Improving Dewatering Performance Of Excess Activated Sludge By Compound Chemical Conditioning Of Peracetic Acid/Polymer Flocculant

Sewage sludge has the characteristics of large output,high moisture content,large volume,complex composition and secondary pollution problems.It's extremely urgent to find an effective way to solve the treatment and disposal of sewage sludge.Small changes in the moisture content of the sludge can cause large changes in the volume of sludge in the case of high moisture content.Thus,it's great significance to optimize the dewater performance of sludge to improve the status of sludge treatment and disposal.The effect of PAA?Peracetic acid?,polymer flocculant and PAA combined with polymer flocculant conditioning on sludge dewatering performance had been studied in this article.The physical and chemical properties of excess activated sludge flocs during conditioning had been analyzed combined with Excitation-Emission-Matrix Spectra.The main contents are as follows:1.It's effective for PAA to oxidize the sludge cells to release the organic substances and intracellular bound water,the oxidation of PAA destroy the integrity of the sludge flocs causing the reduction of particle size of flocs.The optimum reaction time for PAA to oxidize sludge was 50 min and the optimum dosage was0.1035 g/gMLSS.The sludge had a moisture content of 70.6%,SRF?Specific Resistance of Filtration?of 3.42×10¹² m/kg and CST?Capillary Suction Time?of48.1s under the optimum condition,all of which reached the minimum value.Compared with the original sludge,it decreased by 12.60%,33.98%and 40.32%,respectively.The SEPS?Soluble Extracellular Polymer Substances?increased gradually with the increase of PAA dosage,while the LB-EPS?Loosely Bound-Extracellular Polymer Substances?and TB-EPS?Tightly Bound-Extracellular Polymer Substances?showed a decreasing trend.The effect of PAA on the removal of protein-like substances and aromatic proteins from EPS?Extracellular Polymer Substances?was stronger than that of humic acid and fulvic acid.2.PFS,PAC and CPAM had certain extent to improve the dewatering performance of sludge.The optimum dosage of PFS was 6 g/L,while PAC was 3 g/L and 0.06 g/L for CPAM.PFS had a great influence on SRF while CPAM can achieve the lowest moisture content of filter cake.The improvement effect of polymer flocculant on the dewatering performance of sludge was CPAM,PAC and PFS.The median particle size and Zeta potential increased significantly after the treatment of polymer flocculant.Three kinds of polymer flocculant had little effect of the content of humic acid and fulvic acid in EPS,while a certain removal of protein substances in SEPS was observed.PFS and CPAM had a better removal of protein than PAC.Acidic conditions had an adverse effect on the conditioning of CPAM.3.The treatment of PAA combined with polymer flocculants had a further improvement of dewatering performance of sludge.Sludge cells were oxidized and cracked by PAA first to release intracellular bound water,and the sludge floc particles became smaller,the polymer flocculant added later neutralized the negative charges on the surface of the sludge to reduce the repulsive force of sludge particles,small particles destabilized and collided with each other to form large particles which formed large flocs by adsorption bridges.The skeleton structure existing in the sludge reduced the resistance of the filter cake during filtration and the degree of obstruction of the filter by the small particulate matter.The amount of polymer flocculant used in the combined conditioning method was greatly reduced compared with adding polymer floccutant only,the optimum dosage of PFS was 1.5 g/L,while PAC was 0.9g/L and 0.04 g/L for CPAM,respectively.The sludge had moisture contents of 65.8%,66.3%and 61.7%,SRF of 3.24×10¹² m/kg,3.21×10¹² m/kg and 2.88×10¹² m/kg,CST of 31.5s,38.4s and 37.6s under the optimum condition of PAA+PFS,PAA+PAC and PAA+CPAM,respectively.Three kinds of combined conditioning method made great changes in the microscopic morphology of the sludge,the sludge treated by PAA combined with PFS showed a loose,porous and lumpy structure with large porosity,which could easily keep the water channel open during the dehydration process.The PAA combined with PAC conditioned sludge showed a strip-shaped spatial three-dimensional structure.PAA combined with CPAM conditioned sludge showed a layered spatial three-dimensional structure.