In any industrial process certain amount of waste is inevitable and food processing is no exception. Wastes from food processing, restaurant industry, municipal garbage and house holds contain energy which can be extracted through thermal process or fermentation using mixed cultures. Methane generation through fermentation is by now well established and thousands of such small scale gas plants are working especially based on cow dung and other wastes containing utilizable carbon sources. However from the pollution angle methane does produce green house gas CO2, when burned to derive energy, contributing to global warming. Innovative scientific developments in the field of biotechnology have raised the possibility of using carbon contents in the waste products for generating a much cleaner energy source, the Hydrogen which, when used as a fuel, produces only water as the end product of combustion.
Bio-hydrogen is a term extensively used to describe the hydrogen produced through microbiological fermentation process different from that produced from natural gas, coal and water through thermal and electric separation or in the nuclear reactors as a by-product. Most of the hydrogen produced to day is from natural gas by thermal process. Till date no process either biological or thermal or electric has been able to separate hydrogen economically as the energy used to produce this fuel is much more than that used in the production process. Still hydrogen from natural gas or coal does not make much sense because both these sources are not sustainable or renewable though environmentally hydrogen is a cleaner fuel at the consumption point.
Bacteria and Algae are attracting the attention of the scientists as tools for hydrogen separation from complex organic molecules containing this element. Bio-hydrogen gas has been produced, though on a limited scale by dark fermentation ( absence of light), thermophilic fermentation and photo fermentation in presence of light using microbes such as Rhodobacter sphaeroides, Enterobacter cloacae and mixed cultures containing hydrogen producing as well as methane producing organisms. Methane produced in anaerobic digestion of wastes can be steam reformed to give hydrogen. Organic wastes, presently used for land refills and treated to reduce BOD before sending out as safe effluent can become the most sustainable energy source in the coming decades. Pilot plant projects have proved that technically this is a feasible process and there are several such projects working in some countries as living example of the feasibility of bio-hydrogen as a source of renewable energy.
Some of the feed stock suitable for bio-hydrogen generation include wastes from cattle farms, dairy industry, starch industry, paper mills, domestic source, restaurants, distillery, oil refinery, food processing etc. Efficacy of the bio-hydrogen fermentation is generally low with one mole of glucose yielding hardly 1-2 moles of hydrogen. Factors such as pretreatment of the culture, pH of the system, organic loading, temperature and waste water characteristics have critical influence on the process. For successful H2 production, the seed culture has to be pretreated at high temperature and low pH to bring about inhibition of methanogens allowing spore forming Clostridium to dominate in the mixed culture. Efficiency can be increased if a 3 step process is deployed where, after the first stage hydrogen generation by dark fermentation, the residue is integrated with photofermentation and then with methanogenesis which will ensure maximum utilization of the latent energy contained in the feedstock. Algae is another promising biological tool and the microorganism C.reinhardtii, when grown under sulfur starvation, produces hydrogen instead of O2 as the by-product of photosynthesis.
"Garbage is Gold" seems to be the modern slogan and most of the on going projects in many municipal towns in some countries use the garbage for burning in heavy incinerators to raise steam and power generation. Plants with capacities as high as 3000 tons trash/day, generated in urban areas, are in operation. A 700 tons/day "trash to power" plant is believed to be able to generate power equivalent to burning of 120, 000 tons of coal an year in a thermal plant. In a country like the US sufficient waste is generated to produce power which otherwise would need 2 million barrels of fossil fuel per day! It is time for the planners world over to think of bio-hydrogen production from these wastes as it is relatively a clean and green energy source causing no adverse effect to the environment unlike the non-renewable sources of energy..