Dewaterability Enhancement And Process Mechanism Of Sludge Under Pretreatment With Modified Corn-Core Powder

With the rapid development of industrialization and urbanization in China,domestic sewage and industrial wastewater are increasing daily.In sewage treatment,the generation of sludge is inevitable.Usually,the sludge which is produced by the municipal sewage treatment plant contains normally over 90%water.Meanwhile,there is a kind of macromolecular polymer,named extracellular polymeric substances(EPS),encapsulate sludge particles.And EPS block the flowing between inward and outward water,hinder the releasing of inner water,thus making the removing of water more difficult.Moreover,the high moisture content not only bring burdens to the transportation and storage of sludge,but also affect its treatment,disposal and resource utilization.Therefore,it is necessary to find an environmental-friendly way for enhancing sludge dewaterability.Biomass,such as straw and rice husk,could be applied to sludge dewatering treatment directly or after modification.Corn-core,which is widely sourced and high heating value,is a kind of natural polymer material.And it contains hemicellulose,cellulose,and lignin,etc.,all of them have functional groups,which could increase the possibility of modification.In addition,a kind of protrin colloid which named zein is easily degraded.Therefore,it is not have an adverse effect on the environment when the raw material of dehydrating agent is corn-core.Meanwhile,dewatered sludge cake is bulky and difficult to transport.However,it contains a large amount of mineral components,which could provide a certain rigidity for the sludge flocs.Aiming at the problem of high water content of sludge and the difficulty of the decreasing of the moisture.This paper uses corn-core and sludge cakes as raw materials to prepare dehydrants,which name modified corn-core powder(MCCP)and sludge-based biochar(SBB),respectively.After conditioning,the sludge could effectively improve the dewaterability and reduce the toxicity while utilizing the two kinds of waste as resources.Based upon the results,following conclusions are drawn.(1)MCCP,which was synthesized from the alkalization-etherification process,played as dehydrant in sludge dewatering process.Adding 20%DS(mass of dry solids in sludge)of MCCP reduced the moisture content(MC)and the specific resistance of filtration(SRF)of the sludge from 99.35%to 61.68%and from 12.69×10¹² m/kg to5.74×10¹² m/kg,respectively.Based on the analysis of mechanism,it indicated that MCCP which showing positive electric property could neutralize negative charges contained in sludge network,disorder and destroy sludge network,further releasing the intracellular bound water which was wrapped in EPS.Meanwhile,the structure of MCCP could re-agglomerate tiny sludge particles through the function of adsorbing,forming large flocs,finally enhancing sludge settleability and dewaterability.And the correlation between the dewatering performance and the physicochemical properties of sludge was analyzed,indicated that larger particle size of sludge flocs and smaller absolute value of Zeta potential may be propitious to reduce content of bound water in sludge.(2)SBB,which was a skeleton builder,was pyrolyzed under oxygen-free conditions.For further improving dewaterability,a technology that combined the use of both MCCP and SBB was proposed.And sludge which was treated by 20%DS of SBB and 20%DS of MCCP reduced SRF decreased by 76%,enlarged the net sludge solids yield(Y_N)from 3.86 kg/m²·h to 55.02 kg/m²·h.Based on the analysis of mechanism,it indicated that SBB could contribute to the construction of a stable skeleton in the sludge network,and facilitate the formation of a porous network structure with high compressive strength,which improved the performance of sludge filtering.Meanwhile,according to correlation analysis,it demonstrated that the re-agglomeration of organics in TB-EPS could enhance sludge dewaterability.(3)The ultrasonic treatment(UT)could provide cavitation effects in sludge network,produce numerous cavitation bubbles which have high shear stress,further releasing bound water and organics.According to experiment analysis,it indicated that the introduction of UT could improve sludge dewatering performance while decreasing the dosage of MCCP/SBB.And the combination of UT,MCCP at a loading of 5%DS with SBB at a loading of 10%DS,the MC of sludge could reduce to(49.07±0.64)%.(4)The sludge pretreating method could impact the composition type and content distribution of organic matter in EPS.Thereinto,the addition of MCCP could impact the organic matter in three types of EPS,and UT could impact TB-EPS.The effects of protein secondary structures on the fixation of heavy metal and dewaterability was investigated.It indicated that!-sheet in protein could provide hydrophobic sites,and the increasing ratio of!-sheet could enhance agglomeration among cells and flocs,improve sorption effects of heavy metals and enhance dewatering performance.(5)Based on the dewatering mechanical experiments,it indicated that the vacuum filtration could obtain a better dewaterability in this paper.Meanwhile,according to the calculation of benefit cost ratio,it demonstrated that four types of sludge pretreating methods have superior environmental and economic efficiency.