Concentration of ammonium and nitrate from mine water by reverse osmosis and nanofiltration

The mining industry uses large amounts of explosives and a part of them remains undetonated. Since most commercial blasting agents contain ammonium nitrate, there is a direct relationship between explosives use and the ammonium and nitrate levels in mine effluents. Water contamination with nitrogenous compounds can promote corrosion and eutrophication in receiving water bodies and be detrimental to fish. Four commercial thin film composite reverse osmosis (RO) membranes and one nanofiltration (NF) membrane were studied in retaining ammonium and nitrate form mine water. The aim of the filtrations was to produce clean permeate and a concentrate suitable for downstream treatment in nitrifying–denitrifying bioreactors. Selection of membranes and operational pressure was performed with a plate and frame module. The membranes were then tested for continuous concentration with different volumetric reduction factors. RO yielded good quality permeate and concentrate for bioreactor treatment. NF showed poor separation performance.With the selected RO-membrane, the retention of ammonium and nitrate was more than 82% and 90%, respectively, during the concentration. As membrane fouling can be a limiting factor a prefiltration step is recommended before the RO unit.