Efficiency of calcium and magnesium removal by nanofiltration membrane from synthetic water under different operating conditions

ABSTRACT

There are various techniques for reduction or removal of hardness of water each with its own special advantages and disadvantages. Nanofiltration, process due to its simplicity and efficiently, has gained a great attention and is used for removal of various ions and organic matters. The aim of this study was to investigate the evaluation of efficiency of calcium and magnesium removal by a nanofiltration membrane from synthetic water under different operating conditions. This study was performed in laboratory scale using a commercial NF membrane similar to pilot scale. NF experiments were conducted using a calcium initial concentrations [280, 300, 320, 340 and 360 mg/L] and magnesium initial concentrations [60, 80, 100, 120 and 140 mg/L] with flow rate of 0.4 L/min [Qi] and 0.8 L/min [Q[2]]. To investigate the removal of calcium and magnesium as a function of co-existing anions and cations for NF membrane, sodium, potassium, calcium and magnesium ions [as cation] and chloride, nitrate and sulfate ions [as anion] were chosen. The results revealed that with the increase in initial calcium and magnesium concentration, the removal efficiency decreased, with increasing initial calcium concentration from 280 mg/L to 360 mg/L, the removal efficiency decreased from 69.08% to 61.25%, respectively and magnesium removal efficiency declined from 70.05% to 62.25% with increasing concentration from 60 mg/L to 140 mg/L, respectively. In addition, while flow rate varied from 0.4 L/min to 0.8 L/min, calcium and magnesium removal efficiency descended to approximately 5%. Most effectiveness due to anions and cations with calcium and magnesium were related to sulfate and divalent cations and chloride and sodium lowest effectiveness related to choride anion and sodium cation respectively. According to the results, nanofiltration process was applied as efficient and proper method for hardness [calcium and magnesium] removal from water