Enzymatic valorization of food waste leachate into volatile fatty acid-rich carbon source for enhanced denitrification.

Food waste leachate (FWL) is a high-strength organic waste stream that poses increasing disposal and resource recovery challenges. This study developed an integrated enzymatic fermentation strategy to convert FWL into a volatile fatty acid (VFA)-rich carbon source for wastewater denitrification. Screening of ultrasonic, alkaline, alkaline-thermal, and enzymatic pretreatments identified the combined amylase-protease treatment as the most effective for FWL solubilization, increasing SCOD by 23.4% and promoting the release of biodegradable organic matter. During semi-continuous thermophilic anaerobic fermentation (55 ± 2°C, HRT 3 d), the enzymatically pretreated FWL showed enhanced VFAs production compared with the untreated system, with acetate and butyrate as the dominant products. The fermentation broth derived from enzyme-pretreated FWL achieved 99.5% NO3--N removal within 8 h and showed nitrate-removal performance comparable to commercial sodium acetate. Metagenomic analysis indicated that enzymatic pretreatment enriched hydrolytic and acidogenic microorganisms associated with VFAs production, particularly Sporanaerobacteraceae and Tepidanaerobacter, while the VFA-rich fermentation broth promoted the enrichment of denitrifying bacteria such as Thauera and Paracoccus. Moreover, economic analysis shows that using FWL-derived fermentation carbon sources can reduce the estimated annual external carbon source cost by 34.4% compared to sodium acetate. These findings demonstrate a feasible waste-to-resource pathway for recovering intrinsic organic carbon from FWL as an alternative carbon source for wastewater denitrification.