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

The effects of exhaustive swimming and probiotic administration in trained rats: Oxidative balance of selected organs, colon morphology, and contractility

The duration and intensity of exercise are significant factors in oxidative, morphological, and functional changes of the gastrointestinal tract. This study aimed to investigate the effects of both exhaustive swimming and probiotic VSL#3 on rats that had been previously trained with moderate swimming. The rats were divided into four groups labeled: control (C), probiotic (P), exercise (E), and probiotic–exercise (PE). Groups P and PE were fed with probiotic mixture VSL#3. Groups E and PE had a 5-week moderate swimming program (1 h/day for 5 days/week), followed by a 1-week exhaustive swimming program (trained like in moderate program but 3 times with 150 min resting sessions, for 5 days/week). At the end of the program, the rats were euthanized. Malondialdehyde, superoxide dismutase, catalase, and reduced glutathione levels were measured in tissue samples from the gastrocnemius muscle, heart, liver, kidney, and colon. In vitro contractile activity and histomorphology of the colon were also determined. Exercise and/or probiotic decreased the oxidative stress and also increased the level of one or more of the antioxidant enzymes in some of the organs. Probiotics had more pronounced effects on colon morphology than exercise but unexpectedly this effect was non-trophic. In the colon, the thickness of the tunica muscularis and the number of goblet cells were not affected; however, probiotic administration decreased the crypt depth and tunica mucosa thickness. Exercise increased the Emax value of acetylcholine (ACh), while decreased its sensitivity. These findings suggest that exhaustive swimming does not cause oxidative stress and that probiotic consumption improves oxidative balance in trained rats. The probiotic intake does not alter the effect of exercise on the contractile activity of the colon. Colon mucosal changes induced by probiotics are independent of exercise

Whole brain, high resolution spin-echo resting state fMRI using PINS multiplexing at 7 T.

This article demonstrates the application of spin-echo EPI for resting state fMRI at 7 T. A short repetition time of 1860 ms was made possible by the use of slice multiplexing which permitted whole brain coverage at high spatial resolution (84 slices of 1.6 mm thickness). Radiofrequency power deposition was kept within regulatory limits by use of the power independent of number of slices (PINS) technique. A high in-plane spatial resolution of 1.5 mm was obtained, while image distortion was ameliorated by the use of in-plane parallel imaging techniques. Data from six subjects were obtained with a measurement time of just over 15 min per subject. A group level independent component (IC) analysis revealed 24 non-artefactual resting state networks, including those commonly found in standard acquisitions, as well as plausible networks for a broad range of regions. Signal was measured from regions commonly rendered inaccessible due to signal voids in gradient echo acquisitions. Dual regression was used to obtain spatial IC maps at the single subject level revealing exquisite localisation to grey matter that is consistent with a high degree of T(2)-weighting in the acquisition sequence. This technique hence holds great promise for both resting state and activation studies at 7 T

Power Independent of Number of Slices (PINS) radiofrequency pulses for low-power simultaneous multislice excitation.

This communication describes radiofrequency pulses capable of performing spatially periodic excitation, inversion, and refocusing. The generation of such pulses either by multiplication of existing radiofrequency pulses by a Dirac comb function or by means of Fourier series expansion is described. Practical schemes for the implementation of such pulses are given, and strategies for optimizing the pulse profile at fixed pulse duration are outlined. The pulses are implemented using a spin-echo sequence. The power deposition is independent of the number of slices acquired, and hence the power deposition per slice is considerably reduced compared to multislice imaging. Excellent image quality is obtained both in phantoms and in images of the human head. These pulses should find widespread application for multiplexed imaging, in particular at high static magnetic field strengths and for pulse sequences that have a high radiofrequency power deposition and could lead to dramatic increases in scanning efficiency

Whole brain, high resolution multiband spin-echo EPI fMRI at 7 T: a comparison with gradient-echo EPI using a color-word Stroop task.

A whole brain, multiband spin-echo (SE) echo planar imaging (EPI) sequence employing a high spatial (1.5 mm isotropic) and temporal (TR of 2 s) resolution was implemented at 7 T. Its overall performance (tSNR, sensitivity and CNR) was assessed and compared to a geometrically matched gradient-echo (GE) EPI multiband sequence (TR of 1.4 s) using a color-word Stroop task. PINS RF pulses were used for refocusing to reduce RF amplitude requirements and SAR, summed and phase-optimized standard pulses were used for excitation enabling a transverse or oblique slice orientation. The distortions were minimized with the use of parallel imaging in the phase encoding direction and a post-acquisition distortion correction. In general, GE-EPI shows higher efficiency and higher CNR in most brain areas except in some parts of the visual cortex and superior frontal pole at both the group and individual-subject levels. Gradient-echo EPI was able to detect robust activation near the air/tissue interfaces such as the orbito-frontal and subcortical regions due to reduced intra-voxel dephasing because of the thin slices used and high in-plane resolution