Abstract
Arsenic (As) contamination of drinking water is a major cause of As toxicity in many parts of the world. A study was conducted to evaluate As removal from water containing 100–700 μg/L of As and As to Fe concentration ratios of 1:5–1:1000 using the coprecipitation process with and without As/Fe adsorption onto granular activated carbon (GAC). Fe concentration required to reduce As concentrations in order to achieve the WHO standard level of 10 μg/L increased exponentially with the increase in initial As concentration. When small amounts of GAC were added to the As/Fe solutions the Fe required to remove these As concentrations reduced drastically. This decline was due to the GAC adsorption of Fe and As, enhancing the removal of these metals through coprecipitation. Predictive regression equations were developed relating the GAC dose requirement to the initial As and Fe concentrations. Zeta potential data revealed that As was adsorbed on the GAC by outer-sphere complexation whereas Fe was adsorbed by inner-sphere complexation reversing the negative charge on GAC to positive values. X-ray diffraction of the GAC samples in the presence of Fe had an additional peak characteristic of ferrihydrite (Fe oxide) compared to that of the GAC sample without Fe. The study showed that incorporating an adsorbent into the coprecipitation process has the advantage of removing As from waters at all concentrations of Fe and As compared to coprecipitation alone which does not remove As to the required levels if Fe concentration is low.
Highlights
Arsenic (As) contamination of drinking water is a serious water quality problem in many parts of the world, especially Vietnam, Bangladesh, India, Taiwan, Cambodia, and Chile [1,2,3]
Fe was removed in proportion to the removal of As, there was excess Fe in the solution and this increased as the As/Fe ratio decreased
The results indicated that the removal of As and Fe by the adsorption/coprecipitation process increased at a larger granular activated carbon (GAC) dose (Fig. 1.b, Fig. S1.bS4.b)
Summary
Arsenic (As) contamination of drinking water is a serious water quality problem in many parts of the world, especially Vietnam, Bangladesh, India, Taiwan, Cambodia, and Chile [1,2,3]. Two common methods of removing As from drinking water are adsorption and coprecipitation with Fe [1,2,3,9,10,11,12,13,14,15]. The latter method is a natural process where the concentration of Fe found in groundwaters generally increases with As concentration [16]. Very little quantitative information is available on the Fe/As ratio required for reducing the As concentration to the WHO standard level for waters containing diverse As and Fe concentrations [13,14]
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