Ammonium Removal by Reverse Osmosis Membranes
A. Chrysovergi
W.G.J. van der Meer – Mentor
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Abstract
The insufficient prediction of ammonium permeability through RO membranes by calculation software in combination with the high ammonium concentrations in ground water result to the waste of money and time by the drinking water treatment companies. This research is focused on the parameters that affect ammonium permeability by reverse osmosis membranes in an attempt for some general conclusions to be derived and less or no testing experiments to be necessary in the future. During this research project three different reverse osmosis membranes were tested: XLE-440, Espa2max and LG BW 440 R. Artificial, water that composed in the pilot plant, was used during the experiments. Three parameters were investigated for their influence on ammonium removal: the ration between monovalent anions and monovalent cations (molar ratio), the ionic strength and the pH. In order to check the results of each parameter, three groups of experiments were done. In each group, one of the above parameters was changing while all the other characteristics of the feed water were kept the same. Results show that the higher the molar ratio, the higher the ammonium permeability of the 3 RO membranes. XLE has the highest ammonium permeability while LG and Espa2max show approximately similar results. Sodium removal was also checked and it was proved that LG has a strange behavior with ammonium. Regarding the ionic strength, XLE show higher ammonium permeabilities at higher ionic strengths while ammonium permeability of Espa2max and LG was not affected by the increasing ionic strength. Besides, comparison between raw water and artificial water took place. Despite the fact that the solutions had similar characteristics, the permeability of ammonium had a decreasing trend at higher ionic strength when raw water was used while with artificial water the changes in ionic strength did not affect the permeability. The strange behavior of raw water is considered to be caused due to the supersaturation of CaCO3. Finally, the pH, when it ranges between 4.9 and 8.3, seems to have no influence on ammonium permeability in case of Espa2max and LG, in contrast to XLE where the changes in ammonium permeability are significant. These changes do not depend on the fraction of ammonia which is found to be negligible until the pH of 8.2.