Nanofiltration and reverse osmosis membrane for nitrate removal: performance study and economic evaluation

Abstract

Contamination of water with nitrates is a global problem that poses a serious threat to human health. In Morocco, a country characterized by limited water resources, groundwater accounts for almost 32% of total resources. However, 6% of these water resources are estimated to have nitrate levels greater than 50 mg / L, the level recommended by the world health organization for drinking water (WHO) and in some areas of high agricultural activity the nitrate content exceeds 250 mg / L. In the first part of this study, the efficiency of two commercial membranes, Reverse Osmosis and Nanofiltration membranes (Dow-FilmTec) is experimentally compared and assessed for nitrate removal by using real brackish water, containing 850-1100 mg/l of total dissolved solids (TDS) and 119-130 mg/l of nitrate. To accomplish this goal, the influence of operating conditions (pressure, recovery rate) on nitrate removal is discussed. The salt rejection from each membranes and the energy consumption are also calculated to choose the best membrane for nitrate removal and drinking water production. The pilot used in this study (supplied by the French company TIA) is an industrial pilot plant having two modules equipped with various spiral commercial membranes with an area of  7.6 m².  The second part of this study estimates the total cost of the produced water by the application of the two studied membranes (NF and RO) for a plant of nitrate removal having a capacity of production of 2400 m 3 /d (100 m 3 /h) corresponding to a water consumption for 50000 capita following the Moroccan standards in rural medium. The design of the plant was carried out based on the experimental results from the first part of the study corresponding to a recovery rate of 83% and 10 bars of pressure. Technically and economically, the work shows that in this case, the NF process appears more suitable than the RO for nitrate removal.