Patent ID: 8206592

Claim:
A method of removing constituents from water having a pH below about 4.5, the method comprising: directing the water to a first pass reverse osmosis membrane; separating the water into a first permeate and a first concentrate using the first pass reverse osmosis membrane; raising a pH of the first permeate to between about 5.5 and 7.5; adding a chelating agent to the first permeate; directing the first permeate, having said chelating agent and said pH of between about 5.5 and 7.5, to a second pass reverse osmosis membrane; monitoring the second pass reverse osmosis membrane for an indication of an accumulation of solid material and increasing the chelating agent being added to the first permeate in response to the accumulation of solid material on the second pass reverse osmosis membrane; and separating the first permeate into a second permeate and a second concentrate using said second pass reverse osmosis membrane, thereby separating the constituents from the water.