Separation of nutrients from mine water by reverse osmosis for subsequent biological treatment

Nutrients such as ammonium and nitrate from different sources in mining and mineral processing are often discharged during mining operation to surrounding aquatic environment. The aim of this study was to evaluate the applicability of reverse osmosis (RO) to concentrate ammonium and nitrate from three different mine waters for subsequent removal of nutrients from the concentrate in bioreactors. In initial membrane selection tests, reverse osmosis retained the nutrients and the most suitable membrane was studied for subsequent concentrating tests. The volume reduction factor was up to 20. Ammonium and nitrate were enriched by reverse osmosis 3.6 and 5.7 times, respectively. Total salinity increased about 1.5 times in the RO-concentrate. Iron, copper, zinc, lead and cadmium, potential inhibitors of bacteria, were enriched to the brine of mine water 2. In general, the permeate pH decreased slightly during the reverse osmosis concentration. The produced RO-concentrate was suitable for biological removal of total nitrogen. Prevention of membrane fouling due to suspended solids requires prefiltration of feed prior to reverse osmosis. It was estimated that the total costs for reverse osmosis with prefiltration of feed is about 0.34 €/m3.