Effect of microbiological hydrolysis of urea on the nitrification process.

The aim of this study was to determine the causes of previously observed inhibition of stage II of nitrification in nitrifying activated sludge treating industrial wastewaters containing ammonium, urea and nitrates. Experiments made with both industrial wastewaters and synthetic medium containing equivalent concentrations of nitrogen compounds demonstrated that the factor limiting the activity of nitrobacteria is microbiological hydrolysis of urea, the causative agent probably being free ammonia released in the course of this hydrolysis.