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1. WO2012066554 - A PHYSICO-CHEMICAL PROCESS FOR REMOVAL OF NITROGEN SPECIES FROM RECIRCULATED AQUACULTURE SYSTEMS

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[ EN ]

CLAIMS

1. A process for removing nitrogen species from a fresh water recirculated aquaculture system (RAS) so as to maintain the total ammonia nitrogen (TAN) concentration in the water in said system no higher than 50 mgN/L, the process comprising the steps of:

a. maintaining the pH of the water in the RAS below pH 7.5;

b. extracting a portion of the water from the RAS;

c. passing the portion of the water from the RAS through an ion-exchange resin so as to remove N¾+ ions;

d. regenerating the N¾+ enriched ion-exchange resin obtained in step (c) using a solution comprising high concentrations of exchange cation and chloride as the counter anion at concentrations higher than 50 g Cl/L;

e. converting NH4+ ions accumulated in the brine obtained during step (d) to gaseous nitrogen (N2) by electrochemically generating active chlorine species capable of ammonia-to-nitrogen gas oxidation; and

f. optionally, repeating steps (a) to (e) 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 the exchange cation in step (d) is selected from the group consisting of Ca2+, Mg2+, Na+, and K+.

4. The process of claim 3, wherein the exchange cation in step (d) is Ca2+.

5. The process of claim 4 further comprising removing phosphorus species by precipitation with calcium ions released into the water after the ion exchange step (c) when recycling the water back to the RAS or added to the RAS to induce precipitation of calcium-phosphate salts.

6. The process of claim 5, wherein the calcium-phosphate salts are separated from the RAS using an intrinsic solid filter or a separation unit.

7. The process of claim 1, wherein steps (a)-(e) are performed continuously.

8. The process of claim 1, wherein steps (a) - (c) are performed continuously and steps (d-e) are performed during low cost electricity hours.

9. The process of claim 1 , wherein the ion exchange resin is selected from a zeolite and a polymeric cation exchange resin.

10. The process of any one of claims 1 to 9, wherein the pH of the RAS is maintained below 7.5 by addition of acid.

1 1. The process of claim 10, wherein the acid is H2SO4.

12. The process of claim 10, further comprising adding a base during the electrolysis step.

13. The process of claim 12 wherein the base is selected from Ca(OH)2, CaO, NaOH and KOH.

14. The process of claim 10, further comprising stripping of CO2 wherein stripping of

CO2 comprises the addition of pure oxygen or aeration.

15. A process for removing ammonia from a saline water recirculated aquaculture system (RAS) so as to maintain the total ammonia nitrogen (TAN) concentration in the water in said system no higher than 50 mgN/L, the process comprising the steps of:

a. maintaining the pH of the water in the RAS below 7.5,

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 CI2 at concentrations required for attaining breakpoint chlorination; and

d. optionally, repeating steps (a) to (c) in a continuous manner, as needed.

16. The process of claim 15, further comprising the step of recycling at least some of the portion of the water obtained after step (c) back to the RAS.

17. The process of claim 15, wherein steps (b) and (c) are performed continuously. 18. The process of claim 15, wherein step (b) is performed continuously and step (c) is performed during low cost electricity hours.

19. The process of claim 15, wherein the solution comprising CI2 is generated in situ by electrooxidation of seawater, preferably during low cost electricity hours.

20. The process of any one of claims 15-19, wherein the pH of the RAS is maintained below 7.5 by addition of acid.

21. The process of claim 20, wherein the acid is H2SO4.

22. The process of claim 20, further comprising adding a base during the electrolysis step.

23. The process of claim 22, wherein the base is selected from Ca(OH)2, CaO, NaOH and KOH.

24. The process of claim 20, further comprising stripping of CO2 wherein stripping of CO2 comprises the addition of pure oxygen or aeration.