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.