87-15: The Growth and Control of Nitrifying Bacteria in a Urea Plant Cooling

A urea plant cooling water system experienced problems with the growth of nitrifying bacteria which produced nitric acid from ammonia resulting in a sharp drop in the pH of the cooling water was found to drop from 7.5 to 6.1 over a period of 34 days. It was demonstrated in the laboratory that bacteria possessing the enzyme urease were present in the cooling water. A number of biocides were screened for their ability to inhibit growth of ammonia-oxidizing bacteria in both a mineral salts medium and the cooling water in a series of laboratory tests.