Yeraltı sularında bulunan uçucu organiklerin dolgulu kulelerde giderilmesi üzerine bir araştırma

Abstract

Sularda bulunan uçucu organik maddelerin giderilmesi oldukça önemli bir konudur. Zira, bu maddelerin insan sağ lığı üzerine olan olumsuz etkileri yapılan bilimsel çalış malarla gözlenmiştir. Ülkemizde, genel olarak içme suyu ih tiyacı yeraltı ve yüzeysel sulardan karşılanmaktadır. Öy le ise, insan sağlığını olumsuz yönde etkileyen bu maddele rin sulardan uzaklaştırılması gerekmektedir. Bu çalışmada, sularda bulunan ve üzerinde en fazla araştırma yapılan 7 uçucu organik madde üzerinde durulmuş, bunların bazılarının insan sağlığı üzerindeki olumsuz etki lerinden bahsedilmiş ve bu maddelerin sulardan uzaklaştırıl ması için yöntemler araştırılmıştır. Sonuç olarak bu yön temlerin en uygunu olan hava ile sıyırma metodunun üzerinde çalışmalar yapılmış ve bu metodun teorisinden ayrıntılı ola rak bahsedilmiştir. Daha sonra çalışma prensibi hava ile sıyırma olan dolgulu kuleler gözönüne alınarak farklı gider me verimi, farklı sıcaklık farklı sıyırma faktörü ve farklı basınç düşmeleri gibi değişen koşullarda bilgisayar destek li hesap ve tasarımlar yapılmıştır. Bu çalışmanın birinci bölümünde, çalışmanın amaç ve kapsamı açıklanmıştır. İkinci bölümde, uçucu organik mad delerin meydana geliş şekilleri ve insan sağlığı üzerinde ki olumsuz etkilerinden bahsedilmiştir. Üçüncü bölümde uçucu organik maddelerin sulardan giderilmesinde kullanı lan hava ile sıyırma yöntemi tüm ayrıntıları ile incelen miş ve dolgulu kuleler üzerinde durulmuştur. Dördüncü bö lümde hava ile sıyırma prensibi ile çalışan dolgulu kule lerde tasarım esasları incelenmiştir. Beşinci bölümde he sap sonuçları tablolar ve grafikler halinde verilmiştir. Altıncı bölümde maliyet hesapları üzerinde durulmuştur.

As it known, water is the most important factor for the living organism. In recent years, because of the ' mdustrilazition and increasing the population, the neces sity of the water has been gradually increased. As a result of this, has been faced water pollution problems. However using a clean water is an natural rights for the people. It is the fact that, T ground. water has to be con sidered as an drinking water source which other water source are gradually decreasing in our world. Consequently, ground waters has begun to considered as an important natu ral water source in recent years. In USA, 125.000-300.000 m3 drinking water had been obtained from -ground between 1950 and 1990. Today in USA, 1/4 of the fresh water are being obtained from ground and water need of the %50 people are obtained from underground. In Turkey, according to the DSİ datums, annual drawable water potential is 11.6 billion m3. But allocated of these water is only 6.6 billion m3. Lost of the.ground waters are clean and suitable for use. But in recent years, the pollution of these water has increased and faced regional and local pollution problems. It has been deter mined more than 200 pollutant m some water resources and the contamination of drinking water by low molecular weight, volatile organic chemicals has been reported in many areas of the world. It is known that, contaminants which are found in ' ground and surface waters are volatile and harmful for the human life. Concern over this type of drinking water contamination led the U.S. Environmental protection Agency (EPA) to propose maximum contaminant levels for eight volatile organic compounds and recommended maximim contaminant levels in drinking waters. As a result of scientific studies, because of having a volatile and harmful properties of these compounds have XI to be removed from the waters. In this study, it has been investigated methods of removal volatile organic compounds from the water and made a design in Packed Tower which working principle is based on air stripping, that is the best method for removing volatile organic compounds from the water. Design is based on computer programme. In the first chapter, it is given introduction of the study, aim and the contents. In the second chapter, effect of the volatile organic compounds on human life and treatment alternatives has been investigated. Some of the volatile organic compounds in formed by reacting with chlorine of some organic in a form of humic and fulvic acid. At the same time it is known that Trihalomethanes (THMs) is formed in a disinfection process. Other sources of volatile organic compounds which contaminates the water are different production process and distribution, urbanization and agriculture activities and the last, litter leakage water. Removal of volatile organic compounds from water is an important subject. Because existence of these organics in water which is vital for people form a great danger for human life. These organic' s negative effects on human life has been proved by the scientific studies. It has seen that some of these organics effects on a nerveous system, stomoch and liver. It also has seen that some of volatile organic compound cause cancer and effect on human body. In a raw or finished water, some volatile compounds can be found. Main of volatile organics and often seen in waters as follows. - Trichlorocthylene - Tetrachloroethylene - 1,2-Dichloroethane - 1,1,1- Trichloroethane - Carbon tetrachloride - Vinyl chloride - Chloroform Some countries has certain standarts for these com pounds and have an acceptable maximum volatile organic compounds concentration. For example for. Trichloroethy- lene, acceptable maximum concentration is 0,005 mg/L in USA XII and 0,03 mg/L for the world health organisation. In Tur key, there is no standards for any volatile organic com pounds. Other acceptable concentrations chatiging with countries can be seen table 2.1. There are different methods in order to remove volatile organics which are found in waters. These are can be exp lained as follows, - Air stripping - Reverse osmosis - Ozonitation - Oxidation with hydrogen peroxide - Ultraviolet radiation - Land Treatment Between these methods, air-stripping is the best and found place itself in most applications. It has been observed that, by using air-stripping method can be reached high removal efficiencies. In the third chapter, air, stripping is explained in details. Working principle of the air-stripping process is to provide water to get in touch with air in a close position. Then it can be seen that volatile organic com pounds will pass to gas phase from the liquid phase. The kinetic theory of gases stares that molecules of dissolved gases can readily move between the gas and liquid phases. Consequently, if water contains a volatile conta minant in excess of its equilibrium level, the contaminant will move from the liquid phase to the gas phase until equilibrium is reached. Leaving from the equilibrium level cause mass transfer. Equilibrium concentration of the substance depends on Henry constant. Henry's law gives idea about action tendency between gas and liquid phases, so Henry constant can be defined as an action coefficient. Henry constant is quite important while designing the packed tower so it is recommended to determine its value from experimental studies. Air-strigping can bedene different ways. These, are, - Packed Tower Aeration - Diffused Aeration - Tray Aeration - Spray Aeration xm In this study, Packed Towers been considered because of the best way and high removal efficiency. The design of an air stripping column can also be described mathema tically, the equaitons have been well-developed in the literature. The equaitons are derived by setting up a mgss balance in the air stripper. Four basic assumptions are incorporoted in these equa tions. 1, The influent air is free of volatile organic com pound. (VOCs) 2- Plug flow conditions hold for the air water flow, the use of an inlet water distribution system helps to preserve this condition. 3- The changes that occur in the liquid and air volumes during mass transfer are negligible. 4- Henry's law holds true for these conditions. To obtain the best stripping, it must be provided a good mixture and high superficial contact area between the phases. Packed Towers are widely used to obtain high mavss transfer between the phases. Mass transfer rate from the liguid phase to the gas phase can be explained with an equation as follows, JA" KLa