Rapid population growth, urbanization, and industrialization are continuously increasing global energy demand while intensifying climate change associated with fossil fuel consumption. In this context, renewable energy production from organic waste has gained increasing attention as a sustainable and environmentally friendly strategy. Anaerobic digestion (AD) offers significant potential for simultaneous waste stabilization and biomethane generation. However, many previous studies investigating lignocellulosic or nutrient-rich substrates have relied on physical, chemical, or thermal pretreatment methods to enhance biodegradability, despite their additional operational costs, energy consumption, and environmental impacts. Therefore, developing low-cost and pretreatment-free co-digestion strategies remains an important research need. This study investigated the biomethane production potentials of untreated chicken manure (CM) and duckweed (Lemna minor-LM) collected from the final sedimentation tanks of wastewater treatment plants under mono-digestion and co-digestion conditions. The study hypothesized that rapidly growing and widely available LM biomass could enhance methane production without requiring pretreatment. Among all reactors, CM0.75 (75% of the total TS derived from CM and 25% from LM and inoculum) achieved the highest performance with a cumulative biogas production of 5350 mL (74.2% of CH4) and a methane yield of 327 mL CH4/g VS, while mono-digestion of CM resulted in the lowest methane yield of 104 mL CH4/g VS. The results demonstrated that LM biomass naturally proliferating in wastewater treatment plants can be directly utilized as an effective co-substrate to improve biomethane production from poultry wastes. The proposed approach provides a cost-efficient, eco-friendly, and circular-economy-oriented alternative by eliminating the need for pretreatment while simultaneously valorizing problematic biomass generated in wastewater treatment facilities.

The aim of study was to enhance the biogas production from cattle manure in a combined microbial electrolysis cell and anaerobic digestion system (MEC + AD). The MEC + AD reactor were operated on semi continuous mode under different voltage applications and different organic loading rates ranging from 6 g VS/L.d to 30 g VS/L.d. The study was carried out in two parts. In the first part, MEC + AD and conventional anaerobic reactors were compared in terms of biogas production. In the second part, MEC + AD reactor was operated under different voltage applications (0.3, 0.6, and 1.0 V) and organic loading rates. MEC + AD system exhibited 28–52% better biogas production performances (2.03 L/L/d; CH₄:75.5% vs 1.43 L/L/d; CH₄: 70.4%) compared to control reactor in all sets due to voltage application. In the second part, biogas productions of MEC + AD reactor changed between 3.08 L/L/d and 5.13 L/L/d (75–77.8% CH₄) depending on the organic loading rates and applied voltages. Higher voltages (0.6 and 1.0 V) showed better methane production performances especially at high OLRs with respect to lower voltages. Consequently, MEC + AD reactor could be operated efficiently at extreme operational conditions (HRT of 2 days and OLR of 30 g VS/L/d) that conventional anaerobic reactors can not be operated.

This study investigates the biogas production from cattle manure in a combined microbial electrolysis cell and anaerobic digestion system (MEC+AD). The MEC+AD reactors were operated on semi continuous mode under different voltage applications and different organic loading rates varying from 7 g VS/L.d to 30 g VS/L.d. The study was carried out in two parts. In the first part, combined MEC+AD system and conventional anaerobic digestion were compared in terms of biogas production and organic removal performances at hydraulic retention times of 5, 4, and 3 days to see the effects of voltage application. In the second part, MEC+AD reactors were operated under different voltage applications (0.3, 0.6, and 1.0 V) and organic loading rates at constant hydraulic retention time of 2 days. In terms of biogas production and organic removal rate, MEC+AD reactors were superior to anaerobic control reactor owing to the voltage application. The biogas production of MEC+AD reactors increased from 1.75 to 5.13 L/L/d (71.6-77.8 % CH4) with the increase in organic loading rate. On the other hand, the highest methane yield (0.217 L/g VS) was observed at the lowest organic loading rate of 6.72 g VS/L/d at 5 days hydraulic retention time. The effect of different voltages was not significant in the reactors due to the similar biogas productions and organic removal rates. MEC+AD reactors still operated efficiently even at the highest organic loading rate of 30 g VS/L/d without any instability problem.