PURPOSE: To efficiently remove ammoniac nitrogen by combining an ion exchange method with an electrolytic oxidation decomposition method to carry out adsorption of ammoniac nitrogen and regeneration of an adsorbent.

CONSTITUTION: Effluent water contg. ammoniac nitrogen enters ion exchanger- packed tower 1 from line 3 to allow NH+4 to be adsorbed on the exchanger, and it is discharged as H+-contg. treated water from the system through line 4. Next, hydrochloric acid is supplied to tower 1 from line 5 to form a desorbed soln. contg. NH4Cl and HCl as well as to regenerate the exchanger. The desorbed soln. is fed to cell 2 from line 6. In cell 2, nascent chlorine is generated by electrolysis, and the ammoniac nitrogen is decomposed into N2 and H2 gases, which are removed from the system through line 7. H+ is formed at the same time, and it is recycled to regenerate the exchanger.