Biological energy conversion system as photosynthesis might not to be so efficient in the solar energy utilization. However, it is a remarkable process in the viewpoint of energy accumulation. Plants and photosynthetic microorganisms grow by themselves and collect energy. Such spontaneous energy accumulation system is not obtainable in man-made industrial technologies. There are many types of energy carriers as hydrogen, methane, alcohol, and all other biomass, which could be produced biologically from renewable energy sources. Production of methane is not advisable because methane itself is green house gas which on combustion produces carbon dioxide which is another green house gas. Among them, hydrogen is a powerful energy source that does not produce carbon dioxide. Although in the laboratory rather high efficiency of light to hydrogen conversion has been recorded, especially by photosynthetic bacteria, we have to improve the organisms and the reactor system further to realize the potentially high activity under applicational conditions. Not only the biological improvements, but also the engineering aspects are studied here. We should like to describe the basis of hydrogen biological production, genetic engineering and the reactor design and field tests.
Biological H2 production processes can be classified as bio photolysis of water using algae and Cyanobacteria, photodecomposition of organic compounds by photosynthetic bacteria, and fermentativeH2 production from organic compounds. So far H2 production by photosynthetic microorganisms was extensively studied while H2 evolution by fermentation was treated with little attention. The fermentative evolution is more advantageous than photochemical evolution for mass production of H2 by microorganisms, where various wastewaters can be used as substrates. Of late, H2 production through anaerobic fermentation using wastewater as substrate has been attracting considerable attention. Exploitation of wastewater as substrate for H2 production with concurrent wastewater treatment is an attractive and effective way of tapping clean energy from renewable resources in a sustainable approach. This provides dual environmental benefits in the direction of wastewater treatment along with sustainable bio-energy (H2) generation. However, the microbial conversion of substrate by anaerobic fermentation is a complex series of biochemical reactions manifested by diverse group of selective bacteria.
Electrolysis of Water
It is more efficient to produce hydrogen through a direct chemical path than by electrolysis, but the chemical feed source will always produce pollution or toxic by-products as hydrogen is extracted. With electrolysis when energy supply is mechanical (hydropower or wind turbines), or photovoltaic from sunlight, hydrogen can be made via electrolysis of water. Usually, the electricity consumed is more valuable then hydrogen produced so this method has not been widely used in the past, but with electrolysis production of hydrogen , there is virtually no pollution or toxic by-products, and final feed sources are fully renewable, so the importance of electrolysis is increasing as human population and pollution increase, and electrolysis will become more economically competitive as non-renewable resources (carbon-based compounds) dwindle and as government removes subsides on carbon based energies.
When energy supply in the form of heat (solar thermal or nuclear), the path to hydrogen is through high temperature electrolysis .In contrast with low-temperature electrolysis, high-temperature electrolysis (HTE) of water converts more of the initial heat energy into chemical energy (hydrogen), potentially doubling efficiency, to about 50%. Because some of the energy in HTE is supplied in the form of heat, less of the energy must be converted twice (from heat to electricity, and then to chemical form), and so less energy is lost.HTE has been demonstrated in a laboratory, but not at commercial scale. Irrespective of efficiency, hydrogen production by electrolysis is clean and renewable agent for storing electrical and mechanical energy for retrieval on demand.
Thermochemical Production
Some thermochemical processes can produce hydrogen and oxygen from water and heat without using electricity. Since all the input energy for all such processes is heat, they can be more efficient than high –temperature electrolysis. This is because the efficiency of electricity production is in itself fundamentally limited. Thermo chemical production of hydrogen using chemical energy from coal or natural gas is generally not considered, because the direct chemical path is more efficient. Hundreds of thermochemical cycles have been pre-screened.
Some of the most promising ones include:
• Sulphur iodine cycle (S-I).
• Copper chlorine cycle (Cu-Cl)
• Cerium chlorine cycle (Ce-Cl)
• Iron chlorine cycle (Fe-Cl)
• Magnesium iodine cycle (Mg-Cl)
• Vanadium chlorine cycle ( V-Cl)
• Copper-sulphate cycle (Cu-SO4)
There are also hybrid variants, which are thermochemical cycles with an electrochemical step. For all the thermochemical processes, the summary reaction is that of the decomposition of water:
Genetic Engineering
Genetically Engineered E. Coli Shows Increased Hydrogen Production Up to 141 Times Greater Than Wild Type. Researchers at Texas A&M University have genetically modified a strain of E. coli to produce a substantial increase in its fermentative production of hydrogen from formate—up to 141 times greater than in a wild type. In addition, the hydrogen yield from glucose was increased by 50%, and there was threefold higher hydrogen production from glucose with this strain.
Objectives
Anaerobic treatment of waste water is a viable treatment technology for generation of biogas. About 70% of methane is generated from volatile fatty acids and the remaining 30% of methane is generated from hydrogen and carbon dioxide .By altering the conditions in the reactors, production of methane can be suppressed and generation of hydrogen will be favoured.
Hence the specific objectives of the project are
1. Suppression of methanogens in the seed sludge by adopting various pre-treatment methods like acid treatment, chemical treatment.
2. Selection of optimum food to microorganism ratio for generation of hydrogen.
Conclusion
The results of first set of experiments (HCl pretreatment) showed maximum hydrogen production in the food to microorganism ratio of 1.4. The second set of experiments(Orthophosphoric acid pretreatment) and third set of experiments (Chloroform pretreatment) also showed maximum hydrogen production in the 1.4 food to microorganism ratio. Among the three pre-treatment methods performed maximum hydrogen production was obtained for the chloroform pre-treatment. Various pre-treatment methods were preformed to deactivate the methanogens. The various pre-treatment methods tried were acid pre-treatment (HCl and H3PO4) and chemical treatment. And the various food to microorganism ratios tried were 1, 1.4, 1.8. The pH favourable for hydrogen production for acid treated sludge is 3.0.
The gas production was low initially because it takes some time for stabilisation and repeated treatments were not done. Repeated treatments are needed to remove the non spore forming hydrogen consuming microbes. The sludge taken from the UASB reactor contains a mixture of microorganism. Enrichment of the hydrogen producing bacteria in the seed takes longer time. The hydrogen producing bacteria are basically clostridia (spore forming bacteria) which are predominantly present in the sludge and they protect themselves during unfavourable conditions like low PH, heat treatment, etc. Hence these pre-treatments like acid treatment, chemical only suppress methanogenic activity but do not kill hydrogen producing bacteria.