Exogenous Elemental Sulfur Promoting Methane Production and Simultaneous Ammonia Nitrogen Removal in Anaerobic Digestion of Food Waste: Experimental Verification and Mechanism Analysis

The treatment of food waste (FW) via anaerobic digestion (AD) is frequently plagued by a low methane yield and ammonia (NH 4 + ) inhibition. This study demonstrates that the addition of elemental sulfur (S 0 ) effectively mitigates both of these issues. Through batch and continuous experiments, it was found that the specific methane yield was enhanced by up to 48.1% and the NH 4 + concentration decreased by 26.9% at the optimal S 0 dosages of 20 mg/L. Metagenomic analysis revealed a dual mechanism underlying this enhancement: at low dosages, S 0 provides a sulfur-containing functional group for the biosynthesis of methyl-coenzyme M, thereby accelerating the rate-limiting “methyl-transfer” step in methanogenesis; at high dosages, it promotes the biosynthesis of coenzyme A, which markedly enhances acidogenesis. Furthermore, S 0 alleviates NH 4 + inhibition by fostering a synergistic interaction between sulfate-reducing bacteria and anammox bacteria, which convert NH 4 + to N 2 . Continuous operation over 140 days confirmed the long-term stability and effectiveness of this S 0 addition strategy. This study provides mechanistic insights into S 0 -driven methanogenesis in complex organic waste (FW) and offers a cost-effective, sustainable approach to enhancing AD efficiency and stability.