Treating acidic water

Abstract

The invention relates to systems and methods of treating water by directing the water to a first reverse osmosis (RO) membrane; separating the water using the first RO membrane; adding a chelating agent to first permeate and/or raising the pH of the first permeate to between about 5.5 and 7.5 before a second RO membrane; and separating the first permeate into a second permeate and a second concentrate using the second RO membrane, thereby separating constituents from the water.

1 - 35 . (canceled) 
     
     
         36 . A method for treating wastewater having a pH level of about 0.5 to about 4.5 and including an undesirable level of one or more of ammonia, fluoride and phosphate species, the method comprising:
 dosing the wastewater having a pH level of about 0.5 to about 4.5 with a coagulant;   introducing the dosed water to at least one media filter to produce pre-treated water;   introducing the pre-treated water to a first reverse osmosis unit to produce a first permeate;   adjusting a pH level of the first permeate to within a range of about 5.5 to about 7.5;   introducing the first permeate at the adjusted pH level to a second reverse osmosis unit; and   discharging treated water having a pH level of about 6.5 to about 8.5 downstream of the second reverse osmosis unit, the treated water having a predetermined discharge level of one of more of the ammonia, fluoride and phosphate species.   
     
     
         37 . The method of  claim 36 , wherein the water to be treated has a pH level of below about 3.0. 
     
     
         38 . The method of  claim 36 , wherein producing pre-treated water further comprises introducing the dosed water to a cartridge filter downstream of the at least one media filter. 
     
     
         39 . The method of  claim 36 , further comprising introducing an antiscalant to the pre-treated water upstream of the first reverse osmosis unit. 
     
     
         40 . The method of  claim 36 , wherein the pre-treated water has a turbidity of less than about 2 NTU or a salt density index of less than about 4. 
     
     
         41 . The method of  claim 40 , further comprising introducing a concentrate stream from the second reverse osmosis unit to a feed side of the first reverse osmosis unit. 
     
     
         42 . The method of  claim 36 , wherein the coagulant is an organic coagulant. 
     
     
         43 . The method of  claim 36 , wherein the predetermined discharge level is less than about 8 ppm for fluoride, less than about 1 ppm for ammonia, and less than about 0.5 ppm for phosphorous. 
     
     
         44 . The method of  claim 36 , wherein the coagulant is dosed to produce a coagulant concentration of about 8 ppm to about 10 ppm in the dosed water. 
     
     
         45 . The method of  claim 36 , further comprising adding a chelating agent to the first permeate. 
     
     
         46 . The method of  claim 45 , wherein the chelating agent is added to produce a chelating agent concentration of from about 5 ppm to about 50 ppm. 
     
     
         47 . The method of  claim 45 , further comprising monitoring a pH level of the first permeate. 
     
     
         48 . The method of  claim 36 , further comprising introducing the treated water to an ion exchange system. 
     
     
         49 . A system for treating wastewater, the system comprising:
 a source of wastewater having a pH level of about 0.5 to about 4.5 and including an undesirable level of one or more of ammonia, fluoride and phosphate species;   a pre-treatment subsystem comprising a coagulant injection system and at least one media filter, the pre-treatment subsystem fluidly connected to the source of wastewater; and   a reverse osmosis separation subsystem fluidly connected downstream of the pre-treatment subsystem, the reverse osmosis separation subsystem comprising:
 first and second reverse osmosis units, and 
 a pH adjustor system positioned between the first and second reverse osmosis units, 
 the reverse osmosis separation subsystem configured to produce treated water having a pH level of about 6.5 to about 8.5 and a predetermined discharge level of at least one of the ammonia, fluoride and phosphate species. 
   
     
     
         50 . The system of  claim 49 , wherein the predetermined discharge level is less than about 8 ppm for fluoride, less than about 1 ppm for ammonia, and less than about 0.5 ppm for phosphorous. 
     
     
         51 . The system of  claim 49 , wherein the pre-treatment subsystem further comprises a cartridge filter. 
     
     
         52 . The system of  claim 49 , wherein the coagulant injection system is configured to produce a coagulant concentration of about 8 ppm to about 10 ppm. 
     
     
         53 . The system of  claim 49 , wherein the pH adjustor system is configured to adjust a pH level of permeate from the first reverse osmosis unit to within a range of about 5.5 to about 7.5. 
     
     
         54 . The system of  claim 49 , wherein a concentrate stream of the second reverse osmosis unit is fluidly connected to a feed side of the first reverse osmosis unit. 
     
     
         55 . The system of  claim 49 , further comprising an ion exchange system downstream of the reverse osmosis subsystem.