Gas transport in landfill cover system: A critical appraisal. (1st November 2022)

• Record Type: Journal Article
• Authors: Wang, Qiao; Gu, Xiting; Tang, Suqin; Mohammad, Arif; Singh, Devendra Narain; Xie, Haijian; Chen, Yun; Zuo, Xinru; Sun, Zhilin
• Is Part Of: Journal of environmental management. Volume 321(2022)
• Publication Date: 2022-11-01
• Subjects: Landfill cover -- Reactive gas transport phenomena -- Multiphase porous media -- Experimental and numerical studies. contents; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2022.116020
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Landfill gas (LFG) emission is gaining more attention from the scientific fraternity and policymakers recently due to its threat to the atmosphere and human health of the populace living in surrounding premises. Though landfill cover (LFC) (viz., daily, intermittent and final cover) is widely used by landfill operators to mitigate or reduce these emissions, their overall performance is still under question. A critical analysis of available literature, primarily pertaining to (i) the composition of the landfill gases and their migration in the LFC system, (ii) experimental and mathematical investigations of the transport mechanism of gas and (iii) the impact of additives to cover soils on transport and fate of gas, has been conducted and presented in this manuscript. Investigation of the efficiency of modified soil was mainly focused on laboratory test. More field tests and application of amended cover soils should be conducted and promoted further. Studies on nitrous oxide and emerging pollutants, including poly-fluoroalkyl substances transport in landfill cover system are limited and need further research. The transport mechanisms of these unconventional contaminants should be considered regarding the selection of LFC materials including geomembrane and geosynthetic clay liners. The existing analytical and numerical models can provide a basic understanding of LFG transport mechanisms and are able to predict the migration behaviour of LFG; however, there are still knowledge gaps concerning the interaction between different species of the gas molecule when modeling multi-component gas transport. Gas transport through fractured cover should also be considered when evaluating LFG emission in the future. Simplified design method for landfill cover system regarding LFG emission based on analytical models should be proposed. Overall, mathematical models combined with experiments can facilitate more visualized and intensive insights, which would be instrumental in devising climate adaptive landfill covers. Graphical abstract: Image 1 Highlights: Mechanisms of LFG including methane and VOCs transport in LFC are discussed. Gas diffusivities and permeabilities of different cover materials are summarized. The performance of LFC can be improved by additives including biochars and biowastes. Analytical and numerical approaches for LFG transport through LFC are compared. Molecule scale multi-component gas transport in LFC needs further studies.