Publication: Removal of organic matter in 03 application prior to particle aggregation
Abstract
Partikül agregasyonu öncesi o3 uygulamasında organik madde giderimi Organik madde içeren suların arıtımı için proses seçenekleri iyi saptanmış ve anlaşılmıştır. Bununla birlikte çoğu arıtma tesisinde (özellikle alkalinitesi düşük, Spesifik UV Absorbansı-SUVA’sı yüksek suları arıtanlarda), yılın çeşitli dönemlerinde ağır yağış ve eriyen kar sularından ötürü organik madde yüklenmelerinde artış gözlenmektedir. Çözünmüş organik karbon (ÇOK) yükü yüksek olan bu dönemlerde, arıtma tesislerindeki su kalitesi ÇOK, renk ve trihalometan (THM) oluşturma potansiyeli (THMOP) bakımından hızla düşmektedir. Suda bulunan partiküllerin büyüklüğü, yoğunluğu ve sağlamlığı, fiziko-kimyasal arıtma işlemleriyle kirleticilerin giderilmesinde büyük rol oynamaktadır. Genellikle flok olarak adlandırılan bu partiküller, su kaynaklarının çoğunda bulunan askıdaki katılarla ve/ veya organik maddeyle anorganik koagülantların tepkimesi sonucu meydana gelmektedir. Temel katı ayrıştırma işlemleri, suya göre yoğunlukları ve büyüklükleri fazla olan bu flokların bertarafına dayanmaktadır. Bu nedenle yoğunluk ve büyüklükteki değişimler flok bertarafını ve dolayısıyla adsorbe olmuş organik maddelerin giderimini etkiler. Organik madde yükünün yüksek olduğu dönemlerde çöktürme ve yüzdürme işlemlerinde başarısızlıklara sebep olan zayıf flokların oluştuğu gözlemlenmiştir. Ozon, 1970’lerden bu yana su ve atıksu arıtımında dezenfeksiyon, dezenfeksiyon yan ürünlerinin (DYÜ) oluşumunun kontrolü, demir ve mangan oksidasyonu, tat, renk ve koku azaltılması amacıyla kullanılmaktadır. Doğal organik maddenin (DOM) ozonlanması yapısında büyük değişikliklere sebep olmaktadır. Bu sebeple, okside olmuş DOM koagülasyon/ flokülasyon prosesinde farklı davranış sergiler. Ön ozonlamanın organik maddenin flokülasyonunu ve giderimini etkilediğini bildiren çokça çalışma bulunmasına rağmen literatürde birbiriyle çelişen pekçok sonuç yeralmaktadır. Kimi çalışmalar, ozonlamanın organik madde giderimini olumsuz etkilediğini söylerken kimi çalışmaların sonuçları da tam tersini göstermiştir. Bazı çalışmalar ise, etkinin çalışılan şartlara göre değiştiğini bildirmiştir. Literatürde bu kadar farklı sonucun yeralmasının sebebinin çalışılan su örnekleri olduğu düşünülmektedir. Literatürdeki çalışmalar gerçek doğal sularla gerçekleştirilmiştir. Oysa, DOM’un yapısı ve özellikleri bölgesel ve mevsimsel olarak önemli farklılıklar gösterebilmektedir. Bu nedenle, bu çalışmada önerilen gibi, bütün şartların kontrollü tutulduğu bir çalışma, ozonlamanın organik madde giderimine etkisini daha genel sonuçlarla gösterebilmek için önemlidir. Bulgular, düşük hümik asit derişimlerinde, ön ozonlama dozu arttıkça organik karbon gideriminin iyileştiğini; ancak incelenen en yüksek hümik asit derişiminde organik karbon gideriminin azaldığını göstermiştir. Oksitlenmiş daha küçük organik moleküllerin koagülantlarla etkileşime daha yatkın olduğu, oksidasyonla kısmen parçalanmış olsa da aromatik yapılar içeren görece daha büyük moleküllerin, aromatikliği olmayan küçük moleküller kadar iyi giderilemediği düşünülmektedir.
