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The efficiency of organic pollutants degradation in the process of anaerobic digestion of feedstocks with different origin
The study of the degree of degradation of pollutants in the process of anaerobic digestion and their content in digestate is an urgent scientific issue driven by the necessity to confirm the safety of using this product as a biofertilizer to improve the quality of agricultural land. The aim of the article was to determine the efficiency of the degradation of pollutants in the process of anaerobic digestion with the use of various additional treatment methods. A meta-analysis was conducted to establish the patterns of pollutant degradation during anaerobic digestion under different conditions and with the application of additional process intensification technologies (ultrasound, the use of chemical reagents and carbon cloth, interspecies electron transfer, immobilisation of microalgae, etc.). The reliability of the selected hypotheses and the statistical significance of the obtained data were determined using statistical analysis methods. It was found that additional treatment methods allow to increase in the efficiency of degradation of organic pollutants in mixed organic waste by 180% (direct interspecies electron transfer), in animal waste by 115% (alkaline pre-treatment), and in wastewater sludge by 55% (by treating them in a thermophilic aerobic reactor together with anaerobic digestion). The efficiency of the immobilisation of microalgae technology, which provides for the removal of pollutants from the liquid fraction of digestate, is 135%. The presence of a synergistic effect of additional methods of feedstock treatment has also been established, which is illustrated by an increase in the amount of methane production by 98.88-261.56%, depending on the type of waste and the treatment method. The results obtained prove the high efficiency of additional treatment technologies. The practical significance of the results obtained lies in the proven synergistic effect of using additional methods of treatment of feedstocks and digestate due to an increase in the level of degradation of organic pollutants with the production of environmentally safe fertilizer and an increase in biogas yield
Energetic Potential of Tobacco Waste Within Combustion or Anaerobic Digestion
The growing demand for energy biomass encourages the use of waste and by-products from agriculture. The aim of this study was to assess the suitability of tobacco stalks (TSs) for energy use in the combustion and anaerobic digestion (AD) process, as well as the technical and environmental effects of energy production from this waste raw material. Laboratory tests were conducted on the energy parameters of TS biomass, the chemical composition of ash from its combustion, and the efficiency and composition of biogas generated during the AD process of TS silage with various silage additives. The tests were conducted in accordance with the standards applicable to biomass fuels. The energy yield and emission reduction obtained by the replacement of conventional energy sources were calculated. The energy parameters of TS were inferior compared to the raw materials most often burned in boilers (wood, straw). The high ash content (7.31% in dry mass) and its chemical composition may adversely affect heating devices. Methane yield from TS silage was lower (18.55–24.67 m3/Mg FM) than from silage from crops grown for biogas plants (i.e., 105 m3/Mg for maize silage). Silage additives improved TS silage quality and methane yield (from 18.55 to 21.71–24.67 m3 CH4/Mg in case of silages with additives. Energy yield and emission reduction were higher in the case of TS combustion, but AD is a process consistent with the circular economy. Both TS energy management processes are in line with the Sustainable Development Goals as they prevent the devaluation of agricultural waste, providing a valuable resource for bioenergy.