Pre-treatment of landfill leachate by biochar for the reduction of chemical oxygen demand: the effect of treatment time, temperature and biochar dose

Landfill leachate is the liquid formed by the decomposition of waste in the landfill and infiltration of water through that waste. It contains high concentrations of ammonia and organic contaminants (measured in terms of chemical oxygen demand, COD). Biochar, produced from woody residues separated from municipal waste, was used for the reduction of COD of the leachate. The produced biochar was characterized by scanning electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller surface area analysis and x-ray photoelectron spectroscopy. By following response surface methodology and specifically the Box–Behnken design, the optimum conditions and effects of time, temperature and biochar dosage were determined. It was stated that biochar dosage was the most influential factor, whereas adsorption time and temperature had a lesser effect on the process. The optimum conditions for COD removal from the leachate were the following: treatment time 140 min, temperature 31 °C and biochar dosage of 1.95 g, where a 75.5% COD removal was achieved. At these conditions, the NH4+-N concentration was reduced by 23%. The spent biochar sample was regenerated by successively washing it with HF, ethanol and NaOH, and the regenerated sample achieved COD removal rates of 71%, indicating the potential for multiple uses.