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Journal of Environmental Science and Health, Part A Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa20
Simultaneous removal of arsenic and fluoride from groundwater by coagulation-adsorption with polyaluminum chloride a
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Ana M. Ingallinella , Virginia A. Pacini , Rubén G. Fernández , Romina M. Vidoni & Graciela Sanguinetti a
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Center of Sanitary Engineering, National University of Rosario, Rosario, Argentina
Available online: 31 Aug 2011
To cite this article: Ana M. Ingallinella, Virginia A. Pacini, Rubén G. Fernández, Romina M. Vidoni & Graciela Sanguinetti (2011): Simultaneous removal of arsenic and fluoride from groundwater by coagulation-adsorption with polyaluminum chloride, Journal of Environmental Science and Health, Part A, 46:11, 1288-1296 To link to this article: http://dx.doi.org/10.1080/10934529.2011.598835
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Journal of Environmental Science and Health, Part A (2011) 46, 1288–1296 C Taylor & Francis Group, LLC Copyright ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2011.598835
Simultaneous removal of arsenic and fluoride from groundwater by coagulation-adsorption with polyaluminum chloride ´ G. FERNANDEZ, ´ ANA M. INGALLINELLA, VIRGINIA A. PACINI, RUBEN ROMINA M. VIDONI and GRACIELA SANGUINETTI
Downloaded by [Romina Vidoni] at 14:32 06 September 2011
Center of Sanitary Engineering, National University of Rosario, Rosario, Argentina
R The ArCIS-UNR arsenic and fluoride removal system which consists of a coagulation-adsorption process with initial pH adjustment and two filtration stages (up-flow gravel roughing filtration and rapid filtration), has been already described in previous studies. This process has been successfully implemented in full-scale plants in Argentina, with fluoride and total arsenic concentrations in raw water up to 2 mg/L and 200 µg/L, respectively. The aim of the present study is to optimize fluoride removal when it is >2.0 mg/L. The modifications proposed were to decrease the pH level to 6.4–6.6 at the roughing filter inlet and increase the pH level to 7.2–7.6 at the rapid filter inlet to decrease residual aluminum concentration. Laboratory and pilot scale studies were performed using natural water with fluoride concentrations ranging from 2.4 to 3.2 mg/L and arsenic concentrations from 60 to 90 µg/L. An optimal combination of operational parameters and the coagulant dose (polyaluminum chloride, PACl) was found, to achieve final concentrations of fluoride, arsenic and aluminum in treated water lower than those set by the regulations in force. Filtration run time was 10 to 12 hours; research studies are necessary to extend this period.
Keywords: Arsenic, fluoride, groundwater, coagulation, appropriate technology.
Introduction It is estimated that in several Latin American countries including Argentina, Chile, Mexico, El Salvador, Nicaragua, Peru and Bolivia approximately 4,000,000 people are exposed to arsenic levels ranging from 0.002 to 2.9 mg/L.[1] The presence of arsenic in drinking water has caused an increase of Chronic Endemic Regional Hydroarsenicism (C.E.R.HA.), a disease that causes skin disorders that may evolve into more serious diseases such as cancer. In many cases, the occurrence of arsenic is associated with the presence of fluoride. The consumption of water which contains 1.0 to 1.5 mg/L of fluoride, protects children’s teeth up to age of fourteen. Moreover, the same dose of fluoride is necessary to reduce dental caries throughout life. On the other hand, it was demonstrated that fluoride concentrations above 2 mg/L in drinking water results in dental fluorosis or stained teeth. In addition, the prolonged consumption of water with a concentration of fluoride above 4 mg/L can also have a serious effect on skeletal
Address correspondence to Romina Vidoni, Center of Sanitary Engineering, National University of Rosario, Riobamba 245 bis, 2000 Rosario, Argentina; E-mail:
[email protected]
