High-rate carboxylate production in dry fermentation of food waste at room temperature.

Dry fermentation of food waste was optimized to achieve the maximum solid loading rate for carboxylate production without clogging events in a dry fermenter run at neutral pH. High inoculum-to-substrate ratio improved food waste solubilization and carboxylate yield, but the ratio 15% completely clogged the dry fermenter. Higher leachate circulate rate tended to enhance food waste fermentation, but partial clogging was observed at 13.2 L/h of leachate circulation rate. The dry fermenter achieved carboxylate yield of 428.5 g/kg food waste and volatile solid reduction of 79% at the solid loading rate 4.82 kg volatile solids/m-d. This study first tracks chemical oxygen demand (COD) in food waste dry fermentation, showing maximum soluble COD <60% of food waste COD with residual food waste 13.6-16.3%. The operating cost was as low as $1.7/ton FW, implying that food waste treatment will be cost-neutral if recovered carboxylate can create economic benefit over the operating cost.