İçme Sularından Fosfor Giderimi İçin Yeni Bir Yöntem Geliştirilmesi

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Tarih
2013-07-19
Yazarlar
Çetin, Pınar
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Institute of Science and Technology
Özet
Fosfor, temel besin maddelerinden biri olması nedeniyle canlı hayatında büyük önem taşımaktadır. Fosfor, canlılar için temel madde olarak ATP ve DNA’nın yapısında, hücre zarında, kemiklerin yapısında bulunmaktadır ve ayrıca bitki gelişimi ve modern tarım teknikleri için mutlaka gerekli olan temel bir elementtir. Ancak oldukça toksik olarak bilinen kimyasal savaş maddesi ve pestisitte fosfor bulunmaktadır. Ayrıca insan etkisiyle fosfor döngüsüne müdahale edilmesi, döngünün bozulmasına yol açmaktadır. Su yüzeyinde fosfor ve azot miktarının artması, ötrofikasyonun temel nedenidir. Yüksek fosfor konsantrasyonu, genellikle siyano bakterilerin yetişmesiyle ilişkilidir. Yüzeyinde serbest fosfat bulunan sular, suda yaşayan mikro ve makro organizmaların gelişmesini önemli ölçüde teşvik eder. Aşırısı ise durgun sularda ötrofikasyona neden olmaktadır. Göl ve koy gibi kapalı sulardaki organik kirlilik ötrofikasyonu arttırmaktadır. Besin tuzlarının sulardan alınması ötrofikasyonu kontrol edebilmek için önemli bir düşüncedir. Topraktan fosforun serbest kalması, göl ve nehirlerde ötrofikasyona neden olduğundan su kalitesini düşürmektedir. Ötrofikasyon bölgelerinin, besin ve ekolojik durumla karmaşık bir ilişkisi vardır. Bu ilişkinin sonucu olarak alglerin ve su bitkilerinin gelişmesini hızlandırır. Alglerin varlığı, endüstriyel ve günlük kullanım yanında içme sularının kullanımını ve balıkçılığı da önemli derecede kısıtlamaktadır. Ötrofikasyon nedeniyle deniz yosunlarının fazla olması güneş ışığının geçişini engellemekte, fotosentezin durmasıyla sıvıdaki oksijen azalmakta ve bunun sonucu pek çok omurgasız tür ve balık çeşitleri yok olmaktadır. Fosfor tayini, birçok ürünün kalite kontrolü ve bazı çevresel çalışmalar için çok önemlidir. Fosforun tayin edilmesinde oldukça usandırıcı ve zaman alıcı prosedürler kullanılabilmektedir. Fosfat gideriminde kimyasal ve biyolojik yöntemler başarıyla uygulanmıştır. Giderim için bu yöntemlerden adsorpsiyon, diğerlerine kıyasla çok daha başarılı ve ekonomiktir. Son yıllarda, düşük maliyetli uygulamalar ve kolay ulaşılabilen materyal ile atık suların arındırılması üzerinde durulmaktadır. Fosfat giderimi için genellikle kimyasal arıtım kullanılmaktadır. Fosforun analitik kimyası üzerine yaygın olarak çalışılmıştır. Bir çok prosedür fosforu tayin edebilmek için ortofosfata gereksinim duymaktadır. Genellikle kullanılan yöntem, amonyum fosfomolibdat ya da magnezyum amonyum fosfat olarak gravimetrik çöktürmedir; titrimetrik prosedürler redoks, kompleksometrik ve nötrleştirme reaksiyonları gerektirmektedir; spektrometrik yöntemler kolorimetri, alevemisyon spektroskopisi ve atomik absorpsiyon spektroskopisi yöntemlerini içermektedir. Fosfor giderimi için en çok kullanılan yöntem ise UV-Görünür Bölge Spektroskopisi’dir. Bu yöntemde fosfor ortofosfata dönüştürülerek molibdenyum ile reaksiyon vermesi sağlanır. Forfor giderimi için uygulanan diğer yöntemler ise atomik absorbsiyon spektroskopi, titrimetri, volumetri, akış enjeksiyon spektrofotometri, HPLC, indüktif eşleşmiş plazma emisyon spektroskopi ve spektrofotometri şeklinde sıralanabilir. Bu yöntemlerin arasından amonyum molibdat ve molibdovanadatile gerçekleştirilen spektroskopik yöntem en yaygın kullanım alanına sahip olanlarıdır. Bu çalışmada, Melamin Formaldehit Üre (MFU) reçinesi sentezlendi. Sentezlenen reçine, kurutulup öğütüldükten sonra FeCl3 ile çalkalanarak Fe+3 parçacıkları, sentezlenen reçineye immobilize edildi ve maksimum fosfor giderimini sağlayabilmek amacıyla optimum koşullar belirlendi (pH değeri, reçine miktarı, süre). Reçine kapasitesini belirleyebilmek amacıyla izoterm eğrileri çizildi ve literatürle kıyaslanarak metodun geçerliliği belirlendi. Optimum koşullar belirlendikten sonra Fe+3 immobilize edilmiş reçine ile gerçek örneklerden fosfor giderimi sağlandı ve zenginleştirme çalışmaları yapıldı. Bu amaçla, reçineyle muamele edilen ve edilmeyen paralel örneklerden fosfomolibden mavisi kompleksi oluşturularak UV-Görünür Bölge Spektroskopisi ile absorbans değerleri ölçüldü. Farklı eluentlerin, değişen konsantrasyonlarıyla elüsyon çalışmaları yapıldı. Sonuçların doğruluğunu kontrol etmek amacıyla Grafit Fırınlı Atomik Absorbsiyon Spektrofotometresi kullanıldı. Bu geliştirilen yöntem ile fosfor tayini ve fosfor giderimi, ekonomik ve kolay bir şekilde yapılabileceği ortaya kondu.
