Ash and slag disposal areas of Ukrainian thermal power plants accumulate large amounts of waste annually. The aim of the present study was to analyze the composition of ash and slag wastes generated during combustion of coal at Ukrainian thermal power plants and the potential affects of disposal areas on the environment. A literature search was conducted using the Google search engine to access online academic publications indexed in Google Scholar, PubMed, Scopus, Clarivate Analytics (Web of Science), ScienceDirect, ResearchGate and Springer Link from 2011 in English and Ukrainian. After analyzing the 25 academic articles included in the present review, the results indicated that hazardous constituents (oxides of silicon, aluminium, iron, calcium and magnesium) of ash can migrate from the ash dump surface by air and water to contaminate the atmosphere, soil, groundwater and surface water in areas located within a few kilometers from the waste site. By-products of the fuel and energy complex of Ukraine are potentially dangerous sources of environmental pollution. They create risks to the health of the population living in the surrounding territories. Further studies should focus on the features of pollutant transfer from ash dumps, and development of appropriate mathematical models of the pollutant migration to assess pollution levels in soil, groundwater and air. The authors declare no competing financial interests.

An increase in the share of renewables in heat supply systems is a promising direction to reach sustainable development goals and decarbonization. Decision makers should consider various factors, including energy market prices, the availability of biofuels, boiler and auxiliary equipment costs, logistic costs, and the taxation system. In the European Union, the energy crisis causes a rapid increase in fossil fuel prices. Moreover, the use of fossil fuels results in greenhouse gas emissions, which threatens the achievement of sustainable development goals. We studied the influence of the delivery cost and the value of environmental tax rates on the levelized cost of heat. Low-capacity boilers (up to 1 MW) and different fossil and renewable fuels were analyzed. An analysis was carried out on the example of Ukraine. The European trends were factored in. The obtained results showed that biofuel boilers had lower levelized costs of heat than fossil fuel boilers. Delivery costs and environmental taxes have a significant impact on heat energy costs.