Combined biological removal of pesticides and nitrates in drinking waters

In this thesis, biodenitrification in drinking water has been studied to remove pesticides and nitrates, which create problems especially in rural areas with heavy agricultural activities. Evaluation of pesticides use in Turkey has led to a preliminary selection of three pesticides, which are trifluralin, fenitrothion, and endosulfan (a+P) as relevant substances for this study. This selection was based on the quantity of use in the vicinity of Izmir region and persistency of the pesticides. In this thesis, various natural organic solid subtrates (NOSS) were evaluated in order to determine suitable carbon source for biological reactor. Thus, poplar, hornbeam and pine shaving waste materials and wheat straw were selected as a carbon source for biological denitrification. After determining the dissolved organic carbon (DOC) contents of these materials by batch studies, biological denitrification experiments were carried out in a batch unit with the NOSS for about three months. The overall amount of nitrate removed during the batch study amounted to about 30 mg, 40 mg, 60 mg and 185 mg in 250 mL for poplar, hornbeam, pine shaving and wheat straw, respectively. Since the highest elimination of nitrate was observed with the wheat straw, it was selected as a carbon source and support medium for biodenitrification continuous reactor while medium solution was spiked with the selected pesticides. During the continuous experimental study; between 95.4-99,8, 84.4-99.4, and 83.7-97.4 % the removal efficiencies were obtained for trifluralin, fenitrothion and endosulfan (a+p), respectively. Adsorption experiments of the pesticides were conducted with poplar, pine shaving and wheat straw. In order to compare the pesticides removal efficiency of the NOSS, experiments were performed with the activated carbon under the samem conditions. The sequence of the adsorption affinity for the pesticides were similar for activated carbon and other adsorbents (Trifluralin > Endosulfan > Fenitrothion). Biological nitrate and pesticides elimination studies were also performed by using liquid organic substances. In this study, acetic acid and ethanol were applied and compared as to the biological elimination of the nitrate and carbon. Considering the results of the batch experiments; ethanol was selected as a carbon source and optimum ethanol to nitrate-nitrogen (C/N) ratio as 1.5 and pH of the feeding solution as 7.5 for continuous experiment. The biological denitrification study was carried on with the addition of pesticides after determining effects of the hydraulic residence time on the system performance. In this experiment, using plastic coil materials to support particles in continuous reactor, removal efficiency of the pesticides during biodenitrification was determined. Although no significant improvement in nitrate and organic carbon eliminations were observed at 9h=12 hours, 100% of pesticides elimination was obtained. Higher than 95, 91, and 95 % removal efficiencies were observed for trifluralin, fenitrothion, and endosulfan (a+p), respectively when Bj, was lower than 12 hours. Although the high pesticides removal efficiencies were obtained using packed column biological denitrification reactor, effluent water could not be used for drinking purpose, because of the total pesticides concentrations when the 0h was lower than 12 hours. Effluent pesticides concentrations increased with decreasing hydraulic residence times. Pesticides were removed between 20-55% by using slow sand filter for various 9h values.