The factors influencing direct photohydrogen production and anaerobic fermentation hydrogen production combination bioreactors

A system that combines fermentative and photosynthetic bacteria makes combined organic wastewater treatment and energy recycling possible. This study introduces a method to separates useful byproduct, such as volatile fatty acids, to serve as the substrate for a serial photobioreactor from the outlet of anaerobic hydrogen fermentation reactor using a ceramic membrane system. Batch experiments were applied to investigate the metabolic characteristics of Rhodopseudomonas palustris WP3-5 under various conditions during photobioreactor operation. The results indicate that a higher temperature (35 °C) improved poly-β-hydroxybutyric acid (PHB) content and hydrogen accumulation. Maximal hydrogen accumulation and reduced PHB synthesis occurred at lower temperature (25 °C) at an initial pH of 6.8.. Glutamate and peptone were more suitable nitrogen sources for hydrogen production than glutamine and NH4Cl. Photohydrogen production results, using various anaerobic fermentation effluents with a dilution ratio of 0.4X, illustrated that an increased photohydrogen production rate (HPR) could be obtained using an anaerobic fermentation influent with an initial C/N ratio of 4. The result obtained when an anaerobic hydrogen fermentation reactor was connected to the serial photobioreactor showed that when the anaerobic hydrogen fermentation reactor outlet dilution increased from 2.5- to 5-fold, HPR increased. The HPR of the three bioreactors in the serial photobioreactor were 269.2, 345.6 and 256.7 mL-H2/L-reactor/day. A UV-sterilizer, which was placed between the fermentation reactor and photobioreactor, resulted in the longer (336 h) operating duration.

► This study combines anaerobic fermentation bioreactor with the followed serial photobioreactor for hydrogen production.
► Maximal photohydrogen accumulation and reduced PHB synthesis occurred at lower temperature (25 °C) at an initial pH of 6.8.
► Glutamate and peptone were suitable nitrogen sources for photohydrogen production.
► Better photohydrogen production rate could be obtained with an anaerobic fermentation influent with an initial C/N ratio of 4.
► A UV-sterilizer, which was placed between the fermentation reactor and photobioreactor, resulted in the longer (336 h) operating duration.