Klorlama, içme suyu arıtımında kullanılan en yaygın dezenfeksiyon yöntemlerinden biridir. Doğal organik madde içeren suyun klorlanması sonucunda trihalometan, haloasetik asit gibi dezenfeksiyon yan ürünleri oluşmaktadır. Geçmiş yıllarda olduğu gibi günümüzde de klorlama sonucu meydana gelen trihalometan gibi dezenfeksiyon yan ürünleri ölçümleri belirli bir zaman ve çaba gerektiren kullanımı kompleks ve pahalı analitik cihazlarla yapılmaktadır. Bu çalışmada 272 nm dalga boyundaki diferansiyel ultraviyole absorbans ile klorlanmış ham ve koagüle edilmiş sularda meydana gelen toplam trihalometan ve trihalometan bileşikleri arasındaki korelasyonlar incelenmiştir. Doğal organik madde içeren suların klorlanması ile meydana gelen trihalometan oluşumu trihalometan - 272 nm dalga boyundaki diferansiyel ultraviyole absorbans arasındaki korelasyonlar farklı pH seviyelerinde (pH 5, 7 ve 9) lineer denklemler ile gösterilmiştir. Elde edilen deneysel sonuçlara göre pH değeri arttıkça (pH >7) baz- kataliz ve hidroliz reaksiyonları nedeniyle klorlama sonucu meydana gelen trihalometan konsantrasyonları da artmaktadır. Diğer yandan bu çalışmada, farklı pH değerlerinde klorlanmış Büyükçekmece ve Terkos ham ve koagüle edilmiş su numunelerinde belirtilen klor bekletme sürelerinde toplam trihalometan ve trihalometan bileşikleri ile 272 nm dalga boyundaki diferansiyel ultraviyole absorbans arasında R2 >0.97 olan lineer korelasyonların meydana geldiği tespit edilmiştir. Bu araştırmada elde edilen en önemli sonuçlardan biri de, doğal organik madde içeren su numunelerinin klorlanması sonucu meydana gelen toplam trihalometan oluşumlarının diferansiyel spektroskopi yöntemi kullanılarak tespit edilen 272 nm dalga boyundaki diferansiyel ultraviyole absorbans ile trihalometan konsantrasyonları arasındaki istatiksel eşitliklerden yararlanılarak yerinde, kısa bir zaman içerisinde ve sürekli olarak izlenebileceğinin ortaya konulmasıdır. Anahtar Kelimeler: 272 nm dalga boyundaki ultraviyole diferansiyel absorbans, trihalometanlar, klorlama, İstanbul içme suyu kaynakları.Chlorination has been widely used as a disinfection method in drinking water treatment. Disinfection of surface water supplies containing natural organic matter with chlorine leads to formation of disinfection by- products such as trihalomethane and haloasetic acids. These halogenic compounds have adverse health effects on human begin. Epidemiological studies indicated that there is a possible link between disinfection by- products and development of cancer. Concerns regarding the potential health effects of disinfection by- products prompted several industrialized countries to develop a number of regulations. These regulations should provide the safety of drinking water thrrough the elemination, or reduction to minimum concentration of the hazardous substances in water. Subsequently, USEPA promulgated a regulatory standard for trihalomethanes as 80 µg/L. Further, USEPA also introduced a haloasetic acid standard of 60 µg/L for the sum of five spices of haloasetic acids in drinking waters. On the other hand European Union regulated trihalomethane limit at a 100 µg/L. Moreover, Turkish Government recently regulated 150 µg/L trihalomethane limit in drinking water to comply with European Union regulations. The relationship among chlorination conditions, pH, temperature, reaction time, chlorine dosage, natural organic matter concentration and the formation of disinfection by-products are highly complex. Developing formal kinetic or statistical models for disinfection by-products formation require substantial cost and effort of analyzing for disinfection by-products as trihalomethanes. Several people have tried to relate water quality parameters to disinfection by-products formation in an effort to find a useful surrogate parameter to better understand the chemical nature of disinfection by-products formation process. Surrogate parameters that have been used to estimate the formation of disinfection by-products include ultraviole absorbance, spesific ultraviole absorbance which is ultraviole absorbance divided by dissolved organic carbon concentration. Some researches reported that simple and reliable relationships between change in ultraviole absorbance of NOM after chlorination and the formation of chlorinated by-products. Since the aromatic functional groups are thought to be both the dominant chromopheres in natural organic matter and the dominantsites of attack by chlorine on NOM molecule, the ultraviole absorbance at 254 nm has frequently proposed to predict disinfection by-products precursors. However, the use of ultraviole spectroscopy to estimate for formation disinfection by-products such as trihalomethanes is thougt to be problematic by many researches. Therefore, in this study, the potential use of differential ultraviole absorbance at a wavelength of 272 nm to monitor the formation of trihalomethanes in drinking water was investagated. This method is an excellent and practical technique for monitoring instantaneous and continuous the formation of trihalomethanes online. The magnitude of decrease in ultraviole absorbance at a wavelength of 272 nm is an excellent technique of disifection by-products formation from resulting chlorination. All of differential ultraviole spectra for different water sources including natural organic matter have a peak at 272 nm. The other important feature is related to the intensity of differential ultraviole spectra. The intensity of differential ultraviole spectra grows with increasing of chlorine dose and reaction time. The differential ultraviole absorbance at a wavelength of 272 nm technique is used not only detect chromophores destroyed by the chlorination reactions but also to monitor the amount of formation of chlorinated by-products like trihalomethane. During the study, three different raw waters of Terkos, Büyükçekmece and Ömerli were studied for this purpose. Raw water samples are chlorinated at variable pH levels, contact times and Cl2 / dissolved organic carbon ratios. The total trihalomethane versus differential ultraviole absorbance at a wavelength of 272 nm correlations are quantified by linear equations with R2. The results of study were showed that the relationships between THMs and differential ultraviole absorbance at a wavelength of 272 nm are very strong (R2 >0.97) in chlorinated raw water samples at variable reaction conditions. The trihalomethane and differential ultraviole absorbance at a wavelength of 272 nm correlations may have practical value since they provide an alternative approach for monitoring the formation of trihalomethane online, and further, differential ultraviole absorbance at a wavelength of 272 nm can be determined in a short period of time, using a small volume of sample and does not require sophisticated sample pretreatment. Keywords: Differential ultraviole absorbance at 272 nm, trihalomethanes, chlorination, drinking water reservoirs, İstanbul
