Tręšimo nuotekų dumblo kompostu įtaka energinių augalų biomasės formavimuisi ir cheminių elementų kaitai ; Influence of fertilization with sewage sludge compost on biomass formation of energy plants and changes of chemical elements

concerns solar, wind, geothermal, water, biomass. These energy resources are environmentally friendly and are the main instruments for mitigation the climate change (Lithuanian Energy Institute et al., 2008; Sodsai, Rachdawong, 2012; Sokka et al., 2016; Cherubini, Strømman, 2011). The European Union stresses the importance of the biomass use and a variety of opportunities for development, promotes the use of plant biomass as an energy source as intensively and as widely as possible. In Lithuania the use of renewable energy sources, on the basis of the regulating legal instruments, is regarded as one of the priority areas of energy development (WP3 Economic policy, 2007). Energy plants are herbaceous plants and short rotation energy forests that are grown for their biomass to be used for biofuels, electricity and thermal energy production (Lithuanian Biomass Energy Association LITBIOMA, 2008). One of the ways to get energy from plants is to burn them. It is considered that during plant combustion the release of CO2 is equal to that used by plants for the photosynthesis (Ambrulevičius, 2010; Njakou Djomo, 2013, Sodsai, Rachdawong, 2012). Consequently, burning the biomass of energy plants is considered the environmentally friendly way of obtaining energy that does not contribute to global climate change. Not all plant biomass is cost-effective if used as solid biofuels. The studies intended to identify the plants that produce more energy while burning and that cause less damage to boilers are particularly relevant (Keoleian, Volk, 2005; Borkowska and Molas, 2012; Jablonowski et al., 2014; Jablonowski et al., 2016; Njakou Djomo et al., 2015). Sewage sludge disposal is an urgent issue at the moment. Improperly handled or neglected sewage sludge poses a threat to the environment and human health. One of the ways to dispose of it, simultaneously obtaining economic benefits, is composting and use for fertilization of energy plants (Quaye, Volk, 2013). In Western European countries fertilization of plants with sewage sludge and its compost is being studied (Borkowska and Wardzinska, 2003; Kacprzak et al., 2010). Sludge and compost are rich in various elements (N, P, K, Ca, Mg) and bases that are beneficial to plants, they are also characterized by neutral pH, which increases the biological activity of soil, humus content, reduces soil bulk density, acidity (Sevel et al., 2013; Phillips et al., 2014). However, sewage sludge compost, as well as sewage sludge, contain high concentrations of heavy metals, therefore, it is especially important to adjust fertilization so that heavy metals do not adversely affect the environment, including soil properties and cultivated plants. Besides, energy plants fertilized with sewage sludge compost can accumulate particularly high amounts of nitrogen, phosphorus, potassium, chlorine and other elements in their biomass. It is known that the overall emission rate for biofuel-fired boilers strongly depends not only on the boilers and their control, but also on the quality of fuel. For example, nitrogen and chlorine contents in biomass can be reduced by agrotechnical measures and optimization of plant fertilization (Ambrulevičius, 2010). Therefore, during the research optimal rates of compost for different energy plants were assessed in order to get benefits without harming the environment and in accordance with the Lithuanian environmental laws. Hypothesis Fertilization of different willow varieties, mugwort, Virginia fanpetals and giant miscanthus plants, growing in light-textured soils, with sewage sludge compost increases the dry matter yield in plant biomass and heavy metal concentrations in the biomass, but has no adverse effect on the biomass quality or its suitability for use as biofuel. After fertilization of energy plants with sewage sludge compost, the properties of light-textured unfertile soil remain unchanged, but the concentrations of heavy metals in it increase. The aim To assess the possibilities to cultivate energy plants (different varieties of willow and non-traditional herbal plants: Virginia fanpetals, mugwort and giant miscanthus) in lighttextured unfertile soils of South-Eastern Lithuania using sewage sludge compost for fertilization. Research objectives 1. to investigate the influence of fertilization with sewage sludge compost on the growth and biomass formation of different willow varieties and herbaceous plants 2. to determine the parameters of biomass quality of different willow varieties and herbaceous plants fertilized with