Abstract. There are large agricultural land areas overgrown with grasses and not used for agricultural production or having protective environmental status in Latvia. Grass biomass from those areas can be utilised for biogas production, however, the most of abandoned lands are located far from the existing biogas plants and high transportation expenses is often the limiting factor for usage of the grass biomass for biogas production. This problem can be solved by production of grass pellets, having low moisture content (8-12 %), high density and high dry organic matter (DOM) content. Such grass pellets production can be provided on relatively small equipment with the size adapted to the local grass biomass resources. After production, grass pellets can be transported to biogas plants with minimal transport expenses, so providing additional supply of valuable biomass to biogas plants for stable round year biogas production. Investigation of biogas potential from grass hay pellets was carried out using the laboratory facilities. The grass hay pellets were fermented anaerobically in 16 bioreactors operating in batch mode at temperature 38 ºC. On average, 0.666 l·g -1 DOM biogas (0.355 l·g -1 DOM methane) was obtained during 46 days of the anaerobic digestion period. Investigations show that high specific methane yield can be obtained from the grass hay pellets, and its utilisation in biogas plants can be useful taking in account the high content of dry organic matter in the initial biomass. The second study deals with investigation of the methane yield obtainable from co-digestion of the grass hay pellets with sunflower oil and molasses. Addition of sunflower oil increases the methane yield by 28.8 % and addition of molasses increases the methane yield by 8.8 %.Key words: hay, anaerobic digestion, methane. IntroductionAccording to the renewable energy action plans of the member states of the European Union, the share of bioenergy 36 %, including energy from solid biomass 54.5 %, is the largest contribution in renewable energy targets for 2020 [1]. Since the modern society will move towards a low-carbon economy after 2020 or rather towards a bio-economy based on the cascade principle, more biomass will be used for non-energy based purposes, and this requires an effective energy recovery from waste biomass, e.g. for heat production, because the high value biomass will be used for food or feed purposes.The intelligent use of bio-energy will be integrated with other renewable energy sources and organic products, recognizing that wind, solar and bioenergy are complementary energy areas, in order to achieve 100 % renewable heat and power production by the end of the century [2]. Two of the most commonly available residue biomass types in urban areas across Europe are grasses and leaves. In Germany in 2009, it was estimated that biomass potential from the green barrier zones is equal to one million tonnes fresh substances (FM) and its use was proposed for the production of bioenergy [3]. Public parks, lawns, cemeteries an...

Support for biogas production in Latvia has decreased. There is an urgent need to investigate the suitability of various inexpensive renewable biomass resources for energy production. Also, it is necessary to explore the possibilities to improve the anaerobic digestion process with the help of various catalysts. Molasses is a good raw material for co-digestion with biomass having low biodegradability. The article shows the results of studies on biogas (methane) production from dry grain sweeps, birch leaves and from their co-digestion with molasses. The anaerobic digestion process was performed in 0.75 l laboratory digesters, operated in batch mode (38 ± 1.0, 32 days). The average specific biogas or methane production per unit of dry organic matter added (DOM) from molasses was 0.840 l•g-1 DOM or 0.457 l•g-1 DOM respectively. Average specific biogas or methane volume produced from dry grain sweeps (residues) in anaerobic fermentation was 0.777 l•g-1 DOM or 0.402 l•g-1 DOM respectively. Average biogas or methane yield from co-digestion of dry grain sweeps and molasses was 0.772 l•g-1 DOM or 0.433 l•g-1 DOM respectively. Average specific biogas or methane yield from anaerobic fermentation of birch leaves and molasses was 0.737 l•g-1 DOM or 0.369 l•g-1 DOM respectively. All investigated biomass resources can be used for methane production.

According to increasing of prices for energy resources, increasing interest for renewable energy resources. As one of the most profitable is biogas production. In this paper is presented potential of biomass for biogas production. It is presented possibility to produce biogas and energy from different recourses and total 156,9 million m3/year. For development of biogas production is necessary financial support, increasing of research works and education.

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There are significant quantities of different food wastes, which cannot be consumed for food in Latvia. Foods popular in Latvia are rye bread Kursu and potatoes Vineta. The significant part of this food was diverted to waste due to non-standard, surplus production, bad storage conditions, shelf life limitations and wastes accruing during food consumption by consumers. Food wastes, when disposed in landfills, will degrade easy in aerobic conditions releasing harmful gases, including gaseous nitrogen compounds and carbon dioxide. Also, food wastes disposal in landfills are limited now and expected to be avoided in future according to the respective EU Directive on disposal of easy degradable wastes. Damaged bread and potatoes peels may be utilised in the biogas production process. There is an interest to investigate the effect of usage of additives, e.g. catalyst Metaferm, to enhance the methane production during the anaerobic fermentation process. In previous studies, the addition of catalyst Metaferm caused the improvement of methane extraction from substrates with difficultly biodegradable corn silage and dried grains. Therefore, this study continues to examine the effect of the additive Metaferm on more easily fermentable biomass. To find the methane volume obtainable from bread Kursu and potato Vineta wastes, a study was conducted in 16 bioreactors at the temperature of 38 ºC. The specific methane volume 0.459 l•g-1 DOM or 0.515 l•g-1 DOM were obtained from rye bread Kursu or potatoes Vineta respectively, after 30 days anaerobic digestion (AD) process. The addition of Metaferm increases the methane yield by 5.4 % or 2.3 % from rye bread or potato wastes, respectively. Investigation results show that both food wastes can be utilised in biogas plants for energy production successfully.