METHOD AND APPARATUS FOR HIGH WATER EFFICIENCY MEMBRANE FILTRATION TREATING HARD WATER

A method for the treatment of water using reverse osmosis (RO) membranes and nano-filtration membranes wherein the permeate of the membranes is fluid connected to a feed water source via a pressurized storage buffer tank as well as to the fluid connection to use, the method comprising the steps of supplying treated water through a sanitary fully pressurized buffer tank, and supplying waste water through a recirc loop which contains recirculated concentrate and storing treated water in the buffer tank with low total dissolved solids of less than 10% of feed water, low pH of less than pH 7, and of low total organic carbon of less than 25% of feed water ensuring sanitary storage. It further includes opening a waste valve in the recirc loop which purges recirculated concentrate in order to rapidly reduce the conductivity of the water in the recirc loop. It further includes the steps of operating the waste valve such that it maintains the conductivity of the recirculated waste water in the recirc loop within a pre selected range of values and opening the waste valve when a measured conductivity setpoint is exceeded, and closing the waste valve when a measured conductivity setpoint is met.