sewage sludge compost, regarding the use of biomass for solid biofuel 3. to determine the impact of fertilization with sewage sludge compost on chemical properties of soil 4. to investigate the effects of fertilization with sewage sludge compost on heavy metal accumulation in the soil and biomass of different willow varieties and herbaceous plants Research objects 1. Willow Salix spp. varieties ‘Tora’, ‘Tordis’ and ‘Gudrun’, mugwort (Artemisia dubia Wall), Virginia fanpetals (Sida hermaphrodita (L.) Rusby) and giant miscanthus (Miscanthus x giganteus); 2. Sewage sludge compost (SSC) and mineral NPK fertilizers. Novelty of the work Studies show that, after being harvested for fuel, 7–10 years old willows could successfully re-grow and form large dry matter yield of good quality. Variety ‘Tordis’ is the most suitable for solid biofuel. Although its yield was lower than of ‘Tora’ variety, but the biomass is more suitable for biofuel. Cultivation of Virginia fanpetals, mugwort and giant miscanthus for solid biofuel fertilizing them with sewage sludge compost has not yet been studied in Lithuania. Studies showed that giant miscanthus and mugwort fertilized with sewage sludge compost form a high biomass yield of good quality which is suitable for biofuel. Besides, the biomass of these plants accumulates heavy metals, which is helpful to reduce their amount in soil. It was revealed that cultivation of energy plants, using sewage sludge compost for fertilization, does not exhaust the soil. Concentrations of total nitrogen (Nsum.) and mobile phosphorus (P2O5) in the soil substantially increased. In the soil under willows, which were fertilized with sewage sludge compost, concentrations of zinc and copper (p<0.05) substantially increased. In the soil under herbaceous plants concentrations of chromium, copper, lead, zinc, nickel and cadmium were higher (p<0.05) than in unfertilized soil. Statements for defense 1. The fertilization with sewage sludge compost increases the dry matter (DM) yield of biomass in willow varieties ‘Tora’, ‘Tordis’,‘Gudrun’, mugwort, Virginia fanpetals and giant miscanthus cultivated in light-textured soils. 2. The fertilization of willow varieties ‘Tora’, ‘Tordis’, ‘Gudrun’, mugwort, Virginia fanpetals and giant miscanthus with sewage sludge compost has no adverse effect on the biomass quality or its suitability for use as biofuel. 3. After fertilization of willow varieties ‘Tora’, ‘Tordis’, ‘Gudrun’, mugwort, Virginia fanpetals and giant miscanthus with sewage sludge compost the properties of light-textured soil remain unchanged. 4. After fertilization of willow varieties ‘Tora’, ‘Tordis’, ‘Gudrun’, mugwort, Virginia fanpetals and giant miscanthus with sewage sludge compost heavy metal concentrations in light-textured unfertile soils will increase, but will not exceed the maximum allowable concentrations permited under Lithuanian law. Fertilization with sewage sludge compost increases heavy metal concentrations in biomass of different willow varieties and herbaceous plants. Practical applications The results showed that application of 20 t ha-1 sewage sludge compost for fertilization of willow varieties ‘Tora’, ‘Tordis’, ‘Gudrun’ likewise 40, 80 t ha-1 sewage sludge compost for fertilization of mugwort, Virginia fanpetals and giant miscanthus in light-textured unfertile soils of South-Eastern Lithuania results in high dry matter yield of good quality that is suitable for use in solid biofuels without harming the environment and in compliance with environmental requirements. It was assessed that among the tested willow varieties the biomass of ‘Tordis’ is the most suitable for solid biofuels. Biomass of giant miscanthus and mugwort was of higher quality regarding the use for solid fuels that that of Virginia fanpetals. The research results showed that in light-textured unfertile soils of South-Eastern Lithuania sewage sludge compost could be used as energy plant fertilizer; it does not harm the soil properties or contaminate the soil with heavy metals so that their concentration could exceed the maximum allowable concentrations permitted by LAND 20-2005 (The State Gazette., 2001, No. 61-2196; TAR. 2015, No. 20395). Approbation of the results The main results were presented in 2 articles in peer-reviewed periodical journals, and 1 article in other publications. Results of the work were presented at 2 international conferences abroad, 4 international conferences held in Lithuania and 11 national scientific conferences. Two sets of recommendations for agriculture and forestry were prepared “Influence of fertilization on biomass of different willow varieties grown for fuel, its quality and soil properties” and “Formation of energy plant biomass in light-textured soils of diverse fertilization mode”.