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In this paper, the feasibility of hybrid nanofiltration-reverse osmosis (NF-RO) process to remove hardness in brackish water at higher recovery rate and concentrate minimization is investigated. Two nanofiltration (NF) membranes are tested in the first stage for selecting the appropriate membrane on the basis of lower applied pressure and higher permeate flow. Then the evaluation of the performances of hybrid NF-RO system of each stage is studied in terms of recovery rate and Langelier saturation index (LSI) values to prevent the corrosion potential. The blending strategy is adopted with NF brine and reverse osmosis (RO) permeate in order to bring the RO permeate characteristics in accordance with drinking water standards and to minimize the volume of NF brine. Also, energy consumption performance of conventional nanofiltration (NF-NF) and NF-RO hybrid system in hardness removal is compared. The results show that the NF-RO hybrid system combined to blending strategy provides the simplest process but most energy efficient process compared to a single conventional NF-NF. Moreover, including NF upstream of RO is responsible of the increasing of the overall water recovery rate (95 %) and of the permeate quality with lower total dissolved solids (TDS). However, less water with lower salinity treated by RO increases significantly the recovery rate in RO stage up to 80 %. The portion rate of NF brine blending with RO permeate is equal to 32.45 %, corresponding to 240 L/h, which meet the water quality regulations for drinking water. Hybrid NF-RO system has a lower energy cost per m3 than NF-NF, it is around of 0.055 $/m3. At the same time, this procedure minimizes the fraction of brine disposal dumping to sewage, making it environmentally friendly.

Nitrate groundwater contamination is of major interest all over the world. This problem arises in agricultural regions across Morocco. An excess amount of nitrate causes a serious problem in urban water networks and human health. Because of these health risks, considerable attention has been paid to find effective treatment processes to reduce nitrate concentrations to safe levels. The World Health Organization has set an acceptable level for nitrate in drinking water at 50 mg/L. The aim of this study is to reduce the nitrate concentration from groundwater using two membrane processes: Electrodialysis (ED) and Nanofiltration (NF). Efficiencies of these two technologies are compared in respect to nitrate ions removal, cost process and final quality of water. The results of technologies show that, for electrodialysis standards level can be achieved for a demineralization rate of 15% and the physico-chemical quality of the produced water is satisfactory. For nanofiltration we obtain a nitrate removal of 90% but the produced water is very de-mineralized and must be remineralized.

Economic evaluation was carried out for a plant of fluoride removal by nanofiltration having a capacity of 2400 m 3 /d (100 m 3 /h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium. The design of this plant was carried out for the predetermined optimized conditions corresponding to a recovery rate of 84%, a fluoride rejection of 97.8% and a pressure pump of 10 bar. The capital cost was estimated to 748,003 € and the calculated operating cost to 0.212 €/m 3 . These costs were briefly compared to other ones.

An economic study was conducted to evaluate the costs of fluoride removal by electrodialysis on the basis of industrial and economic data. The investment and operating costs were estimated for an industrial plant with a capacity of 2200 m 3 /d water consumption for 50,000 per capita according to Moroccan standards for rural areas. The capital cost was estimated to be € 833,207 and the calculated operating cost to be € 0.154/m 3 .

Fluoride contamination of groundwater becomes more and more a worldwide preoccupation, especially in Morocco. With the decrease in water resources, especially underground water, and the frequent excess observed during these last decades, the dilution solution becomes unattainable in a short term. So to prevent this situation, the National Office of Potable Water (ONEP) has initiated studies in collaboration with Ibn Tofail University to investigate remedial options. The study on the comparison of the performances of electrodialysis and nanofiltration in the fluoride removal was started two years ago. In previous works, results of electrodialysis performances and preliminary results of nanofiltration performances have been presented. In this work, comparison of the performances of three commercial membranes in fluoride removal by nanofiltration in continuous mode was carried out. The pilot used (supplied by the French Company TIA, Techniques Industrielles Appliquees) is an industrial nanofiltration pilot plant having two modules equipped with various spiral commercial membranes with an area of 7.6 m2. Many configurations were tested: simple pass, double pass with one type of membranes and combination of two types of membranes and supplied batch configuration. The water parameters were followed as a function of the running conditions (time, pressure, fluoride content, etc.) in order to follow the behaviour of the membranes tested.

Studies have been conducted on a groundwater containing 850–1100 mg/l of total dissolved solids (TDS) and 80 mg/l of nitrate to remove nitrate by coupling electrodialysis and bioreactor. The performances of the pilot plant during the period of the tests (more than one year) were proved. The optimisation of recovery rates was carried out by the study of the influence on the water recoveries of the addition of acid and antiscalant to the brine stream. The moderated performances of the bioreactor were shown.

Nitrate content in surface water and especially in ground water have increased in Morocco and other areas of the world. Several processes including degradation processes and separation processes can remove nitrate from water. As separating processes, an electrodialysis operation was performed to remove nitrate from a ground water. Preliminary a brief reviews of the nitrate ground water pollution in Morocco was presented. A preselection of several commercial membranes was carried out to determine the best anionic exchange membrane for nitrate removal. The selected membrane transports anions in the following order: NO3− > Cl− > HCO3− > SO42−. The results show that a desired product water quality can easily be obtained by electrodialysis. The electrodialysis is a simple process to remove nitrate from ground water.

Studies have been conducted to reduce fluorine by electrodialysis from a brackish water containing 3000 ppm of total dissolved solids (TDS) and 3 ppm of fluoride. Two methods have been proposed and described to minimize the precipitation risks of the bivalent salts in the concentrate compartment. Measurements indicate that after electrodialysis, the targets concerning the quality of produced water were all achieved. The method without chemical pretreatment seems more simple to conduct and more adapted to environmental requirements than the method with pretreatment. From these studies it is demonstrated that electrodialysis is a reasonable process for removing fluoride from brackish water.