Commercialization of Biohydrogen Production Process from Organic Waste
With global issues such as climate change and other energy-related problems, the need of the hour is an efficient fuel with zero carbon footprints and this path can be achieved by using hydrogen and other environment-friendly options such as biofuels. Biofuels can be produced from different organic wastes that can be harnessed easily. It can also be used in existing combustion engines after blending with methane from natural gas. Hydrogen, with the highest energy density (143 kJ/g), is a clean and environment-friendly fuel.
Biohydrogen production using renewable resources (solid wastes/wastewaters) is a promising economical and sustainable energy source as compared to photobiological processes mainly due to very high hydrogen production rate and being less energy intensive. The organic wastes are responsible for environmental pollution to a great extent.
Dark fermentation of organic wastes may be carried out by mesophilic and thermophilic organisms. The dark fermentation at thermophilic temperatures (60 o C) has many attractive advantages. Many industrial organic wastewaters are discharged at elevated temperatures such as palm mill effluent, distillery effluent, etc. that can be directly used. Moreover, higher temperature condition leads to pathogenic destruction, lower risk of contamination by methanogenic archaea, higher rate of hydrolysis, and higher H2 yield. In addition, during fermentation process excess heat is generated that requires cooling for mesophilic cultures. Bioprocess engineering lab of the Indian Institute of Technology Kharagpur is known for accentuating research on various routes of biohydrogen production in India. Over the years, this lab has developed a comprehensive and refined expertise in the field of biohydrogen production. All the domains related to hydrogen production through biological routes have been explored. The main objective of the research work is to improve the biohydrogen production process with main emphasis being to increase yields of hydrogen from the existing processes and its generation from organic wastes. A wide range of potential H2 producing microorganisms (which includes thermophiles and mesophiles) have already been identified. Different high rate hydrogen producing microorganisms have been identified from different sources, e.g., Enterobacter cloacae has been identified from the leaf of a local flower plant; Bacillus coagulans from sewage sludge; Citrobacter freundii from high oil containing soil; mesophilic acidogenic mixed culture from the anaerobic digester; and thermophilic mixed culture from the hot spring. Amongst these microorganisms, Enterobacter cloacae IIT BT08 produces hydrogen at high rate as compared to other microbes. Redirection of the biochemical pathways of E. cloacae IIT BT08 is done by blocking alcohol and some of the organic acids formation during their metabolism for the improvement of the hydrogen production. The principle being that nicotinamide adenine dinucleotide (reduced form) (NADH) is usually generated by catabolism of glucose to pyruvate through glycolysis. The conversion of pyruvate to ethanol, butanediol, lactic acid, and butyric acid involves oxidation of NADH. The concentration of NADH would be increased if the formation of these metabolites could be blocked. Double mutants of E. cloacae IIT BT08 with defects in both alcohol and organic acid formation pathways are able to enhance H2 yield as compared to wild type strain (3.8 mol H2 /mol glucose). It has been well established that the biomethanation from the organic wastes is governed by two groups of microflora: acidogens and methanogens. Recently, acidogenic microbial mixed consortium obtained from the anaerobic digester is also found suitable for hydrogen production.
To make biohydrogen production sustainable, its feedstock should be renewable in nature and should be widely available. Suitability of different organic feedstocks for hydrogen production has been studied. Attempts have been made to explore the use of algal biomass, de-oiled cakes, starchy wastewater, lignocellulosic » Different deoiled cake used as nutrient supplement in the biohydrogen production process using different organic wastes biomass, cane molasses, etc., as feedstock.
Usually, wastewaters have lack of nutrients for the growth of the microorganisms. Efforts have been made to identify cost-effective nutrient-rich supplement for the improvement of hydrogen production using wastewater as substrate. For that purpose, use of deoiled cakes as nitrogen supplements has been explored. The maximum cumulative hydrogen production and hydrogen yield on using deoiled cakes are 3.2 L h-1 and 11.2 mol H2 /kg COD removed, respectively. Groundnut and coconut de-oiled cakes appear most promising as a substrate as well as nutritional supplement in the hydrogen production process. The suitability of cane molasses as substrate for continuous biohydrogen production has been demonstrated using a 20 L bioreactor. The maximum rate of hydrogen production and yield achieved are 67 L h-1 and 18.54 mol H2 / kg COD removed, respectively. H2 is the main product of dark fermentation process. So, the accumulation of H2 inhibits the product formation, which is in accordance with Le Chatelier’s principle.
