Treatability of persistent organic pollutants in aqeous solution by nanoparticles

The chemicals used against pests such as harmful insects, plant pathogens and weeds are generally called as pesticides. As a result of widespread worldwide usage of pesticides, especially in agriculture, pesticide residues are attained in soil, atmosphere and water resources. Although these pesticides were realized life-saving products in the past, significant toxic effects on human and other living organisms have been demonstrated in recent years. It is determined that particular characteristics of organochlorine pesticides, such as persistence and accumulation in oil, affect all living organism in food chain from microorganisms to humans. These pesticide residues that are resistant to biological degradation can be transported long distances via atmospheric oscillation and may be found long-lasting in the atmosphere. Due to these characteristics, it would not be possible to mention that the health effects of these substances are just limited to people working in the field of agriculture. In this regard, due to prohibition of persistent organic pollutants, which are affecting environment and human health adversely, by Rotterdam and Stockholm Conventions, which Turkey become a party to both in 2005; a considerable attention was increased on these pollutants. Because of having strength bonds against degradation, biological degradation of pesticides is considerably difficult. Appropriate treatment techniques to remove these substances, which can be found in our country's water resources, are needed to be developed. Currently for the removal of pesticides, treatment methods like adsorption, chemical oxidation, electrochemical treatment and membrane systems are frequently used in literature. The most investigated one within these methods is advanced oxidation processes. As an alternative for adsorption processes, nanoparticles which have more surface areas and pores than traditional adsorbents, can adsorp pollutans as well as give fenton like reactions. Even though the investigations about usage of nanoparticles in order to control environmental pollution are generally on soil remediation, in recent years the slow growth in numbers of investigations on water pollution shows that the use of nanoparticles will gain importance globally in the future. The most applied ones within these mentioned nanoparticles are carbon nanotubes, titanium oxide and nano zero-valent iron. Limited numbers of articles about removal of only a few pesticides from aquatic environment by nanoparticles indicate that effective use of nanoparticles is observed. In this doctoral thesis, firstly optimum nano zero valence iron (nZVI) synthesis method has been modified by using multiple optimization method in terms of both particle size and zeta potential of borohydride method, which is the most used synthesis method in the literature. Selected independent variables are iron sulfate concentration, ethanol ratio and borohydride solution. With the optimum synthesis method determined, the lowest particle size was obtained as 70nm only when the particle size was taken into consideration, whereas 88.2nm nZVI could be produced when both the particle size and the zeta potential were taken into consideration. In addition, bimetallic Fe / Pd nanoparticles were synthesized using a catalytic element palladium for increasing the effect of nZVI, and the removal of DDT,which is the most commonly used persistent organic pollutant pesticides in the world, was investigated by both the nZVI and Fe / Pd nanoparticles. Contrary to the work done in very high concentrations of DDT in the literature, in this doctoral thesis, studies were carried out with concentrations that can be found in water as DDT concentration. In these studies performed at low concentrations, the effects of pH, adsorbent concentration, initial DDT concentration and contact time variables were investigated and GC-MS library scanning was performed to reveal the mechanism of removal. The effect of both nZVI and Fe/Pd bimetallic nanoparticles has been demonstrated by observing whether the mechanism of dechlorination is effective other than adsorption. The highest initial DDT concentration that could be used to achieve DDT effluent concentration below the carcinogenic limit of 0,23 μg/L was investigated for both nZVI and Fe / PD bimetallic nanoparticles. The highest concentration that can be purified with nZVI was 88.33 mg/L, whereas this concentration with Fe/Pd was 109.95 mg/L. In the study with the initial DDT concentration of 88,33 mg/L, 48,6 minutes contact time and 550 mg / L adsorbent concentration were required to achieve carcinogenic limit by nZVI, while the contact time was 44.3 minutes and the adsorbent concentration was 472 mg / L by Fe/Pd.