The efficiency of removal of cellular organic matter (COM) of cyanobacteria Microcystis aeruginosa from water with ferric sulfate is influenced primarily by coagulant dosage and reaction pH. Therefore, optimization of the reaction conditions is a prerequisite for efficient purification of surface waters. Because the isoelectric point of COM occurs at a low pH, the purification of waters containing this organic matter should take place in an acidic pH range. It was also found that proteins are removed more efficiently than other organic substances (mainly polysaccharides). Water Environ. Res., 81, 514 (2009).
This paper summarises the preliminary results from the research into the influence that conditions of agitation have on the progression of the aggregation process and on some of the properties of formed aggregates affecting the efficiency of separation processes. These results show that the applied velocity gradient G, the period of its action T and the distribution of a velocity field in the agitated volume of water influence the number of aggregates, their size and shape in a significant manner. Smaller and denser aggregates of a homogeneous size that are more resistant to breaking up are formed with higher velocity gradient.
The term mixing is confusing because it is used to describe transport mechanisms for both flash mixing (reagent dispersion and homogenisation with water mixing) and agitation (flocculation mixing) because each of these mechanisms requires different flow characteristics in order to take place with maximum efficiency. Flash mixing should take place under conditions of mixing on macro-scale with macro-turbulent eddies being formed and agitation under conditions of mixing under microscale with micro-turbulent eddies being formed. Agitation takes place under high-or low-intensity agitation. Only the conditions of agitation can be characterised by velocity gradient. Differentiation between flash mixing and agitation is discussed.
Basic types of pollutants in surface waters and methods for their removal are reviewed. Guidelines are provided for selecting the most effective hydrolysing destabilisation reagent (coagulant) for a particular quality surface water, which is polluted with different types of impurities, and optimising the reaction conditions under which its purification takes place.
This paper investigates the best attainable treatability to which a water polluted with a technologically significant concentration of organic matter is treatable by different cation-active polyelectrolytes and their blends with mineral coagulants in comparison to that attainable by traditional hydrolysing coagulants. The negative influence of these reagents used as primary coagulants on the treated water quality is demonstrated in the case of Saulspoort Waterworks.
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