Fluoride removal from brackish groundwater by direct contact membrane distillation

Abstract

The direct contact membrane distillation (DCMD) applied for fluoride removal from brackish groundwater is presented. The self-prepared polyvinylidene fluoride membrane exhibited high rejection of inorganic salt solutes and a maximum permeate flux 35.6 kgm 22 h 21 was obtained.The feed concentration had no marked impact on the permeate flux and the rejection of fluoride.The precipitation of CaCO 3 would clog the hollow fiber inlets and foul the membrane surface with the increase of concentration factor when natural groundwater was used directly as the feed, which resulted in a rapid decline of the module efficiency. This phenomenon was diminished by acidification of the feed. The experimental results showed that the permeate flux and the quality of obtained distillate kept stable before concentration factor reached 5.0 with the acidified groundwater as feed. The membrane module efficiency began to decline gradually when the feed continued to be concentrated, which can be mainly attributed to the formation of CaF 2 deposits on the membrane surface. Finally, a 300 h continuous fluoride removal experiment on acidified groundwater was carried out with concentration factor at 4.0, the permeate flux kept stable and the permeate fluoride was not detected.

Water Defluoridation: Nanofiltration vs Membrane Distillation

“…In this context, membrane distillation (MD) has been recently proposed as a possible alternative to NF and RO in desalination , and defluoridation − processes. The cross-sectional diagrams of NF and MD are depicted in Figure , in order to stress the main differences between the two processes.…”