Community level defluoridation of groundwater with limestone derived adsorbent

Fluorosis is a worldwide, chronic degenerative disease caused by excessive level of fluoride in drinking water, mostly impacting rural, resource poor communities. Success of any technological solution to this problem, by reducing fluoride in water to safe level, is contingent on its feasibility to be implemented under resource limited circumstances for extended periods. Keeping these constraints in mind, we have developed a method to adsorb fluoride using surface modified limestone, using a simple and scalable process. The adsorbent was prepared using crystalline calcium carbonate, calcium chloride and monobasic sodium phosphate as the main ingredients. Surface and elemental analyses showed that fluoride constituted up to 3.8% of the surface of the saturated adsorbent. Kinetic data showed that the diffusional resistance was a rate limiting step to water defluoridation. Pilot scale operation of the process in a rural tenement with local help to prepare the adsorbent and treat 7001 of groundwater each day for 4 months was demonstrated. During this period the average fluoride concentration of the feed water was 7.1 ppm, and was reduced to 1.0 ppm by the treatment. We also show that the saturated adsorbent could be regenerated by acid wash followed by surface modification. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.