In the last 20 years, the widespread adoption of shallow tubewells in Nepal Terai region enabled substantial improvement in access to water, but recent national water quality testing showed that 3% of these sources contain arsenic above the Nepali interim guideline of 50 microg/L, and up to 60% contain unsafe microbial contamination. To combat this crisis, MIT, ENPHO and CAWST together researched, developed and implemented a household water treatment technology by applying an iterative, learning development framework. A pilot study comparing 3 technologies against technical, social, and economic criteria showed that the Kanchan Arsenic Filter (KAF) is the most promising technology for Nepal. A two-year technical and social evaluation of over 1000 KAFs deployed in rural villages of Nepal determined that the KAF typically removes 85-90% arsenic, 90-95% iron, 80-95% turbidity, and 85-99% total coliforms. Then 83% of the households continued to use the filter after 1 year, mainly motivated by the clean appearance, improved taste, and reduced odour of the filtered water, as compared to the original water source. Although over 5,000 filters have been implemented in Nepal by January 2007, further research rooted in sustainable development is necessary to understand the technology diffusion and scale-up process, in order to expand access to safe water in the country and beyond.

In the rural Terai region of Nepal, many tubewell drinking water sources are microbially and/or arsenic contaminated and consequently, millions lack access to “safe” water. Those who drink contaminated water may suffer from preventable water-borne diseases such as diarrhoea, stunting, skin lesions, and cancer. To combat this problem, a team comprising researchers from Massachusetts Institute of Technology (MIT), together with two local partners, Environment & Public Health Organization (ENPHO), and Rural Water Supply and Sanitation Support Programme (RWSSSP), have developed an award-winning household water filter, the Kanchan™ Arsenic Filter (KAF), for simultaneous arsenic and pathogen removal. The KAF is constructed using locally available labour and materials and is optimised based on the local socio-economic conditions. The first part of this paper explains the technology development process and the technical details of this innovation. The second part of this paper describes the dissemination activities since 2004. This dissemination model not only built capacity in local people towards long-term, user-participatory safe water provision, but also made a contribution to the local economy. As of January 2006, over 25,000 people have gained access to safe water as a result of the implementation of the KAF.

In the lowlands of Nepal (Terai), the WHO drinking water guideline concentration of 10 μg/L for arsenic (As) is frequently exceeded. Since their introduction in 2006, iron-assisted bio-sand filters (Kanchan filters) are widely used to treat well water in Nepal. The filters are constructed on the basis of As-removal with corroding zero-valent iron (ZVI), with water flowing through a filter bed of iron nails placed above a sand filter. According to several studies, the performance of Kanchan filters varies greatly and depends on the size of the iron nails, filter design, water composition and operating conditions, leading to concerns about their actual efficiency. This study examined 38 Kanchan household filters for which insufficient As-removal was reported, to evaluate the reasons for limited removal efficiency and to define measures for improved performance. The measured arsenic removal ranged from 6.3% to 98.5 %. The most relevant factors were the concentrations of As and Fe in the raw water, with the best removal efficiency observed for water with low As (124 µg/l) and high Fe (4.94 mg/l). Although the concentrations of other elements, pH, flow rates, and contact time with ZVI also played a role, the combined evidence indicated that the reactivity of the frequently drying nail beds between filtrations was insufficient for efficient Asremoval. Optimized filters with added top layers of sand and raised water outlets with flow restrictions to keep nails permanently immersed and to increase contact times, should be able to achieve higher and more consistent arsenic removal efficiencies.

The effects of grain size, hydraulic loading rate, batch residence time and diffuser design on the performance of the CAWST version 10 biosand filter was investigated.  Two types of sand gradations were prepared – fine sand (ES = 0.20, UC = 2.3) and a coarse sand (ES = 0.25, UC = 2.9).  The fine sand and coarse grains resulted in initial hydraulic loading rates of 0.3 m3/m2 min and 0.75 m3/m2 min, respectively.  Flow restrictions were installed on 2 coarse grain filters such that their initial hydraulic loading rates were 0.3 m3/m2 min.  For the range of grain size and flow rates investigated in this paper, coarse grain size leads to lower bacterial removal efficiencies compared to the fine grain size.  The addition of flow restrictions on filters with coarse grain size did not result in improvement in bacterial removal efficiencies. Two different diffuser designs were also investigated (hole size of 1/8 inch or 3.2 mm and 0.5 inch or 12.7 mm spacing, hole size of 3/16 inch or 9.5 mm and 0.5 inch or 12.7 mm spacing).  These filters were compared to the standard design of CAWST version 10 filter, i.e. control filter, which has a hole size of 1/8 inch (3.2 mm) and 1 inch (25.4 mm) spacing.  Diffuser design was found to have an effect on the bacterial removal efficiency. The two diffuser investigated (smaller hole size, tighter spacing) resulted in lower bacterial removal efficiencies, compared to the CAWST specified diffuser design.   Batch residence time was found to have a significant effect on bacterial removal.  The deficiencies caused by diffuser design, coarse grain size were compensated by a higher batch residence time.

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