Co-fermentation of Food Waste and Swine Manure for VFA Production: Condition Optimization and Resource Recovery

Globally, the management of food waste and livestock waste (such as swine manure) is becoming an increasingly severe environmental challenge. Improper disposal of these organic wastes can easily lead to greenhouse gas emissions, water pollution, and public health risks. However, from the perspective of a sustainable circular economy, they are regarded as potential “urban mines,” rich in organic matter that can be transformed into high-value products. Among these, volatile fatty acids (VFAs), as important platform chemicals, are widely used in bioplastic production, chemical feedstocks, and bioenergy preparation. This study focuses on the anaerobic co-fermentation technology of food waste and swine manure, systematically exploring the impact of key operational parameters such as hydraulic retention time, pH, and substrate ratio on VFA yield. The aim is to provide a scientific basis and technical guidance for the large-scale and efficient recovery of resources from organic waste. I. Experimental Design and Research Methods To comprehensively evaluate the influence of different conditions on the co-fermentation process, this study designed a rigorous comparative experiment. The research was conducted under mesophilic conditions (30-35°C) with a constant organic loading rate. The core variables of the experiment included two hydraulic retention times (5 days and 10 days), two pH levels (5.5 and 9.0), and five different substrate mixing ratios: 100% food waste, 80% food waste:20% swine manure, 50% food waste:50% swine manure, 20% food waste:80% swine manure, and 100% swine manure. This multi-factorial experimental design can clearly reveal the effects of individual factors and their interactions on VFA yield and composition. II. Key Research Findings Through in-depth analysis of the experimental data, this study revealed the key condition combinations for optimizing VFA production. 1. Optimal Condition Combination: Maximizing Yield The results indicated that among all tested condition combinations, the co-fermentation system achieved the highest VFA yield of 1,200 mg COD/L under the conditions of 80% food waste mixed with 20% swine manure, at pH 5.5 and a 10-day hydraulic retention time. This yield was significantly higher than other test groups. This suggests that a moderate substrate mix (predominantly easily degradable food waste supplemented with more nutritionally comprehensive swine manure), a slightly acidic environment, and sufficient fermentation time are the golden rules for synergistically promoting the efficient conversion of organic matter into VFAs.

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