Acetate and butyrate as substrates for hydrogen production through photo-fermentation: Process optimization and combined performance evaluation☆

Abstract

Abstract Organic acids viz., acetate and butyrate were evaluated as primary substrates for the production of biohydrogen (H 2 ) through photo-fermentation process using mixed culture at mesophilic temperature (34 °C). Experiments were performed by varying parameters like operating pH, presence/absence of initiator substrate (glucose) and vitamin solution, type of nitrogen source (mono sodium salt of glutamic acid and amino glutamic acid) and gas (nitrogen/argon) used to create anaerobic microenvironment. Experimental data showed the feasibility of H 2 production along with substrate degradation utilizing organic acids as metabolic substrate but was found to be dependent on the process parameters evaluated. Maximum specific H 2 production and substrate degradation were observed with acetic acid [3.51 mol/Kg COD R -day; 1.22 Kg COD R /m 3 -day (92.96%)] compared to butyric acid [3.33 mol/Kg COD R -day; 1.19 Kg COD R /m 3 -day (88%)]. Higher H 2 yield was observed under acidophilic microenvironment in the presence of glucose (co-substrate), mono sodium salt of glutamic acid (nitrogen source) and vitamins. Argon induced microenvironment was observed to be effective compared to nitrogen induced microenvironment. Combined process efficiency viz., H 2 production and substrate degradation was evaluated employing data enveloping analysis (DEA) methodology based on the relative efficiency. Integration of dark fermentation with photo-fermentation appears to be an economically viable route for sustainable biohydrogen production if wastewater is used as substrate.