Coupling of purple phototrophic bacteria with bioelectrochemical blessing constructed wetland for wastewater treatment and electricity generation

Abstract

In this study, a conceptual bioelectrochemical cell coupled with electroactive constructed wetland (ECW) and purple phototrophic bacteria (PPB) (termed as PPB-ECW) was constructed to systematically investigate its mechanisms and operational characteristics in wastewater treatment and electricity generation. A porous pottery pot was employed to replace the conventional proton exchange membrane, forming an open and electroactive environment. In the anode region, typical electroactive bacteria (EAB), represented by Hydrogenophaga and Ignavibacterium, were enriched and primarily facilitated efficient pollutant removal through the oxidation of organic substrates and electron release. In contrast, the cathode was dominated by Rhodopseudomonas palustris, a phototrophic and electroactive bacterium, which established an electrosyntrophic metabolic network characterized by electron transfer and light-driven energy utilization. The direct electron transfer (DET) of cathode PPB mainly depends on the outer membrane c-type cytochrome combined with light-driven cyclic electron flow. This coupling mechanism significantly enhanced pollutant degradation efficiency, with removal efficiencies of COD, TN, NH4+-N, and NO3--N reaching 98 %, 87 %, 88 %, and 100 %, respectively, among which NO3--N exhibited the most pronounced removal. The system achieved a maximum voltage output of 246 mV and a peak power density of 31 mW/m3. Compared with existing bioelectrochemical systems studies based on phototrophic microorganisms, this study systematically explained the synergistic mechanisms between anodic and cathodic microbial communities, and revealed the advantages of PPB in electron uptake and metabolism at the cathode. These findings provide both conceptual support and potential practical implications to further expand the scope of bioelectrochemical-based CW for wastewater treatment and energy recovery.