Photo-fermentative hydrogen production from mixed substrate by mixed bacteria

Photo-fermentative H₂ production by mixed bacteria and pure bacterium Rhodopseudomonas faecalis RLD-53 using single and mixed substrate as carbon source was investigated in batch culture. Experimental results showed that 60 mmol/L acetate was the optimal concentration for mixed bacterial H ₂ production and maximum cumulative H₂ volume was 2468 ± 123 mL H₂/L-culture. It was also found that propionate or butyrate was a key factor for enhancing H₂ production in mixed substrate system. Photo-H₂ production can be greatly promoted when proper concentration of propionate and butyrate were added into acetate medium as mixed substrate and a higher H₂ yield of 2931 ± 146 mL H₂/L-culture was obtained. In addition, it was worth noting that when the strain RLD-53 was added into mixed bacteria with different concentration ratios, H₂ yield did not yet increase. Interestingly, H₂ production capacity gradually decreased with ratio of strain RLD-53 to mixed bacteria from 8:0 to 4:4, and then gradually increased from 4:4 to 0:8. This implied that the competition relationship between strain RLD-53 and mixed bacteria in substrate utilization strongly influenced their H₂ production.