Unlocking the potential of purple phototrophic bacterial for microbial electrochemical system performance by...

Purple Phototrophic Bacteria (PPB), owing to their unique metabolism and electron transfer capabilities, hold great promise for application in microbial electrochemical systems (MES). This study proposes a new strategy by incorporating solid waste-derived materials (HySludge, HyGreen, and HyOrange) produced by HydroThermal Carbonization (HTC), as functional electroactive carbonaceous materials in PPB-based MES. The study focuses on evaluating the impact of these materials on PPB growth, electrochemical reaction, and microbial community composition under both non-polarized and polarized conditions, with Graphite serving as a control. This study addresses 3 core issues: a) the potential of hydrochars to serve as a stable platform for attachment and electron exchange between PPB and electroactive bacteria (EAB); b) the feasibility of achieving effective extracellular electron transfer (EET) through surface functional groups, despite low electrical conductivity of materials; and c) the capacity of hydrochars to generate electron output under light-driven conditions. The results indicate that HySludge (sludge-derived hydrochar) supported efficient PPB growth and nutrient uptake under non-polarized conditions, achieving removal efficiencies of 95.2 % for acetate and 91.9 % for NH₄⁺. Polarization further enhanced the synergistic coexistence of photoelectroactive and EAB communities such as Rhodopseudomonas, Cereibacter, and Pseudomonas in HySludge systems. It achieved complete removal of acetate and NH₄⁺, generated current density of 1.6 A/m³ with a coulombic efficiency of 1.1 %. Although its conductivity is inferior to that of Graphite, HySludge still demonstrated electrochemical functionality and biological compatibility, indicating its potential as a viable alternative to conventional electrode material.