The use of organic residues and waste for production of biogas as an energy source is a viable option for waste management and reduction of greenhouse gas emissions. However, before any eventual utilization of biogas, hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ) must be removed since those contaminants are highly undesirable in combustion systems. This work deals with the construction and examination of a laboratoryscale, low-cost test stand for quick evaluation of the existing and new methods for H 2 S and CO 2 removal from biogas. The test stand consists of two sections: one based on absorption in liquid phase (barbotage process) and the other adsorption in a bed of solid reagent. Seven different reagents of various concentrations were used in the experiment: sodium hydroxide (NaOH), ethylene glycol (EG), ethanoloamine (EA), diethanoloamine (DEA), and distilled water (H 2 O) in the barbotage section of the test stand, and bog iron ore (BIO) and activated carbon (AC) in the adsorption column. In the absorption tests, treating biogas with 1M NaOH solution and 100% EA resulted in complete removal of H 2 S and CO 2 . For 100% DEA, high H 2 S and moderate CO 2 absorption efficiency were achieved. EG and H 2 O allowed the removal of H 2 S only to a very limited extent. Both reagents used in the tests with adsorption in a bed, BIO and AC, were able to eliminate H 2 S from biogas, but practically did not change the concentration of CO 2 .

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Polymers and plastics are crucial materials in many sectors of our economy, due to their numerous advantages. They also have some disadvantages, among the most important are problems with the recycling and disposal of used plastics. The recovery of waste plastics is increasing every year, but over 27% of plastics are landfilled. The rest is recycled, where, unfortunately, incineration is still the most common management method. From an economic perspective, waste management methods that lead to added-value products are most preferred—as in the case of material and chemical recycling. Since chemical recycling can be used for difficult wastes (poorly selected, contaminated), it seems to be the most effective way of managing these materials. Moreover, as a result this of kind of recycling, it is possible to obtain commercially valuable products, such as fractions for fuel composition and monomers for the reproduction of polymers. This review focuses on various liquefaction technologies as a prospective recycling method for three types of plastic waste: PE, PP and PS.

It is known that biogas without prior purification to biomethane is a commonly used fuel only for the stationary internal combustion engines but not for vehicle engines. The current study evaluates the use of biogas without its prior upgrading to biomethane as fuel for tractor engines. The following tests were carried out: biochemical methane potential tests, dynamometer engine tests, and field tests with the use of a tractor. The average methane content in biogas obtained from vegetable wastes exceeded 60%. The tests performed on the engine dynamometer showed that the engine powered by dual fuel worked stably when diesel was replaced by 40% biogas (containing 50% of CO2) or 30% methane. Dual fuel supplying of the engine caused an increase in the concentration of hydrocarbons and carbon monoxide in the exhaust gases and a decrease or no effect in the concentration of particulate matter and nitrogen oxides. It did not significantly affect the dynamics of the vehicle and its useful properties. Biogas that contains a maximum of 50% CO2 and from which H2S, moisture, and siloxanes have been largely removed, is suitable as a fuel for tractors. Such biogas can be obtained in biogas plants from different substrates, e.g., vegetable or agriculture wastes as well as biodegradable municipal wastes.