Retention of Phosphate by Bentonite-Amended Fly Ash Liner

Municipal solid waste (MSW) is typically composed of organic and inorganic constituents that can decompose and release substantial amounts of phosphate into the environment, while impoundments contain the same phosphate-contaminated leachate. Stormwater retention ponds, on the other hand, have high concentrations of phosphate resulting from surface runoff. Infiltration of these waste liquids into the subsurface can contaminate the groundwater which necessitates the use of engineered liners to prevent such conditions. Compacted clay and geosynthetic clay liners are commonly used liners in these waste containment systems, but availability of these materials in remote areas of developing countries is challenging. This study proposes using bentonite amended fly ash as a potential sustainable alternative liner. Fly ash is a locally available by-product of coal combustion at power plants, and use of this will prevent its disposal and utilize it as a useful resource material. Preliminary studies showed 80% fly ash and 20% bentonite mix proportion is optimal to provide required hydraulic conductivity. The present study reports laboratory testing to investigate phosphate retention at this optimal mix conditions. Batch tests are conducted using fly ash and bentonite to determine their removal potential under different phosphate concentrations. In addition, column experiments were conducted on optimal bentonite-amended fly ash to assess the hydraulic conductivity and phosphate retention potential. Overall, the test results showed that the optimized bentonite-amended fly ash will serve as an effective low permeable liner with efficient phosphate retention.