SUPPORT MATERIAL ALTERNATIVES FOR BIOLOGICAL FILTER REACTORS (BFRs)

Biyolojik Filtre Reaktörler (BFR) klasik filtre sistemlerinin modifiye edilerek atıksu arıtımı amacıyla kullanıldığı yeni teknolojilerdir. Günümüzde farklı isimler altında geliştirilen biyolojik filtreleri birbirinden ayıran özelliklerin başında filtrelerde kullanılan dolgu malzemeleri gelmektedir. Sunulan makalede “pellet†olarak isimlendirilen, su yumuşatma sistemlerinden atık olarak çıkan bir malzemenin BFR'de dolgu malzemesi olarak kullanılabilirliği incelenmiştir. Bu kapsamda, Türk Standartları Enstitüsü'nün (TSE) ilgili şartnamelerinde açıklanan analiz yöntemleri kullanılarak malzemenin tane boyutu dağılımı, özgül ağırlık, birim hacim ağırlık, porozite, özgül yüzey alanı gibi fiziksel özellikleri belirlenmiştir. Laboratuvarda kurulu bir filtre kolonundan yararlanılarak malzemenin akışkanlaşma özellikleri (minimum akışkanlaşma hızı) araştırılmıştır. Ayrıca, yukarı akışlı akışkan yatak olarak işletilen bir reaktöre “pellet†doldurularak malzemenin atıksu arıtımı amacıyla kullanılabilirliği incelenmiş; organik madde giderimi esas alınarak arıtma verimi değerlendirilmiştir. Biological Filter Reactors (BFRs) are modified conventional filter systems which were used for wastewater treatment in recent years. One of the most substantial differences among the BFRs, which are currently developed with various trade names, is the nature of support material. In this study, a new support material called as “pellet†which is the waste material of water softening process was investigated as filter media in the BFRs. The major physical characteristics of pellet such as particle size distribution, specific weight, porosity, specific surface area were determined by using standard test methods set by Turkish Institute of Standards (TSE). Fluidisation characteristics such as minimum fluidisation velocity of pellets were also studied in a deep bed filter column. In addition pellet material was used in an up-flow fluidised bed filter reactor and the performance of the reactor in terms of COD removal was evaluated