tissues (skeletal fluorosis).[2] The World Health Organization (WHO) Expert Committee on Oral Health Status and Fluoride Use has recommended a fluoride level of from 0.5 to 1.0 mg/L in the drinking water, depending on the climate.[3] High levels of arsenic and fluoride in groundwater have been reported around the world, including Argentina, Mexico, China, India and Pakistan.[4–9] In Argentina, most of the largest cities are supplied with drinking water from surface water sources; however, most of small and mid-sized towns are supplied with poor quality groundwater: high salinity and high arsenic, fluoride, nitrate, iron, manganese levels, among others. The provinces most affected by the presence of both arsenic and fluoride ´ in their water are Santa Fe, Cordoba, Tucum´an, Santiago del Estero, Buenos Aires and La Pampa (Table 1).[10–14] In 2007 the Argentine Food Code set the maximum permissible value for arsenic concentration in water at 10 µg/L, value to be in force for 5 years.[20] Thus, the affected population has significantly increased and the need for appropriate technology to be used has become even more important. In Argentina, the maximum concentration for fluoride in drinking water is set up depending on the regional temperature and ranges from 0.8 to 1.7 mg/L.[20] As mentioned
Using polyaluminum chloride for As and F removal from groundwater Table 1. Arsenic and fluoride simultaneous concentrations in several provinces of Argentina. Provinces
Arsenic (µg/L)
Fluoride (mg/L)
Buenos Aires
50–100(15)
Chaco ´ Cordoba La Pampa Santa Fe Santiago del Estero
10–800(16) 50–250(17) 50–5000(15) 50–200(15) 100–2000(15) (up to 13,000)(19) 20–760(11) 2.0–8.3(11)
Tucum´an
1.9–4.0 (up to 7.0) (this research) 0.5–4.2(16) 1.0–3.0 (up to 12.0)(17) 0.03–29.0(18) 0.9–2.0 (this research) 1.0–4.0 (up to 16.0)(19)
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Refs. [11,15–19]
above, the presence of high levels of arsenic and fluoride in drinking water may cause health problems and, as these chemical elements are frequently associated, it is important to have appropriate treatment technologies in place to enable their simultaneous removal.
Technologies available for the simultaneous removal of arsenic and fluoride Some of the technologies that allow the simultaneous removal of arsenic and fluoride are the following: activated alumina, ion exchange, reverse osmosis and coagulationadsorption. Activated alumina is used with more efficiency at high levels of total solids. High removals of arsenic and fluoride are better achieved at a low pH, but this treatment process is very sensitive to minimum pH variations.[21] Disadvantages of this method are the need of qualified personnel and the high associated cost. Ion exchange resins can be used in water treatment to remove unwanted concentrations of dissolved solids, although the United States Environmental Protection Agency (USEPA) recommends not to use them when they are above 500 mg/L and when sulfate concentration is above 120 mg/L.[22] In addition, when arsenic and fluoride are simultaneously present, as they compete for adsorption sites, runs are very short and the removal efficiency is low. The advantages of the applicability of this process are the wide range of pH and the possibility of simple resin regeneration.[18] Reverse osmosis, can remove most of the salts present in water and its use is recommended when salinity content in water is greater than the allowed limit. It is proposed as a very effective technology for arsenic and fluoride simultaneous removal. However, it has certain disadvantages, such as high installation and operation costs, high water rejection, the need of trained personnel, high energy consumption and imported inputs. In Argentina, poor experiences have been recorded in relation to reverse osmosis appli-
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cation, as communities could not afford the high running cost, so many plants are no longer in operation. Currently, water suppliers in small and mid-sized towns oppose to reverse osmosis plants installation, especially when total salinity content in water is low and the only purpose is to remove arsenic and/or fluoride. Therefore, alternative solutions were needed and alternative, cost-effective and user-friendly treatments could be used. Coagulation-adsorption on iron and aluminum hydroxides flocs, is particularly applicable to remove arsenic from low hardness and low salinity water. In this case, this process competes favorably with the reverse osmosis approach. This technology is appropriate for its simplicity and cost effectiveness. As a disadvantage, after the treatment, residual iron or aluminum might be present in treated water. Iron salts do not remove fluoride hence they are very suitable only when arsenic should be removed. Tests carried out at the National University of La Plata (Argentina), demonstrated that the coagulation process for arsenic and fluoride removal was efficient using pre-chlorination, aluminum sulfate and a cationic polyelectrolyte as coagulant.[23] The Nalgonda technique[24] uses coprecipitation by adding aluminum sulfate and calcium hydroxide to promote the formation of aluminum fluoride and hydroxides precipitates where fluoride adsorption takes place. Nalgonda method can be used only for water with fluoride concentrations