Removal of organic matter in 03 application prior to particle aggregation Process options for the treatment of organic matter containing waters are well established and understood. However, in many treatment plants (especially those treating waters with low alkalinity, and high specific UV absorbance), an increase in organic matter loadings due to heavy rainfall and snowmelt is observed in various periods of a year. In these periods when the dissolved organic carbon (DOC) load is high, the water quality in treatment plants drops rapidly in terms of DOC, colour, and trihalomethane (THM) formation potential (THMFP). Size, density and strength of particles present in water play a major role in the removal of pollutants by physico-chemical treatment. These particles, commonly referred as flocs, are a result of the reaction between suspended solids and/ or organic matter that are present in majority of water resources and inorganic coagulants. Basic solids separation processes are based on the elimination of these flocs, which have larger size and higher density than water. Hence, changes in density and size affect the removal of flocs, hence the elimination of adsorbed organic matter. It has been observed that during periods of high organic matter loads, weak flocs are formed bringing about failures in sedimentation and flotation. Ozone has been used in water and wastewater treatment since 1970s in the control of disinfection, and disinfection by-products (DBPs), for the oxidation of iron and manganese, and for the reduction of taste, colour and odour. Ozonation of natural organic matter (NOM) yields major changes in its structure. Therefore, oxidised NOM exhibits a different behaviour in the coagulation/ flocculation process. Despite the fact that there are many studies in literature reporting the effects of pre-ozonation on organic matter flocculation and removal, many of them contradict one another. Some studies denote that ozone influences the removal of organic matter adversely, whilst others inform the opposite. Some studies have reported that the effect of pre-ozonation depends on the conditions studied. It is thought that the nature of water samples is the main reason why so many different results are involved in literature. Those studies were carried out with natural waters. However, the structure and characteristics of NOM may exhibit significant regional and seasonal variations. Hence, a study in which all conditions are controlled, as recommended in this study, is essential to expose the effect of ozonation on the removal of organic matter with more general conclusions. Findings showed that at lower humic acid concentrations, organic carbon removals were improved with increasing pre-ozone dose whereas at the highest humic acid concentration studied, organic carbon removal was hindered. Oxidised smaller organic molecules were likely more prone to interact with the coagulants, although shorn by oxidation, relatively larger molecules that still contained aromatic structures might not be removed as well as smaller molecules that lacked aromaticity.
Removal of organic matter in 03 application prior to particle aggregation Process options for the treatment of organic matter containing waters are well established and understood. However, in many treatment plants (especially those treating waters with low alkalinity, and high specific UV absorbance), an increase in organic matter loadings due to heavy rainfall and snowmelt is observed in various periods of a year. In these periods when the dissolved organic carbon (DOC) load is high, the water quality in treatment plants drops rapidly in terms of DOC, colour, and trihalomethane (THM) formation potential (THMFP). Size, density and strength of particles present in water play a major role in the removal of pollutants by physico-chemical treatment. These particles, commonly referred as flocs, are a result of the reaction between suspended solids and/ or organic matter that are present in majority of water resources and inorganic coagulants. Basic solids separation processes are based on the elimination of these flocs, which have larger size and higher density than water. Hence, changes in density and size affect the removal of flocs, hence the elimination of adsorbed organic matter. It has been observed that during periods of high organic matter loads, weak flocs are formed bringing about failures in sedimentation and flotation. Ozone has been used in water and wastewater treatment since 1970s in the control of disinfection, and disinfection by-products (DBPs), for the oxidation of iron and manganese, and for the reduction of taste, colour and odour. Ozonation of natural organic matter (NOM) yields major changes in its structure. Therefore, oxidised NOM exhibits a different behaviour in the coagulation/ flocculation process. Despite the fact that there are many studies in literature reporting the effects of pre-ozonation on organic matter flocculation and removal, many of them contradict one another. Some studies denote that ozone influences the removal of organic matter adversely, whilst others inform the opposite. Some studies have reported that the effect of pre-ozonation depends on the conditions studied. It is thought that the nature of water samples is the main reason why so many different results are involved in literature. Those studies were carried out with natural waters. However, the structure and characteristics of NOM may exhibit significant regional and seasonal variations. Hence, a study in which all conditions are controlled, as recommended in this study, is essential to expose the effect of ozonation on the removal of organic matter with more general conclusions. Findings showed that at lower humic acid concentrations, organic carbon removals were improved with increasing pre-ozone dose whereas at the highest humic acid concentration studied, organic carbon removal was hindered. Oxidised smaller organic molecules were likely more prone to interact with the coagulants, although shorn by oxidation, relatively larger molecules that still contained aromatic structures might not be removed as well as smaller molecules that lacked aromaticity.