Arsenic removal from drinking water by chemical methods

Arsenik içeren su kaynakları dünyanın pek çok ülkesinde karşılaşılan bir sorundur. Dünya Sağlık Örgütü, 1993 yılında yapmış olduğu düzenlemeyle içme sularında izin verilen azami arsenik miktarını 50 µg/L’den 10 µg/L’e indirmiştir. Ülkemizde de, “İnsani Tüketim Amaçlı Sular Hakkında Yönetmelik” kapsamında içme ve kullanma sularında 50 μg/L olan arsenik limiti, 2005 yılı itibariyle 10 μg/L şeklinde değiştirilmiş ve 2008 yılından bu yana uygulamaya konmuştur. Arsenik standardının 10 μg/L olarak uygulanması, ülkemizdeki bazı su kaynaklarının kullanımını kısıtlamıştır. Özellikle batı bölgelerimizdeki birçok yerleşimde (Kütahya, Emet, Simav, Uşak, İzmir, Manisa, vb.) arsenik kirliliğinin kontrolüne yönelik önlemler alınması ihtiyacı ortaya çıkmıştır. Gerek literatürde, gerekse uygulamada (laboratuvar ve arazi ölçeğinde) arsenik ile ilgili çeşitli arıtma yöntemleri mevcuttur. Bu yöntemler i) arıtılacak suyun miktarına (debisine), ii) sudaki arsenik konsantrasyonuna ve formuna (As3+ ve/veya As5+), iii) su içinde bulunan diğer parametrelere (pH, sülfat, fosfat, organik madde, silikat, vb.) bağlı olarak farklılıklar gösterir. Sunulan makalede arsenik arıtımında kullanılan kimyasal destekli yöntemler incelenmiştir. Bu kapsamda kireç-soda yöntemi, konvansiyonel koagülasyon-filtrasyon, koagülasyon destekli mikrofiltrasyon ve oksidasyon-filtrasyon yöntemleri irdelenmiş; karar alma sürecinde yapılması gerekenler özetlenmiştir. Ülkemizdeki içme suyu arıtma tesislerinde genellikle kimyasal arıtma ve filtrasyon üniteleri kullanılmaktadır. Arsenik bakımından problemli yerlerde mevcut içme suyu arıtma tesislerinde modifikasyonlar yapılarak arsenik giderimi sağlanabilir. Bu kapsamda ön oksidasyon kademesinin eklenmesi, koagülan türü ve dozunun optimizasyonu, konvansiyonel filtrelerin modifikasyonu (adsorban özelliği olan malzemelerin kullanılması), tesis sonunda adsorpsiyon, iyon değişimi, membran filtrasyon gibi sistemlerin kullanılması önerilmektedir. Anahtar Kelimeler: Arsenik, filtrasyon, kimyasal arıtma, kireç soda ile yumuşatma, koagülasyon, oksidasyon.Arsenic in natural waters is a worldwide problem. Weathering of arsenic rich minerals and volcanic activities are natural sources releasing arsenic to the environment. Apart from the natural phenomena, anthropogenic (man-made) inputs are also responsible from the arsenic contamination. Effluents from metallurgical industry, glassware and ceramic industries, dye and pesticide manufacturing industries, petroleum refining, leather processing, and other organic and inorganic chemical industries are major anthropogenic sources of arsenic. Furthermore agricultural uses of pesticides, herbicides, insecticides, defoliants, and soil sterilants which include arsenic and arsenic compounds increase the arsenic content in water resources. Arsenic is a fairly common environmental contaminant. Both groundwater and surface water sources of drinking water can contain arsenic. The levels of arsenic are typically higher in groundwater sources. Arsenic levels in groundwater tend to vary geographically. The major routes are through inhalation, skin absorption .and ingestion. Ingestion is the predominant form of exposure among others. High doses of arsenic can cause acute toxic effects including gastrointestinal symptoms (poor appetite, vomiting, diarrhea, etc.), disturbance of cardiovascular and nervous systems functions (e.g. muscle cramps, heart complains) or death. Because of the proven and widespread negative health effects on humans, in 1993, the World Health Organization (WHO) lowered the health-based provisional guideline for arsenic concentration in drinking water from 50 to 10 µg/L. The United States Environmental Protection Agency (USEPA) subsequently revised the maximum contaminant level (MCL) as 10 µg/L in 2001. New standards have been adopted as a national standard by most countries, including Japan, Jordan, Laos, Mongolia, Namibia, Syria and the USA, and the European Union (EU). However, many countries have retained the earlier WHO guideline of 50 µg/L as their standard or as an interim target including Bangladesh, India, Bahrain, China, Egypt, Indonesia, Philippines, Saudi Arabia, Sri Lanka, Vietnam, etc.. Since implementation of the new guideline value of 10 µg/L requires certain investments, those countries need additional time and support to harmonize their national standards with new regulations. Turkey is a country facing and struggling with those emerging arsenic problems. Stringent standards of drinking water were promulgated by Ministry of Health (MoH) in 2005, and arsenic level was lowered from 50  g/L to 10  g/L. The new standard has been enforced since February 2008. After this limitation a number of wells which have been (planned being) used for potable water supply are considered as "arsenic-contaminated". Besides prolonged drought induced by climate change caused release of arsenic from aquifer sediments and this resulted in elevated concentrations in groundwater sources. This fact triggered problems stemming from arsenic in water in some areas. Particularly, western parts of central Anatolia (e.g. Kutahya, Emet, Simav, Usak) have high risk due to their geological formations and geothermal inputs which pose suitable conditions for arsenic contamination of water resources. Inventory study results carried out by General Directorate of Mineral Research and Exploration (MTA) showed elevated arsenic concentrations in the Kutahya-Emet-Hisarcik and Nevsehir Basins (20-200 µg/L). There are several treatment technologies that are available for arsenic removal from drinking water. The most commonly used technologies include oxidation, co-precipitation and adsorption onto coagulated flocs, lime treatment, adsorption onto sorptive media, ion exchange resin and membrane techniques. Selection of an appropriate method is a quite complex decision and affected from a number of factors (e.g. arsenic compound, raw water quality, target arsenic concentration, existing water treatment plant, land availability, operational and maintenance costs, etc.). In the presented paper, chemical treatment methods used in arsenic removal (i.e. chemical oxidation, conventional coagulation and filtration, coagulation assisted microfiltration, oxidation filtration and lime-soda method etc.) are evaluated considering treatment performance, costs, operational features. In Turkey, generally chemical processes and filtration have been used in many water treatment plants. Existing water treatment plants can be modified for arsenic removal. In this framework, involvement of pre-oxidation stage, optimization of the coagulant type and dose, modification of conventional filters (utilization of adsorbent based filter materials), utilization of adsorption, ion exchange, membrane filtration processes for post-treatment purpose are recommended. Keywords: Arsenic, filtration, chemical treatment, coagulation, lime - soda softening, oxidation