Integrative Biological Hydrogen Production: An Overview

Abstract

Biological hydrogen (H 2 ) production by dark and photo-fermentative organisms is a promising area of research for generating bioenergy. A large number of organisms have been widely studied for producing H 2 from diverse feeds, both as pure and as mixed cultures. However, their H 2 producing efficiencies have been found to vary (from 3 to 8 mol/mol hexose) with physiological conditions, type of organisms and composition of feed (starchy waste from sweet potato, wheat, cassava and algal biomass). The present review deals with the possibilities of enhancing H 2 production by integrating metabolic pathways of different organisms-dark fermentative bacteria (from cattle dung, activated sludge, Caldicellulosiruptor, Clostridium, Enterobacter, Lactobacillus, and Vibrio) and photo-fermentative bacteria (such as Rhodobacter, Rhodobium and Rhodopseudomonas). The emphasis has been laid on systems which are driven by undefined dark-fermentative cultures in combination with pure photo-fermentative bacterial cultures using biowaste as feed. Such an integrative approach may prove suitable for commercial applications on a large scale.

Production of Polyhydroxyalkanoate Co-polymer by Bacillus thuringiensis

“…However, it was soon realized that to make the whole process economical, we need to derive other products as well such as H 2 and PHB [1,5]. Efforts to produce H 2 , PHB and methane in different stages from the same feed have been found to be feasible [13,[17][18][19]. Now the issue is to improve the quality of PHB, which is otherwise very brittle in nature.…”

Biorefinery for Glycerol Rich Biodiesel Industry Waste

“…Approaches to integrate dark and photosynthetic hydrogen production processes are being advocated to break the barrier of 4 mol H 2 /mol hexose sugar [60,61]. Rhodopseudomonas palustris grows well and can produce H 2 on glycerol as feed.…”

Biodiesel Industry Waste: A Potential Source of Bioenergy and Biopolymers

“…Citrobacter, Clostridium, Enterobacter, Klebsiella, and Thermotoga are among those few organisms which have been widely studied for their BHP abilities [17,19]. More recent scrutiny of the large number of studies done on BHP have made very interesting revelations: (1) dark-fermentative process operative in batch culture can lead to a H 2 yield in the range of 0.16-3.8 mol/mol hexose sugar, (2) photo-fermentative routes functioning in photosynthetic organisms can help in achieving a target of 0.23-7.2 mol H 2 /mol hexose sugar, (3) metabolism of biowastes by dark-fermentative followed by photo-fermentative routes can allow H 2 yields in the range of 0.6-8.3 mol H 2 /mol hexose sugar [2,[17][18][19]. This sequential fermentation route can allow us to surpass the theoretical H 2 yields of 4 mol/mol hexose sugar [2,17,20].…”