Fluoride removal by nanofiltration: experimentation, modelling and prediction based on the surface response method
Fatima Zahra Addar, Soufiane El-Ghzizel, Mustapha Tahaikt, Mustapha Belfaquir, Mohamed Taky, Azzedine Elmidaoui
Abstract
ABSTRACT Fluoride ions contamination of groundwater becomes more and more a worldwide preoccupation, especially in Morocco. Indeed, they constitute a potential risk that can have adverse effects on human health (for instance, dental fluorosis, skeletal fluorosis, osteosarcoma, etc.) and effects on water resources. The aims of this study are to compare and evaluate the performance of three membranes in the removal of fluorides by nanofiltration (NF) on NaF doped groundwater. In the first part of this study, the influence of different operating conditions (initial fluoride concentration and transmembrane pressure) on the reduction of fluoride ions is investigated. Secondly, three separate predictive models are developed for optimization and modeling of the permeate concentration (mg L –1 ), fluoride rejection (%) and permeate flux (L m –2 h –1 ) in NF. Response surface methodology based on central composite design is employed to experimental design and a cumulative study of the effects of various operating parameters such as initial fluoride concentration and transmembrane pressure. Analysis of variance for developed quadratic models exhibits high significance and applicability. The initial fluoride concentration is the most significant factor that has a predominant effect on the permeate concentration for both TR60 and NF270 membranes. Indeed, both membranes exceed the standards, 7 mg L –1 for TR60 and 5.5 mg L –1 for NF270. But for NF90 the influence of the initial fluoride concentration is not significant. In addition, the model is analysed graphically for its predictive ability. Finally, under optimized conditions, fluoride rejection obtained are 79.69%, 72% and 98.75% for TR60, NF270 and NF90 respectively.