The Timok River (202 km long, 4547 km2 basin area) is located in East Serbia. It is a right tributary of the Danube River and one of the most polluted watercourses in Serbia. On the basis of the data provided by the Republic Hydrometeorological Service of Serbia, the paper presents an analysis of water quality and pollution using the combined physico-chemical WPI index (Water Pollution Index) calculated for two periods - 1993-96 and 2006-2009 at four hydrological stations: Zaječar-Gamzigrad (Crni Timok River), Zaječar (Beli Timok River), Rgotina (Borska Reka River) and Čokonjar (Timok River). The following parameters were taken into consideration: dissolved O2, O2 saturation, pH, suspended sediments, Five Day Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (CODMn), nitrites, nitrates, orthophosphates, ammonium, metals (Cu, Fe, Mn, Hg, Ni, Zn, Cd), sulphates and coliform germs. The average WPI values were calculated for the observed periods based on the comparison of the annual average values of the listed parameters and defined standard values for the I water quality class (according to the Regulation on the Hygienic Acceptability of Potable Water of the Republic of Serbia). The highest pollution degree was recorded in the Borska Reka River, where heavy metal levels (especially manganese and iron) were significantly increased. These metals are indicators of inorganic pollution (primarily caused by copper mining). Also, increased values of the organic pollution indicators (ammonium, coliform germs, Five-Day Biological Oxygen Demand - BOD5) in the Borska Reka and the Timok rivers are the result of uncontrolled domestic wastewater discharge.
The objective of the experiment was to evaluate the energy efficiency of the phytoremediation process, supported using energy crops. The scope of conducted work includes the preparation of a field experiment. During the evaluation, 2 factors were into consideration – total energy demand and total energy benefit. The case study, used as an origin of data, consists a 3-years field study, conducted with the use of 2 energy crops – Phalaris arundinacea L. and Brassica napus L. The area subjected to the experiment was polluted with polycyclic aromatic hydrocarbons (PAHs) and herbicides, classified as phenoxy acids (2, 4 D). The experimental design consisted of 4 groups of fields, divided according to the used plant species and type of treatment. For each energy crop, 2 types of fertilization strategies were used. Therefore the 1st and 3rd sets of fields were not treated with any soil amendment while the 2nd and 4th sets were fertilized with compost. The obtained data allowed to observe that the cultivation of P. arundinacea L. and B. napus L. allowed a positive energy balance of the process to be achieved. However, it should be noted, that the B. napus L. growth in the first vegetation season was not sufficient to fully compensate a total energy demand. Such a goal, in the mentioned case, was possible after the 2nd vegetation season. The collected results show also that the best energetic potential combined with the most effective soil remediation were obtained on the fields with the cultivation of P. arundinacea L. fertilized with compost. The number of biofuels, collected from the 1 ha of such fields, can reach a value equal even to12.76 Mg of coal equivalent.