Abstract

The use of iron (Fe) (III) salts as fluoride coagulants in water is challenged by the requirement of high pH for maximum efficiency. At their natural pH, these salts have low fluoride removal efficiency. This study examines the effect of amaranth plants on enhancement of the defluoridation efficiency of Fe (III) salts as coagulants. Amaranthus hybridus plants were suspended in fluoride water treated with varying concentrations of Fe (III) with its roots immersed completely in fluoride water for varying time from 720 to 1440 min. The study shows that fluoride coagulation by Fe (III) in the absence of plants is limited to 10%, whereas when plants were introduced, it increased from 10 to 40%. These results suggest that amaranth plants enhance the defluoridation efficiency of Fe (III). This enhanced removal may be attributed to increased coagulation effected by exudates released by plant root which contain organic compounds and CO₂ or charged root surfaces by the formation of Fe (III) oxide film. The exact factor that has a major contribution to enhanced removal observed remains to be subject of further studies.

Key words: Coagulation, defluoridation, iron (III) salts, phytoremediation, plant exudates.