Electrochemical treatment of ammonia in waste-water

Abstract

In a sewage treatment plant, dissolved ammonium is extracted from the waste-water stream, and is transferred to a body of secondary water. The secondary water is passed through an electrolysis station, where the ammonium is transformed to nitrogen gas. The capture and transfer can be done by ion-exchange, the electrolysis then being done on the regenerant water. Or the capture and transfer can be done by first transforming the dissolved ammonium to ammonia gas by raising the pH of the waste-water, then passing the ammonia gas through acidic secondary-water, in which the ammonia dissolves, the electrolysis then being done on the acid-water. The electrolysed, ammonium-diminished, secondary-water can be re-used in further capture/transfer episodes. The secondary-water does not mix with the waste-water stream.

1 . Apparatus for diminishing the concentration of ammonium in waste-water, and for disposing of the ammonium as nitrogen gas, wherein: 
 the apparatus includes an ammonium-extraction-and-transfer station, which:—
 includes a waste-water entry port, for receiving a stream of the waste-water to be treated;  
 is operable to extract ammonium out of solution from the waste-water stream;  
 includes a treated-water discharge port, for discharging the waste-water stream, now with its dissolved ammonium content reduced, from the apparatus;  
   the apparatus includes a body of secondary-water;    the apparatus includes a secondary-water circuit, comprising water-containment components, which contain the body of secondary-water;    the ammonium-extraction-and-transfer station is operable to transfer the ammonium extracted from the stream of waste-water into solution in the body of secondary water;    the apparatus includes an electrolysis station;    the secondary-water circuit is operable to convey the secondary-water between the ammonium-transfer station and the electrolysis station;    the electrolysis station includes an electrolytic cell, which is operable upon being supplied with electrical energy:—
 to electrolyse the secondary-water, and to oxidise the ammonium dissolved therein;  
 to thermodynamically favour the transformation of the nitrogen component thereof to nitrogen gas;  
   the apparatus includes a nitrogen-discharge port, for discharging the resulting nitrogen gas from the electrolysis station.    
     
     
         2 . Apparatus of  claim 1 , wherein the stream of waste-water being treated passes through the apparatus, and is discharged, without itself being subjected to electrolysis.  
     
     
         3 . Apparatus of  claim 1 , wherein the stream of waste-water being treated passes through the apparatus, and is discharged, without touching the body of secondary-water.  
     
     
         4 . Apparatus of  claim 1 , wherein the apparatus is operable to recirculate the body of secondary-water through and between the ammonium-extraction-and-transfer station and the electrolysis station.  
     
     
         5 . Apparatus of  claim 4 , wherein the apparatus is operable to perform electrolysis on the body of secondary-water in the electrolysis station, at the same time.  
     
     
         6 . Apparatus of  claim 5 , wherein the apparatus is operable to perform the electrolysis periodically, while the body of secondary-water is recirculating through the ammonium-extraction-and-transfer station.  
     
     
         7 . Apparatus of  claim 1 , wherein the ammonium-extraction-and-transfer station comprises an ion-exchange station, and wherein: 
 the ammonium-extraction-and-transfer station includes a sorbent-container, in which is contained a sorbent-body, which is effective to sorb ammonium from water passing therethrough;    the secondary-water comprises regenerant-water, being water that contains, in solution, a regenerant-substance, which is of such nature, and of such concentration, as to have an ion-exchange relationship with respect to ammonium ions sorbed onto the sorbent-body;    the ammonium-extraction-and-transfer station includes connecting conduits and operable flow valves;    the valves are operable in a sorption-mode, and in a regenerant-mode;    in the sorption-mode, the valves are arranged so that waste-water passes from the waste-water entry port, through the sorbent-container, and out of the treated-water discharge port;    in the regenerant-mode, the valves are included in the secondary-water circuit, in which the regenerant-water, having passed through the sorbent-container, passes then through the electrolytic cell.    
     
     
         8 . Apparatus of  claim 7 , wherein the secondary-water circuit is operable to recirculate the regenerant-water through the sorbent-container and the electrolytic cell.  
     
     
         9 . Apparatus of  claim 1 , wherein:—
 the body of secondary-water comprises a body of acid-water;    the ammonium-extraction-and-transfer station comprises an alkali-acid station, including:—
 a means for elevating the pH of ammonium-laden waste-water entering the waste-water entry port to at least ten;  
 an alkali-station, comprising a waste-water conduit containing the alkaline waste-water and a gas conduit, and the alkali-station is so structured that ammonia gas emanating from the alkaline waste-water in the waste-water conduit is captured and carried away in the gas conduit;  
 a means for maintaining the pH of the acid-water at no more than four;  
 an acid-station, which includes the gas conduit and an acid-water conduit containing the acid-water, and the acid-station is so structured that ammonia gas contained in the gas conduit is taken into solution in the acid-water in the acid-water conduit;  
   and the secondary-water circuit includes the acid-water conduit, in which the acid-water, having passed through the acid-station, passes then through the electrolytic cell.    
     
     
         10 . Apparatus of  claim 9 , wherein the secondary-water circuit is operable to recirculate the acid-water through the acid-station and the electrolytic cell.  
     
     
         11 . Water treatment plant, for treating both a lower-flowrate stream of higher-concentration waste-water and a higher-flowrate stream of lower-concentration waste-water, wherein: 
 the plant is operable to pass the lower-concentration stream through the ion-exchange apparatus of  claim 7 , and the higher-concentration stream through the alkali-acid apparatus of  claim 9;     and the plant is operable to mix the treated waste-water effluent from the alkali-acid apparatus with the waste-water stream entering and passing through the ion-exchange apparatus.    
     
     
         12 . Procedure for diminishing the concentration of ammonium in waste-water, and for disposing of the ammonium as nitrogen gas, including: 
 passing a stream of the waste-water to be treated in through a waste-water entry port, through an ammonium-extraction-and-transfer station, and out through a treated-water discharge port;    operating the ammonium-extraction-and-transfer station to extract ammonium out of solution from the waste-water stream;    passing a body of secondary-water around a secondary-water circuit, comprising water-containment components, which contain the body of secondary-water;    operating the ammonium-extraction-and-transfer station to transfer the ammonium extracted from the stream of waste-water into solution in the body of secondary water;    passing the secondary-water circuit between the ammonium-transfer station and an electrolysis station, containing an electrolytic cell;    supplying electrical energy to the electrolysis station and operating same to electrolyse the secondary-water, and to oxidise the ammonium dissolved therein, and to thermodynamically favour the transformation of the nitrogen component thereof to nitrogen gas;    discharging the resulting nitrogen gas from the electrolysis station.