Abstract. The main goal of this paper is to analyse physical and chemical aspects affecting the structure and strength of flocs, which are created during coagulation and flocculation of water impurities, from the point of view of process computer simulation. Proposed mathematical dependencies were used for computer modelling of the process as well as visualisation of the obtained results. The results of algorithms operation and visualization were shown as graphical representation. Laboratory studies were carried out to check the realism of the proposed algorithm.

Commissioning of new dissolved air flotation (DAF) installations and optimization of already existing installations takes at least one year of laboratory and pilot plant experiments. Such studies are labor-intensive. Using mathematical modeling, it is possible to minimize time and costs. For such purposes, mathematical model of the DAF process was developed based on the law of momentum (impulse) behavior and Navier-Stokes equations. The model allows to describe the kinetic relations between the water stream, air bubbles and aggregates arising as a result of coagulation of surface water pollution. The model takes into account the exchange of impulses between different phases as a result of laminar and turbulent flow. The developed model was used to prepare a simulation computer program. In order to check the feasibility of the model, laboratory tests were carried out under static conditions. Comparison of the results of laboratory tests with the results of computer simulation showed its suitability for analyzing the effectiveness of removing solid phase from water by means of dissolved air flotation. Proposed model was also compared with models proposed by different authors.

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There were operational problems of not having the ability to remove manganese compounds in one of the country's groundwater treatment plants, despite the fact that the filters were some years earlier fitted with the Multiman 3M catalytic bed inserts. The paper presents the results of analysis of morphological characteristics of fresh and blocked catalytic grains. An equivalent diameter, circularity, convexity, and compactness were used to describe the morphological characteristics of the catalytic mass grains. The obtained results confirmed the assumption that the grains of the catalytic mass were blocked by iron hydroxide and that the cause of WTP operating problems was the failure of the aerator, which resulted in the penetration of iron hydroxide through the upper sand bed layer into the lower catalytic mass layer.

Chlorination of waters containing natural organic matter (NOM) produces disinfection by-products (DBPs) including harmful THMs and HAAs. A collective parameter and toxicity index of all chlorination products contained in finished water is the total concentration of organic-bound halogen compounds (TOX). Determination of this indicator is carried out by adsorption-pyrolysis method, which is complicated and requires specialized apparatus. The competitive method of TOX concentration determination in water is differential absorbance. Effect of natural organic matter removal from surface waters in coagulation as well in coagulation and adsorption processes on the decrease of TOX concentration measured by differential absorbance was determined.