Application of Bio-Hydrolizer for the Treatment of Urea Bearing Wastewater

Abstract

Coal-based nitrogenous fertilizer industries in India produced mostly ammonia, urea, nitric acid, ammonium nitrate and ammonium bicarbonates using coal and fuel oil as raw materials. Coal is converted into carbon dioxide. Ammonia is manufacture from atmospheric nitrogen (air) and steam. Urea and ammonium bicarbonate are manufactured from carbon dioxide and ammonia. Ammonium nitrate is synthesized from nitric acid and ammonia. Therefore, the wastewater from fertilizer industry contains nitrogenous compounds viz, urea, ammonia, nitrate and bicarbonate. As urea cannot be oxidised by usual oxidation methods, microbiological hydrolysis of urea is necessary for removal of urea from wastewater. Biological stabilization of urea is a two staged process; (i) urea hydrolysis and (ii) ammonia stripping/nitrification-denitrification.

Hydrolysis of urea in the fertilizer industry is brought out by employing microbiological techniques, in which, ureolytic bacteria Bacillus pasteurii convert urea into ammonium carbonate as an intermediate product and then into ammonia and carbon dioxide as the end products. Ammonia thus produced is either stripped off by usual methods or after converting into nitrate using chemoautotraphic bacteria. Nitrosomonas sp., which oxidizes ammonia into nitrate and further by Nitrobacter sp. into nitrate. On dentirification, nitrate is finally converted into nitrogen gas by means of heterotrophic bacteria.

Based on microbiological treatment technique, an additional unit of urea bio-hydrolyser at existing effluent treatment plant to treat-urea and ammonia bearing wastewater was designed, installed and operated at a fertilizer industry. In presence of ureolytic bacteria and paddy straw, urea from fertilizer industry wastewater was hydrolysed into ammonia and carbon-dioxide. Paddy straw works as a carbon source for microorganism. On air stripping of ammonia, nitrogen free treated wastewater is obtained by routing ammonia stripped wastewater along with septic tank sewage from industry and township through series of ponds cultured with algae. The final treated effluent confirmed standards prescribed by regulatory agencies for discharge of effluent into inland surface water. Evaluation of a full-scale effluent treatment plant was undertaken and modifications were suggested to improve the quality of treated effluent. After incorporating the suggested modifications, post evaluation was carried out. The results of post evaluation studies are presented in this paper. The findings of low cost method of treating nitrogenous wastewater from fertilizer industry will be mostly useful in developing countries.