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Socio-Economic and Techno-Economic Aspects of Biomethane and Biohydrogen
Published in Sonil Nanda, Prakash K. Sarangi, Biomethane, 2022
Ranjita Swain, Rudra Narayan, Biswa R. Patra
Biomass precursors are generally converted into sugar or carbohydrate and then fermented by anaerobic organisms for the production of biohydrogen. The bacterial species such as Clostridium pasteurianum, Clostridium beijerinckii and Clostridium acetobutylicum are the key microorganisms responsible for biohydrogen production (Cabrol et al., 2017). Photo-heterotrophic bacteria convert organic acids into hydrogen in the existence of light (Sarangi and Nanda, 2020). Photosynthetic bacteria like Rhodobacter sphaeroides, Rhodospirillum rubrum and Rhodopseu- domonas palustris are also found to be efficient microorganisms for the production of biohydrogen (Kapdan and Kargi, 2006). Photo-bioreactors like bubble column and tubular reactors are often used for the production of biohydrogen.
Nitrogen Fixation
Published in Yeqiao Wang, Terrestrial Ecosystems and Biodiversity, 2020
The symbiotic process of N2 fixation by leguminous plants plus associated root nodule bacteria (Rhizobium species) is of greatest practical importance to agriculture, but there also are a number of free-living bacteria capable of N2 fixation. The first of these recognized was the anaerobic organism Clostridium pasteurianum as reported by Winogradsky in 1893.[2] In 1901 Beijerinck recorded that the aerobic bacterium Azotobacter chroococcum also fixed N2.[2] These early observations were followed by practical applications, and the practice of inoculation of leguminous seeds with cultures of the rhizobia became widespread. The bacteria were grown commercially and farmers applied these bacteria to leguminous seeds at the time of planting. There is a specificity between the plants and bacteria, and this gave rise to the recognition of cross-inoculation groups, i.e., groups of plants all of which are nodulated by the same species of rhizobia. For example, Rhizobium leguminosarum infects garden peas, sweet peas (Lathyrus odoratus), common vetch (Vicia faba), hairy vetch (Vicia villosa), and lentil (Lens culinaris), whereas Rhizobium japonicum is rather specific for soybeans (Glycine max). Not all strains of root nodule bacteria that infect a plant are equally effective in N2 fixation, and this is referred to as strain variation. Because of strain variation, commercial inoculants often are a mixture of effective strains. Inoculants are grown as large batches of effective organisms in liquid culture, and then these cultures are mixed on a peat base. The finely ground peat retains moisture, and the microorganisms remain viable for long periods. The peat culture is mixed with seeds before planting, and the viable organisms are in proximity when the seeds germinate and produce roots. The bacteria induce curling of root hairs and invade the plant through the root hairs. After invasion they induce the production of root nodules and proliferate in the nodules. The bacteria undergo morphological and metabolic changes in the nodule and are referred to as bacteroides. Bacteroides in the nodule are capable of fixing N2 from the air.
Progress in microbiology for fermentative hydrogen production from organic wastes
Published in Critical Reviews in Environmental Science and Technology, 2019
As shown in Table 1, the hydrogen-producing strains can be categorized into mesophiles, thermophiles and psychrophiles, according to the cultivation temperature. For the mesophiles, temperature ranges from 30 °C to 40 °C, and initial pH 5.5-9.0 have been regarded as optimal conditions for fermentative hydrogen production by different studies. As to the thermophiles, adaptive conditions for hydrogen production ranges from 40 °C to 60 °C, and the initial pH 6.5-8.0. At present, pure cultures belong to psychrophiles have not been used as sole inoculum for fermentative hydrogen production. Besides temperature, the strains can also be categorized in to anaerobes (Clostridium spp.), facultative anaerobes (Enterobacter spp.) and aerobes (Bacillus lichenformis etc.) based on their tolerance to oxygen. The anaerobes have been proved to have higher hydrogen yield, while facultative anaerobes and aerobes can help to consume the oxygen present in a system, creating anaerobic environment for anaerobes and keeping a stable operation. Table 2 summarizes the characteristics of some typical hydrogen producers and their performances in dark fermentation. Among all the species, mesophiles are most widely used. Strains belonging to Clostridium butyricum were the most widely used and showed the highest potential in hydrogen yield. Other Clostridium spp. like Clostridium beijerinckii, Clostridium pasteurianum also displayed good capacity in hydrogen production. Species belonging to Enterobacter spp. and Bacillus spp. showed lower hydrogen yield comparing with Clostridium spp., but their tolerance to oxygen makes them more applicable in practical use.