Effect of Co-Digestion Ratios and Temperature on Biomethane Production in Anaerobic Co-Digestion of Cheese Whey and Tomato Waste

Tomato processing and dairy industries generate significant effluents worldwide, contributing to environmental pollution and nutrient loss. Anaerobic digestion (AD) offers a sustainable solution by treating these effluents while recovering nutrients and producing biomethane. Substrate composition and temperature play a key role in AD efficiency. This study investigates the batch co-digestion of tomato waste (TW) and cheese whey (CW) under mesophilic (37 °C) and thermophilic (55 °C) conditions over 20 days. Fresh cow manure (CM) served as the inoculum, maintaining a substrate-to-inoculum ratio of 1 (S/I = 1) across all digesters. The co-digestion ratios (CDRs), expressed as CW/TW (gVS/gVS), were set at 4.6, 1.7, 0.8 and 0.3. Co-digestion of TW with CW produced 2.5 times higher methane yield than mono-digestion of TW in both temperature conditions. Similarly, among all digesters set under both temperature conditions, digester 2 (CDR = 4.6) exhibited the highest performance, producing 44 mL/gVS-added cumulative methane under mesophilic conditions and 182.5 mL/gVS-added under thermophilic conditions. Across all CDRs, thermophilic digesters outperformed mesophilic ones, generating three times more biomethane. The modified Gompertz model effectively described the experimental data, achieving R2 values between 0.97 and 1, confirming an excellent fit.