Research perspectives on constraints, prospects and opportunities in biohydrogen production

Hydrogen gas can be formed from sewage sludge treatment via anaerobic digestion (AD) as this sludge contains large amount of organic matters. In this review, a comprehensive attempt has been made to revisit the main updates, advantages and disadvantages surveyed in recent research (2012–2017) on fermentative hydrogen production from a variety of biomass. The main findings of this review are now stated. The biological hydrogen production processes consist of indirect and direct biophotolysis, dark fermentation, two-stage fermentation and photo-fermentation. To maximize hydrogen gas yield via such technique, the activity of hydrogen-consuming bacteria should be inhibited at the acetate and hydrogen formation stage to stop or reduce hydrogen consumption. The major constraints in biological hydrogen production processes are raw material cost, low hydrogen evolution rate and yield at large scale. Lignocellulosic materials generate low yield of hydrogen gas due to the presence of refractory lignin while food waste containing carbohydrates and starch yields more hydrogen gas. Effective pretreatment of substrates and inoculum can enhance hydrogen yield. In dark fermentation process, better performance can be obtained with pretreatment. Nitrogen sources such as yeast result in higher biohydrogen generation rate and cell growth from the presence of amino acids and proteins. In photo-fermentation, better results can be obtained by using a combination of photosynthetic bacteria and green microalgae, as it enhanced solar energy utilization. Future development such as genetic manipulation could be employed, which mainly focuses on the disruptive characteristics of endogenous genes. The efficiency of biohydrogen production can also be increased by lowering the costs of delivery, production, conversion, storage and practical applications. Apart from using biodegradable wastes, green wastes will be the mostly preferable targeted feedstock for hydrogen fermentation because of their large quantity and having simultaneous waste treatment benefit.