High recovery integrated uf/ro system

Abstract

This specification describes membrane based filtration and softening systems and methods. A system has a microfiltration or ultrafiltration (MF/UF) membrane unit upstream of a nanofiltration or reverse osmosis (NF/RO) membrane unit, optionally with no intermediate tank. In some cases, the system and method may be used with feed water provided at municipal line pressure to the membranes. NF/RO permeate is collected in a tank and then pumped to a header. Treated water may be drawn from the header for use or recycled to the system, for example to backwash or flush one or both of the membrane units. In a combined process, NF/RO permeate flushes the feed side of the NF/RO unit and then backwashes the MF/UF unit. In another process, the MF/UF unit and NF/RO unit are filled with NF/RO permeate before being placed in a standby mode.

We claim: 
     
         1 . A water softening system adapted for use in a building with a municipal water supply at a line pressure comprising,
 a microfiltration or ultrafiltration (MF/UF) membrane unit connected to the municipal water supply;   a nanofiltration or reverse osmosis (NF/RO) membrane unit connected to a permeate outlet of the MF/UF unit;   a tank connected to a permeate outlet of the NF/RO unit;   a pump having an inlet connected to the tank; and,   a header connected to the outlet of the pump and adapted to supply water pressurized by the pump to the building.   
     
     
         2 . The system of  claim 1  wherein the permeate outlet of the MF/UF unit is connected to the NF/RO unit without an intervening tank. 
     
     
         3 . The system of  claim 1  wherein the header is connected to the inlet of the MF/UF unit. 
     
     
         4 . The system of  claim 1  wherein the header is connected to the inlet of the NF/RO unit. 
     
     
         5 . The system of  claim 1  wherein a retentate outlet of the NF/RO unit is connected to the permeate outlet of the MF/UF unit. 
     
     
         6 . The system of  claim 1  wherein the system can be configured to temporarily provide a flow path from the header through the feed side of the NF/RO unit and to the permeate side of the MF/UF unit. 
     
     
         7 . The system of  claim 1  wherein the system can be configured to temporarily provide a flow path from the header through the MF/UF unit and through the NF/RO unit.