Introduction
1.1 OVERVIEW
Introduction
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24 districts of Assam have groundwater with arsenic content exceeding 50 µg/L (Mahanta et al., 2004). Therefore, efforts have to be directed to look for such methods/techniques for fluoride and arsenic removal along with iron removal from the groundwater which is acceptable and easily adaptable to communities – especially for rural and semi-urban areas lacking piped water supply – so as to ensure acceptable quality potable water on a sustainable basis at an affordable cost.
Adsorption has been considered as the most effective and applicable technology for the removal of pollutants from wate/wastewater (Bhatnagar and Sillanpaa, 2010;
Gupta and Suhas, 2009; Jiuhui, 2008; Demirbas, 2008; Foo and Hameed, 2010;
Rafatullah et al. 2010). Studies carried out with granular ferric hydroxide (Driehaus et al., 1998), iron oxide coated sand (Joshi and Chaudhuri, 1996), iron-coated sand and iron impregnated activated carbon (Petrusevski et al., 2002), iron oxide impregnated activated carbon (Reed et al., 2000) and iron rich Sylhet sand (Hoque et al., 2007) have shown its effectiveness in removing arsenic from ground water. Some researchers have even reported that iron oxide along with some other oxide could be effective in removing fluoride from groundwater (Wu et al., 2007; Zhao et al., 2007). These studies have highlighted the possibility of removal of fluoride and arsenic from the groundwater with iron-coated adsorbents.
The presence of iron in the groundwater above regulatory limits makes the water unusable mainly from aesthetic considerations such as discoloration, metallic taste, odour, turbidity, staining of laundry and plumbing fixtures. Moreover, iron oxides, which are formed in reservoirs upon aerial oxidation of dissolved iron promotes growth of micro-organism in water. Therefore, World Health Organization (WHO) has set a guideline value of 0.3 mg/L for iron in drinking water (WHO, 1984) and many countries including India (IS 10500, 1991) have adopted this value in their national drinking water standards. Aeration and separation is the most common method for removal of iron from groundwater in public water supply systems, which is however, not so popular amongst rural and semi-urban communities lacking piped water supply.
Other methods available for iron removal from groundwater are ion-exchange (Vaarmaa and Lehto, 2003), oxidation with oxidizing agents such as chlorine and potassium permanganate (Ellis et al., 2000), adsorption on activated carbon and other adsorbents (Munter et al., 2005) and treatment with limestone (Aziz et al., 2004).
TH-945_05610401
Introduction
Intensive research have been undertaken in the last few decades in developing countries such as Sri Lanka, Ghana, Burkina Faso, Argentina, South Africa, Uganda, India which has yielded many different methods, designs and configurations of iron removal units to be used at the community level (Andersson and Johansson, 2002; Chibi, 1995). But surprisingly none of these methods, designs and configurations of iron removal units so developed has found its place in the rural and semi-urban areas either at community levels or at an individual household level in this region. This could probably be due to high capital costs and complicated operation and maintenance requirements of these methods, designs and configurations.
One of the potential strategies is to look for what is being practiced by the communities of rural and semi-urban areas in this region in order to manage the high levels of iron in their groundwater. A field survey was carried out in Assam – a northeastern hilly province (area ≈ 78438 km2, population ≈ 27 million) of India, where the groundwater contains 1-25 mg/L or more of iron (Das et al., 2003; Singh, 2004;
Mahanta et al., 2004). The rural and semi-urban population of Assam, based on their experiences of past few generations, use different variants of indigenous household iron filter units – which are fabricated using local materials such as community prepared wooden charcoal (CPWC), river sand (RS) and gravel (Ahamad and Jawed, 2007). The communities using indigenous household iron filter units believe that wooden charcoal and river sand (two of the common media used) helps in reducing concentration of the iron from the groundwater. The wooden charcoal used in these units are prepared indigenously from woods specially procured from hilltops (not from plain lands) located in and around the communities. The procured woods are cut into smaller pieces, dried in sun and burnt partially in air (not to ashes), and then cooled and washed with surface water resulting in individual wooden charcoal pieces of 2.5 cm × 1.5 cm × 1.5 cm to 4 cm × 2.5 cm × 1.5 cm. Sand and gravels are washed, dried and re-used.
Wooden charcoal gets completely disintegrated during use, and therefore, is replaced with a new stock.
Even though, different variants of indigenous household iron filter units have been in use for generations in Assam, very limited scientific studies have been carried
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out to understand the role of the media used in these filter units for the removal of dissolved iron, fluoride and arsenic from the groundwater as well as not much efforts have been made to improve the performance of these filter units. Therefore, there is an obvious need to assess these media scientifically with an aim to improve the performance of indigenous household iron filter units. At the same time it is important to preserve the overall configuration of the units as developed over past generations by the rural and semi-urban communities so as to ensure its adaptability even after improvement. Results of this study may add to the state-of-the-art knowledge of the low cost technology for sustainable potable water availability at individual household levels. As a first step in this direction, one of the objectives of the present work is to assess the potential of the wooden charcoal – prepared indigenously by the rural and semi-urban communities and river sand for the removal of dissolved iron [Fe(II)] from groundwater. The different variants of indigenous household iron filter units are primarily used to reduce the concentration of iron from the groundwater. At present, the rural and semi-urban communities in Assam are not making any efforts to reduce fluoride and arsenic levels in the drinking water. Therefore it is imperative to assess the indigenous household iron filter units for their effectiveness in reducing the levels of fluoride and arsenic along with iron and to carry out suitable modification/improvement of the filter units if possible. The potential of media, therefore, would be assessed for removal of Fe(II), F− and As(III) through kinetics (in batch mode), equilibrium (in batch mode) and column (in continuous mode) studies from individual mono-, binary- and ternary-metal ion systems comprising of Fe(II), F− and As(III) ions. The ultimate aim of this work is to design an improved filter unit for simultaneous removal of Fe(II), F− and As(III) from groundwater.