This study delves into advanced methane purification techniques within anaerobic fermentation bioreactors, focusing on selective CO2 absorption and comparing photosynthetic bacteria (PNSB) with chemical adsorbents. Our investigation demonstrates that MgO-Mg(OH)2 composites exhibit remarkable CO2 selectivity over CH4, substantiated through rigorous bulk and surface modelling analyses. To address the challenges posed by MgCO3 shell formation on MgO particles, hindering CO2 transport, we advocate for the utilisation of MgO-Mg(OH)2 composites. In on-site experiments, these composites, particularly saturated MgO-Mg(OH)2 solutions (S2), achieved an astonishing 100% CO2 removal rate within a single day while preserving CH4 content. In contrast, solid MgO powder (S3) retained a mere 5% of CH4 over a 10 h period. Although PNSB (S1) exhibited slower CO2 removal, it excelled in nutrient recovery from anaerobic effluent. We introduce a groundbreaking hybrid strategy that leverages S2's swift CO2 removal and S1 PNSB's nutrient recovery capabilities, potentially resulting in a drastic reduction in bioreactor processing time, from 10 days when employing S1 to just 1 day with the use of S2. This represents a remarkable efficiency improvement of 1000%. This pioneering strategy has the potential to revolutionise methane purification, enhancing both efficiency and sustainability. Importantly, it can be seamlessly integrated into existing bioreactors through an additional CO2 capture step, offering a promising solution for advancing biogas production and promoting sustainable waste treatment practices.
Keywords: MgO-Mg(OH)2 composites; anaerobic fermentation bioreactors; bulk and surface modelling; methane purification; photosynthetic bacteria (PNSB); selective CO2 absorption.