The decrease in partial pressure H2 also contributes towards metabolic shift during fermentation. It leads to formation of reduced end products such as ethanol, propionate, lactate, butanol, and acetone. Many strategies are used for the removal of H2 from the fermentation system. A sophisticated ‘Automatic Logic Control System’ has been developed for the operation of continuous hydrogen production under reduced partial pressure conditions. Reduced partial pressure always helps in improving the kinetics of hydrogen production. Maintenance of a reduced partial pressure on the overhead space of a reactor has been made automated by implementation of this system. This has made the process easy to operate and also helped in improving the overall H2 yield. Recently, thermophilic biohydrogen production process has also been explored. Thermoanaerobacterium thermosaccharolyticum ST1 has been isolated which yielded a maximum of 2.7 mol H2 /mol glucose. Use of this organism in continuous hydrogen production in packed bed reactor shows higher hydrogen yield and rates as compared to mesophilic system. A detailed continuous hydrogen production using high temperature effluent such as starchy wastewater has shown that with variation in organic loading rate, the hydrogen production improved. Another interesting observation is the inverse relationship between NADH/NAD+ ratio with rate of hydrogen production. NADH is the reducing equivalent that is required to produce molecular hydrogen via Fe-Fe hydrogenase pathway. Mutants have been developed that have suppressed competing pathways and higher pool of NADH for improvement of hydrogen production.
production. A substantial research has been carried out on development of continuous hydrogen production process, especially in customized bioreactors. Mathematical modelling and simulation on the biohydrogen production processes has been carried out. The efficiency of biohydrogen production can be analysed by defined mathematical models. These models also increase understanding the effect of substrate concentration, feedback inhibition, and effect of different substrate on hydrogen production. The kinetic parameters determined from unstructured mathematical models could help in designing and scaling up of bioreactors. A substantial research has been carried out on development of continuous hydrogen production process, especially in customized bioreactors. A prototype 20 L packed bed reactor has also been developed for continuous hydrogen production using immobilized E. cloacae IIT-BT 08. Such type of packed bed reactor uses cheaper agro-residues as matrix for whole cell immobilization. Pilot plant study has been successfully carried out using an 800 L. The Ministry of New Renewable
Energy (MNRE), Government of India, has already prepared a hydrogen roadmap in India. IIT Kharagpur is the leading Group in India involved on the Technology Mission Project titled ‘Hydrogen production through biological routes’ under this programme. Our endeavour with large-scale biohydrogen production has motivated us to commercialize biohydrogen production process for decentralized energy solution. One 10,000 L biohydrogen pilot plant was indigenously developed in both IIT Kharagpur and IICT Hyderabad under the above Technology Mission Project. 10,000 L biohydrogen pilot plant at IIT Kharagpur comprises two 3,000 L feed tanks along with 50 L and 500 L inoculum vessels with the temperature control and gas collection facilities. The hydrogen gas generation was monitored with the help of hydrogen flow meter. The gas line is directly connected with the gas chromatograph to find out the composition of the gas. The gas is stored in a gas collector of capacity 2,000 L. Total H2 production of 76.2 ± 2.5 m3 was obtained from the 10,000 L reactor using cane molasses as the major carbon source. The live demonstration of the process has been uploaded on the website . To make dark fermentative hydrogen production worthy of commercialization, it is necessary to integrate it with the other energy generation processes, such as photofermentation, biomethanation, microbial fuel cell, etc. Biomethanation technologies are found most promising and are easy to scale up. The spent media of the dark fermentation is rich in VFAs that would be an ideal substrate for the methanogens. The integration of biohydrogen production process with that of biomethanation is known as ‘biohythane’. The integrated process leads to 50%–60% gaseous energy recovery. One Technology License Agreement for the commercialization of Biohydrogen Production process from Distillery Effluent was signed on May 3, 2019, between Indian Institute of Technology Kharagpur and M/s Dhampur Sugar Mills Ltd., Dhampur. Preliminary research work indicates suitability of the cane molasses-based distillery effluent for the biohydrogen production. Recently, TATA Steel Plant Ltd., Jamshedpur has also shown keen interest to use our technology to treat their food wastes. So, the biohydrogen production technology surely helps our distillery and other biochemical/chemical industries to treat their wastes and to generate hydrogen, which is environmentally friendly.
Article by: Dr Debabrata Das, Visiting Professor, Former Head and Renewable Energy Chair Professor, Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India.