Use of mixed culture bacteria for photofermentive hydrogen of dark fermentation effluent

•Mixed culture bacteria is a good candidate for photofermentive hydrogen process.•Photofermentive hydrogen process is HRT and OLR dependant.•R. palustris species is dominat bacteria in the photobioreactor.•H2 yield was mainly due to the conversion of COD in the soluble form.•CODt/NH4-N ratio (8.8–12.8) does not influence the amount of hydrogen yield.

Hydrogen production (HP) from dark fermentation effluent of starch wastewater via vertical tubular photo-bioreactor was investigated. The reactor was inoculated with mixed culture of bacteria and operated at light intensity of 190 W/m2. Hydraulic retention time (HRT) and organic loading rate (OLR) was varied between 0.9 to 4.0 h and 3.2 to 16 g COD/l.d., respectively. Increasing the HRT from 0.9 to 2.5 h, significantly (P < 0.05) increased HP from 1 ± 0.04 to 3.05 ± 0.19 l/d, respectively. However, minimal increase in HP occurred when increasing the HRT up to 4.0 h. The HP remained unaffected when increasing the OLR from 3.2 to 6.4 g COD/l.d. Further increase in the OLR up to 8.2 and 16 g COD/l.d., resulted in a drop in HP i.e. 0.96 and 0.19 l/d, respectively. Microbial community analysis of the reactor samples showed the presence and dominance of hydrogen producing purple non-sulfur phototrophic (PNS) bacterium, Rhodopseudomonas palustris in the reactor.