Generation of Hydrogen Gas from Crude Glycerol by Purple Non-Sulfur Photo Fermentative Bacteria, Rhodobacter Meghalophilus
Abstract
As the world is progressing faster with new technological innovations, the need and demand for energy is also constantly expanding. In the light of conventionally available fossil fuel reserves being exhausted extensively that has left a very deep scar on environment, the urge for alternative environment friendly energy source is the need for energy sustenance. Hydrogen gas is distinct for its high calorific value, clean fuel characteristic and suitability for wide applications. Chemical method likes steam reforming, coal gasification are established technologies available for industrial hydrogen needs but are high in terms of cost and energy input. Biological methods are promising routes for hydrogen gas generation as they can be cost effective and use a variety of organic materials as substrates. The current study is focused on generation of hydrogen gas using Rhodobacter meghalophilus, a mesophilic, and purple non sulfur photo fermentative bacteria. Crude glycerol, byproduct from biodiesel plants is used as carbon substrate because of its rich organic content. Experiments were carried out to study the effect of process parameters viz. volume of crude glycerol, pH and light intensity on generation of hydrogen gas. Crude glycerol in the media was varied from 5 – 15% (v/v), pH between 5.8 – 8.3 and the light intensity at 500, 1000 and 2000 Lx respectively. At 15% (v/v) of crude glycerol, pH of 7.8 and 1000 Lx, the volume of hydrogen gas obtained was 490 ml/L with the substrate to hydrogen gas conversion rate as 0.012 mol/ mol of crude glycerol with light conversion efficiency of 1.16%.
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Introduction
The world is progressing ahead with tremendous improvement in technology and is also facing challenges on energy survival. The world had largely relied on the use of fossil fuels to meet its energy needs. The energy needs have been increasing enormously with advancements in industrial, transport, agricultural sectors, causing rapid depletion of fossil fuels that have been the prime fuel reserve. The liberal use of fossil fuels has also left a serious impact on the ecosystem. The burning of fossil fuels has released exorbitant amount of carbon di oxide that is changing the ecological and geological characteristics of our planet. With the depleting fossil fuel sources, ever rising demand for energy and the hazardous damages caused by fossil fuels, the world’s energy requirements rely largely on the search for other alternative resources.
The potential of solar, wind, ocean, geothermal and hydrogen energies are being tapped in for bridging the energy gap. The advantage of these alternative sources is that they are also renewable and environment friendly. Vast amount of research has been carried out to study the potential methods to optimize the energy derivation form these renewable sources. Of these, studies on hydrogen gas as an alternate energy source has gained more momentum due to their advantages that it has high energy content and is eco-friendly, producing only water as it’s by product on burning (1). These advantages have proved to show that hydrogen fuel can be seen as a positive substitute to reduce our dependency on fossil fuels.
Conclusion
Hydrogen gas can be a promising alternative source of energy that can drive the future world. While the industrial demand for hydrogen gas is currently met by energy intensive, chemical methods of production, they are unsustainable in terms of production cost and environmental pollution. Biological methods can be promising as they do not demand energy and can employ wide family of bacterial species that can act on various organic waste materials to generate hydrogen gas. This is seen as a promising way to meet the future energy demand. In the present study, Rhodobacter meghalophilus from the family of Rhodobacter was identified and investigated for its capability to generate hydrogen gas. As crude glycerol is used as carbon substrate for the bacterium in the fermentation process, its effect on hydrogen gas generation was studied by varying the volume of crude glycerol in the nutrient medium in 5, 8, 10 and 15% (v/v). pH and light intensity are two other significant parameters that impacts the bacterial growth and the hydrogen gas generation in photo fermentation process. pH of the medium was varied between 5.8 to 8.3 and the light intensity of 500, 1000 and 2000 lx was used in photo fermentation runs.
From the experimental runs carried out with the above study parameters, 490 ml/L of gas was collected with the hydrogen concentration of 457 mg/L by using 15% (v/v) of crude glycerol in the nutrient medium, pH of 7.8 and light intensity of 1000 lx. As the bacteria are photo fermentative, the process needs the presence of light along with a carbon substrate for its energy supplementation and hydrogen gas generation. Thus, to make the process further sustainable, solar cells could be used to power the light source for the photo fermentation process.