System and Method for Treatment of Acidic Wastewater

Abstract

A method for removing contaminants from an influent wastewater stream includes initially chemically adjusting a pH of the influent wastewater stream to less than about 3.5 or maintaining the pH of the influent stream at less than about 3.5. After initially adjusting or maintaining the pH of the influent wastewater stream, the wastewater is directed to a first reverse osmosis system and contaminants are removed from the wastewater. The wastewater is then directed to a second reverse osmosis where additional contaminants are removed from the wastewater. After the wastewater has been subjected to treatment in the first reverse osmosis system and prior to treatment in the second reverse osmosis system, the pH of the wastewater is adjusted upwardly.

1 . A method of removing contaminants from an influent wastewater stream, the method comprising:
 a. initially chemically adjusting a pH of the influent wastewater stream to less than about 3.5 or maintaining the pH of the influent stream at less than about 3.5;   b. after initially adjusting or maintaining the pH of the influent wastewater stream, directing the wastewater to a first reverse osmosis system and removing contaminants from the wastewater;   c. directing the wastewater from the first reverse osmosis system to a second reverse osmosis system and removing contaminants from the wastewater; and   d. adjusting the pH upwardly after the wastewater has been subjected to treatment in the first reverse osmosis system and prior to treatment in the second reverse osmosis system.   
     
     
         2 . The method of  claim 1  including adjusting the pH of the wastewater upwardly to at least about 6 or higher before the wastewater is directed through the second reverse osmosis system. 
     
     
         3 . The method of  claim 2  including maintaining the wastewater effluent from the first reverse osmosis system at about 6 or higher prior to the wastewater being directed through the second reverse osmosis system. 
     
     
         4 . The method of  claim 1  wherein the wastewater to be treated includes fluorides, silica, phosphates, calcium, and sulfates, and wherein after initially adjusting the pH of the influent wastewater stream to less than about 3.0, maintaining the pH of the influent wastewater to less than about 3.0 prior to entry into the first reverse osmosis system so as to condition the influent wastewater stream to favor the formation of complexing species of silica and fluoride and which further favor the formation of bisulfates, thereby reducing the scaling potential in the first reverse osmosis system due to silica, calcium fluoride, calcium sulfate, calcium phosphate or metals. 
     
     
         5 . The method of  claim 4  wherein adjusting the pH of the wastewater effluent from the first reverse osmosis system upwardly forms conditions in the wastewater that favor the formation of fluoride and silicate ions or converts any weakly ionized acids into salt form; and wherein at least 90% of the fluorides, silica, phosphates, calcium and sulfates are removed by the first and second osmosis systems. 
     
     
         6 . The method of  claim 5  wherein the wastewater being treated also includes ammonia, phosphates or metals and wherein initially adjusting the pH of the influent wastewater stream comprises controlling the pH of the influent wastewater stream to condition the wastewater to favor the formation of phosphoric acid and ammonium ions that reduce scaling potential in the first reverse osmosis system due to calcium phosphate and improves ammonia removal in the first reverse osmosis system; and wherein adjusting the pH upwardly of the wastewater effluent from the first reverse osmosis system conditions the wastewater to favor the formation of phosphate ions which contribute to the removal of phosphates in the second reverse osmosis system and further conditions the wastewater to generally increase the solubility of organics and thereby contributes to the removal of the organics in the second reverse osmosis system. 
     
     
         7 . A method of influent wastewater and removing fluorides and silica from the influent wastewater, the method comprising:
 a. inhibiting conditions in the influent wastewater that promote the formation of at least one of fluoride ions or silicate ions and promoting conditions in the wastewater that favor the formation of hydrofluorosilicic acid by initially chemically adjusting a pH of influent wastewater to less than about 3.5 and thereafter maintaining the pH of the influent wastewater to less than about 3.5;   b. removing fluorides and silica in the form of hydrofluorosilicic acid from the wastewater by directing the wastewater through a first reverse osmosis system;   c. after initially adjusting the pH of the influent wastewater to less than about 3.5 and after the wastewater has been treated in the first separation system, promoting conditions that favor the formation of fluoride and silicate ions by adjusting the pH of the wastewater upwardly to at least about 6 or higher; and   d. directing the wastewater, including the fluoride and silicate ions, through a second reverse osmosis system and removing from the wastewater the fluoride and silicate ions.   
     
