Sustainable Biomethane Production from Sewage Sludge and Wheat Straw Co-Digestion in the Presence of Polypyrrole Fe₃O₄ Nanoparticles and Alkaline Pretreatment: Life Cycle Assessment Point of View

Biogas production from sewage sludge can be valued in different scenarios of energy usage such as the electricity, heating, and transportation system. Improving the energy production value is the main reason for using different ways such as alkaline pretreatment and nanoparticles (NPs). This investigation uses life cycle assessment (LCA) for evaluating the biomethane production from co-digestion of sewage sludge and wheat straw in the presence of polypyrrole Fe₃O₄ nanoparticles (0, 20, 40, 60, and 80 mg) and NaOH alkaline pretreatment (0 and 5 mg) at mesophilic anaerobic digestion along with optimization for sustainable biomethane production. Results indicated that retention time (RT) and NaOH concentration had a significant effect on biomethane production. But, the effect of NP concentration on biomethane production was not significant. Also, the maximum biomethane production was obtained by NP40Na0 (about 50% higher than the control). On average, adding the NaOH and NPs improved the biomethane yield by about 25–40% vs in comparison with the control. The maximum biogas production yield was related to NP40Na0 with an enhancement of about 35% in comparison with the control. On average, adding nanoparticles and NaOH alkaline pretreatment improved the biogas production by about 10–20% in comparison with the control. Sustainable biomethane production can be obtained at an NP concentration of 50.24 mg and NaOH concentration of 24.04 mg, which increased the biomethane production by about 198%, and reduced human health, ecosystem quality, climate change, resources, and economic cost by about 87, 86, 92, 95, and 87%, respectively, in comparison with the control.