Effects Of Sawdust On Industrial Sludge Dewaterability

In recent years,with the increase of sewage treatment,the amount of sludge production increase.The composition of sludge is complex,and the most difficult part of sludge treatment prior to disposal is the reduction of the moisture content of sludge.The highly compressible nature of the sludge solids makes the dewatering difficult even at the high pressures of mechanical dewatering.Adding physical additives can improve the sludge structure and increase the dehydration efficiency.Adding physical conditioner can improve the sludge structure and increase the sludge dewaterability.In addition,the papermaking process generates a large amount of solid waste from the branches.This study took the ’industrial sludge as samples.The effects of sawdust and Na2FeO4,FeCl3 and Al2(SO4)3 pretreatment on the sludge dewatering performance and its relevant mechanisms were investigated in this study.The main contents of this study could be summarized as following:Sawdust was used as a skeleton builder in combination with Na2FeO4 to condition sludge.The results showed that pretreating the sludge with a combination of sawdust and Na2FeO4 considerably improved sludge dewaterability over Na2FeO4 conditioning alone.The optimum Na2FeO4 and sawdust dosages were 10%(dry solid)and 40%,respectively,which generated a minimal time to filter(209 s)and a maximal yield at 90%degree of the filtration completion(0.32 kg/(m2·s)).The change of TOC value in the supernatant indicates that the strong oxidizing property of sodium ferrate can effectively crack the cell structure of microorganisms in the sludge and improve the moisture distribution of the sludge.Specific resistance to filtration(SRF)and compressibility and porosity measurements and scanning electron microscope(SEM)images indicated that the sawdust formed a porous and incompressible structure during mechanical dewatering.Sawdust was used as a filter aid for the sludge dewatering.Results showed that sawdust conditioning in FeCl3 presented much better dewaterability than FeCl3 alone.The optimal FeCl3 and sawdust dosage for the best dewaterability was found to be 4.5%and 40%,the time to filter and the yield at 90%degree of the filtration completion were 890 s and 0.16 kg/(m2·s)under the conditions,respectively.Specific resistance to filtration(SRF),compressibility,Zeta potential,porosity measurements and scanning electron microscope(SEM)images showed that the addition of ferric chloride can play a role in the flocculation of sludge.Continued addition of sawdust can further increase the pore channel of the flocculated sludge and maintain the permeability of the mud cake.Sawdust was used as a skeleton builder in combination with aluminum sulfate to condition sludge.The results showed that pretreating the sludge with a combination of sawdust and aluminum sulfate considerably improved sludge dewaterability over aluminum sulfate conditioning alone.The optimal aluminum sulfate and sawdust dosage for the best dewaterability was found to be 60%and 30%,the time to filter and the yield at 90%degree of the filtration completion were 208 s and 0.73 kg/(m2·s)under the conditions,respectively.Specific resistance to filtration(SRF),compressibility,and Zeta potential showed that aluminum sulfate can play a role in electrically neutralizing and settling impurities in the sludge.The addition of wood chips also helps to further increase the dewatering performance of the sludge.In this study,the optimum conditions of "FeCl3 and sawdust" were determined,which provided theoretical guidance for the utilization of industrial sludge.