## 5 Household Filter for Arsenic Removal for Drinking Water
Also, the filter is relatively cheap costing about $40 for over five years operation and capable of producing 20-30 L/hour to support one to two families drinking and cooking needs [158]. The approval for use of the filter was granted by government and at the early stages about 30,000 of these filters were provided throughout Bangladesh. Its use subsequently spread to India, Nepal and Pakistan. The National Academy of Engineering has recognized the innovation of the SONO filter for arsenic removal by awarding it the Grainger Challenge Prize for sustainability due to \"its affordability, reliability, ease of maintenance, social acceptability, and environmental friendliness [158]\".  
With regards to ongoing maintenance of SONO filters, an important requirement is the need to flush each bucket with 5 L of hot water to eliminate pathogenic bacteria and minimize coliform counts. The filter is expected to last for five years, but if the flow rate decreases, it can be improved by removing the sand layers for washing and reuse or replacement with new sand.  
Another commonly used arsenic filter for treatment of contaminated water for arsenic removal is the KanchanTM Arsenic Filter (KAF) [159]. This filter was developed in 2003 through a collaborative effort between the Massachusetts Institute of Technology (MIT) and Environment and Public Health Organization on the mitigation of arsenic contamination of groundwater [160].  
Figure 5: SONO Filter. (**a**) Schematic and (**b**) in domestic use [158]. Reproduced with permission from Taylor & Francis.  
Figure 6 shows that the components of a KAF include a plastic container, PVC pipe, diffuser basin, brick chips, iron nails, fine sand, coarse sand and gravel [160]. The arsenic contaminated groundwater is poured into the diffuser basin where it comes into contact with the brick particles and iron nails. Upon contact with water and air, the iron nails rust, consequently producing ferric hydroxide particles that quickly adsorb arsenic from the water. The adsorption process is repeated when new iron surfaces are exposed as the outer surfaces scale off. These continuous processes result in the retention of arsenic on the filter components and produce drinkable filtered water. In addition, the KAF is capable of removing pathogens from the water.  
Factors influencing the performance of a KAF include arsenic concentration, duration of use, filter maintenance, flow rate, monitoring and handling and other water components (such as water hardness, iron, chloride and phosphate concentrations) [161]. The effectiveness of KAFs in reducing the concentration of arsenic in groundwater to less than 50 \(\upmu\)g/L has been demonstrated [160]. But the effectiveness of the filter can be affected occasionally by the unexpected and unpredictable variability of groundwater conditions, arsenic concentration and climatic conditions.  
One of the more recently developed filters is the Pakistan Arsenic Filter (PAF) [162]. This unit employs three different forms of iron (mesh, nails and slag). The iron is held down in a plastic bucket (25 L) with diffuser plates. A tap is attached to the bucket to enable the adjustment of water level and for taking samples at the completion of the treatment, as shown in Figure 7.  
Figure 6: Components of a Kanchan Arsenic Filter [160]. Reproduced with permission from Taylor & Francis.  
Figure 7 shows the specific components of a PAF. The round gravel layer overlaid by sand layer can be seen at the bottom. The unit used 1 kg of iron (mesh, nails and slag) contained within the diffuser plate in the bucket and the rate of water flow through the filter is 30 L/min which decreased over an 8-week trial period to 20 L/min [162]. The arsenic contaminated groundwater goes through a diffuser plate and then passes through the sand and gravel. Treated water is transferred through a plastic pipe via a tap, as shown in Figure 7. The highest efficiency achieved for arsenic removal was with the use of iron mesh due to its larger surface area which generates more ferric hydroxide. The PAF was produced at a cost of US$ 5 which is affordable and accessible to more people [162].