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ABSTRACT:The flocculating efficiency of some hydrophilic/hydrophobic cationic polyelectrolytes on montmorillonite suspension in water was investigated as a function of both the polycation structure and the flocculation parameters: polycation/montmorillonite contact time, suspension pH, polycation dose, and temperature. Cationic polyelectrolytes with quaternary ammonium salt groups in the backbone and hydrophobic side chains (hexyloxypropyl, PCA 5 H 1 and PCA 5 H 2 ; and decyloxypropyl, PCA 5 D 1 , respectively) were used as flocculants. The flocculation was time dependent. A negative influence of the stirring time and of the abrupt variation of pH from basic to acidic on the separation efficiency was evidenced. The increase of the polycation dose from 0.58 mg polycation/g montmorillonite up to 1.74 mg/g montmorillonite showed a positive influence on the sedimentation of montmorillonite particles for all the polycations taken into account. The influence of the polycation structure was reflected in the lower turbidity found in the case of the polycation PCA 5 D 1 compared with that of PCA 5 H 1 , at the same concentration; this reflects the positive influence of the hydrophobicity increase on the suspension separation. A common characteristic for all the polycations is that, for more than about 60 min of settling, the lowest turbidity was found at 25°C and the highest at 5°C. The turbidity found at 15°C was in between, both before and after 60 min of settling time.

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Abstract. The aim of presented research was to optimize the treatment process of the Prut River water. In order to realize the proposed goal, there were studied the following factors which can improve the process of coagulation: (i) the infl uence of stirring speed during coagulation and (ii) the infl uence of the concentration of the coagulant solution added in the process of coagulation. The optimal conditions of coagulation were established using the Jar-test method. Application of the recommended procedure contribute to the reduction of the coagulant dose, the contact time, the aluminum concentration in water and the expenses for water treatment.Keywords: coagulation, aluminum sulphate, Jar-test method. IntroductionNatural water is a heterogeneous medium due to the presence of particulate materials and micro-bubbles of gas. The particulate materials of natural waters are distinguished by their size. The particles with sizes of less than 10μ have a sedimentation velocity less than 0.01 cm/s, and are evenly distributed throughout the water horizon [1]. With decreasing of particle size, the time required for settling has increased. Due to very small dimensions, the only way to separate the particles is their agglomeration into bigger ones that settles easier. Rejecting electrostatic forces prevent the particles to reach each other, and the suspension is stable [2].For removal of fi ne-dispersed and colloidal impurities, the methods of coagulation and fl occulation are often applied. Coagulation is based on the interaction of colloid and fi ne-dispersed particles with aggregates formed upon adding of coagulants. This method was fi rst used at the beginning of XX century [1]. Coagulation can be used both on treatment of drinking water [3][4][5][6][7] and on the purifi cation of waste water [8][9][10].The role of coagulation is to overcome the factors that contribute to the stability of the given system. It is achieved using the suitable chemical substance, typically aluminum or iron salts, so-called coagulants. The coagulation process takes place in two distinct steps. The fi rst step is the adding of coagulant; as a result, the destabilization of colloidal suspension occurs and the fl ocs are formed. During second step, the formation of agglomerates, large agglomerates, takes place, which can easily be separated by gravitational sedimentation [2].The most widely used coagulant is the aluminum sulphate, which has been used for water treatment [2] applied in a number of countries since the early 1900 [11]. It, usually, is obtained by reaction of bauxite with sulphuric acid [2,12].Coagulation is the main reaction stage for the removal of natural organic matter and other contaminants in water treatment processes. The choice of a coagulant has a major infl uence on the performance of the coagulation process [13]. The aluminum sulphate is used at the purifi cation of water with high turbidity. This coagulant is characterized by relatively low cost, good solubility, no special requirements for the use of dry and disso...