As EU is steadily moving in the direction of emission reduction, each country must develop plans to decarbonise the transport and energy sectors. In Latvia, transport sector is one of the biggest emission sources. The heating applications come next. Both require carbon containing fuels and a transfer to carbon neutral fuel is necessary; therefore, hydrogen may be the answer to achieve the overall EU targets. As Latvia has renewable energy sources, some production, storage and use of hydrogen are possible. Currently clear guidelines for Latvia have been investigated. The existing natural gas network may be used for two tasks: large-scale hydrogen transportation and decarbonisation of natural gas network. To open the natural gas networks for hydrogen, the first evaluations are made and a possible scenario for hydrogen implementation in network supplying consumers in the household sector is analysed to evaluate decarbonisation with an overarching goal of carbon neutrality.
Laboratory-scale experiments were carried out to evaluate the effect of initial acidification of feedstock consisting of different components on biogas production and composition. Feedstock containing different agricultural wastes, biomass, and microorganisms was collected from five full-scale biogas plants. Two continuously stirred tank reactors were used. The fermentation temperature was 37 °C. The pH value was adjusted to 6.0 in the first reactor at the beginning of the experiment, and an initial pH value of 7.0 was implemented after 48 H. The second reactor was used as a control reactor with a constant pH of 7.0. The experiment lasted a total of 7 days. In the reactors, the gas phase was dominated by CH4 , CO2 , and N2 . The results showed that acidification increased biogas and carbon dioxide production in five cases, increased methane production and reduced nitrogen production in four cases, and reduced methane content in biogas in four of five cases. Only feedstock composed of 74% of different manures and 26% of plant material reduced the production of methane and increased the production of nitrogen after acidification. Other feedstock contained 47% to 96% plant material. An initial pH value of 6 could be recommended for mesophilic single-phase methanogenesis with a prevalence of plant material.
Microorganisms are capable to produce hydrogen during fermentation of organic substrates and industrial waste products can be used as feedstock for hydrogen producing bacteria. One of the substrates that can be effectively used for microbial hydrogen production is glycerol, which is a by-product from the process of biodiesel production, but glucose is mainly used as a model substrate. Different bacterial isolates were tested for hydrogen gas production rates from glucose and glycerol with test-systems constructed in our laboratory. Test-systems were optimised to allow adequate substrate and bacterial strain hydrogen productivity estimation in the liquid and gaseous phases. It was concluded that several of the isolated bacterial strains are suitable for bio-hydrogen production using glycerol as a substrate. Assessment was developed to establish whether microbial conversion of glycerol is an economically and environmentally viable possibility for bio-hydrogen production. The raw material cost noticeably decreases because of large quantities of available crude glycerol after biodiesel production and the highly reduced nature of carbon in glycerol per se.Key words: bio-hydrogen, fermentation, substrates, prototype bioreactor INTRODUCTIONBiological production of hydrogen using bacteria is a promising and advantageous area, especially when hydrogen is gained from a variety of renewable resources [1,2]. Industrial and agricultural organic waste used as feedstock for hydrogen producing bacteria is a perspective way for alternative energy production and it noticeably decreases the raw material cost. During the conversion of organic wastes, in anaerobic environment, hydrogen gas is produced as a by-product. Substantial factors like availability and cost are highly important in the selection of waste materials to be used in hydrogen production with fermentative bacteria [3]. One of the substrates that can be effectively used for microbial hydrogen production is glycerol, which is a by-product from the process of biodiesel production. Because of large quantities available of crude glycerol and the highly reduced nature of carbon in glycerol per se, microbial conversion of it seems to be economically and environmentally viable possibility, 125Assessment of bio-hydrogen production from glycerol and glucose by fermentative bacteria especially because over the last several years the demand and production of biodiesel has remarkably increased [4,5]. Recently several authors have investigated hydrogen production using glycerol as a substrate by fermentative bacteria. Mangayil et al. [6] investigated optimal conditions (pH 6.5; 40 °C and 1 g/L raw glycerol) for hydrogen production using crude glycerol with microbial consortium mainly dominated by Clostridium species. Environmental conditions like medium pH and temperature are the major parameters to be controlled in the hydrogen production because they affect the qualitative and quantitative content of bacterial produced gas and the hydrogen yield and rate. Hydrogen production usi...
Biogas is a fuel obtained from organic waste fermentation in an anaerobic digestion plant and can be burned in a cogeneration unit to produce heat and electricity. In Latvia, biogas plants are popular among farmers, as electricity is mostly sold to the centralized electricity grid, receiving a subsidy in the form of a mandatory procurement component. Political circles are discussing the reduction or even abolition of this support, so the question of where to put the produced biogas is topical. Recently, many European countries have incentivized the production of biomethane to be injected into natural gas grids or compressed and used as biofuel in vehicles. The implementation of biogas upgrading unit into an existing anaerobic digestion plant to convert biogas to biomethane (<97%) can be performed by means of various technologies, physical and chemical absorption, adsorption, membrane and cryogenic separation. There are also biological pathways for biogas upgrading -biological conversion of residual CO2 and external hydrogen to methane carried out by hydrogenotrophic methanogens. The aim of this research is to give a review about latest developments in technologies and update views of biogas producers on possible upgrading of bio-methane concentration in the fermentation process. The main research results have indicated that farmers have interest in technological achievements of biological CO2 reformation, as well as specific changes in the fermentation process. They are supporting production of new kind of renewable fuel with possible application for vehicles, also indicate high costs in reformation and mechanical separation processes.
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