Multi-valent ion concentration using multi-stage nanofiltration

Abstract

A system and method for producing from saline source water a product containing an increased ratio of multi-valent ions to mono-valent ions, which includes multiple nanofiltration units arranged to selectively remove mono-valent ions from the water fed into each nanofiltration stage in the nanofiltration permeate stream while retaining multi-valent ions in the nanofiltration reject stream. The rate at which the increase in the multi-valent ion to mono-valent ion ratio is obtained may be enhanced by introduction of lower salinity water into the nanofiltration reject between stages, and by recirculating a portion of downstream nanofiltration reject flow into an upstream nanofiltration unit. The enhanced multi-valent ion product is suitable for multiple uses, including irrigation of plants and remineralization of desalinated water. The relative concentrations of the multi-valent ions in the product may be adjusted, for example by selection of nanofiltration membrane technologies which have higher or lower rejection for specific multi-valent ions.

1 .- 18 . (canceled) 
     
     
         19 . A multi-valent ion concentration system comprising:
 a plurality of nanofiltration (NF) units arranged in series, wherein each NF unit comprises one or more feed water inlet, a membrane configured to reject multi-valent ions, one or more NF unit permeate stream outlet configured to output a NF permeate stream, and one or more NF unit reject stream outlet configured to output a NF reject stream, and   piping configured to fluidically connect the plurality of NF units arranged in series,   wherein a NF reject stream outlet of an upstream NF unit is fluidically connected to a feed water inlet of a downstream NF unit by piping between the upstream NF unit and the downstream NF unit and wherein a NF reject stream outlet of the downstream NF unit is fluidically connected to a feed water inlet of a further downstream NF unit by piping between the downstream NF unit and the further downstream NF unit, and   wherein a first one of the plurality of NF units is configured to receive a saline source water at a feed water inlet, and wherein
 at least one of: a) piping between the upstream NF unit and the downstream NF unit and b) the downstream NF unit, and 
 at least one of: a) piping between the downstream NF unit and the further downstream NF unit and b) the further downstream NF unit, 
   are configured to individually receive a lower total dissolved salts (TDS) water stream that comprises a TDS content lower than a TDS content of the saline source water, to form a diluted NF reject stream at a volume ratio of 2:1 to 5:1 of the lower TDS water to the NF reject stream prior to contact with the membrane.   
     
     
         20 . The multi-valent ion concentration system of  claim 19 , wherein a last one of the plurality of NF units in the series is configured to output an NF reject stream comprising a ratio of multi-valent ions to mono-valent ions that is increased by at least 200% as compared to a ratio of multi-valent ions to mono-valent ions in the saline source water. 
     
     
         21 . The multi-valent ion concentration system of  claim 19 , wherein the system is configured to reduce a concentration of Na +  and Cl −  in a NF reject stream to at least ⅙ th  a concentration of Na +  and Cl −  in the saline source water. 
     
     
         22 . The multi-valent ion concentration system of  claim 19 , wherein the system is configured to produce a diluted NF reject stream comprising a concentration of CaSO 4  that is less than 250% of a CaSO 4  saturation concentration. 
     
     
         23 . The multi-valent ion concentration system of  claim 19 , further comprising recirculation piping configured to fluidically connect at least a portion of a NF reject stream from one or more NF units and provide the at least a portion of the NF reject stream to one or more feed water inlets of one or more NF units upstream in the series. 
     
     
         24 . The multi-valent ion concentration system of  claim 23 , wherein the recirculation piping is configured to fluidically connect a feed water inlet of the first one of the plurality of NF units in the series with a NF reject stream of a NF unit downstream in the series. 
     
     
         25 . The multi-valent ion concentration method of  claim 23 , wherein the recirculation piping is configured to fluidically connect at least a portion of the NF reject stream of a last NF unit of the series with a NF unit upstream in the series. 
     
     
         26 . The multi-valent ion concentration method of  claim 23 , wherein the recirculation piping is configured to fluidically connect at least a portion of the NF reject stream of a penultimate NF unit of the series with a NF unit upstream in the series. 
     
     
         27 . The multi-valent ion concentration system of  claim 19 , further comprising permeate recirculation piping configured to receive at least a portion of a NF permeate stream and provide the permeate stream to one or more feed water inlets of one or more NF units downstream in the series. 
     
     
         28 . The multi-valent ion concentration system of  claim 27 , wherein the permeate recirculation piping is configured to fluidically connect at least a portion of the NF permeate stream of the first one of the NF units in the series with a feed water inlet of a NF unit downstream in the series. 
     
     
         29 . The multi-valent ion concentration system of  claim 27 , wherein the permeate recirculation piping is configured to fluidically connect at least a portion of a NF permeate stream to a feed water inlet of a last one of the NF units in the series. 
     
     
         30 . The multi-valent ion concentration system of  claim 19 , comprising at least four NF units in the series. 
     
     
         31 . The multi-valent ion concentration system of  claim 19 , wherein the NF unit reject stream outlet from a last one of the NF units in the series is fluidically connected with a concentration unit configured to concentrate the NF reject stream of the last one of the NF units in the series.