Universidad Católica Argentina1, Escuela Superior Técnica Grl M.N. Savio2, Escuela Superior Técnica Grl M.N.Savio3, Escuela Superior Técnica M.N.Savio4
Arsenic Removal from Water Using Industrial steel wool in a continuous-flow reactor Yonni, Fernando1,2; Moschetto, Alejandro2; Fasoli, Hector1,2; Alvarez, Horacio1,2; Parizzia Alberto1 1. Escuela Superior TÃ©cnica Grl N.M. Savio. Intituto Universitario del Ejercito Argentino 2. Facultad de Ciencias FisicomatemÃ¡ticas e IngenierÃa. Universidad Catolica Argentina Introduction Widespread arsenic (As) contamination in drinking water has been recognized as a serious threat in many countries. In the Americas, rural populations in Canada, United States, Chile, Peru, Bolivia, Mexico, El Salvador and Argentina, are exposed to significant levels of arsenic in drinking water (Henke 2009; Yajuan Xia and Jun Liu, 2004; Smedley and Kinniburgh 2002). In Argentina, the population exposed to arsenic contamination in drinking water is estimated at 1,800,000 inhabitants. Most of the affected population, which lives in rural and remote areas, consumes untreated water (Biagini 1975; Bocanegra and Alvarez 2002) Conventional treatment techniques for removal of arsenic from aqueous solutions have generally proven to be expensive and ineffective for use in rural areas. For these areas adsorption has been proposed as a relatively simple and efficient method of removal of arsenic from drinking water at the household level. Although there is a wide range of adsorbents available on the market, the search for new, low-cost and efficient adsorbents for removal of aqueous arsenic is intense (Mondal et.al. 2007; Vukasinovic-Pesic,et.al. 2012). The idea of reusing waste materials has been promoted in various fields of application; however their use as sorbent material in the treatment of drinking water is far from widespread. The aim of this paper is to investigate whether steel wool, an industrial byproduct of the machining of metal parts, can be used as a sorbent for aqueous arsenic removal under continuous flow conditions on the scale of typical rural consumption. Steel shavings used are locally available and inexpensive making them particularly suitable for application in rural areas. Methods/Materials Continuous-flow experiments were designed to study the effectiveness of utilizing waste material for removing arsenic from water. The reactor used consists of a PVC tube (15.5 cm in diameter and 50 cm tall), sealed at the bottom with a PVC disc. A glass tube (internal diameter: 0.6 cm) was used to direct the arsenic solution to the bottom of the reactor tube. The sorbent used were shavings obtained from the machining of mild steel, SAE 1010 steel and SAE 1045 steel. The treated solution was filtered upon exiting the reactor, through a series of glass and glass filters. The concentration levels of As in the filtrate was measured at intervals between 48 hours and 72 hours; Fe, Mn, conductivity, dissolved oxygen and pH were measured once a month. Arsenic concentration levels were determined using a highly sensitive technique based on the reaction of arsine with a Reactive HgBr2 fiber. The method was contrasted with the measurement by atomic absorption spectrometry (AAS) with the formation of hydrides. Manganese (Mn) and iron (Fe) were measured at the reactor output by flame AAS. A laboratory pH meter (HI 98185 ) was used for pH measurements. The concentration of dissolved oxygen in water was measured using a Lutron DO-5510. Results and Discussion. Assays were performed in a thermostatised room at 25oC in batches containing As (III) or As (V) at concentrations of 0.25 mg /L. The amount of steel iron shavings was set at 400g for a volume of solution in the reactor of 500 mL. The time during which the steel shavings were in contact with the solution varied from 0,021hs (flow equivalent of 0.5 L /day) to 0,0125hs (flow equivalent of 3 L /day). The optimal residence time of the solution with the absorbent was found to be 0.083h (flow equivalent of 2 L /day). Sampling of the treated solution was performed every 72 hours, following filtration through a 100% natural wool filter; pH analysis at entry and upon exit from the reactor showed that the presence of the absorbing material (steel shavings) and of oxides generated in the sorption process (which caused a strong porous reddish hue on the surface of the sorbent material ) did not change the pH of the solution containing arsenic, used as a reference. The dissolved oxygen concentration both at entry and upon exit of the reactor was kept constant at a value of 7,8 mg / L. Mild steel (granular) proved the least effective for arsenic removal (average removal rate of 60%) during approximately 40 day. The time to exhaustion occurred at approximately 60 days. The best results were produced with steel 1010, which showed an average removal rate of 85% during at least 400 days (the system is still working). ConclusiÃ³n The results indicate that a byproduct of machining steel parts can be used to reduce arsenic levels in drinking water use. This study also determined that 1010 steel wool was the most efficient in terms of arsenic adsorption capacity in the range of 80 % to 90 % during a time period longer than 400 days. Thus, the material is suitable for use in water treatment systems with continuous flow reactors. For technical, economical and chemical reasons, this reactor could possibly be used in the treatment of aqueous solutions with food purposes in rural areas. 1. Henke, K.R., (2009) "Arsenic in Natural Environments". London, Arsenic: Environmental Chemistry, Health Threats and Waste Treatment, (Henke, K.R., eds.), Wiley, 69-235. 2. Smedley, P. L. & Kinniburgh, D. G. 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