ARSENIC REMOVAL FROM DRINKING WATER USING FLYASH AS AN ADSORBENT
Nowadays water pollution has become a major problem that is being faced by the human kind. Among various pollutants present in water, arsenic is gaining much importance because of the toxicity of its compounds. Hence it is very much necessary to find the best suitable technique for removal of arsenic from drinking water. In the present study, the removal of Arsenic from synthetic sample on coated fly ash has been carried out at room temperature 32 ± 1 o C. Initially raw fly ash was used for the experiment and it was seen that the residual arsenic concentration increased hencebatch tests were conducted for the removal of Arsenic on iron sulphate coated fly ash for optimum parameters such as dosage, pH, time, initial concentration and agitation rate. The maximum removal efficiency was obtained at an optimum dosage of 0.5gms. It was found that 100% removal can be achieved at slightly alkaline pH condition. The optimum time, initial concentration and agitation rate were found to be 15mins, 140µg/l and 150RPM respectively. Arsenic is the 20th most abundant element found in the earth's crust. It occupies nearly 0.00005% of the entire earth's surface (2). Arsenic occurs naturally and sometimes can be produced by anthropogenic sources such as mining, industrial and agricultural activities. It is found naturally in the geologic substrate and also can be produced during volcanic eruptions. Arsenic occurs in organic and in-organic forms. It is present in the organic form in food in small amount which is required for the body. In natural waters, it is present in the in-organic form namely As (III) and As (V). These two ions namely, arsenic trioxide and arsenic pentoxide are either naturally occurring or byproducts of industrial waste. The predominant species for As (III) are H3AsO3 and for As (V) are H2AsO 4- and HAsO4 2-. These chemicals can badly affect human health(10)when they are consumed in large amount. The ground water at various locations in Bangladesh, West Bengal, some parts of Bihar& Karnataka in India, has been noticed to be contaminated with Arsenic (As) in excess of its permissible limit. Recently 14 out of 20 villages at Surpur taluq of Yadgir district, Karnataka state (India) has been found to be affected by Arsenic content.Several incidents have demonstrated that Arsenic in water may be carcinogenic. Acute poisoning by Arsenic involves the central nervous system leading to coma and for doses of 70-80 mg to death. The gastro-intestinal tract, nervous system, the respiratory tract, and the skin can be severely affected (4). It is recommended that, when water is found to contain Arsenic in excess of 0.01 mg/L (W.H.O), the water is considered to be unfit for drinking. Arsenic can be removed by many conventional and non-conventional methods. Adsorption is used widely to remove Arsenic metal from water and industrial wastewater. Adsorption offers significant advantages like low cost, availability, profitability, ease of operation and efficiency, in comparison with conventional methods especially from economical and environmental points of view. Many attempts have been made to remove arsenic from water using various adsorbents. Fly ash is a by-product that is produced by coal fired thermal power plant. From literature review it can be concluded that fly ash has sorptive properties with regard to heavy metals (3).And it was also found that iron containing adsorbents were effective in arsenic removal from aqueous solution hencefly ash coated with iron sulphate was used in the present study (5).
Sorption properties of fly ash from brown coal burning towards arsenic removal
In the present work, the sorptive capacity of fly ash from the combustion of brown coal in relation to arsenic(III) removal from the standard solution as well as the potential application of fly ash in actual wastewater purification have been evaluated.
Simultaneous treatment of both As ( III ) and As ( V ) with Iron-Coated Sand ( ICS ) and Manganese-Coated Sand ( MCS )
From the natural geochemical process and anthropogenic activities such as mining wastes, petroleum refining, and agricultural chemicals, surface and groundwater are widely contaminated with arsenic (Bhumbla and Keefer, 1994). Inorganic arsenic is commonly present as arsenite and arsenate depending on the aquatic redox systems. In anoxic systems such as groundwater, the stable form of arsenic is As(III) which is more toxic and mobile than As(V). Although several methods such as activated alumina, coagulation, membrane or electrolysis have been identified as promising techniques in the treatment of As(V) (Chent al., 1999), these processes were partly effective to treat As(III), requiring a highly effective and economic technique on the oxidation of As(III) to As(V) as a pre-treatment . In this study, as a promising technique for the treatment of both As(III) and As(V) at the same time in a single reactor, reactor systems containing both manganese-coated sand (MCS) and iron-coated sand (ICS) were used to investigate the oxidation kinetics of As(III) and adsorption of As(V) with variation of the configuration of MCS and ICS in column experiments.