Disclosed are: a catalyst which can exhibit an excellent catalytic activity and excellent durability for a long period in the
wet oxidation treatment of waste water; a
wet oxidation treatment method for waste water using the catalyst; and a novel method for treating waste water containing a nitrogenated compound, in which a catalyst to be used has a lower catalytic cost, the waste water containing the nitrogenated compound can be treated at high purification performance, and the high purification performance can be maintained. The catalyst for use in the treatment of waste water comprises an
oxide of at least one element selected from the group consisting of iron,
titanium,
silicon, aluminum,
zirconium and
cerium as a component (A) and at least one element selected from the group consisting of silver, gold,
platinum,
palladium,
rhodium,
ruthenium and
iridium as a component (B), wherein at least 70
mass% of the component (B) is present in a region positioned within 1000 [mu]m from the outer surface of the component (A) (i.e., the
oxide), the component (B) has an average particle
diameter of 0.5 to 20 nm, and the
solid acid content in the component (A) (i.e., the
oxide) is 0.20 mmol / g or more. The waste
water treatment method uses a catalyst (a pre-catalyst) which is placed on an upstream side of the direction of the flow of the waste water and can convert the nitrogenated compound contained in the waste water into
ammoniacal nitrogen in the presence of an
oxidizing agent at a temperature of not lower than 100 DEG C and lower than 370 DEG C under a pressure at which the waste water can remain in a
liquid state and a downstream-side catalyst (a post-catalyst) which is placed downstream of the direction of the flow of the waste water and can treat the waste water containing
ammoniacal nitrogen.