Dimethyl phthalate degradation by Peroxymonosulfate (oxone)/UV-C photochemical process

Ftalik asit esterleri (ftalatlar) kağıt, karton, kozmetik, deterjan, şampuan, sabun, tıbbi malzeme, plastik kap ve boya üretiminde hammadde veya yardımcı kimyasal madde olarak kullanılmaktadır. Endüstrilerde, malzemelerin esneklik özelliğini arttırmak için kullanılan ftalatlar, toksik özellik gösteren, kanserojen, endokrin bozucu ve birikme potansiyeline sahip maddelerdir. Ftalatların arıtımında konvansiyonel arıtma prosesleri ile yüksek giderme verimleri elde edilememekte ve bu nedenle arıtımlarında adsorpsiyon ve ileri oksidasyon proseslerinden yararlanılmaktadır. Bu çalışma kapsamında endokrin bozucu ve toksik etkileri nedeniyle kullanımlarında yasal düzenlemeler yapılmış ftalatlara örnek teşkil etmek üzere seçilen dimetil ftalat (DMF) model kirleticisinin sulu çözeltisinin fotokimyasal ileri oksidasyon proseslerinden olan peroksimonosülfat (PMS-okson)/UV-C ile arıtımı incelenmiştir. Giriş PMS konsantrasyonunun ve başlanıç pH değerinin proses giderim verimi üzerine etkisi araştırılmış ve prosesin arıtma performansı DMF ve TOK ölçümleri yapılarak değerlendirilmiştir. Gerçekleştirilen deneysel çalışmalarda PMS/UV-C prosesi ile DMF’nin gideriminin birinci dereceden hız kinetiğine uyum sağladığı belirlenmiştir. Belirli bir değere kadar (50mM) artan PMS konsantrasyonu ile DMF giderimi için birinci dereceden hız sabitinin arttığı tespit edilmiştir. En yüksek hız sabiti k40mM= 0.276 L/dk olarak bulunmuştur ve PMS konsantrasyonu 50 mM’a arttırıldığında hız sabiti k50mM= 0.246 L/dk değerine düşmüştür. TOK giderimi incelendiğinde ise artan PMS konsantrasyonu ile tam mineralizasyonun sağlandığı arıtma süreleri azalmaktadır. Optimum PMS konsantrasyonunda (40mM) 40. dakikanın sonunda tam mineralizas-yon sağlanmıştır. Elde edilen sonuçlar ışığında DMF gideriminde PMS/UV-C prosesinin uygulanabilir etkin bir arıtma prosesi olduğu sonucuna varılmıştır.  Anahtar Kelimeler: Dimetil ftalat; elektrik enerjisi tüketimi; endokrin bozucu maddeler; fotokimyasal arıtma; kimyasal oksidasyon; peroksimonosülfat (okson).Phthalate esters (PAEs) are used as plasticizers to impart flexibility and resilience to plastic products. Other uses of phthalates are in ceramic, paper, cosmetic, ink, and paint industries. In recent years, PAEs have become a controversial issue because many phthalates are suspected to be mutagens, hepatotoxic agents and endocrine disruptors, and can lead to adverse effects on organisms even in a low concentration. The short-chained esters such as dimethyl phthalate (DMP), which mainly originate from industrial wastewater discharge and leaching and volatilization from plastic products during their usage and after disposal, are among the most frequently, identified PAEs in diverse environmental samples including marine water, surface waters and sediments. Studies of DMP?s biodegradation in fresh water, marine water, sediment, wastewater and sludge, have revealed a low degradation rate in the range of several days to a few months. Thus the destruction of these bio-recalcitrant organic pollutants requires the application of vigorous oxidizing agents, such as those used in advanced oxidation processes (AOPs). Recently, sulfate radical based-AOPs have attracted great scientific and technological interest in the area of wastewater treatment and other environmental applications. OxoneÒ, the commercial name of potassium peroxymonosulfate, is a triple salt with the composition of 2KHSO5·KHSO4·K2SO4 is a convenient source of generating sulfate radical (SO4·-). Peroxymonosulfate (PMS), is a mono-SO3- substituted hydrogen peroxide (H2O2) and has been used in a restricted way as an oxidant in light induced processes. Radiolysis, photolysis, or thermal activation of PMS leads to the formation of both SO4·- and hydroxyl radical (HO·). The use of UV light leads to the generation of SO4·- and HO· through the photolysis of the PMS. SO4·- is a very strong oxidant (Eo = 3.1 eV) and engages in at least three reaction modes with organic compounds similar to HO·: by abstracting a hydrogen atom from saturated carbon, by addition to unsaturated or aromatic carbon, and by removing one electron from carboxylate anions and from certain neutral molecules which may eventually lead to the mineralization of the organic substance. The main targets of the present study were: to assess the performance of PMS/UV-C process in the treatment of aqueous solution of DMP (100 mg/L) selected as a model PAE and to explore the effect of some important operating parameters, such as reaction pH (3-9), initial PMS concentration (0-60 mM) and reaction time (0-120 min) on DMP and organic carbon abatement rates. The results of this study is expected provide fundamental and practical information as a guide for the treatment of bio-recalcitrant organic pollutants by the PMS/UV-C process. For the initial pH values tested, it was found that lowering the initial pH of the aqueous DMP solution slightly improved the degradation rate of DMP. For instance, higher than 95% DMP abatement was achieved after 60 min at pH 3 while the extended reaction times, i.e. 90 and 120 min, required in order to achieve the same level of DMP reduction at initial pH values of 6 and 9 for 5 mM initial PMS concentration, respectively. However, TOC abatements were slightly enhanced with increasing the initial pH. Based on these results pH 3 was selected as the most effective pH for the degradation of DMP. DMP abatement increased with elevating initial PMS concentrations from 5 to 40 mM. Further increase in initial PMS concentration to 50 and 60 mM, however, slightly reduced the extent of DMP removal. With an initial DMP concentration about 100 mg/L, more than 95% of DMP could be removed at time of 20 min under an initial PMS concentration of 40 mM. DMP degradation by PMS/UV-C process successfully represented by a pseudo first-order kinetic model and the highest reaction rate constant was calculated as 0.276 L/min for 40 mM initial PMS concentration. As aforementioned further increase of the PMS concentration slightly reduces the DMP removal rates to 0.246 L/min for 50 mM and 0.243 L/min for 60 mM initial PMS concentrations. The photodegradation of aqueous organic pollutant is an electrical-energy-intensive process, and electrical energy typically represents a major fraction of the operating costs. The lowest electrical energy per order (EE/O) value for DMP oxidation by PMS/UV-C process was calculated as 2.9 kWh m-3 order-1 at the case of 40 mM PMS concentration. Keywords: Dimethyl phthalate; operating cost analysis; endocrine distrupting compounds; photochemical treatment; peroxymonosulfate (oxone), chemical oxidation