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Decarboxylation of short chain carboxylic acids or volatile fatty acids for bioelectricity generation was explored using mixed photosynthetic bacteria as biocatalyst in a single chambered photo-bioelectrocatalytic system (PBES)/biophotovoltaic system. Acetate rich wastewater (ARW) and butyrate rich wastewater (BRW) were synthetically prepared to be used as substrates for the comparative evaluation of photo bacteria catalysed decarboxylation towards bioelectrogenic ability. Bioelectrogenic activity in terms of open circuit voltage, current, and power density in ARW (605 mV; 2.14 mA; 112.20 mW m−2) was 55 per cent higher than that of BRW (208 mV; 0.49 mA; 10.50 mW/m⁻²). The first derivative of cyclic voltammograms also depicted the role of redox shuttles viz., Cytochrome-b and NADPH as electron carriers, detected as peaks in ARW operation in enhancing the performance of PBES. In addition, the phylogenetic inventory illustrated the dominance of proteobacteria such as Rhodopseudomonas sp. and Thiorhodovibrio sp. including N2 fixers (Amoebobacter sp.), which are the potent bio-electrogens. Anoxygenic photosynthesis by purple non-sulphur bacteria has the potential for the treatment of acidogenic effluents from biohydrogen reactor with simultaneous yield of reducing equivalents for power generation. The integration of PBES with conventional biohydrogen production by dark fermentation has a potential application in the field of acidogenic waste valorization, which is in concurrence with the concept of biorefinery.