Work

Integrated resource recovery from co-fermentation of food waste and sludge: Balancing denitrification potential and biogas recovery

Year: 2026

Type: article

Abstract: Replacing fossil-based carbon sources with sustainable alternatives for denitrification supports nitrogen compliance, lowers indirect emissions, and mitigates cost increases in WWTPs. This study investigated the pilot-scale fermentation of food waste (FW) and primary sludge (PS) at different ratios to produce volatile fatty acids (VFA) and lactic acid, for use as carbon source in denitrification. Four substrate ratios (FW:PS) were tested (100:0, 50:50, 25:75, and 0:100) under mesophilic conditions (34 ± 0.4 °C) without pH control. Fermentates from the tests produced a wide range of sCOD (6–82 g COD/L) and VFA concentrations (3–56 g VFA COD /L). No statistically significant differences in VFA yields between reactors were detected, whereas a significant difference in COD yields were observed. Higher FW proportion increased VFA concentrations and shifted the VFA composition towards lactic and propionic acid. Despite these differences, denitrification rates remained consistent (7–9 mg NO 3 − -N/g VSS∙h), suggesting the microbial community's functional flexibility in utilising varying VFA profiles. Methane potential analysis of the solid residues after fermentation and VFA removal indicated that FW-fermentate maintained biogas yields, whilst PS-fermentate showed a 50 % reduction compared to untreated substrates. Estimated carbon source volume demands in large-scale applications varied significantly due to differences in sCOD and nutrient concentrations. Co-fermentation of PS with 25 % and 50 % FW reduced volume requirements by a factor of 8 and 12, respectively, compared to fermenting PS alone. These findings demonstrate the feasibility of fermenting FW and PS to balance denitrification efficiency, biogas recovery, and resource utilisation at WWTPs. • PH and substrate type strongly influence fermentation and microbial dynamics. • FW produces lactic acid profiles, increasing PS shifts fermentation toward propionate. • Co-fermenting PS and 25 % FW balances carbon yield, denitrification and biogas recovery. • Denitrification rates remained stable despite varying VFA compositions.

Source: Journal of Environmental Management

DOI: 10.1016/j.jenvman.2025.128470

Authors: A. Carranza-Muñoz, C. Baresel, A. Malovanyy, A. Singh, A. Schnürer

Institutions: Swedish University of Agricultural Sciences, IVL Swedish Environmental Research Institute, Uppsala University, Ganpat University

Language: English

Topic: Anaerobic Digestion and Biogas Production

Subfield: Building and Construction

Field: Engineering

Domain: Physical Sciences

SDGs: Responsible consumption and production, Climate action, Clean water and sanitation, Affordable and clean energy

Open Access status: hybrid

Estimated APC paid: $3,750