Anaerobic Treatment of Potato Processing Wastewater in an Upflow Anaerobic Sludge Blanket Reactor and Ex Situ Biomethanation in a Trickle Bed Reactor

Anaerobic digestion enables simultaneous organic waste treatment and renewable energy production. However, the presence of CO2 in biogas limits its calorific value and restricts its direct use as a fuel, making upgrading processes necessary. This study investigated an integrated approach combining anaerobic treatment of potato processing wastewater in a 12 L Upflow Anaerobic Sludge Blanket (UASB) reactor with ex situ biomethanation in a Trickle Bed Reactor (TBR). The UASB reactor was operated for 170 days under different hydraulic retention times (HRTs) and organic loading rates (OLRs), while ex situ biomethanation was subsequently evaluated in the TBR using green hydrogen and a synthetic CH4/CO2 gas mixture representative of the UASB-derived biogas composition. The UASB reactor achieved a maximum biogas production rate of 14.5 ± 3.2 L d−1 with a methane content of 74.5 ± 2.1% at an OLR of 3.5 g COD L−1 d−1 and an HRT of 1.2 days. Subsequent biomethanation in the TBR increased biomethane purity to 98.1%, demonstrating effective CO2 conversion through hydrogenotrophic methanogenesis. Process performance was further evaluated using Anaerobic Digestion Model No. 1 (ADM1), providing mechanistic insights into reactor operation and stability. The results demonstrate that combining UASB treatment with subsequent TBR biomethanation enhances carbon utilization and biomethane quality, offering a sustainable pathway for energy recovery from industrial wastewater.