Biological Wastewater Treatments for Metallurgical Industries

Variable contents of nitrite (NO2 -)- and nitrate (NO3 -)-nitrogen are present in wastewater of metallurgical cylinder-producing industries after treatment in a physical-chemical plant. Biological denitrification and oxidation treatments to reduce the oxidized nitrogen forms to within legal limits were evaluated. Wastewater streams were characterized and quantified in order to build a pilot plant, improve strategies to reduce environmental impact and increase water recycling. Initial sedimentation of raw mixed streams reduced iron and zinc contents by 87% and 71%, respectively. The resulting COD was refractory to be used in biological phases and an added carbon source was necessary to optimise the denitrification process. The biological treatment gave good results even without subsequent physical-chemical treatments, lowering NO2 - and NO3 - values to below the 0.6 and 20 mg L-1 limits respectively.