Techno-economic and life cycle assessment of renewable natural gas production from brewery wastewater via anaerobic digestion and biomethanation.

This study assessed the techno-economic feasibility and environmental impacts of renewable natural gas (RNG) production from brewery wastewater via anaerobic digestion (AD) coupled with in-situ and ex-situ biomethanation. Four scenarios were examined: scenario 1 employed ex-situ biomethanation with grid electricity, whereas scenarios 2-4 utilized in-situ biomethanation powered by grid electricity alone, grid electricity supplemented with thermoelectric generator (TEG), and grid electricity supplemented with solar panels, respectively. Techno-economic analysis (TEA) showed that the minimum selling price of RNG (MSPR) varied from 2.14 to 2.50 USD/m3, which could be reduced to 1.16-1.65 USD/m3 through process optimization and material cost reductions. Life cycle assessment (LCA) showed that net greenhouse gas (GHG) emissions ranged from 16.6 to 26.9 g CO2-eq per MJ of fuel in the four scenarios, with in-situ biomethanation scenarios exhibiting emissions at the lower end. AD and water electrolysis were the dominant contributors, accounting for 61-65% and 24-31% of total emissions, respectively, driven primarily by steam demand for digestion and electricity use for electrolysis. While process optimization via TEG integration reduced emissions marginally due to the limited electricity production from the waste heat, solar PV integration achieved the largest reduction among all scenarios. Overall, these findings demonstrate that AD coupled with in-situ biomethanation and renewable electricity integration offers an economically promising, low-GHG emissions pathway for brewery wastewater valorization and RNG production.