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A novel anthraquinone-2,6-disulfonate/MnOx-doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation.

Biocathode microbial fuel cell performances with respect to azo dye decolorization and electricity generation were examined using two anodic inoculums, textile dyeing sludge (MFC-I) and municipal sludge (MFC-M), to determine the potential performance regulation of the MFC via the selection of anodic inoculum. The results showed that the MFC-I exhibited excellent performance in Congo red decolorization, whereas the MFC-M performed well in electricity generation. The MFC-I achieved fast Congo red decolorization with a first-order rate constant k = 0.0501, which was 34% higher than that obtained by MFC-M (k = 0.0375). The MFC-M exhibited 3.22 times higher power output (29 mW/m2 vs. 9 mW/m2) and 38.0% lower anode impedance (749 Ω vs. 1208 Ω) compared to MFC-I. The functional stains isolated from the anodic biofilm of MFC-I were identified as Pseudomonas sp. and Aquamicrobium sp., while isolates from MFC-M belonged to Pseudomonas sp. and Bacillus sp. Four selected isolates were proved to be exoelectrogens and bacterial decolorizer simultaneously but exhibited different bioelectrocatalytic activities and dye decolorizing capabilities, which could partly explain the performance difference between the two MFCs with different anodic inocula.

High-concentration nitrogen removal coupled with bioelectric power generation in an algal-bacterial biocathode photo-bioelectrochemical system (PBES) was investigated. The PBES can self-sustaining operation with continuous power output under day/night cycle by alternately using photosynthetic dissolved oxygen and nitrate/nitrite as cathodic electron acceptors. The PBES generated a high maximum power of 110mw/m2 under illumination and relatively lower power of 40mw/m2 under dark. The bioelectricity generation was accompanied by high-concentration nitrogen removal in the algal-bacterial biocathode. The NH4 N was removed completely within 120 h while maximum NO3 N removal efficiency of 86% and maximum total nitrogen removal efficiency of 83% can be reached after 192 h at initial NH4 N concentration of 314 mg/L and NO3 N concentration of 330 mg/L. Combined processes of bioelectrochemical reduction and algal-bacterial interactions provided multiple approaches for nitrogen removal in the biocathode, including nitrifying using photosynthetic oxygen, bioelectrochemical denitrification using the cathode as electron donor, heterotrophic denitrification using photosynthetically produced dissolved organic matters as carbon source and algal-bacterial uptake. Accelerated nitrogen removal with simultaneously improved cathode performance was observed at high concentration of nitrogen and phosphate buffer due to enhanced algal activities for photosynthetic oxygen release and enhanced algal-bacterial interactions for nitrogen transformation. Addition of external organic carbon negatively affected nitrification and decreased cathode potential due to oxygen consumption by aerobic carbon oxidation but enhanced denitrification due to continuous release of high concentration of photosynthetically produced dissolved organic matters by alga. The PBEC was demonstrated as an energy-saving approach for high-strengthen nitrogenous wastewater treatment.