Effective fluoride removal using granular bauxite filter media as an affordable and sustainable alternative to activated alumina†
Despite centuries of advancements in water treatment, hundreds of millions of people worldwide continue to suffer detrimental health impacts from drinking water with unsafe fluoride levels. Our study compares the performance of low-cost mildly heated bauxite ores and commercial activated alumina (AA) in treating a synthetic groundwater matrix representative of global, fluoride-contaminated aquifers. Batch kinetics studies of fluoride adsorption onto global bauxite ores and AA follow a pseudo-second order rate law, with adsorption increasing exponentially in the first few hours. Fluoride removal efficiencies increase from 73.5% to 85.5% as media particle sizes decrease from 0.6–1.2 mm to <0.1 mm. Column studies demonstrate that increasing the ratio of reactive media in filters from 1 to 100 weight percent increases the volume of treated water from 0.2–56.1 L for Guinea bauxite (GB) and from 0.5–58.3 L for AA. We predict the performance of large-scale columns by modifying the bed depth service time (BDST) model to scale breakthrough time with adsorbent mass rather than with column height. Our modified BDST model predicts that large-scale columns using 1039 kg AA and 1436 kg GB can treat 405 444 L and 338 859 L of potable water in 1.4 and 1.1 months. We also demonstrate application of the rapid small scale column test (RSSCT) model to design smaller lab-scale columns with lower resource, cost, and time inputs by scaling down known field systems parameters including column height, pump flow rate, empty bed contact time, and approach velocity.