Phosphorus is an important constituent in all tissues of organisms. The total amount of phosphorus constitutes about one percent of the body weight and found more than calcium in human body. In bones the proportion of calcium to phosphorus is much higher than that of calcium. Most of this phosphorus is in organic combinations. Phosphorus compounds play a crucial role in life processes, forming part of the ‘stuff of life’, DNA, and being involved in metabolic energy transfer as ATP and related compounds. Phosphorus is best known as a nutrient for its part in the creation of bones and teeth. It helps the body absorb and make use of calcium, and with the mineral magnesium, Vitamin D, and Vitamin C, it serves in the formation of the hard surfaces of bones and teeth. It has a role also in the working of the body s muscular system and is therefore important heart beat. It is specifically associated with the smooth and regular contraction of the body s muscles, as well as with the nerves and their ability to communicate. When plant materials and waste products decay through bacterial action, the phosphate is released and returned to the environment for reuse. Much of the phosphate eventually is washed into the water from erosion and leaching. Again water plants and algae utilize the phosphate as a nutrient. Studies have shown that phosphate is the limiting agent in the growth of plants and algae. Lack of phosphate causesslow growth or stunning in plants while excess amount causes over-growing, particularly in algae. A large percentage of the phosphate in water is precipitated from the water as iron phosphate which is insoluble. If the phosphate is in shallow sediments, it may be readily recycled back into the water for further reuse. In deeper sediments in water, it is available for use only as part of a general uplifting of rock formations for the cycle to repeat itself. Phosphorus which is both hero and villain in the history of earth, forms some of the most toxic chemicals known, organophosphates, which have been used in applications as diverse as pesticides and nerve agents, and which have left a legacy of severe contamination. In between these extreme situations, lie a whole host of others applications of phosphorus, from fertilisers and foodstuffs to detergents, catalysts, biomaterials, medicines, fire retardansts, stabilisers, radioactive element hosts and more. Futhermore phosphorus is an essential element for plant growth and considered necessary for modern agricultural techniques. Phosphorus is present in low concentrations in wastewater but its release to a receiving water body is of environmental significance because it is an essential, often limiting nutrient for plants and microorganisms, and is therefore a cause of eutro-phication. Eutrophication is defined by Pierzynski et. al. (2002) as ‘An increase in the fertility status of natural waters that causes accelerated growth of algae or water plants’. Therefore, the over enrichment of surface water with nutrients (phosphorus and nitrogen) is the major cause of eutrophication. Also the feature of accelerated eutrophication is lead to extensive de-oxygenation of the water, and reduced species diversity of aquatic flora and fauna. The negative effects of eutrophication include increased plant growth, shifts in phytoplankton species, water transparency loss, problems with taste and odor, oxygen depletion, increase of winterkills, and losses in biodiversity. The increase in plant growth is due primarily to the increase of the limiting nutrients of P and N. The rapid influx of nutrients allows free-floating phytoplankton and other plants to easily asorb the high demand nutrients that are suspended throughout the water column, supporting plant growth. The rapid increase in nutrients can lead to a shift in phytoplankton species. In many lakes, cyanobacteria or blue green algae is the kind of algae that becomes dominant in eutrophic lakes. The increase and presence of eutrophication causes loss of water quality. Organic pollution in closed water bodies such as bays and lakes has been increasing by eutrophication, and removal of nutrient salts from the receiving water is an important consideration to control eutrophication. Phosphorus removal from wastewater is a complex process due to diferences in its forms and in the composition of wastewater. The amount of phosphorus in typical raw domestic sewage is also highly variable, but the approximate concentrations of the various forms have been estimated as orthophosphate (5 mg PL-1), tripolyphosphate (3 mg P L-1), pyropho-sphate (1 mg P L-1), and organic phosphates (1 mg P L-1). Apart from the organic phosphorus species, other organic constituents, both soluble and in solid form, span a wide range of chemical structures and molar masses. A considerable amount of general information is available, related to the classification of dissolved organic matter in wastewater. The control and prevention of eutrophication from nonpoint pollution by agriculture is a tough and difficult task. Every water system is different and combining the right set