Phosphorus concentration in rivers results from both external inputs and internal loading from the bottom sediments. Seasonal, spatial, and multi-annual dynamics of phosphorus forms in bottom sediments and their interstitial water for the river Prut (Moldova) were evaluated. In order to determine content of total phosphorus in the bottom sediments, fresh (wet) samples were subjected to persulfate oxidation. The content of inorganic phosphorus was determined after acidic oxidation of samples. The amount of organic phosphorus was obtained by subtracting inorganic phosphorus from the amount of total phosphorus. Content of phosphorus forms in interstitial water was determined after centrifugation of fresh (wet) sediments. In general, the shape of dynamics of the amounts of inorganic phosphorus in sediments was close during years 2009, 2010, and 2011, with registered higher contents of this form on the middle course of the river. The spatial dynamics of organic phosphorus is less homogeneous along the Prut River. During 2009, higher amounts of organic phosphorus were recorded on the middle sector. During the spring of year 2010, the content of organic phosphorus in sediments was practically not changed along the river. The ratio of inorganic/organic phosphorus in bottom sediments was similar during the researched years, with the predominance of the inorganic phosphorus being recorded. Also, the increasing tendency of the percentage of organic phosphorus from spring to summer was identified. Generally, appropriate spatial and seasonal dynamics of phosphorus forms in bottom sediments and their interstitial water were recorded, although sometimes with some differences.
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...
Abstract. Bottom sediments of the river are repositories for various elements, acting both as sinks and sources of supplying of elements to overlying water horizon. Re-suspension of the bottom sediments of the Prut River was performed in fi eld conditions by "aquarium" method. The results suggest that during the re-suspension, bottom sediments can become a relevant source of heavy metals and phosphorus forms which are mobilized in the water horizon overlying the bottom sediments.
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