Coagulant Cost Optimization for Surface Water Coagulation Process

K e y w o r d s : Coagulation; Costs; Hydrolysis; Optimization; Organic substance; pH correction. 3/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 153 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 3/2018 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 8 0 4 8 M . W o l s k a , M . M o ł c z a n , A . S o l i p i w k o P i e ś c i k , H . U r b a ń s k a K o z ł o w s k a 154 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 3/2018 coagulation. This group is subject to research that shows higher increase in efficiency of dissolved organic carbon (DOC) removal with increase in the pre-hydrolyze level [11]. Pre-hydrolyzed coagulants are more effective in a larger range of water pH in comparison to non pre-hydrolized coagulants [12]. During coagulation by pre-hydrolyzed coagulants efficiency of water colour decrease is higher than that of non prehydrolyzed coagulant, indicating that the necessary doses of pre-hydrolyzed reagents are lower [13]. Guminska [14] presented that the pre-hydrolyzed coagulants are more useful for mountain water treatment (which is characterized by lower water temperatures). The most recent coagulant modifications [15] concern joining coagulation mechanisms with ion transfer [15]. This allows for an improved removal of low molecular mass organic substances, which were not effectively removed with conventional coagulants. In order to aid coagulation, ion exchange resins or powdered activated carbon are also used, as they not only improve effectiveness, but also widen the size ranges of molecules that are removed [16, 17]. These substances are used before flocculation or sedimentation. Such modifications most often result in increased process costs, which in the case of sewage treatment or water treatment for industrial use is necessary due to the specific quality requirements for such water. However, from the point of view of residential customers, it is important to purchase good quality water for the lowest price possible. Therefore, the overarching goal of water utilities is producing water satisfying the requirements for drinking water at the lowest possible process costs. The aim of this study was an evaluation of the effectiveness of currently used coagulants at the water treatment plant as compared to others available on the market, as well as the choice of coagulant/coagulants which will enable a sufficient organic substance removal effectiveness for drinking water while maintaining low process costs. 2. MATERIALS AND METHODS The study was conducted with the use of surface water (Oława river) uptaken by a water treatment plant (“MokryDwór” in Wrocław) with a throughput of about 60 000 m3/day, supplying drinking water. 10 aluminum coagulants available on the market were used in this study (Table 1), chosen due to their varied properties (degree of pre-hydrolization, aluminum content and presence of additives) and their price. The optimal coagulation process consisted of the least expensive treatment along with the most effective coagulant and lowest dosage. The studies were performed in two stages. In the first stage, the effectiveness in removing organic substances for all analyzed coagulants was evaluated at dosage ranges of 1.0 to 6.0 gAl/m3. For the second stage, four coagulants having the highest removal Table 1. Characteristics of used coagulants Coagulant Aluminum(Al+3) Chlorides (Cl-) Alkalinity * pH Density, 20°C Price Additives % % % g/dm3 PLN/kgAl C1; PAX16 8.2 ±0.2 19 ±2.0 37 ±5 1.