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This paper deals with the problem of chromium recovery from chrome-tanned waste and thus with reducing the environmental impact of the leather industry. Chrome-tanned waste was transformed by alkaline enzymatic hydrolysis promoted by magnesium oxide into practically chromium-free, commercially applicable collagen hydrolysate and filtration cake containing a high portion of chromium. The crude and magnesium-deprived chromium cakes were subjected to a process of thermal decomposition at 650°C under oxygen-free conditions to reduce the amount of this waste and to study the effect of magnesium removal on the resulting products. Oxygen-free conditions were applied in order to prevent the oxidation of trivalent chromium into the hazardous hexavalent form. Thermal decomposition products from both crude and magnesium-deprived chrome cakes were characterized by high chromium content over 50%, which occurred as eskolaite (CrO) and magnesiochromite (MgCrO) crystal phases, respectively. Thermal decomposition decreased the amount of chrome cake dry feed by 90%. Based on the performed experiments, a scheme for the total control of chromium in the leather industry was designed.

Contamination of soil and groundwater with pesticides is mainly caused by old ecological burdens. This study focuses on the treatment of groundwater contaminated with chlorinated pesticides. The contaminants mainly include α-HCH, β-HCH, γ-HCH, HCB, DDE, DDD and DDT. Reverse osmosis technology using RO98pHt polyamide membranes was used to remove the pollutants under batch process conditions. The observed rate of removal ranged from 98.4% to 99.7%. Total dissolved content solids decreased from 1.35 g/dm 3 to below 0.05 g/dm 3 .

Abstract. In this paper the mathematical modeling of collagen hydrolyzate yield from shavings, a leather waste material, is dealt. Besides its function, leather industry is perceived as a consumer of resources and producer of pollutants. The process of alkaline enzymatic hydrolysis offers a reasonable method of processing part of solid waste arising from leather industry with the aim of further utilization of collagenous share. The model is based on the total mass and dry matter balances of technology and its individual components to optimize the hydrolysate yields. The results are visualised in 3D. The experimental laboratory data of alkaline enzymatic hydrolysis are used for comparison with the model and are discussed.

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