Techno-economic analysis for barrier materials in landfills

Abstract

The safe disposal of waste materials, both domestic and hazardous, requires a detailed geoengineered solution, with the isolation of the waste material from the environment being the main consideration. Generally, the low permeability soil (k < 10−9 m/s) is used as a barrier material in landfills so that it could resist the infiltration of leachate into the soil. Composite clay liner (CCL) consisting of a fine-grained soil layer with low hydraulic conductivity, overlain by a geomembrane are commonly used to line and cover municipal solid waste landfills. But it is not always possible to find the clays with low permeability locally. Sand–bentonite mixtures can be used as a fabricated soil liner (FSL) material as an alternative. The addition of adequate amounts of bentonite (5–30%) can improve the performance of granular material providing both low permeability and an enhanced mechanical stability. This paper includes results of an experimental study on FSL to study their behaviour by blending locally available sandy/silty soil with bentonite varying from 0 to 40% for sand and 0 to 15% for silt. The experimental program comprising evaluation of basic index properties such as Atterberg Limits, specific gravity, compaction tests, etc. and a detailed study of the compressibility and hydraulic characteristics of the sand–bentonite and silt–bentonite mixes was done. The optimum range of bentonite content for sand and silt are arrived as 10–15% and 5–10%, respectively. In many cases, a geosynthetic clay liner (GCL) is also used as liner material, which is factory-manufactured clay liner consisting of a thin layer of bentonite encased between two geotextiles or glued to a geomembrane. The paper also overviews the relative merits/ demerits of different barrier materials regarding their suitability for application in varied field conditions. A comparative cost analysis to the use of CCL, FSL and a GCL as a barrier material in landfills/waste containment facilities in order to judge the economic viability of different materials is presented. It has been analysed that FSL is more economical as compared to other engineered liner types for a lead beyond 100 km. GCLs can be used when both bentonite and suitable clay are not available nearby and have to be transported from long distances.