People in many parts of the world are exposed to arsenic levels greater than 10 ppb in their drinking water. This is the maximum allowable concentration for drinking water recommended by the World Health Organization and enforced by the US EPA. Contamination is mainly due to erosion of natural arsenic deposits into the groundwater supply. Conventional treatment methods typically require centralized treatment facilities which may be inaccessible to poor rural communities on account of being expensive, energy intensive and requiring highly technical maintenance.

In previous work, cactus mucilage, a natural hydrocolloid, was shown to flocculate suspended solids and remove arsenic from water. Cactus mucilage is an extract from the Opuntia ficus-indica also known as Nopal and Prickly pear cactus. In the current study, we are investigating the mechanism by which the mucilage removes arsenic from water, with the aim of optimizing the process.

Batch kinetic column-depth experiments were performed in which the mucilage was contacted with aqueous arsenic solutions. The arsenic concentration was detected with hydride generation atomic fluorescence spectroscopy.

Our results suggest that a complex is formed between the sugars and carbohydrate compounds of the cactus mucilage and the solvated arsenic ions. Removal of the complex lowers arsenic concentration in the solution.

It is envisaged that the water treatment technology developed from cactus mucilage will solve the arsenic problems facing poor rural communities on the basis of being relatively inexpensive, easy to use, and requiring little or no electrical energy to operate.