Removal of chemical oxygen demand from landfill leachate using cow-dung ash as a low-cost adsorbent

•Very first application of activated cow dung ash for the removal of organic contaminants (COD) from landfill leachate.•79% load of COD was reduced using ACA at 30°C (pH 6.0 using 20g/L dose).•Freundlich and Langmuir adsorption isotherms indicate good fits to the experimental data.•SEM image shows that activated carbon particles make the surface of ACA more porous, leading to high adsorption efficiency.•Comparatively ACA proves to be cost-effective as it has high COD removal efficiency from the wastewater.