The present invention relates to methods for the removal of organic nitrogen, organic and inorganic contaminants from an aqueous liquid. More particularly, the present invention related to a process for the removal of organic and inorganic contaminants such as organic nitrogen and all other organic and inorganic contaminants from wastewater and ground water by conducting a two step method which includes the step of adding nitrosonium ion generator such as nitrous acid and nitrite in acidic media to remove organic nitrogen and followed by the step of adding hydrogen peroxide and activated carbon to remove all the other organic and inorganic contaminants.