Physico-chemical process for removal of nitrogen species from recirculated aquaculture systems

Abstract

The present invention provides processes for removing nitrogen species from fresh water or high salinity water recirculated aquaculture systems. The processes are based on physico-chemical treatments which are performed at ambient temperatures and at low pH values thus keeping the total ammonia nitrogen concentrations below a value which is considered detrimental for the growth or survival rate of cultured fish/shrimp.

1 . A process for removing ammonia from a saline water recirculated aquaculture system (RAS) while maintaining a total ammonia nitrogen (TAN) concentration in the water in said system between 15 and 50 mgN/L, the process comprising the steps of:
 a. maintaining the pH of the water in the RAS below 7.5 by adding a strong acid,   b. extracting a portion of the water from the RAS,   c. oxidizing the ammonia in the portion of the water to nitrogen gas by electrochemical treatment or by breakpoint chlorination in the presence of a solution comprising Cl 2  at concentrations required for attaining breakpoint chlorination; and   d. optionally, repeating steps (a) to (c) in a continuous manner, as needed.   
     
     
         2 . The process of  claim 1 , further comprising the step of recycling at least some of the portion of the water obtained after step (c) back to the RAS. 
     
     
         3 . The process of  claim 1 , wherein steps (b) and (c) are performed continuously. 
     
     
         4 . The process of  claim 1 , wherein step (b) is performed continuously and step (c) is performed during low cost electricity hours. 
     
     
         5 . The process of  claim 1 , wherein the solution comprising Cl 2  is generated in situ by electrooxidation of seawater, preferably during low cost electricity hours. 
     
     
         6 . The process of  claim 1 , wherein the strong acid is H 2 SO 4  or HCl. 
     
     
         7 . The process of  claim 1 , further comprising adding a base during the electrolysis step. 
     
     
         8 . The process of  claim 7 , wherein the base is selected from Ca(OH) 2 , CaO, NaOH and KOH. 
     
     
         9 . The process of  claim 1 , further comprising stripping of CO 2  wherein stripping of CO 2  comprises the addition of pure oxygen or aeration. 
     
     
         10 . The process of  claim 1 , wherein the recirculated aquaculture system (RAS) has a total ammonia nitrogen (TAN) concentration at about 40 mgN/L.