Pilot-Scale Field Demonstration of Environmental Nanotechnology for Groundwater Defluoridation

Abstract

Fluoride contamination in groundwater is a global issue. Nanoscale oxides of Zr(IV), Al(III), and Ti(IV) can form the inner-sphere complex with fluoride through ligand exchange, offering a new chance for efficient groundwater purification. However, pilot-scale field demonstration of nanotechnology in groundwater defluoridation is very rare. Herein, we conducted a 150-day field defluoridation study using the nanocomposite HZO@D201, which was prepared by encapsulating nano-hydrated zirconium oxide (HZO) inside the strongly basic anion exchanger D201. The HZO@D201 beads were packed in five-stage series columns (40 L for each column), and the groundwater was pumped through the columns sequentially. The effective treatment amount for the single column ([F–] < 1.0 mg/L) exceeded ∼3000 bed volume (BV). The exhausted HZO@D201 was fully refreshed through ex situ treatment with NaOH–NaCl solution for repeated use without significant loss in defluoridation reactivity. Owing to the specific interaction with HZO, the fluoride concentration could be steadily reduced below 1.0 mg/L throughout the 150-day field demonstration, while the common anions coexisting in groundwater (K+, Na+, Ca2+, Mg2+, SO42–, Cl–, etc.) remained almost unchanged. The operational cost for deep defluoridation was estimated as 0.574 RMB per ton of groundwater, much less than that of the widely studied reverse osmosis. TEM, XPS, and Fourier transform infrared (FTIR) analysis indicated that negligible change occurred in the structure and chemical composition of HZO@D201 after the long-term field assay. This study may inspire more attempts at the pilot scale and engineering demonstration of nano-enabled water treatment techniques.