Strategies for improvement of biohydrogen production from organic-rich wastewater: A review

• We reviewed the technologies and the process parameters for optimal biohydrogen production.
• Selection of biohydrogen specialists and enhancing of biomass retention are critical for good biohydrogen production.
• Use of cheap and abundant raw material will be useful in reducing cost of production.
• Subsequent co-production of biohydrogen and methane has the potential to make the process cost effective.
• Metabolic engineering should be the long term strategy for improving existing metabolic pathways and creating new ones.

Biohydrogen can be produced from organic wastewater but the process is limited by low production yields. The aim of this review is to summarize the production strategies which are recently researched for enhancing biohydrogen yield and productivity from organic wastewater. The survey of published work indicates that the dark hydrogen fermentation is the most promising production mode. Current strategies geared towards improving biohydrogen production include: microbial culture immobilization, bioreactor modifications, the optimization of process conditions (temperature, pH, OLR and HRT), culture selection and enrichments, substrate choice, and the metabolic engineering of biohydrogen specialists. Comparative analysis of energy recovery from anaerobic digestion using vinasse-related substrates indicates that the production of methane has a higher energy yield than production of hydrogen. A sequential combination of biohydrogen and biomethanation production phases has the potential for even higher bioenergy recovery from organic wastewater.