Abstract

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 respon-sible from the arsenic contamination. Effluents from metallurgical industry, glassware and ceramic in-dustries, dye and pesticide manufacturing industries, petroleum refining, leather processing, and other organic and inorganic chemical industries are ma-jor anthropogenic sources of arsenic. Furthermore agricultural uses of pesticides, herbicides, insecti-cides, defoliants, and soil sterilants which include arsenic and arsenic compounds increase the arsenic content in water resources. Arsenic is a fairly com-mon 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 ab-sorption .and ingestion. Ingestion is the predominant form of exposure among others. High doses of arse-nic can cause acute toxic effects including gastroin-testinal symptoms (poor appetite, vomiting, diar-rhea, etc.), disturbance of cardiovascular and nerv-ous 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) low-ered the health-based provisional guideline for ar-senic 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, Indone-sia, 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 har-monize their national standards with new regula-tions. 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 low-ered from 50 μg/L to 10 μg/L. The new standard has been enforced since February 2008. After this limi-tation 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 forma-tions and geothermal inputs which pose suitable conditions for arsenic contamination of water re-sources. Inventory study results carried out by Gen-eral Directorate of Mineral Research and Explora-tion (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 oxi-dation, co-precipitation and adsorption onto coagu-lated flocs, lime treatment, adsorption onto sorptive media, ion exchange resin and membrane tech-niques. Selection of an appropriate method is a quite complex decision and affected from a number of fac-tors (e.g. arsenic compound, raw water quality, tar-get arsenic concentration, existing water treatment plant, land availability, operational and mainte-nance costs, etc.). In the presented paper, chemical treatment methods used in arsenic removal (i.e. chemical oxidation, conventional coagulation and filtration, coagulation assisted microfiltration, oxi-dation filtration and lime-soda method etc.) are eva-luated considering treatment performance, costs, operational features. In Turkey, generally chemical processes and filtration have been used in many wa-ter treatment plants. Existing water treatment plants can be modified for arsenic removal. In this frame-work, involvement of pre-oxidation stage, optimiza-tion of the coagulant type and dose, modification of conventional filters (utilization of adsorbent based filter materials), utilization of adsorption, ion ex-change, membrane filtration processes for post-treatment purpose are recommended.

Download paper here

Recommended citation: Alpaslan, M.N; Dölgen, D.; Boyacooğlu, H.; Sarptaş, H. (2010): “Arsenic removal from drinking water by chemical methods”, İTÜDERGİSİ/e, 20, (1).