A novel variable pH control strategy for enhancing lipid production from food waste: Biodiesel versus docosahexaenoic acid

Highlights: • A variable pH control strategy was developed for lipid production from food waste. • The produced lipid contained about 5% DHA by adopting the proposed strategy. • The lipid production was increased over 80% after removed the Maillard reaction. • Lipid fermentation coupled with biofertilizer and CH₄ production is more profitable. • Engineering feasibility and economic viability of the proposed strategy was clarified. -- Abstract: A novel variable pH control operation strategy was developed for maximizing energy and resource recovery from food waste by integrating the ultra-fast hydrolysis and lipid fermentation. Food waste after fast hydrolyzed by homemade hydrolytic enzymes, the separated solids can be directly applied as biofertilizer, while the liquor was used for microbial lipid production with oleaginous yeast Rhodosporidium toruloides 2.1389. A novel variable pH control strategy was thus developed for enhanced lipid production. As such, a lipid yield of 11.10 g/kg food waste was obtained, which contained about 5% of highly value-added docosahexaenoic acid (DHA). The residual soluble COD (SCOD) after lipid fermentation was used as organic source for further biomethane production by anaerobic digestion with a biomethane yield of 0.287 L CH₄/g SCOD removed. According to these results, it was estimated that about 7713 tonnes of biodiesel and 422 tonnes of high-value DHA could be produced yearly from Singapore's food waste, together with 32,392 tonnes of dry biofertilizer and 6.48 × 10⁶ m³ of methane gas. Compared to the conventional lipid based-biodiesel production, the total economic revenue could be increased by a factor of 2.03 by adopting the proposed variable pH control strategy due to the high commercial value of DHA. It is expected that the approach developed in this study can open a new window for future food waste management.