A laboratory study for the treatment of arsenic, iron, and manganese bearing ground water using Fe³⁺ impregnated activated carbon: Effects of shaking time, pH and temperature

Abstract

This paper deals with the experimental investigation related to removal of arsenic from a simulated contaminated ground water by the adsorption onto Fe³⁺ impregnated granular activated carbon (GAC-Fe) in presence of Fe²⁺, Fe³⁺, and Mn²⁺. Similar study has also been done with granular activated carbon (GAC) for comparison. The effects of shaking time, pH, and temperature on the percentage removal of As(T), As(III), As(V), Fe²⁺, Fe³⁺, and Mn have been discussed. The shaking time for optimum removal of arsenic species has been noted as 8 h for GAC-Fe and 12 h for GAC, respectively. As(T) removal was less affected by the change in pH within the pH range of 2–11. Maximum removal of As(V) and As(III) was observed in the pH range of 5–7 and 9–11, respectively, for both the adsorbents. Under the experimental conditions at 30 °C, the optimum removal of As(T), As(III), As(V), Fe, and Mn are 95.5%, 93%, 98%, 100%, and 41%, respectively, when GAC-Fe is used. For GAC these values are 56%, 41%, 71%, 99%, and 98%. The adsorbent dose (AD) and its particle size (PS) for both GAC and GAC-Fe were 30 g/l and 125–150 μm, respectively. The initial arsenic concentration in the synthetic water sample was 200 ppb.

Introduction

Arsenic, the world's most hazardous chemical [1] is found to exist within the shallow zones of ground water of many countries like Argentina, Bangladesh, India, Pakistan, Mexico, Mongolia, Germany, Thailand, China, Chile, USA, Canada, Hungary, Romania, Vietnam, Nepal, Myanmar, Cambodia, etc. in various concentrations. In some places in Bangladesh its concentration is as high as 1000 μg/l [2].

Arsenic contamination in water has posed severe health problems around the world. Considering the lethal impact of arsenic on human health, environmental authorities have taken a more stringent attitude towards the presence of arsenic in water. World Health Organization (WHO) in 1993 and National Health and Medical Research Committee (NHMRC), Australia, in 1996 had recommended maximum contaminant level (MCL) of arsenic in drinking water as 10 and 7 μg/l, respectively [2], [3]. The MCL of arsenic in drinking water has also been reduced from 50 to 10 μg/l by European Commission in 2003 [4].

EPA has decided to move forward in implementing the same MCL of arsenic that is recommended by WHO for drinking water in 1993 [5]. Japan and Canada has reduced the MCL for arsenic in drinking water to 10 and 25 μg/l, respectively. The MCL for arsenic in countries like India, Bangladesh, Taiwan, China, Vietnam, etc. is also 50 μg/l [6].

As the diagnosis and medication of the arsenic related diseases are difficult the treatment of contaminated water as a preventive measure appears to be an effective alternative to combat arsenic poisoning.

Use of surface-modified adsorbents is becoming a recent research field for the development of cheaper arsenic removal technique. Recently, some adsorbents like Cu-impregnated coconut husk carbon, iron oxide coated polymeric materials, iron oxide coated sand, iron oxide coated cement, bead cellulose loaded with iron oxy hydroxide, etc. have been reported [2] for effective adsorption. Relatively very little information is published on the adsorption of arsenic species by activated carbon; however, the use of iron-impregnated GAC has been reported by some researches [7], [8], [9], [10] for removing arsenic from water. In these reports the complete account on the removal of total arsenic As(T), As(III), and As(V) are not mentioned. The optimization of the process parameters, the comparison between the adsorption efficiency of the GAC and iron-impregnated GAC, and the effect of other metal ions, which are frequently present in contaminated ground water, on the removal of arsenic species have rarely been discussed. Wide range of shaking time (10 min to 72 h) has been considered in these studies. Although the effect of pH on the percentage removal of As(III) and As(V) in absence of other metals is reported by some researchers, its effect on the removal of other metals like Fe and Mn is hardly reported. The effect of temperature is also rarely reported.

In this paper attempts have been taken to explore the possibility of the use of the ferric chloride-impregnated GAC to remove arsenic species in presence of iron and manganese ions, which are available frequently in ground water. The effects of shaking time, pH, and temperature on the removal of arsenic species along with Fe and Mn have been reported. The adsorption capacity of GAC and iron-impregnated GAC for the removal of Fe and Mn has also been compared.