Wood ash is a complex mixture of inorganic and organic compounds. It is heterogeneous in composition, which can vary considerably. Ash is mainly disposed of in landfills, which creates a risk for air, soil and groundwater contamination by trace elements. In order for wood biomass ash to be used as a secondary raw material, it is necessary to perform leaching tests, to determine which microelements it contains, and which of them could be released into the environment during the ash disposal. Sequential extraction (SE) showed that in the exchangeable and carbonate fraction, the most volatile metals As, Cd, Zn and Pb are released the most from the ash of deciduous trees, while the leaching of ash from coniferous trees is significantly lower. The evaluation of risk assessment code (RAC) for the tested biomass ash samples, indicates that Pb is a high-risk leaching element due to its condensation on the ash particles. By performing toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) tests, it was established that the released concentrations of tested metals are below the maximum allowable concentration, given by the regulation. The leaching tests of composites, prepared from wood ash in combination with cement, indicate that the leaching of ash is reduced to a minimum, and that all heavy metals are bound in a cement matrix, which indicates the possibility of using wood ash for construction purposes.

The electrooxidation (EO) of three important environmental contaminants, anticorrosive 1H-benzotriazole (BTA), plasticizer dibutyl phthalate (DBP), and non-ionic surfactant Triton X-100 (tert-octylphenoxy[poly(ethoxy)] ethanol, t-OPPE), was studied as a possible means to improve their elimination from wastewaters, which are an important emission source. EO was performed in a batch reactor with a boron-doped diamond (BDD) anode and a stainless steel cathode. Different supporting electrolytes were tested: NaCl, H₂SO₄, and Na₂SO₄. Results were analysed from the point of their efficacy in terms of degradation rate, kinetics, energy consumption, and transformation products. The highest degradation rate, shortest half-life, and lowest energy consumption was observed in the electrolyte H₂SO₄, followed by Na₂SO₄ with only slightly less favourable characteristics. In both cases, degradation was probably due to the formation of persulphate or sulphate radicals. Transformation products (TPs) were studied mainly in the sulphate media and several oxidation products were identified with all three contaminants, while some evidence of progressive degradation, e.g., ring-opening products, was observed only with t-OPPE. The possible reasons for the lack of further degradation in BTA and DBP are too short of an EO treatment time and perhaps a lack of detection due to unsuitable analytical methods for more polar TPs. Results demonstrate that BDD-based EO is a robust method for the efficient removal of structurally diverse organic contaminants, making it a promising candidate for advanced water treatment technologies.

In this paper, the corrosion test of copper in hydrocracked base oil HC-6 was performed in the presence of an additive for extremely high pressures (EP additive) in different concentrations. EP additives are used to reduce wear in industrial applications, under high load conditions. Since most of these additives are sulfur-based, whose compounds can be corrosive at high temperatures, their use leads to corrosion of some materials. To prevent corrosion in the base oil with the EP additive, three commercial corrosion inhibitors are added. By chemical composition, the inhibitor RC 8210 is a derivate of dimercaptothia-diazole, RC 4220 is a synthetic neutral calcium sulfonate, and IRGAMET 39 is a derivative of tolutriazole. Efficiency of the inhibitors was monitored by standard test methods for corrosiveness to copper arising from petroleum products by the copper strip test (ASTM D-130) and the gravimetric method, while oxidation stability of the base oil was monitored by peroxide number determination. Oxidation was performed at 100±1°C for 3 and 24 h. Results of these studies have shown that IRGAMET 39 is the most effective inhibitor in the presence of the EP additive at both examined oxidation times.

This study explores the effectiveness of electrocoagulation (EC) for removing toxic hexavalent chromium (Cr(VI)) from industrial wastewater using iron and aluminum electrodes in both batch and continuous modes. Iron electrodes demonstrated superior performance, achieving up to 99.8% Cr(VI) removal in batch mode at an optimal current density of 5 mA/cm2, while continuous operation at 50 L/h achieved comparable removal after 30 minutes, with slightly lower efficiency due to reduced retention time. The lowest specific energy consumption (2.82 kWh/kg Cr(VI)) was also recorded under these optimal conditions, highlighting economic feasibility. Fourier-transform infrared (FTIR) analysis of the sludge confirmed the reduction of Cr(VI) to the less toxic Cr(III), primarily in the form of Cr(OH)3. Characteristic peaks indicate Cr-O vibrations in chromium hydroxide, while the presence of hydroxyl (-OH) groups confirms the formation of iron hydroxide complexes that facilitate Cr(VI) adsorption and precipitation. Additional spectral features suggest the presence of iron oxides, further supporting the electrocoagulation mechanism involving the generation of coagulant species in situ. Overall, the results affirm EC as a highly efficient and cost-effective treatment method, particularly suitable for large-scale applications.

In addition to the already well-known application in metal production, electroplating, electrochemical energy sources, electrochemistry is also applied in other branches of industry. Today, electrochemical technologies for the treatment of wastewater and drinking water are increasingly present. In recent years, new advanced oxidation processes based on electrochemical technology - Electrochemical advanced oxidation processes (EAOPs), have been developed for the treatment of persistent pollutants, which cannot be removed by conventional water treatments. EAOPs are based on “in situ” electrolytic formation of strong oxidants in an electrochemical reactor, able to degrade almost all organic pollutants. Despite their effectiveness in degrading different types of pollutants, the biggest challenge for EAOPs is high electricity demand to power these systems, which can have serious consequences from both an ecological and an economic point of view. The use of electricity from the distribution network to power electrochemical reactors is the biggest barrier to achieving commercial success of this technology. A possible solution to this challenge is the application of direct solar UV radiation to produce electric energy by use of a solar photovoltaic (PV) arrays for power supply of EAOPs. The aim of the research was to demonstrate the feasibility of using EAOPs directly powered by PV systems, as a sustainable system for efficient water treatment.

Leather making is a very long process and consists of many different chemical and mechanical operations. The most important operation of the whole leather making process is the tanning, which is performed mainly by vegetable or chrome tanning. With this work, we wanted to establish a connection between the way leather is tanned and its physical and mechanical properties. For this purpose, certain physical and mechanical properties of bovine, sheep and goat leather, which were obtained by chrome and vegetable tanning, were examined. Tests were performed on commercially available leathers. The selected leather samples were tested for thickness, mass per unit area, apparent density, braking force and breaking elongation, while other dimensions were calculated based on previously measured values. After the measurements, the results were compared according to the type of leather and the method of tanning. The obtained results showed better physical and mechanical properties of chrome-tanned leather compared to vegetable-tanned leather, with the highest breaking strength of chrome-tanned bovine leather (70.7 N/mm2). However, for a more precise analysis, when examining the physical and mechanical properties, it is necessary to have more precise data of the origin, tanning parameters and applied leather finishing. The chrome tanning process has advantages in terms of the shorter duration of the tanning process, but chrome tanning process has significant limitations in terms of environmental requirements, which is why the vegetable tanning process is becoming more relevant again.