Polyphosphate metabolism by purple non-sulfur bacteria and its possible application on photo-microbial fuel cell

A purple non-sulfur bacterium, Rhodopseudomonas palustris G11, was isolated from an activated sludge plant that treats domestic wastewater. This isolation resulted in the effective accumulation of polyphosphate in cells upon reaching the stationary growth phase. However, when the carbon and/or energy source were/was removed, this bacterium released intracellular polyphosphate or poly-β-hydroxybutyrate to obtain energy to grow or maintain its growth. Furthermore, a novel photo-microbial fuel cell (PMFC) design was proposed. The unique capability of purple non-sulfur bacteria to capture light energy for polyphosphate accumulation was maximized. After R. palustris G11 accumulated considerable polyphosphate and was transferred to a fresh medium, the PMFC system exhibited a maximum voltage of approximately 0.03 V undt illumination. The chemical oxygen demand removal efficiency, Coulomb efficiency, and power density were 95.8%, 0.62%, and 0.15 mW/m², respectively. The test microorganisms converted most of the light energy in growth and caused the low power production. The microorganisms grew slowly and produced less power under dark conditions than under light illumination. However, these microorganisms used the previously stored polyphosphate or poly-β-hydroxybutyrate for electricity production when they were incubated in a growth-insufficient condition. This novel concept can be improved and optimized in the future for new PMFC applications, such as rechargeable cells, to treat wastewater and restore energy simultaneously.