Removal of selenocyanate from refinery sour water stripper wastewater

Abstract

Systems and methods for removing heavy metals such as selenium from wastewater with zero valent iron media. Air may be introduced directly into a reaction zone of a fluidized bed reactor filled with the media to catalyze treatment.

What is claimed is: 
     
         1 . A system for the removal of selenium from sour water stripper wastewater, the system comprising:
 a fluidized bed reactor including:
 a reactor body; 
 a mixer disposed in a lower portion of the reactor body; 
 a reaction zone defined about the mixer; and 
 an air supply configured to inject air directly into the reaction zone. 
   
     
     
         2 . The system of  claim 1 , wherein the reaction zone is located in a lower portion of the fluidized bed reactor. 
     
     
         3 . The system of  claim 2 , wherein the fluidized bed reactor further comprises a chimney disposed within the reactor body, and the reaction zone is defined below the chimney. 
     
     
         4 . The system of  claim 1 , comprising a plurality of fluidized bed reactors fluidly connected in series. 
     
     
         5 . The system of  claim 1 , wherein the fluidized bed reactor includes zero-valent iron media. 
     
     
         6 . The system of  claim 5 , wherein the zero-valent iron media is coated with an iron oxide. 
     
     
         7 . The system of  claim 6 , wherein the zero-valent iron media is coated with magnetite. 
     
     
         8 . The system of  claim 1 , further comprising a source of Fe 2+  ions in fluid communication with fluidized bed reactor. 
     
     
         9 . The system of  claim 1 , further comprising a source of a pH adjustment agent in fluid communication with fluidized bed reactor. 
     
     
         10 . The system of  claim 1 , further comprising an aeration basin in fluid communication downstream of the fluidized bed reactor. 
     
     
         11 . The system of  claim 10 , further comprising a source of pH adjuster in fluid communication with the aeration basin. 
     
     
         12 . The system of  claim 10 , further comprising a solids/liquid separator in fluid communication downstream of the aeration basin. 
     
     
         13 . The system of  claim 12 , wherein the solids/liquid separator is configured to produce a supernatant and settled sludge and to direct at least a portion of the settled sludge into the fluidized bed reactor. 
     
     
         14 . The system of  claim 1 , further comprising an equalization vessel in fluid communication upstream of the fluidized bed reactor. 
     
     
         15 . The system of  claim 14 , wherein the equalization vessel includes a sour water stripper wastewater inlet in fluid communication with a source of sour water stripper wastewater. 
     
     
         16 . The system of  claim 14 , further comprising a source of pH adjuster in fluid communication with the equalization vessel. 
     
     
         17 . The system of  claim 14 , further comprising a source of oxidizer in fluid communication with the equalization vessel. 
     
     
         18 . The system of  claim 1 , further comprising an oxidation vessel in fluid communication downstream of the fluidized bed reactor. 
     
     
         19 . The system of  claim 1 , further comprising a flocculation vessel in fluid communication downstream of the fluidized bed reactor. 
     
     
         20 . The system of  claim 1 , wherein the air supply is configured to inject the air into the reaction zone above the mixer. 
     
     
         21 . The system of  claim 1 , wherein the air supply is configured to inject the air into the reaction zone below the mixer. 
     
     
         22 . The system of  claim 1 , wherein the air supply is configured to inject the air into the reaction zone at substantially a same depth as the mixer. 
     
     
         23 . A method of removing heavy metals from wastewater, the method comprising:
 directing the wastewater into a fluidized bed reactor including a zero-valent iron media;   mechanically mixing the wastewater in the fluidized bed reactor with a mixer to contact contaminants in the wastewater with the zero-valent iron media; and   injecting an oxygen containing gas into a reaction zone defined about the mixer.   
     
     
         24 . The method of  claim 23 , wherein injecting the oxygen containing gas into the reaction zone includes injecting the oxygen containing gas into a lower portion of the fluidized bed reactor. 
     
     
         25 . The method of  claim 24 , wherein the wastewater includes selenium and the method includes removing approximately 75% or more of the selenium from the wastewater in a single pass through a system including the fluidized bed reactor. 
     
     
         26 . The method of  claim 25 , wherein the method includes removing approximately 99% or more of the selenium from the wastewater in a single pass through a system including the fluidized bed reactor. 
     
     
         27 . The method of  claim 23 , wherein the wastewater includes selenium and the method includes reducing a concentration of selenium in the wastewater to below 50 ppb in a single pass through a system including the fluidized bed reactor. 
     
     
         28 . The method of  claim 23 , wherein the wastewater includes selenium and the method includes reducing a concentration of selenium in the wastewater from above 400 ppb to below 5 ppb in a single pass through a system including the fluidized bed reactor. 
     
     
         29 . The method of  claim 23 , wherein directing the wastewater into the fluidized bed reactor including the zero valent iron media includes directing the wastewater into a fluidized bed reactor including zero valent iron media coated with magnetite. 
     
     
         30 . The method of  claim 29 , further comprising adding a source of Fe 2+  ions into the fluidized bed reactor. 
     
     
         31 . The method of  claim 30 , wherein the source of Fe 2+  ions is added to the fluidized bed reactor at a flow rate that maintains the concentration of Fe 2+  ions in the wastewater coming into contact with the zero-valent iron media in a range of between about 5 mg/L and about 50 mg/L. 
     
     
         32 . The method of  claim 30 , wherein the source of Fe 2+  ions is added to the fluidized bed reactor at a flow rate that maintains the concentration of Fe 2+  ions in the wastewater coming into contact with the zero-valent iron media in a range of between about 0 mg/L and about 5 mg/L. 
     
     
         33 . The method of  claim 23 , wherein a pH adjustment agent is added to the fluidized bed reactor at a flow rate that maintains a pH of wastewater in the fluidized bed reactor between about 6.0 and about 8.0. 
     
     
         34 . The method of  claim 23 , further comprising contacting the wastewater with an oxidizer prior to introducing the wastewater into the fluidized bed reactor. 
     
     
         35 . A method of increasing the selenium removal efficiency of a fluidized bed reactor including a zero valent iron media, the method comprising relocating a site of injection of an oxygen containing gas from a location proximate a top of the fluidized bed reactor to a location in a reaction zone defined about a mixer in a lower portion of the fluidized bed reactor.