Globally, every year we currently consume the equivalent of over 11 billion tonnes of oil from fossil fuels. Crude oil reserves are vanishing at the rate of 4 billion tonnes a year (CIA world fact book), at this pace without any increase for our growing population all known oil deposits will be gone by 2052. The world is now turning to a search for clean energy source to mitigate coming climate change and the impending shortage of readily available fuel. Hydrogen can be an alternative source of fuel energy being eco-friendly and having a high energy density (122KJ/g). A lot of research is being carried out to find the most sustainable and renewable way of producing hydrogen. Biological dark and photo fermentation of biomass to liberate hydrogen has found light in recent times due to its efficiency. But finding an appropriate biomass that is both sustainable and cost effective is the main concern.
Low hydrogen yield, high cost of substrate and inoculum are the major bottlenecks in biohydrogen production through fermentation. Using algal residue as substrate and digested sludge as inoculum could be used to overcome these limitations. Extraction of oil from algae is another field of research taking light these days, but what is the fate of the algal cake or residue after extracting the oil? Is it going to be another hazard to the environment? These are some of the questions which may arise and the corresponding answer would be to use the residue effectively to produce hydrogen. It’s known that more than 20 strains of algae have the potentiality to yield oil and only the lipid fraction of the algae contributes towards the yield. Algae are composed of 25-30% of lipid and the remaining 70% is composed of carbohydrate and proteins [1]. Therefore, the left over carbohydrate fraction can be effectively utilized to produce hydrogen through fermentation. This overcomes the problem of high cost substrate.
On the other hand, digested sludge can be used as a source of inoculum or microorganism for fermentation, as the sludge is readily available and will not cease to exist until the end of human race. Using digested sludge solves another drawback of high inoculum cost; however, some effort has to be put into optimizing the sludge to suit the requirement of the process. But a lot of study has been undertaken pertaining to cost-effective optimization of sludge [2]. Optimization of the entire Fermentation process itself could alleviate the hydrogen yield from algal residue and would be the key to sustainable biohydrogen generation.
Although researches have been done on hydrogen production from algal biomass, hydrogen from algal residue has not been exploited yet. Therefore, this opens new vistas for researchers to identify an effective and sustainable way of complete biomass conversion of algae to hydrogen.
References:
[1] http://www.oilgae.com/algae/oil/yield/yield.html
[2] Mishma S. Stanislaus, et.al., Ipomoea aquatica as a new substrate for enhanced biohydrogen production by using digested sludge as inoculum, Energy Journal 118 (2017) 264 - 271.
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