Comparative life cycle assessment (LCA) of up-flow anaerobic sludge blanket fixed-film (UASFF) reactor and continuous stirred tank reactor (CSTR) for biohydrogen production treating palm oil mill effluent (POME)

Abstract

This study conducts a life-cycle assessment (LCA) comparing the environmental efficiency of biohydrogen production from palm oil mill effluent (POME) using laboratory-scale up-flow anaerobic sludge fixed-film (UASFF) and continuous stirred-tank reactor (CSTR) systems. The novelty was conducted granular analysis of energy and carbon dynamics of the system within the LCA framework, following ISO 14040 standards. The LCA evaluates cradle-to-gate impacts (raw material and energy inputs) per functional unit of 1 kg biohydrogen, using SimaPro software and Ecoinvent 3.6 database. System boundaries included inputs (electricity, molasses) and outputs (biogas, effluent), excluding avoided burdens from POME utilization. Both reactors operated at a 24-hour hydraulic retention time (HRT). Energy consumption for CSTR (water bath, stirrer, pumps) and UASFF (water bath, pumps) was measured. Results indicated CSTR outperformed UASFF by 7% in carbon footprint (kg CO2e/kg H2) and energy consumption (MJ/kg H2). The water bath was the largest impact contributor, followed by pumps in both systems. In conclusion, CSTR demonstrated better environmental performance in biohydrogen production, primarily due to lower energy use. The study highlights the significance of operational parameters and component energy efficiency in LCA outcomes, emphasizing the need to prioritize energy-saving measures in reactor design to minimize carbon footprints. Molasses' negative emissions further suggest integrating carbon-sequestering inputs could enhance sustainability in biohydrogen systems.