     
         8 . A method of removing fluorides from influent wastewater comprising:
 a. directing the wastewater to a first reverse osmosis system and removing fluorides from the wastewater;   b. prior to the wastewater entering the first reverse osmosis system, chemically adjusting or maintaining the pH of the wastewater to less than about 3.5;   c. directing the wastewater from the first reverse osmosis system to a second reverse osmosis system and removing fluorides from the wastewater;   d. adjusting the pH of the wastewater upwardly after the wastewater has been subjected to treatment in the first reverse osmosis system and prior to treatment in the second reverse osmosis system; and   e. removing at least 90% of the fluorides from the wastewater with the first and second reverse osmosis systems.   
     
     
         9 . The method of  claim 8  wherein the influent wastewater also includes calcium, sulfates, phosphates and silica, and wherein at least 90% of the calcium, sulfates, phosphates and silica are removed by the first and second reverse osmosis systems. 
     
     
         10 . The method of  claim 8  including filtering the wastewater prior to the wastewater being directed to the first reverse osmosis system. 
     
     
         11 . The method of  claim 8  wherein the influent wastewater includes an initial pH and wherein the method includes maintaining the pH of the wastewater at or below its initial pH at least until the wastewater has been treated by the first reverse osmosis system. 
     
     
         12 . The method of  claim 8  including adjusting the pH of the wastewater upwardly to at least about 6 or higher before the wastewater is directed through the second reverse osmosis system. 
     
     
         13 . The method of  claim 8  wherein the wastewater includes silica, phosphates, calcium and sulfates and wherein the method includes conditioning the wastewater prior to entry into the first reverse osmosis system to favor the formation of complexing species of silica and fluoride and which further favor the formation of bisulfates, thereby reducing the scaling potential in the first reverse osmosis system due to silica, calcium fluoride, calcium carbonate, calcium sulfate, calcium phosphates and metal scales. 
     
     
         14 . The method of  claim 13  wherein adjusting the pH of the wastewater effluent from the first reverse osmosis system upwardly conditions the wastewater to favor the formation of fluoride and silicate ions or converts any weakly ionized acids into salt form. 
     
     
         15 . The method of  claim 11  wherein the wastewater includes calcium, ammonia and phosphates or metals, and wherein the method includes conditioning the wastewater prior to entry into the first reverse osmosis system to favor the formation of phosphoric acid and ammonium ions and that reduce scaling potential in the first reverse osmosis system due to calcium phosphate and improves ammonia removal in the first reverse osmosis system; and conditioning the wastewater effluent from the first reverse osmosis system to favor the formation of phosphate ions which contribute to the removal of phosphates in the second reverse osmosis system and further conditions the wastewater to generally increase the solubility of organics and thereby contributes to the removal of the organics in the second reverse osmosis system. 
     
     
         16 . The method of  claim 8  wherein the wastewater includes calcium, phosphates, and sulfates, and the method further comprises conditioning the wastewater to reduce the potential for the formation of calcium fluoride, calcium phosphate or calcium carbonate and calcium sulfate. 
     
     
         17 . The method of  claim 16  wherein adjusting the pH of the wastewater effluent from the first reverse osmosis system upwardly causes fluorides and silica in the wastewater to assume the form of fluoride and silicate ions which are removed from the wastewater in the second reverse osmosis system. 
     
     
         18 . The method of  claim 16  wherein the wastewater also includes sulfates, phosphates and ammonia, and wherein prior to entering the first reverse osmosis system the wastewater is conditioned to favor the formation of bisulfates, phosphoric acid and ammonium ions, and wherein adjusting the pH of the wastewater effluent from the first reverse osmosis system upwardly conditions the wastewater to favor the formation of phosphate ions and generally increases the ionization of some organics which contribute to the removal of phosphates, organics, and ammonia from the wastewater. 
     
     
         19 . The method of  claim 8  wherein the wastewater originates from an influent wastewater stream having a pH of 3.5 or less, and wherein the wastewater is subject to one or more pretreatments upstream of the first reverse osmosis system, and wherein the method includes maintaining the pH of the wastewater at 3.5 or below as the wastewater passes through the one or more pretreatments and prior to the wastewater entering the first reverse osmosis system. 
     
     
         20 . The method of  claim 19  wherein the pH of the wastewater is maintained at 3.5 or below until the wastewater exits the first reverse osmosis system.