Enhancing bio-electrochemical hydrogen production and organic matter removal from wastewater using Rhodopseudomonas palustris 42OL

Introduction: Rising energy costs in Europe are diminishing economic competitiveness, particularly impacting sectors like food processing. Beer production is energy-intensive and generates significant amounts of brewer's waste (BW)1. While BW is an environmental problem due to its high chemical oxygen demand (COD), it also offers opportunities for resource recovery and sustainable energy production1. Bio-electrochemical systems (BESs) are a promising method for improving BW. They use bacteria to transfer electrons between electrodes. Purple non-sulfur bacteria (PNSB), such as Rhodopseudomonas palustris, are electroactive and can be integrated into BESs, using electrons from the bio-cathode to enhance H₂ yields while reducing total COD at the anode2. This strategy could offer a sustainable approach to support circular economy goals by minimizing waste and generating bioenergy. Materials and Methods: BESs experiments were performed in triplicate in 250 mL single-chamber reactors fed with sterile BW. Each chamber was inoculated with R. palustris 42OL. The system was operated under anaerobic conditions with continuous illumination. Different conditions were compared to explore the effect of cathodic polarization: −0.3V, -0,6V, and -0.8V (vs. Ag/AgCl); furthermore, a control without electrodes was set up. A graphite rod was used as the working electrode, with reference to an Ag/AgCl reference electrode, and a platinized titanium mesh as counter electrode. A non-polarized reactor was operated as a control. COD, gas production, total organic carbon, total nitrogen, and optical density were measured over time. Results and discussion: H2 production in BESs increased when R. palustris 42OL was cultured in the presence of an electrode as an electron donor. The maximum H2 production was obtained with a potential of -0.6V vs Ag/AgCl (Fig. 1). The presence of the electrode also promoted higher % COD removal. At a more negative potential (-0.8V vs Ag/AgCl), the removal was about 70% (Fig. 2).