Performance of nf90 and nf270 commercial nanofiltration membranes in the defluoridation of algerian brackish water

Abstract

Fluoride is one of those ions that cause acute human health problems among the inhabitants of southern Algeria. Naturally occurring high levels of fluoride are closely linked to interactions between groundwater and volcanic rocks. Among the water treatment techniques applied to remove fluoride, nanofiltration (NF) was studied in this work. Fluoride removal operations were carried out on NaF 10–3 and 10–2 M model solutions and on natural groundwater (Kouinine) in a pilot cross-flow filtration unit at different pressures. The performance of two commercial NF composite thin-film membranes (NF90 and NF270) was evaluated in terms of productivity, desalination efficiency and energy consumption. The results showed that NF90 had the highest retention efficiency while NF270 had the highest permeate flow rate. However, it was observed that the NF90 membrane retained more than 88% of the fluoride ions of a complex natural matrix (Kouinine), while NF270 can retain 79%. The fluoride content of the permeate (0.35 and 0.62 mg L–1) was well below the World Health Organization (WHO) threshold and Algerian standards. The water recovery rate (γ) has a strong impact on salt rejection and energy consumption. The best compromise was obtained by using NF90 with a quality of produced water that complies with the requirements of the WHO and the Algerian standards.