Çelik elektrotların kullanıldığı elektrokoagülasyon yöntemi ile florür giderimi
Fluroide removal with electrocoagulation using steel electrodes
Yazar: KÜBRA KONUK
Danışman: PROF. DR. NURAY IŞIK KABDAŞLI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
Florür iyonu vücutta bulunması gereken temel bileşenlerden biridir. Ancak bu iyonun yüksek miktarlarda suda bulunduğu zaman insan sağlığına olumsuz etkilerinden dolayı arıtılma ihtiyacı gündeme gelmektedir.  
Elektrokimyasal yöntemlerden biri olan elektrokoagülasyon prosesi son yıllarda su ve atıksu arıtımında kullanılmaya başlanmış olan uygulanması kolay, çoğu organik ve inorganik kirleticinin gideriminde etkili bir yöntemdir. Florürün insan ve çevre sağlığı açısından olumsuz etkilere sahip olmasından dolayı Dünya Sağlık Örgütü (WHO) ve Türk Standartları Enstitüsü (TSE) tarafından içme sularında bulunabilecek maksimum florür konsantrasyonu 1.5 mg/L olarak sınırlandırılmıştır.
İçme suyunda olduğu kadar birçok endüstriyel atıksuyun arıtımında elektrokoagülasyon prosesi tercih edilmektedir.  Buna rağmen elektrokoagülasyonun florür gideriminde kullanımı ile ilgili literatürde yer alan çalışmalar oldukça kısıtlıdır. Bu çalışmalarda çoğunlukla alüminyum elektrotunun elektroliz ile defloridasyon prosesinde kullanımı üzerine odaklanmıştır. Yapılmış olan araştırmalar elektrokoagülasyonu esas alan geleneksel anlayış çerçevesinde ele alınmış diğer bir deyimle giderilecek kirleticilerin elektrotların çözünmesi ile oluşan alüminyum hidroksit yumakları üzerinde adsorpsiyon ve kimyasal çöktürme mekanizmaları çerçevesinde bağlanıp sudan uzaklaştırılmasını ve bu şekilde arıtımın gerçekleştirilmesini hedeflemişlerdir. Bu çalışmada çelik elektrotlar kullanılarak elektrokoagülasyon prosesi gerçekleştirilmiş olup, optimumu işletme koşularının belirlenmesi hedeflenmiştir.
Bu çalışmada sentetik olarak hazırlanan numuneler üzerinde çelik elektrotlar kullanılarak elektrokoagülasyon yönteminin uygulandığı florür giderimi ile ilgili deneysel çalışmalar yürütülmüştür. Birinci bölümde çalışmanın anlam ve önemi, amaç ve kapsamı belirtilmiştir.
İkinci bölümde flor elementi ve florürün özellikleri, kullanım alanları ve kaynakları açıklanmıştır. Florun insan sağlığı üzerindeki etkisi anlatılmış; Türkiye'de flor içeren sular ile ilgili yapılan çalışmalardan söz edilmiştir. Üçüncü bölümde Türk Standartları Enstitüsü 266 ve Dünya Sağlık Örgütü'ne (WHO) göre içme suyu standartları ile farklı kurumlarca belirlenen florür standartları belirtilmiştir. Sulardan florür arıtma metotlarından bahsedilip literatürdeki uygulamalardan örnekler verilmiş, elektrokoagülasyonun tanımı yapılıp bu prosesi etkileyen faktörler üzerinde durulmuştur. Elektrokoagülasyon yöntemi ile florür giderim mekanizması açıklanıp, literatürde sulardan elektrokoagülasyon metodu kullanılarak yapılan florür arıtma uygulamaları anlatılmıştır. Üçüncü bölümde deneysel çalışmanın yürütülüşü verilmiş,  içme sularından alüminyum elektrotların kullanıldığı elektrokoagülasyon prosesi ile yapılan florür gideriminde optimum işletme koşulları belirlenmiştir. Dördüncü bölümde ise tartışma ve yorum açıklanmıştır.

Abstract:
Fluoride ion is one of the basic components that must be present in the body. However, when high amount of this ion is found in water, it has negative effects on human health; so it needs to be treated. 
World's Health Organization (WHO) and Turkish Standards Institution 266 have been limited fluoride consantration with 1.5 mg/L. In this case, to control fluoride at the drinking water sources, some treatment methods have been developed over the history. Chemicel precipitation, adsorption, coagulation-flocculation, ion exchange, membrane processes are some of these treatment methods. At the beginning of twenty first century, there was a big need to develeop a new technology for especially to treat micropollutants but also can be used for the conventional pollutants. At this point electrooxidation and electrocoagulation processes are investigated because of their advantages according to the other treatment options.
Electrocoagulation process is one of the electrochemical methods that has been developed for water and wastewater treatment in recent years. It is an easy and effective method for the removal of organic and inorganic pollutants.
