Treatment of sodium nitrite-containing boiler wastewater

Abstract

An integrated process for treatment of wastewater from steam boiler clean operations, containing sodium nitrite and also usually heavy metal ions such as Cu, Fe, Pb, Cr, Cd, Zn and Ni, as well as suspended solids and sludge, to remove the nitrite, substantially reduce the amount of such metal ions and remove suspended solids and sludge in the treated wastewater. The process comprises adding sulfamic acid to the wastewater, particularly in about stoichiometric proportions with respect to sodium nitrite to form gaseous nitrogen. The reaction takes place at ambient temperature and atmospheric pressure. An alkali such as sodium hydroxide is added to the resulting solution in amount sufficient to raise the pH thereof to about 10, and precipitating the metal ions. The precipitates and suspended solids and sludge are removed from the resulting wastewater by settling and filtration, and the wastewater free of nitrite and of substantially reduced metal ion content and free of suspended solids as well as sludge, is in condition for discharge to sewers.

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