhance the dewaterability of sludge.After conditioning,the moisture content of the filter cake was reduced by 6.61%,from 81.28%to 74.67%;the specific resistance of sludge was reduced by 87.28%,from3.57×10¹²m/kg to 3.96×10¹¹ m/kg;the TOC content in the filtrate reached 210.35 mg/L,which was 1.86 times of the original sludge.Meanwhile,the heavy metal contents such as Cd,Cr,Ni,Pb,Zn,and Cu in sludge were all reduced,especially Cr and Ni,obtaining removal rates of 38.89%and 33.63%,respectively.In all,the optimal Fenton reagent ratio was selected to be 90 mg/g DS?dry sludge?Fe²⁺,30 mg/g DS H₂O₂ and 90 mg/g DS CaO.?2?Combining bichar and Fenton reagent can improve the settlebility and dewaterability of sludge.After conditioning,the water content and the specific resistance of the sludge decreased significantly,and the TOC content of the filtrate increased.Moreover,there is a direct correlation between the amount of biochar and the rangebility.After adding 500mg/g DS biochar and Fenton reagent,the moisture content of sludge was decreased by 13.23%,from81.28%to 68.05%;the resistance of sludge was decreased by 93.28%,from 3.57×10¹²m/kg to2.87×10¹¹m/kg;the TOC content in the filtrate increased from 112.95mg/L to 220.35mg/L,which was 1.95 times of the original sludge filtrate.The concentration of Cd,Cr,Ni,Pb,Zn,and Cu in the combined conditiong sludge were reduced to 3.65 mg/kg,106.24 mg/kg,38.61mg/kg,153.47 mg/kg,207.60 mg/kg and 96.49 mg/kg,respectively,with the removal rates of50.49%,57.57%,51.86%,31.62%,35.29%,and 42.40%,respectively,within the sludge agricultural standards;the BCR extraction results show that the none of the conditioning methods can achieve the common stabilization of heavy metals in sludge.Fenton conditioning sludge can increase the proportion of residual Cu and Ni increasing the stability relatively,but it will lead to a decrease in the proportion of residual Pb,and the relative stability will be poor;the TOC content in the combined conditioning sludge was reduced by 14.26%,from 226.86g/kg to 194.51 g/kg;the TN content decreased from 27.17g/kg to 25.65g/kg;the TP content was decreased by 41.44%,from 38.97g/kg to 22.82g/kg;the TK content was increased from1.87g/kg To 2.48g/kg.?3?The three-dimensional fluorescence measurement results showed that Fenton and combined conditioning mainly affect T-EPS to improve sludge dewatering performance.After combined conditioning or Fenton conditioning alone,the fluorescence intensity of protein-like substance fluorescence peak in T-EPS was much lower than that of the original sludge,PAM,and biochar conditioning sludge.And the corresponding TOC concentration also decreased significantly,from 131.75 mg/L to 38.6.mg/L.The fluorescence peaks in the Fenton-conditioned sludge were blue-shifted,and the fulvic-like substance fluorescence peak and the humic acid-like substance fluorescence peak appeared.By correlation analysis,a good linear correlation between the tyrosine-like fluorescence peak and the tryptophan-like fluorescence peak intensity in T-EPS was found,with a R² of 0.9532.And these two peaks showed high correlation witht the TOC concentration with a R² of 0.8901 and 0.9814,respectively.?4?Sludge conditioned by biochar and Fenton show better performance than other groups during the bio-drying process.The sludge with 500 mg/g DS biochar could reach 48.9°C and its moisture content was reduced to 58.51%on the 6th day,which could meet the needs of subsequent sludge treatment and disposal.