Mechanisms Of Geotextile Bio-Clogging In MSW Landfills Co-Disposed With MSWI Bottom Ash

Incineration has received extensive attention and it is the main municipal solid waste(MSW)disposal method in China.However,incineration produces considerable amounts of bottom ash(BA)as the main by-products.The increasing amount of BA has become a challenge for waste management.Although BA can be utilized as a construction material,its use is not prevalent due to the environmental impacts and market demands.The primary treatment of BA is co-disposed in MSW landfills.Moreover,clogging of leachate collection system(LCS)is a common phenomenon in landfills.As a filter of LCS,geotextiles were often clogged in landfills.But few studies addressed the potential geotextile clogging caused by the co-disposal of BA.With the increased prevalence of waste incineration and co-disposed BA in landfills,it is critical to understand the mechanisms of geotextile clogging and develop bio-clogging mitigation methods for the design of effective LCS.In this study,geotextile clogging was investigated and compared in a simulated MSW landfill leachate(MSWL)and a BA co-disposed landfill leachate(BAL)at different landfill stages.Moreover,the effect of different BA co-disposal ratios on geotextile clogging was studied,including MSW,low ash co-disposed(BA?L),high ash co-disposed(BA?H)landfills,and BA mono-fill.Confocal laser scanning microscopy(CLSM)and metagenomics were used to investigate the characteristics of geotextile bio-clogging and the potential roles of quorum sensing(QS).Furthermore,graphene oxide(GO)was coated in geotextiles to evaluate its potential for bio-clogging mitigation in landfills.The main conclusions are as follows:(1)The effects of BA co-disposal on geotextile clogging were compared.The BA?L increased the geotextile clogging compared to that of MSW,while BA?H and BA decreased the geotextile clogging.Moreover,no obvious clogging was observed in the BA mono-fill.Chemical precipitation was influenced by the changes in the leachate characteristics,including the p H,calcium,alkalinity,and COD.In addition,the BA co-disposal ratios changed the microbial community in the leachate.Consequently,instead of co-disposing BA with MSW,BA should be mono-filled to eliminate the clogging in landfills.(2)Co-disposal of BA with MSW can increase the risk of geotextile Ca CO₃ precipitation,as well as bio-clogging.The formation of biofilm was the main contributor for the geotextiles clogging in both BAL and MSWL,accounting for 44%–77%and 79%–97%on a mass basis,respectively.Moreover,geotextile clogging varied with landfill age due to the change of leachate characteristics.As the leachates stage increased,the clogging material formed in geotextiles increased.The clogging mass in BAL was 1.4-1.6 times of that in MSWL.(3)Co-disposal of BA in MSW landfill accelerates bio-clogging due to the high calcium concentration in BA.The high calcium concentrations accelerated the microbial genes and diversity,increasing the bio-clogging in BA co-disposal landfills.The percentage of cells in BAL was 1.6 times of that in MSWL,while the cell copies of BAL were 1.9 times of that in MSWL.Co-disposal of BA accelerated the secretion of extracellular polymeric substance(EPS).The total amount of EPS in BA?G was 1.5 times of that in MSW?G.Moreover,the bio-clogging formed in BA co-disposal landfill had a higher density with less thickness.(4)BA co-disposal accelerated bio-clogging due to the increasing AHLs contents and QS genes.The bio-clogging mass and QS genes amount in BA?G were 1.6 times of those in MSW?G.Moreover,the bio-clogging was also attributed to QS genes and EPS.Biofilm formation was a balanced result of QS and quorum quenching.Two types of AHLs signal(C₆-HSL and C₈-HSL)were detected in both landfills.The C₈-HSL was the dominant AHLs.(5)The GO-coated geotextile could kill microbes and mitigate bio-clogging in the leachate.After GO was coated,the bacteria counted was decreased by two orders of magnitude.The percentage of live cells was decreased by 24.7%.Also,the EPS contents of bio-clogging were reduced by 56.5%.The mitigation of bio-clogging was attributed to the electrostatic repulsion and increased hydrophilicity.Microbial diversity also changed due to the presence of GO.Bacilli and Clostridia were the most resistant to GO-GT in this study.However,Limnochordia and Symbiobacteriia were very sensitive in the presence of GO.In summary,the co-disposal of BA changed the geotextile clogging by leachate characteristics and microbial community.Moreover,bio-clogging played an important role in geotextile clogging.The co-disposal of BA increased the AHLs contents and QS genes,which further increased the live cells and EPS secretion.In addition,the GO coated geotextile could mitigate the bio-clogging.BA monofill was suggested to the practical landfills to clogging controlling.