of natural and anthropogenic methods will take time and practice to achieve success. Artificial means are often necessary in many water systems because eutrophication is too late of a stage for it to be naturally corrected. However, there are natural methods available, and along with changes in economic, societal, agricultural practices, and governmental policies nonpoint pollution and eutrophication can be control and prevented. In wastewater treatment technology, various techniques have been used for phosphate removal. Various methods, including biological processes, ion-exchange, tertiary filtration, chemical precipitation, electrocoagulation, crystallization, and adsorption, have been applied to remove phosphorus from water and wastewater. Phosphate removal is currently achieved largely by chemical precipitation, which is expensive and causes an increase of sludge volume by up to 40 %. An alternative is the biological phosphate removal (BPR). Adsorption is one of the other techniques, which is an attractive method for removal of phosphorus because of its high removal efficiency, relatively simplicity, economy in application and straightforward operation. Adsorption and membrane-filtration processes are widely used as physical methods. Adsorption is a well known equilibrium separation process and an effective method for water decontamination applications. The application oflow cost and easily available adsorbents in wastewater treatment has been widely investigated. Some of the most commonly used solid phase adsorbents are hydrotalcites, allophane and imogolite, iron and iron oxides, aluminium and aluminium oxides, activated aluminia, red mud, fly ash, expanded clay aggregates, blast furnace slag, rare earth modified clays, carbonates, soils, sands and gravels etc. The effectiveness of each class of adsorbent as measured by its adsorption capacitiy and relative cost, cover a wide range in most instances and there are considerable overlaps between the different classes. In addtion, there are substantial diffenrences in sensitivity of adsorbents to changes in ph and redox conditions. To provide some structure to a rational approach for selecting the optimum adsorbent for a particular application, it is helpful to consider several different model cases, and to look at some of the constraints which apply to different adsorbents. In subject of this study, phosphate removal, preconcentration and elution from environmental and potable water were investigated. Methylene blue which is also known as tetramethyl thionine was used as a model dye to obtain the optimal conditions for the adsorptive treatment process. Parameters as granule size, pH, contact time, quantitative of resin, elution process were studied by batch and column respectively. In order to remove phosphorus from water, the melamine-formaldehyde-urea (MFU) resin was synthesized in the mole ratio of 1 : 3 : 1, respectively, using the procedure of Wohnsiedler1; pH value for synthesis was maintained by NaOH addition. The synthesized resin was then washed with 1 M HCl, 1 M NaOH and sufficient water to obtain neutral pH in the filtrate, dried, grounded and screened to the desired particle size. A melamine-formaldehyde-urea (MFU) resin was used as adsorbent to clean wastewater containing phosphorus. White-colored resin was agitated with 0,5 M FeCI3 to remove the maximum quantity of phosphorus. In consequence of process, FeCI3 was immobilized on MFU resin and the white color of the resin turned into orange. Throughout the phosphorus removal, high efficiency was achieved due to the immobilization of FeCI3. The pH value for efficient removal was maintained as 2 for all adsorption process and minimum resin quantity of 0,5 g and 60 minutes contact time were determined as optimum conditions for the samples. At the end of the adsorption process, the concentration of residual methylene blue remaining in solution (Ce) was determined spectrophotometrically. The measurements were made at the wavelength 826 nm which corresponds to maximum absorbance. Solutions containing no methylene blue were used as blank. The amounts of methylene blue adsorbed and the resin capacity were calculated with the aid of the concentrations of the solutions before and after the adsorption process. HCI, NaOH, NaCI, KCI solutions at different concentrations and distilled water were tested for elution process. 0,5 M HCI was decided as elution solution to get maximum efficiency and in behalf of ease of the process. Genuine samples provided 69,00 % phosphorus removal during column study. Reduction of the percentage was caused by adsorption of anionic ions within the real water samples. Moreover enrichment studies represented 90,23 % efficiency. Graphite Furnace Atomic Absorption Spectrometry was used to control the results. A new, accurate practical and low cost phosphorus determination removal method has been developed.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2013
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2013
Anahtar kelimeler
Fosfor, ötrofikasyon, reçine., Phosphorus, eutrophication, resin.
Alıntı