Natural waters and wastewaters often contain heavy metals, e.g., iron. Iron ore mining contaminates groundwater with iron up to 30 maximal permissible concentrations (MPC) as this element gets washed out from rock and soil. Adsorption is the most effective and economically feasible method of additional purification of natural and wastewater from iron. Its efficiency depends on the type of adsorbent. The research objective was to select the most efficient sorption material to eliminate water from iron, as well as to establish the adsorption patterns for different sorbents, thus creating sustainable and effective purification. The study featured carbonaceous sorbent of the SKD-515 grade, mineral sorption materials with aluminosilicate of the AC grade, and silicate-based sorbent of the ODM-2F grade. The porous structure was studied by porometry methods while the surface image was obtained using scanning electron microscopy. Other indicators included equilibrium, kinetics, and dynamics of iron adsorption by various sorbents. The Freundlich and Langmuir equations made it possible to calculate the key adsorption parameters. The Gibbs energy values were obtained from the Langmuir equation and equaled 11.93–20.66 kJ/mol, which indicated the physical nature of the adsorption process. Under static conditions, the sorbents demonstrated a high adsorption capacity with respect to iron, depending on the structure, and could be arranged as AC > SKD-515 > ODM-2F. In SKD-515, iron adsorption occurred in micropores; in AC and ODM-2F, it took place in mesopores. The kinetics of iron extraction showed that the adsorption process was limited by external mass transfer. The research provided a new understanding of iron adsorption by materials of various structures. The conclusions were supported by scanning electron microscopy images. Initial concentration, flow velocity, and loading layer height were studied in dynamics, i.e., during continuous operation of the adsorption column. The system proved extremely effective and reached 99.0% Fe3+ extraction under the following conditions: flow rate = 1 L/min, loading column height = 0.15 m, column diameter = 0.05 m, initial concentration = 0.5 mg/L (5 MPC). The column performance was tested at an initial concentration of iron ions of 50 MPC, which simulated the wastewater treatment at industrial enterprises. This comprehensive study of iron adsorption from wastewater proved the efficiency of the mineral sorption materials with aluminosilicate of AC grade.

Introduction. Canning requires thermophysical calculations for thermal or cold processing. These calculations are based on thermophysical characteristics of raw materials. The research objective was to analyze the thermophysical characteristics of tropical fruits. Study objects and methods. The study featured kiwi, papaya, avocado, and figs. Their thermal conductivity was analyzed with the help of stationary fiber plate method. The cryoscopic temperature was determined from the flat area of the thermogram obtained during freezing. The heat capacity and the amount of frozen moisture were determined by calculation based on the available data on the chemical composition of the fruits. The density was defined by using the hydrostatic weighing method, the sugar content – by the refractometric method, the moisture content – by drying to constant mass. Results and discussion. The research revealed the physicochemical parameters of kiwi, avocado, papaya, and figs. Papaya demonstrated the highest moisture content – 86.32 ± 0.02%, while kiwi appeared to have the highest density – 1,065 ± 1 kg/m3. Figs had the highest sugar content – 16.0 ± 0.1%. The thermal conductivity coefficient of fresh and frozen tropical fruits was determined experimentally and increased after freezing. Frozen avocado showed only a slight increase in thermal conductivity coefficient because of its low moisture content while frozen figs demonstrated a significant increase in the thermal conductivity coefficient – by 3.3 times. This product possessed the highest thermal conductivity: 0.63 ± 0.02 W/(m·K) for the fresh samples and 2.06 ± 0.02 W/(m·K) for the frozen samples. The thermal conductivity coefficient of kiwi and papaya increased by 2 and 4.2 times, respectively. The experiment also examined the effect of protective plastic wrap and ripeness on the thermal conductivity coefficient. The film proved to have a negative effect on the reliability of thermophysical analysis. The cryoscopic temperature was determined empirically. Such thermophysical properties as heat capacity, thermal diffusivity, and frozen moisture were based on the available chemical composition. Conclusion. The research revealed the physicochemical parameters of kiwi, avocado, papaya, and figs. It included a set of experiments on the thermal conductivity coefficient of fresh and frozen tropical fruits. The obtained values can be used to develop the optimal parameters of thermal processing, refrigeration, and thermal treatment of new products. They can also be useful for fortifying dairy and bakery products with exotic fruits.

There is a growing demand for rapid cooling in modern food industry. Traditional methods of fish cooling involve cold air, cold liquid, and ice. These methods have a number of disadvantages. For instance, they may have a negative effect on the appearance of the product, require a longer cooling time, or make fish absorb extra moisture. As a result, the quality of the product and its shelf life decrease, which results in demand contraction. Carbon dioxide is becoming increasingly popular in closed refrigeration systems. It is one of the most promising refrigerants, since traditional refrigeration technologies for fish cooling have a number of serious drawbacks. The paper introduces a utilization method for carbon dioxide obtained at alcohol processing plants. The authors analyzed the prospects of using carbon dioxide in combination with a binary mixture for cooling trout. A series of experiments proved the technological advantages of this technology. The paper features heat transfer in roundfish during cooling with water ice, a mixture of water ice and snow-like carbon dioxide, and snow-like CO2 in pure form. The obtained results show the effect of the concentration of snow-like carbon dioxide in water ice on the intensity of the cooling process. A higher intensity of the cooling process reduced the cooling time and the amount of water ice. The study of quality indicators of trout proved that the environment of water ice and carbon dioxide increased its shelf life by several times. The paper contains temperature graphs and duration curves at different concentrations of CO2.

Refrigeration machines are widely used in various industries to produce artificial cold. In the process of maintaining low temperatures, the refrigeration machine generates a lot of heat to compress a refrigerant, which is not used in the future, and during the condensation it is released into the environment in the form of water vapor. This negatively affects to the environment because of increasing the concentration of greenhouse gases in the atmosphere. And the use of chlorine-containing refrigerants causes the destruction of the ozone layer. To reduce environmental damage, it is necessary to increase the energy efficiency of refrigeration machines and develop schemes that allow the use of low-grade heat, which is released during operation. In the work, a scheme of a refrigeration machine was developed, which allows utilizing the heat of condensation, using it for various consumers of thermal energy, therefore allowing to reduce emissions of harmful substances into the Earth’s atmosphere and increase technological capabilities of cooling.