Design of household level arsenic treatment system in Cambodia : system design and performance

Abstract

The aim of this study was to design a household arsenic (As) removal unit which is to be easily operated and maintained by the villagers in Cambodia, and it should use materials that are locally available and produce water that meets drinking water quality standards. A household As removal unit was designed to purify groundwater from Cambodia with high levels of As concentration and low natural iron. This As removal system incorporates a tray with evenly distributed holes and an adsorbent bed of materials comprising non-galvanised iron nails, sand, laterite and wood charcoal chips in a plastic container which can be placed in the homes of the villagers in Cambodia. Iron nails are used as an additional source of iron oxides that can adsorb As. When water is poured into the container, the water is first aerated and sprayed over the adsorbent bed media; iron nails come into contact with dissolved oxygen and water and corrode to form iron hydroxides or hydrous ferrous oxides (HFO). Arsenite (As(III)) is oxidised to arsenate (As(V)) resulting from the formation of HFO and As(V) is then adsorbed onto the surface of the iron nails and HFO, which are retained by the sand layer. Column studies have shown that the rusted iron nails and sand configuration at an empty bed contact time of 2.9 hours and 5 hours respectively can reduce As(III) concentration in synthetic groundwater from 715 μg/L to below 100 μg/L. Laterite is a type of rock that is commonly found in Cambodia and acts as a polishing unit to further reduce the As concentration to below the Cambodian standard of 50 μg/L. Wood charcoal chips are good adsorbents and are placed at the bottom of the container to remove any dissolved organic matter, colour and odour before the water leaves the container. This design is able to remove other trace elements like iron, manganese and aluminium from groundwater in addition to As, meeting World Health Organization and U.S Environmental Protection Agency drinking water quality standards.