Today it is obvious that the existing linear model of the economy does not correlate with the principles of sustainable development. The circular economy model can replace the current linear economy whilst addressing the issues of environmental deterioration, social equity and long-term economic growth. In the context of effectively implementing circular economy objectives, particular importance should be attributed to wastewater treatment sludge management, due to the possibility of recovering valuable raw materials and using its energy potential. Anaerobic digestion is one of the methods of recovering energy from sewage sludge. The main goal of this study is to make a preliminary evaluation of possible sewage sludge biogas and biomethane solutions using a computation model called MCBioCH4 and compare its results with laboratory tests of sewage sludge fermentation from the northern wastewater treatment plant (WWTP) of Ekaterinburg (Russian Federation). Laboratory experiments were conducted to determine the volume and qualitative composition of biogas produced throughout anaerobic fermentation of raw materials coming from the WWTP. The specific productivity of samples ranged between 308.46 Nm3/tvs and 583.08 Nm3/tvs depending if mesophilic or thermophilic conditions were analyzed, or if the experiment was conducted with or without sludge pre-treatment. Output values from the laboratory were used as input for MCBioCH4 to calculate the flow of biogas or biomethane produced. For the case study of Ekaterinburg two possible energy conversion options were selected: B-H (biogas combustion with cogeneration of electrical and thermal energy) and M-T (biomethane to be used in transports). The results of the energy module showed a net energy content of the biogas between 6575 MWh/year and 7200 MWh/year. Both options yielded a favorable greenhouse gas (GHG) balance, meaning that avoided emissions are higher than produced emissions. The results discussion also showed that, in this case, the B-H option is preferable to the M-T option. The implementation of the biogas/biomethane energy conversion system in Ekaterinburg WWTP necessitates further investigations to clarify the remaining technical and economic aspects

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Abstract.The current obstacles to the sustainable development of the vehicle fleet present one of the most serious and complex challenges for technogenic civilization in view of the consumption of rapidly depleting oil and gas resources and the increasing emissions of the products of fuel combustion. The aim of this paper is to study and discuss the impact patterns of the quality of fuel on the environmental and performance characteristics of vehicles and to develop an approach towards improving the quality of fuel as a means of increasing the sustainability of vehicles. The patterns of influence of the chemical composition of the fuel on the temperature conditions in the engine, the emissions of toxic substances and carbon dioxide from the fuel's combustion, the toxicity of the gasoline vapor, carbonization, fuel consumption, engine power and the requirements for a gasoline octane rating have been identified. The use of a fuel additive has been proposed which improves fuel injection in the engines and excludes tarry deposits in the fuel system through the effective detergency and catalyzes the gasification reactions in the engine. The developed fuel additive was shown to have a positive effect by significantly reducing fuel consumption and toxic emissions and improving the performance of vehicles.

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The operation of modern vehicles requires the introduction of package of fuel additives to ensure the required level of operating characteristics, some of which cannot be achieved by current oil refining methods. The use of additives allows flexibility of impact on the properties of the fuel at minimal cost, increasing the efficiency and environmental safety of vehicles. Among the wide assortment of additives available on the world market, many are surfactants. It has been shown that the introduction of some surfactants into gasoline concurrently reduces losses from gasoline evaporation, improves the mixture formation during injection of gasoline into the engine and improves detergent and anticorrosive properties. The surfactant gasoline additive that provides significant improvement in the quality of gasoline used and environmental and operating characteristics of vehicles has been developed and thoroughly investigated. The results of studies confirming the efficiency of the gasoline additive application are herein presented.

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Nowadays, when the energy, industry and transport sectors are adapting to climate change and need to reduce their environmental impact, it is vital that the optimal solutions are found for individual countries and their different circumstances. Territories, which have a hydrocarbon deficit, should use non-conventional energy sources while the countries with substantial resources of hydrocarbons should be focused on the strategy of raising the energy efficiency, i.e. to reduce the specific consumption of fuel consumed. The paper discusses these scenarios and describes some innovative technologies for both cases. Energy production from biomass is encouraged in some European countries by the granting of generous economic subsidies so that renewable energy plants, such as anaerobic digestion plants that produce biogas for use in internal combustion engines, in particular, are receiving much funding. An alternative technology for biogas valorisation could be that of biomethane (so called green gas) production through biogas purification and upgrading processes to remove CO 2 , H 2 S and water vapour. Different technologies have been proposed to remove CO 2 from gas streams, such as physical absorption, absorption by chemical solvents, cryogenic and membrane separation and CO 2 fixation by chemical or biological methods. Production of biomethane and its introduction into the natural gas grid or its use as a fuel for vehicles could increase the energy efficiency and reduce specific emissions (combined cycle gas turbines, district heating of CHP units, methane powered vehicles). A simple and low-cost method of improving energy efficiency and environmental safety of transport by introducing into hydrocarbon fuels micro doses of a universal multifunctional additive is proposed. The method will make a significant contribution towards solving the problems of adapting to global climate change and improving the environment. It is capable of reducing specific fuel consumption by up to 12% and the requirements for a gasoline octane number by 10 points. It significantly reduces emission levels of greenhouse gases and toxic substances and provides complex improvement of the properties of fuels and the condition of engines.