Françoise Persin

Fluoride removal from diluted solutions by Donnan dialysis with anion-exchange membranes

Too many or too few fluoride ions in drinking water are harmful to the consumers health. The acceptable fluoride concentration is generally in the range of 0.5 to 1.5 mg.L−1. In the present study, Donnan dialysis (DD) with an anion-exchange membrane (AEM) was applied for the defluoridation of diluted NaF solutions. The initial concentration of the feed solution was maintained at 10−3 mol.L−1, corresponding to a 19 mg.L−1 fluoride concentration. Five kinds of AEMs (DSV, AFX, AFN, AMX, ACS) were tested. First, membrane properties were studied at equilibrium. The values of the exchange capacity of the membranes in Cl− and F− form, water content, selectivity coefficient for the Cl−F− exchange, diffusion coefficient of Cl− and F− ions in the membrane, were determined for each membrane. DD experiments, performed using a laboratory cell, showed that the DSV membrane is the most effective AEM, despite its electrolyte leakage. Subsequently, a pre-industrial pilot with a total membrane area of 1760 cm2 was used to study the different physico-chemical and hydrodynamic parameters of the process. As the driving ion, the chloride ion is more efficient than the sulfate ion. At flow rates lower than 0.6 L.h−1, the fluoride concentration remains lower than the permitted values despite the presence of others anions generally present in ground water such as chloride, sulfate and bicarbonate ions.

Defluoridation of groundwater by a hybrid process combining adsorption and Donnan dialysis

According to World Health Organization norms, the upper limit of fluoride concentration in drinking water was 1.5 mg 1−1. The purpose of this study is to apply a hybrid process that combines the adsorption on conventional solid adsorbents such as aluminum and zirconium oxide along with a specific Donnan dialysis (DD) procedure to treat groundwater with an excessive fluoride concentration of 4 mg 1−1 resulting from phosphate mining in Morocco. The DD pre-industrial pilot was equipped with ACS anion-exchange membranes (Tokuyama Co.) having a total area of 0.176 m2. The DD process was studied under two circulating modes of the receiver solution, single pass and batch, whereas the feed solution flowed continuously as a single pass. To maintain the fluoride concentration below the acceptable values at the outlet of the feed compartment, the extracted fluoride ions are adsorbed by Al2O3 and ZrO2, which were added in the receiver solution. The mineralization of the treated groundwater was not modified. The cation composition remained unchanged, whereas anions, except chloride, were partially eliminated and substituted by chloride ions, giving a fluoride concentration below the acceptable values.

Comparison of different methods for deacidification of clarified passion fruit juice

Abstract The high acidity of passion fruit limits its addition in food preparation. In order to easy the uses of this juice to formulate high aroma and flavour products, its citric acid content must be decreased. Various methods such as calcium salts precipitation, ion-exchange resins and electrodialysis with homopolar and bipolar membranes were investigated to increase the pH of a clarified passion fruit juice from 2.9 to 4.0. Each deacidification process was compared in terms of characteristics of deacidified juices such as concentration of inorganic and organic ions, colour and flavour. The deacidification by precipitation using CaCO 3 was not recommended because of CO 2 release. The ion-exchange process gave a poor quality juice in terms of organoleptic characteristics. Electrodialysis with homopolar membranes induced an increase in the sodium concentration. Precipitation with Ca(OH) 2 and electrodialysis with bipolar membrane were the most suitable processes in terms of sensorial properties of juices treated. The physico-chemical analyses showed an increase in the calcium concentration with the use of Ca(OH) 2 that could cause some precipitation problems in the final product. Inorganic anions were eliminated together with citrate by using electrodialysis and resins. Nevertheless, electrodialysis with bipolar membranes presented great advantages: it was a continuous process without reagent addition moreover allowing the production of a valuable solution of citric acid.

Denitrification of drinking water by the association of an electrodialysis process and a membrane bioreactor: feasibility and application

Abstract A hybrid process combining electrodialysis and a membrane bioreactor was investigated to treat ground waters with excessive nitrate concentrations. Electrodialysis (ED) allowed the nitrate separation producing, on one hand, partially demineralized waters whose ion concentrations were in agreement with the norm, and on the other hand, brines that were treated by a membrane bioreactor. Experiments performed at laboratory scale with synthetic solutions and pre-industrial scale to treat a ground water contaminated by nitrates showed high efficiency of the hybrid process. The nitrate concentration of the treated water remained below the acceptable value (50 mg/l−1) and even below the recommended value (25 mg/l−1) for drinking water. Moreover, the ED treatment induced a softening of the treated water. The biological denitrification allowed the almost total removal of nitrates (99%) with kinetics close to 0.3kgN NO3/kg MVS/d and a limited sludge production of 0.5 gV.S.S./gN NO3.

Use of a membrane bioreactor for denitrification of brine from an electrodialysis process

Electrodialysis (ED) is an efficient process for the treatment of drinking water with high nitrate concentration. However it achieves only a transfer of pollution by producing concentrated brines. This study demonstrated the feasibility of ED brine denitrification in a membrane bioreactor (MBR). The results showed the high efficiency of the MBR despite the drastic conditions of nitrate concentration, pH and salinity of the ED concentrates. The denitrification kinetics close to 0.01 mgNO 3 – -N mgVSS –1 h –1 were in agreement with the literature values obtained with usual conditions. Next, the efficiency and performance of the hybrid process to treat ground water contaminated by nitrate was demonstrated in situ at Rodilhan (France). After ED treatment, the nitrate concentration of the treated water remained below the acceptable value (50 mg l –1 ) and a softening of the treated water was obtained. The membrane bioreactor allowed the almost total destruction of ED concentrate nitrate (99 %) with kinetics close to 0.3 kgNO 3 – -N kgVSS –1 d –1 and a sludge production of 0.5 gVSS gNO 3 – .

Development of electrodialysis with bipolar membrane for the treatment of concentrated nitrate effluents

Abstract The reprocessing of nuclear combustibles results in the generation of concentrated liquid wastes. An important effluent produced is ammonium nitrate solution. The treatment of this solution by electrodialysis using bipolar membranes is complicated by the leakage of ammonia through the membranes. The treatment involves a two-step process: ammonia stripping after neutralization of NH4NO3 by NaOH (or KOH) followed by a regeneration of NaOH (or KOH) by electrodialysis with a bipolar membrane, which also produces HNO3. This process allows the regeneration of nitric acid and base which can be recycled in the industrial process and is an example of a clean technology with zero effluent production (zero nitrate rejection).