Effect of aeration, iron and arsenic concentrations, and groundwater matrix on arsenic removal using laboratory sand fil
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ORIGINAL PAPER
Effect of aeration, iron and arsenic concentrations, and groundwater matrix on arsenic removal using laboratory sand filtration Cynthia A. Coles
. Danial Rohail
Received: 29 January 2020 / Accepted: 9 July 2020 Ó The Author(s) 2020
Abstract Natural groundwater from the towns of Wabana and Freshwater and treated well water from the town of Wabana in Newfoundland and Labrador, Canada were tested separately and together in sand columns to study the removal of arsenic. The most ideal conditions for arsenic removal appeared to include an arsenic concentration of approximately 35 lg/L and lower, an Fe:As mass ratio in the order of 65 and lower, and aeration of the sand media. Active aeration by pumping air though the filter, passive aeration by scraping off top layers of sand and virtual aeration by diluting the strength of the water being treated, were employed and compared. For tests where groundwater from the towns of Wabana and Freshwater was combined, arsenic removal was optimized and other elements, in addition to iron, were also correlated with effluent arsenic. Further, for these same tests there was a gradual increase in effluent pH that could have been due to oxygen depletion or gradually more reducing conditions in the sand column. Where Ni, Mn and Zn were correlated with effluent arsenic it was concluded that the increase in C. A. Coles (&) Department of Civil Engineering, Memorial University of Newfoundland, 40 Arctic Avenue, St. John’s, NL A1B 3X7, Canada e-mail: [email protected] D. Rohail Infrastructure Ontario, Suite 2000, 1 Dundas St. West, Toronto, ON M5G 1Z3, Canada
pH increased heavy metal removal and arsenic release. In the test where the treated Wabana water made up a greater proportion of the mix than the Wabana groundwater, lithium was also correlated with arsenic. Keywords Arsenic removal Iron–arsenic ratio Sand filtration Groundwater matrix Metals
Introduction Many soils in Newfoundland and Labrador (NL), Canada have elevated levels of arsenic and so arsenic in drinking water from wells in the rural communities is not uncommon (Rageh 2008). Up to 3000 mg/kg of arsenic was measured in the iron sulfide sedimentary rock on Bell Island in NL (Onishi and Sandell 1955) and arsenic is often found in sulfide minerals and in sedimentary rock that is high in iron, manganese and aluminum (Jovanovic et al. 2011; Onishi and Sandell 1955). The average abundance of arsenic in the earth’s crust in the USA is about 7.2 mg/ kg (Schacklette and Boerngen 1984) and in uncontaminated groundwater the arsenic can be less than 1–2 lg/L (Jovanovic et al. 2011). Arsenic has four oxidations states (- III, 0, ? III and ? V), though arsenite or As(III) and arsenate or As(V) are most important in soils and water. Arsenite dominates under anoxic/reducing conditions and
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Environ Geochem Health
arsenate is more abundant under aerobic/oxidizing conditions (Sarkar and Paul 2016). Groundwater can contain either or both species (Jovanovic et al. 2011) an
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