Degradati̇on of endocrin disrupting compounds in raw freshwater by advanced oxidation processes

Advanced oxidation processes (AOPs) have been a matter of recent scientific and technological interest in water treatment technologies. AOPs are mainly employed to effectively oxidize, transform or remove recalcitrant compounds from industrial and municipal wastewater including resistant organics (pesticides, surfactants, coloring matters, pharmaceuticals and endocrine disrupting chemicals) based on the parameters assessed, removal efficiencies and the degradation mechanisms of pollutants. There are a variety of advanced oxidation processes including: homogenus ultraviolet irridation (UV) - either direct irradiation of the contaminant or photolytic oxidation mediated by hydrogen peroxide (UV/H2O2), and/or ozone (UV/H2O2/O3 or UV/O3), fenton and photo fenton processes, heterogeneous photocatalysis using semiconductor catalysts (e.g. UV/TiO2), X-ray or Gamma ray radiolysis, ultrasonic irradiation and electron beam radiation. Although these technologies involve different methods of activation, as well as oxidant generation, most of them are electric-energy-driven and share the common denominator of hydroxyl radical chemistry for contaminant removal. Natural or industrial endocrine disrupters, which are taken to the living organism externally, are risk factors against health because of their potential of imitating the hormonal activity in natural life. Endocrine disrupting compounds are defined as health threatening substances and/or mixtures that change the endocrine system(by inhibition of normal synthesis and hormonal functions by imitating the natural hormons, release of stock hormons, inhibition of secretion and transport machanisms, combining and inactivate natural hormons etc.) of healthy living organisms or their future generations. In recent years, sulphate radical based photochemical advanced oxidation processes gain importance for the removal of endocrine distrupters and their decomposition products. Bisphenol A (2,2-bis(4-hydroxyphenyl)propane; BPA), is a chemical being widely used as a monomer for the production of epoxy resins and polycarbonate, unsaturated polyester-styrene resins and flame retardants. The final industrial products are used as coating materials on cans, as powder paints, additives in thermal paper, in dental fillings and as antioxidants in plastics. It has been postulated that BPA has estrogenic activity and is classified as an endocrine disrupting compound (EDC). Due to its high consumption rate and adverse health effects on wildlife, BPA is known as one of the industrial pollutants that have generated significant academic as well as public interest recently. BPA is being released into the natural environment as well as surface water during its manufacturing and by leaching from final products If not treated properly, effluent containing BPA is a potential source of contamination in the aquatic environment. Due to the fact that biotreatment requires long retention times and cannot degrade BPA completely rapid and efficient treatment processes including advanced oxidation processes (AOPs) have successfully been developed for the efficient treatment of BPA. Alkylphenol ethoxylates are complex and organic compounds, which usually degrades hardly. For this reason, their biological treatability in domestic and industrial wastewater treatment plants are limited, and usually they leave conventional wastewater treatment plants without having any important structural change and meet the environment. In addition, their biodegration products are usually more toxic and refracter than the original product. Nonylphenol and octylphenol ethoxylates (OPEO) are most widely used alkylphenol ethoxylates and they create important environmental problems. Nonylphenol and OPEO which used to dominate the surfactant market almost all consumption, have been the most preferred nonionic surface active compound. They are functionally used as cleaning and washing agents, surface active agents and foaming agents. The industrial activities use nonylphenol ethoxylates for industrial and institutional cleaning, textile auxiliaries, leather auxiliaries, emulsion polymerization, agricultural pesticides, cosmetics, cleaning products and office products such as correction fluids and ink. In this study, BPA, being among the most intensively studied, well-known endocrine disrupting compounds, as well as the nonionic surfactant OPEO (commercial name: Triton X-45), whose metabolite octylphenol's endocrine disrupting impact is very evident although its concentration in natural water is relatively low, was treated with sulfate (persulfate/UV-C) and hydroxyl (hydrogen peroxide/UV-C) radical-based photochemical oxidation processes in pure (distilled) and real raw freshwater samples. Within the scope of this study, the selected photochemical oxidation processes that comparatively evaluated in terms of BPA, OPEO and their organic carbon removal efficiencies and rates, as well as oxidant consumption efficiencies and rates. Besides treatment performance, dominant/effective active oxidant types were established. The major purpose was to comparatively evaluate the sulfate and hydroxyl radical-based oxidation processes more comprehensively. Moreover, the acute toxicity of the selected endocrine disrupting model pollutants and their advanced oxidation products were determined by a series of battery bioassays in which aquatic organisms selected from three different trophic levels (Vibrio fischeri, Daphnia magna and Pseudokirchneriella subcapitata) were employed. Besides changes in their toxic effects, their estrogenic activities were followed during photochemical treatment. Within the scope of this work, it could be concluded that two advanced oxidation processes were capable of effectively/completely removing the endocrine disrupting compounds and their organic carbon content in pure as well as real freshwater. During photochemical treatment, the toxic and endocrine disrupting effects of the model pollutants generally speaking decreased gradually and could be completely eliminated. However, this was strongly related to the type of photochemical treatment process as well as sensitivity of the selected bioassay's test organisms. Toxicity changes could be associated with the evolution of advanced oxidation products; for example the acute toxicity increased during the serial shortening of the polyethoxylate chain of the surfactant Triton X-45, but decreased at the later stages of photochemical treatment due to the progress in complete oxidation (mineralization). Results of this experimental study showed that; distiled water and fresh water samples containing 20 mg/L BPA, 2,5 mM oxidant PS/UV-C as well as H2O2/UV-C photochemical advanced oxidation processes could been able to effectively treat BPA (five minutes for PS/UV-C and seven minutes for H2O2/UV-C in distiled water; 20 minutes for PS/UV-C and 30 minutes for H2O2/UV-C in fresh waters). These two processes have been able to treat The necessery treatment durations determent in these two processes as; 5 minutes for OPEO in distiled water, 10 minutes (fresh water1) and 20 minutes (fresh water2) for PS/UV-C, 20 minutes (fresh water1) and 30 minutes (fresh water2) for H2O2/UV-C under the same conditions. For organic matter treatment yield which is showed by total organic carbon (TOC) parameter, 70% and 84% mineralization is reached on treatment of BPA containing distiled water within 120 minutes treatments for PS/UV-C and H2O2/UV-C processes respectively. For treatment of OPEO containing distiled water, 92% TOC removal occurred within 120 minutes both treatment processes. In the experimental treatment of BPA, with 120 minutes treatment process 25% (fresh water1), 28% (fresh water2) TOC removal occurred for PS/UV-C process and 45% (fresh water1), 48% (fresh water2) TOC removal occurred for H2O2/UV-C process under the same conditions as above. In the experimental treatment of OPEO, at the end of 120 minutes process 74% (fresh water1 and fresh water2) TOC removal occurred for PS/UV-C and 69% (fresh water1) 67% (fresh water2) TOC removal occurred for H2O2/UV-C under the same conditions as above. Toxicity test results for BPA indicated that complete detoxification was achieved after 10 min for Vibrio fischeri and 90 min for Pseudokirchneriella subcapitata for PS/UV-C process and at 120 min for Vibrio fischeri, Pseudokirchneriella subcapitata and 60 min for Daphnia magna for H2O2/UV-C process in real raw freshwater samples, respectively. Toxicity test results indicated for OPEO that complete detoxification was achieved at 120 min for Vibrio fischeri and Pseudokirchneriella subcapitata for PS/UV-C process and at 10 min for Vibrio fischeri and 120 min for Pseudokirchneriella subcapitata, Daphnia magna for H2O2/UV-C process in real raw freshwater samples.