Regular monitoring of water quality of the Danube river in the backwater zone includes analysis of the sediment. It is well known that sediment is a sink place for the non degradable compounds and it reveales the long term water quality status in the reservoir. This paper presents the general results on the Iron Gate reservoir siltation. as well as some data regarding pollution level, based on investigations carried in the period of 2001-2002. The investigations included organic load of the sediment, heavy metals and organic pollutants content. The degree of pollution is evaluated on the basis of various criteria, also compared to results of previous case studies.

The paper deals with pilot-scale investigations of the effect of preozonation on NOM removal from groundwater by coagulation and flocculation processes. It was found that the preozonation increased the efficiency of organic matter removal by coagulation and flocculation from 23.6 to 47.2% as judged on the basis of KMnO4 values. From the aspect of the change of content of trihalomethanes precursors preozonation exhibits both the positive and negative effects if their content in the water after coagulation is considered in dependence of the applied ozone dose. The obtained values siggest the necessity of careful optimization of the processes of preozonation, coagulation, and flocculation, especially from the aspect of the change in content of the precursors of disinfection byproducts.

The paper deals with determining the dependence of trihalomethanes forming (chloroform, bromdichlormethane, dibromchlormethane and bromoform) on the contents of natural organic matters from groundwater. The analyses was made bay calculating correlation of trihalomethanes forming potential (THMPF) with UV absorbance and permanganate number as surogates parameters for defining in content NOM in water. These were used to observe the changes in the content of organic matters after coagulation. A good correlation of THMPF, PF chloroform and UV absorbance (254 nm) (coeficient of correlation 0.72 and 0.87) was observed as well as a good with UV absorbance (254 nm) (coeficient of correlation - 0.88) and with PN (coeficient of correlation - 0.80) in coeficient of correlation in bromated trihalomethanes forming.

The work considers the effect of the ozonization process on the change of contents of natural organic matter (NOM) and formation of byproducts in the groundwater pretreated by preozonation (2.0 g O3/cubic m) and coagulation with polyaluminium-chlorosulfate (5 and 10 g Al/cubuc m). Experiments were carried out on a semi-industrial plant of capacity of 2 cubic m/h, using groundwater with a high content of NOM (5.1 mg/l TOC). It was found that in the course of ozonization NOM content shows a decrease (18-64%), as well as the potential of formation of trihalomethanes, PFTHM (12-59%), whereas content of aldehydes increases by 3.0-7.7 microgram/l, depending on the water pretreatment and applied ozone dose. It was found correlation between specific aldehyde content and decrease of the specific PFTHM (r=0.815-0.998).

The paper presents the results of a pilot study of the combined process of ozonation and filtration through biologically activated carbon to remove residual organic matter in the process of drinking water production. It was established that the application of these procedures resulted in the removal in average of 74% PB, 50% TOC, 60% of total aldehydes, and 54% PFTHM, the result being a consequence of the adsorption/biosorption processes involved.