Coal fly ash and lime addition enhances the rate and efficiency of decomposition of food waste during composting

To evaluate the use of coal fly ash (CFA) on the decomposition efficiency of food waste, synthetic food waste was mixed with lime at 1.5% and 3% (equivalent to 0.94% and 1.88% CaCO3, respectively), CFA at 5%, 10% and 15% with lime so as to achieve CaCO3 equivalent of 1.88% and composted for 42 days in a thermophilic 20 l composter with two replicates each. Alkaline materials at 1.88% CaCO3 equivalent successfully buffered the pH during the composting and enhanced the decomposition efficiency. When these buffering was achieved with CFA + lime, the composting period could be shortened to ∼28 days compared with ∼42 days in 3% lime. Organic decomposition in terms of CO2 loss, carbon turnover and nitrogen transformation were significantly higher for treatments with 1.88% CaCO3 equivalent. Nutrient transformations and compost maturity parameters indicated that addition of CFA (5–10%) with lime at 1.88% CaCO3 equivalent enhances the decomposition efficiency and shortens the composting period by 35%.