Five bacterial isolates were tested for their ability to generate hydrogen during anaerobic fermentation with various carbon sources. One isolate from sheep rumen was identified as Escherichia coli and four isolates belonged to Clostridium spp. Glucose, arabinose, ribose, xylose, lactose and cellobiose were used as carbon sources. Results showed that all bacterial strains could utilize these compounds, although the utilization of pentoses diminished growth yield. The excretion of monocarboxylic acids (acetate, propionate, formiate, butyrate) into medium was changed after replacing glucose by other carbon sources. Di- and tricarboxylic acids were excreted in negligible amounts only. Spectra of excreted carboxylic acids were unique for each strain and all carbon sources. All isolates produced H2 between 4—9 mmol·L−1 during the stationary phase of growth with glucose as energy source. This value was dramatically reduced when pentoses were used as carbon source. Lactose and cellobiose, starch and cellulose were suitable substrates for the H2 production in some but not all isolates. No H2 was produced by proteinaceous substrate, such as blood. Results show that both substrate utilization and physiological responses (growth, excretion of carboxylates, H2 production) are unique functions of each isolate.
The present review aims to provide an up-to-date summary of bio-methane (CH 4 ) gas production, which use as is a renewable energy source. Burned bio-methane gas used for water heating, space heating, drying, or cooking. CH 4 is also used in an automotive to produce both heat and electricity. The bio-methane gas is produced by anaerobic digestion (AD) technology of food waste, agricultural waste, municipal waste, green waste, manure, and sewage. AD technolog is promising technology; having the potential to convert several bio-masses into bio-gas rich with methane gas, which is alternative to fossil fuels. The hydrolysis, acidogenesis, acetogenesis, and methanogenesis are essential steps of AD process. The steps are proceeding by different kind of bacteria such as, acidogenic, acetogenic, and methanogenic bacteria. An effective process to increase the productivity of an anaerobic digestion process by combining it with a microbial electrosynthesis system (MES) was developed. Percentage compositions of CH 4 from anaerobic digestion of a different feedstock were between 50% -84%. The various physical, chemical, physiochemical and, biological pretreatments methods were applied to break the complex biomass into easily digested components. The AD system has many advantages, like low energy consumption, low nutrient and chemical requirement, improved sanitation, pathogens reduction, reduction of disease transmission, greenhouse emissions and nitrous oxide emissions reduction, etc. And some of the anaerobic digestion disadvantages are a long start-up, high buffer requirements for pH controlling, higher sensitivity of microorganisms to pH and temperature, etc. More advantages and disadvantages are discussed in this review. In the future, will be solutions to problems that limits production yield.
The study had aimed to characterize the production of hydrogen gases by anaerobic bacteria. One isolate was found in sheep ruminal fluid and four isolates were obtained from the activated sludge. These isolates were identified by microscopic methods and by rRNA sequences. One ruminal bacterium was identified as Escherichia coli, and it was found that these isolates from activated sludge were related to Clostridium botulinum, C. perfringens and C. difficile. One strain could not be assigned to any species but was similar to C. botulinum. Growth and production of the metabolic gases with molasses as sole carbon source were measured during the anaerobic cultivation by Micro-Oxymax (Columbus Instruments, Columbus, OH, U.S.A.) gas analyzer. One of the most available saccharidic waste products is molasses. The growth on molasses as carbon source was done to test the production of H 2 . It was found that all tested Clostridium isolates (AK 1-4, AK 1-5, AK 1-9 and AK 1-12) and E. coli isolate (No 2-24) had utilized molasses as carbon source monitored by production of CO 2 gas. All these strains produced H 2 gas, and CO gas in concentration range 102 µmol L -1 , and H 2 S gas in concentrations lower by one order of magnitude. Kinetics of evolution of these gases was different suggesting that they are produced by independent processes. Results show that metabolic gases are produced mainly in the exponential phase of growth.
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