Improvement of biohydrogen production through combined reuses of palm oil mill effluent together with pulp and paper mill effluent in photofermentation

Rhodobacter sphaeroides NCIMB8253 and palm oil mill effluent (POME) were applied as the purple nonsulfur bacteria and substrate, respectively, to produce biohydrogen in the photofermentation process. Due to the dark color of POME, pulp and paper mill effluent (PPME) was used as a diluting agent to reduce the turbidity of substrate and, thus, improve light penetration. Anaerobic batch experiments were performed by varying the concentration of POME from 12.5 to 100 (v/v) with 10 (v/v) inoculum in a total of 100 mL of substrate. The highest biohydrogen yield of 4.670 mL H2/mL medium was obtained using NS4 treatment containing 25 and 75 (v/v) of POME and PPME, respectively. A maximum production rate of 0.496 mL H2/mL medium?h and light efficiency of 2.40 were also achieved in NS4. Furthermore, a simultaneous 28.8 of total chemical oxygen demand (CODtotal) removal was obtained after 3 days of photofermentation. An additional increase of POME concentration (>25 , v/v) did not support higher production of biohydrogen due to the increase of turbidity (>16 450 NTU) which resulted in a hindrance of light penetration. This study showed the potential of reusing and combining two different effluents together, in which case one had lower turbidity than the other wastewater, for improving light penetration and, thus, photobiohydrogen production.