Consumption of arsenic contaminated groundwater poses a public health threat to millions of people globally, particularly those in developing communities without conventional, centralized water treatment facilities. Accessible technologies are needed which are easy to implement, operate and maintain and require little or no fossil fuel energy to work.
Cactus mucilage, extracted from the Opuntia ficus-indica (also known as Nopal and Prickly Pear cactus), is a natural flocculant shown to interact with dissolved arsenate. Ferric ions were introduced to the system to capitalize on the strong affinity of arsenate for ferric hydroxides. In batch experiments, ferric (Fe(III)) ions were contacted with arsenate (As(V)), then treated with cactus mucilage in a cylindrical column. After equilibration, sample aliquots were taken from the top and bottom of the column and tested for As and Fe. The mucilage accelerated precipitate formation and settling within 15 min of addition, achieving 90% arsenic removal as indicated by difference between initial and final dissolved As concentration in the column. Arsenic removal improved with increasing both mucilage concentration and Fe concentration. The role of the mucilage was demonstrated by untreated solutions showing no concentration difference. The mucilage is thought to assist the precipitation by providing a matrix for stable floc formation which leads to the removal of both iron and arsenic simultaneously, providing safe drinking water. This mucilage-based technology has the potential to be relatively inexpensive, and an environmentally sustainable alternative to synthetic polymer flocculants for removing arsenic from drinking water.