Mechanism And Abatement Approaches Of Clogging Of Leachate Collection System In MSW Landfill

The clogging of the leachate collection system（LCS）is a common issue in most landfills in China,which would cause the accumulation of the undrainable leachate within the landfill body and be the causation of series problems on both safety and environment.Because of the higher food waste proportion in Chinese MSW,more leachate is generated and higher concentrations of particulate matters and volatile fatty acids（VFAs）are contained in the leachate.All these leachate characteristics are conducive to the clogging development.Meanwhile,some MSW landfill sites are also applied as the final disposal facilities for the sewage sludge and incineration ash.As regarded the collection of particulate matters and Ca²⁺,these waste landfilling would accelerate the clogging process furtherly.Facing the serious clogging challenge in landfilling,this thesis conducts the researches by progressive type.Firstly,enlightened by the field investigations,systemic experiments are carried out to clarify the mechanisms on both the physical clogging caused by the particulate matters retaining and the bio-chemical clogging caused by the VFAs degradation and metal ion precipitation,separately.Secondly,a numerical simulation model is developed to evaluate the dynamic evolution of the LCS clogging in China based on the mechanisms and parameters observed in the above experiments.Finally,supported by the model,the controlling methods for the integrated leachate drainage and landfill management are proposed.The main results from this research are as follows:The suspended particulate matters were mainly generated by the food waste in China and characterized by larger particle size（>30%TSS particles>15μm）and higher concentration(TSS level>2200 mg L^-1)in the raw leachate.The filtration test indicated that the hydraulic conductivity of the geotextile layer could decrease to 10^-8-10^-9 m s^-1 if the filtration flux beyond 1 m³ m^-2.A set of column experiments carried out by the synthetic leachate irrigation proved that the coralline-like clogging materials were inert biofilms and precipitated CaCO₃.Meanwhile,the abundant VFAs in the leachate led to the CaCO₃ formation was restricted by Ca²⁺concentration.The geotextile,as the good carrier for microbial growth,clogged much quicker than the gravel layer.Within 200 days operation,the hydraulic conductivity of it could decrease by 5 orders of magnitude.Based on the clogging mechanism and parameters obtained from the field investigation and above experiments,a finite element numerical model was developed to coupling analyze the LCS clogging development and the leachate accumulation in long-term.The results showed that the retained particulate matters（66.7%）and biofilms（29.3%）could fill up the pore of geotextile within 1 year landfilling.This would make the equivalent vertical hydraulic conductivity of the entire LCS less than 10^-8 m s^-1 and result the leachate accumulation in the waste layer rapidly.With the increase of operation time,the clogging dominated by biochemical reactions was developing gradually and continuously.About 17 years later,the layer was completely invalid by the inert biofilm（34.7%）and the deposited CaCO₃（52%）,resulting the sharp increasing of the stagnant water level in the landfill body and the leachate head above the bottom liner.The simulation results of different scenarios indicated that the LCS service life could extend from less than 1 year to about 6 years by removing the geotextile filter layer.After that,the new-layered drainage system was required.Furthermore,when enlarging the gravel layer thickness or the drainage pipe diameter by 10%,extra 5.2%or 3.7%operational life could span.If the food waste proportion could halve by mixed waste classification and treatment,the clogging time would delay by 39.5-81.3%（without/with geotextile layer）.In addition,the dewatered sewage sludge and MSWI fly ash should be isolated from the MSW and equipped with the independent leachate drainage system to decelerate the clogging development.