Migration and transformation law of DOM from landfill leachate in sandy soil

ZHAO Li; ZHANG Yiyang; JIN Yi; ZHANG Qing; LIU Jingyu; WEI Jie; HE Shichang

doi:10.16186/j.cnki.1673-9787.2021100070

Abstract：Objective Jiaozuo municipal solid waste sanitary landfill has a long operating period(more than 10 years),with problems such as aging of the anti-seepage layer and high risk of leachate leakage into groundwater.Methods In this study,the old landfill leachate diluted 5 times was taken as injected leachate,and the silty sand soil obtained from the landfill was used as the medium.The indoor soil column simulation experiment was carried out under the condition of hydraulic retention time of 32 h to analyze the law of mi-gration and transformation of dissolved organic matter(DOM)in aged landfill leachate.Results The results showed that within 0-2618 hours,the variation patterns of dissolved organic carbon(DOC),chemical oxygen demand(COD),and UV absorbance(UV254)at 254 nm wavelength per cell path in groundwater were simi-lar,and the linear correlation among the three was significant,indicating that the DOM component was mainly composed of aromatic compounds;CXTFIT2.1 software fitting results showed that DOC and COD blocking coefficients(3.01 and 1.96)and attenuation coefficients were at a low level,indicating that sand adsorption of organic matter is limited.In the early stage of the experiment,FI of leached solution was al-ways higher than FI of leached solution,indicating rapid growth of microorganisms in the early stage of the experiment.The fluorescence index FI values of all samples were consistently higher than that of the leach-ate,indicating rapid microbial growth in the early stage of the experiment.The Landfill leachate DOM con-tained a significant amount of fulvic acids(peak A,peak C),humic acids(peak E)and a small amount of protein-like substances(peak T2).The microbial metabolites(peak B)of microbial metabolite in S1 was from the sandy soil used in the experiment.The peak B in S1 and T2 in S2 disappeared over time,leaving behind difficult to degrade the peaks A,C and E.The organic components of leached liquid changed obvi-ously,and the simple protein-like substances gradually disappeared,and complex difficult-to-degrade humic substances gradually accumulated.During the experiment,the total fluorescence peak intensity of unit or-ganic carbon in leachate was higher than that in leachate,indicating that the degree of aromatization and hu-mification of leachate increased during the migration and transformation process.Conclusion The results can provide reference for the disposal of landfill leachate and environmental risk assessment.