Patent ID: 8758621

Claim:
A method of purifying impure water contaminated with a filterable impurity and a dissolved impurity, the method comprising: filtering the impure water in a primary microfiltration or ultrafiltration unit to remove the filterable impurity and produce impure filtered water contaminated with the dissolved impurity; directing the impure filtered water through a first fluid line fluidly connecting an impure filtered water outlet of the primary microfiltration or ultrafiltration unit to an inlet of a reverse osmosis unit; filtering the impure filtered water contaminated with the dissolved impurity in the reverse osmosis unit to produce a potable water stream and a residual reverse osmosis stream; directing the residual reverse osmosis stream into a second fluid line fluidly connecting a residual reverse osmosis stream outlet of the reverse osmosis unit to an inlet of a secondary microfiltration or ultrafiltration membrane filter; filtering the residual reverse osmosis stream by passing the stream through the secondary microfiltration or ultrafiltration membrane filter to produce a filtered saline solution; directing the filtered saline solution into a third fluid line fluidly connecting an outlet of the secondary microfiltration or ultrafiltration membrane filter to the impure filtered water outlet of the primary microfiltration or ultrafiltration unit; blocking flow of the filtered saline solution from the outlet of the secondary microfiltration or ultrafiltration membrane filter to the inlet of the reverse osmosis unit during backwashing of the primary microfiltration or ultrafiltration unit with the filtered saline solution by closing a valve in the first fluid line during backwashing of the primary microfiltration or ultrafiltration unit; and backwashing the primary microfiltration or ultrafiltration unit with the filtered saline solution.