Treatment of wastewater and wash water by electrocoagulation has been practiced for most of the 20th century with increasing popularity. In the last decade, this technology has been increasingly used in the United States, South America and Europe and also Turkey for treatment of industrial wastewater containing metals. It has also been noted that in North America electrocoagulation has been used primarily to treat wastewater from pulp and paper industries, mining and metal-processing industries. In addition, electrocoagulation has been applied to treat water containing foodstuff waste, oil wastes, dyes, marinas, public transit, wash water, ink, suspended particles, chemical and mechanical polishing waste, organic matter from landfill leachates,defluorination of water, synthetic detergent effluents, and solutions containing heavy metals. 
In its simplest form, an electrocoagulation reactor is made up of an electrolytic cell with one anode and one cathode. When connected to an external power source, the anode material will electrochemically corrode due to oxidation, while the cathode will be subjected to passivation.
An electrocoagulation system essentially consists of pairs of conductive metal plates in parallel, which act as monopolar electrodes. It furthermore requires a direct current power source, a resistance box to regulate the current density and a multimeter to read the current values. The conductive metal plates are commonly known as "sacrificial electrodes." The sacrificial anode lowers the dissolution potential of the anode and minimizes the passivation of the cathode. The sacrificial anodes and cathodes can be of the same or of different materials.
The arrangement of monopolar electrodes with cells in series is electrically similar to a single cell with many electrodes and interconnections. In series cell arrangement, a higher potential difference is required for a given current to flow because the cells connected in series have higher resistance. The same current would, however, flow through all the electrodes. On the other hand, in parallel or bipolar arrangement the electric current is divided between all the electrodes in relation to the resistance of the individual cells, and each face on the electrode has a different polarity.
During electrolysis, the positive side undergoes anodic reactions, while on the negative side, cathodic reactions are encountered. Consumable metal plates, such as iron oraluminum, are usually used as sacrificial electrodes to continuously produce ions in the water. The released ions neutralize the charges of the particles and thereby initiate coagulation. The released ions remove undesirable contaminants either by chemical reaction and precipitation, or by causing the colloidal materials to coalesce, which can then be removed by flotation. In addition, as water containing colloidal particulates, oils, or other contaminants move through the applied electric field, there may be ionization, electrolysis, hydrolysis, and free-radical formation which can alter the physical and chemical properties of water and contaminants. As a result, the reactive and excited state causes contaminants to be released from the water and destroyed or made less soluble.
In this study, experimental work was carried out about the removal of fluoride for which electrocoagulation method was applied to the samples of synthetic solution containing fluoride using steel electrodes. In the first part; the meaning, importance, purpose and scope of the study were stated. In the second part, properties, usage areas and sources of fluoride were explained. In this part, it was mentioned about the effect of fluoride on human health and some researchs made about water containing fluoride in Turkey. Drinking water standards according to Turkish Standards Institution 266 and World Health Organization and fluoride standards set by different corporations were demonstrated.  
Methods for the removal of fluoride from water were mentioned and examples from the applications in literature were given. Definition of electrocoagulation, factors affecting this process and mechanism for removal of fluoride with this process were stated, applications about this process found in literature were evaluated. 
In the third part, outline of experimental work was given and optimum conditions for the removal of fluoride ion from drinking water by electrocoagulation method using steel electrodes were stated. First part of the study was to determine current density effect on electrocoagulation process. The effects of current density on electrocoagulation process is determined by the interval of  0.75 – 15.16 mA/cm2 current density. It is observed that optimum current density was 3.79 mA/cm2 and experiments are carried out with this value of current density. Then, electrolyte type and concentration effect is observed. NaCl and KCl electrolytes were used and determined that NaCl is more effective than KCl as an electrolyte on flüoride removal by electrocoagulation process. Beginning concentration of fluoride is effective on removing fluoride with electrocogulation. At this point, to evaluate the effect of  beginning concentration of fluoride on electrocoagulation, 2 – 5 mg/L fluoride containing samples are prepared and experiments are performed. With 3.79 mA/cm2 applied current density and 2 and 3 mg/L fluoride concentration, at the end of 240 minutes electrocoagulation, results showed that 1.5 mg/L fluoride standards were achieved. To investigate pH effect on fluoride removal by electrocoagulation, pH level is changed between 3 and 6. pH 3 was the most effective pH value as an starting pH of fluoride removal by electrocoagulation.
In this study, steel electrodes are used as electrodes of electrocoagulation process for the removal of fluoride and with the beginning of 5 mg/L fluoride concentration, 50 mg/L NaCl concentration, 3.79 mA/cm2 current density and starting pH value as 3 is observed as the optimum conditon.
In the last part of this sudy, discussion, comments and suggestions were stated.