Unlocking the potential of purple phototrophic bacterial for microbial electrochemical system performance by waste-derived materials.

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.