Method and System for Treating Wastewater

Abstract

Methods and systems for treating brine to produce distilled water and dried NaCl are disclosed. The brine enters a crystallization plant and is heated. Once heated, the brine is circulated to an evaporator. The evaporator increases the concentration of NaCl in the brine to a point about the super saturation level. Once above the super saturation level, NaCl crystals are formed. The larger crystals are circulated to a centrifuge for drying and the smaller crystals are recirculated through the evaporator for continued growth. The NaCl crystals are dried in the centrifuge.

What is claimed is: 
     
         1 . A system for treating wastewater comprising:
 a storage tank for storing wastewater having a total dissolved solids (“TDS”) concentration of at least 150,000 mg/L;   a pretreatment system configured to pretreat the wastewater to produce a pretreated wastewater suitable for evaporation/crystallization;   an evaporation/crystallization unit configured to produce, from the pretreated wastewater, a concentrated brine comprising calcium chloride, a salt slurry comprising sodium chloride, and a distilled water;   a concentrated brine treatment system comprising:
 a lithium recovery system configured to recover a lithium product from the concentrated brine; and 
 a second stage thermal mechanical evaporation/crystallization unit configured to produce a high-purity calcium chloride product from the concentrated brine; 
   a salt slurry treatment system configured to produce sodium chloride crystals from the salt slurry; and   a purification system configured to remove contaminants from the distilled water to produce a purified water therefrom.   
     
     
         2 . A system according to  claim 1 , wherein the second stage thermal mechanical evaporation/crystallization unit is further configured to generate solid crystals from the concentrated brine, the solid crystals comprising one or more of: barium, strontium and sodium. 
     
     
         3 . A system according to  claim 1 , wherein the second stage thermal mechanical evaporation/crystallization unit comprises a circulation type cooling crystallizer. 
     
     
         4 . A system according to  claim 1 , wherein the high-purity calcium chloride product comprises approximately 35% w/w calcium chloride. 
     
     
         5 . A system according to  claim 4 , wherein the concentrated brine comprises approximately 18% to 20% w/w calcium chloride. 
     
     
         6 . A system according to  claim 1 , further comprising a dryer configured to dry the high-purity calcium chloride product such that calcium chloride pills may be created therefrom. 
     
     
         7 . A system according to  claim 1 , wherein the lithium product comprises lithium carbonate. 
     
     
         8 . A system according to  claim 1 , wherein the salt slurry treatment system comprises a centrifuge. 
     
     
         9 . A system according to  claim 1 , further comprising a circulation line connected to the salt slurry treatment system and the evaporation/crystallization unit, the circulation line configured to route back to the evaporation/crystallization unit a centrate/filtrate produced by the salt slurry treatment system. 
     
     
         10 . A system according to  claim 9 , wherein the centrate/filtrate from the circulation line is mixed with the pretreated wastewater as the pretreated wastewater is fed to the evaporation/crystallization unit. 
     
     
         11 . A system according to  claim 1 , further comprising a washing system configured to wash the salt slurry with a portion of the distilled water. 
     
     
         12 . A system according to  claim 1 , wherein the sodium chloride crystals produced by the salt slurry treatment system comprise greater than 98% w/w sodium chloride. 
     
     
         13 . A system according to  claim 1 , further comprising a post-treatment system configured to convert the purified water from the purification system into a de-wasted water. 
     
     
         14 . A system according to  claim 13 , wherein the post-treatment system comprises at least one of an ion exchange system and a reverse osmosis system. 
     
     
         15 . A system according to  claim 13 , wherein the de-wasted water comprises a chemical oxygen demand (“COD”) of less than or equal to 15 mg/L, a methanol concentration of less than or equal to 3.5 mg/L, a nitrite-nitrate nitrogen concentration of less than or equal to 2 mg/L, a sodium concentration of less than or equal to 25 mg/L, a TDS concentration of less than or equal to 500 mg/L, and a total suspended solids (“TSS”) concentration of less than or equal to 45 mg/L. 
     
     
         16 . A system according to  claim 1 , wherein the evaporation/crystallization unit is a mechanical vapor recompression (“MVR”) crystallizer. 
     
     
         17 . A system according to  claim 1 , wherein the purification system comprises:
 an anoxic treatment system configured to denitrify nitrogen compounds in the distilled water under anaerobic conditions to produce a denitrified distilled water therefrom;   an aerobic treatment system configured to nitrify additional nitrogen compounds in the denitrified distilled water under aerobic conditions to produce a nitrified distilled water therefrom; and   a membrane separation system comprising a membrane, the membrane separation system configured to remove the contaminants from the nitrified distilled water to produce the purified water.   
     
     
         18 . A system according to  claim 17 , wherein:
 the second stage thermal mechanical evaporation/crystallization unit is further configured to produce a second distilled water; and   the anoxic treatment system is further configured to denitrify nitrogen compounds in the second distilled water.   
     
     
         19 . A system according to  claim 1 , wherein the pretreatment system comprises one or more of: a pH adjustment/chemical addition tank, a flocculation tank, a clarifier, and an equalization tank. 
     
     
         20 . A system according to  claim 1 , further comprising a methanol treatment system for removing methanol from the wastewater.