Value-added utilization of vegetable waste for the production of caproate through carbon chain elongation

With the increasing global population and food consumption, the generation of vegetable waste (VW) has been increasing continuously, causing environmental pollution. Caproate is a fundamental chemical widely used in food and chemical production. Currently, caproate is synthesized by a carbon chain elongation process mainly using ethanol from grains, which leads to potential competition with food and animal feed. This study established an integrated “lactate fermentation + carbon chain elongation” process using VW as a cheap carbon source. The effects of fermentation parameters and pretreatment methods on lactate fermentation were investigated. The highest lactate selectivity of 0.62 g/gVS was obtained, demonstrating the successful conversion of VW into lactate as a substrate for the carbon chain elongation reaction. Furthermore, using the lactate produced from VW, the addition of acetate as an electron acceptor was more effective than butyrate for caproate production. The maximum caproate selectivity of 0.25 g/gVS and carbon utilization rate of 54 % were achieved by adding acetate as an additional electron acceptor in the carbon chain elongation process. These findings not only demonstrated an innovative strategy for caproate production through the integrated process but also proposed a promising approach for efficiently recycling and reutilizing VW to reduce waste pollution and generate value-added chemical products simultaneously.