Indigenous ureolytic bacteria that are suitable for the method of the invention are non-pathogenic bacteria which constitutively express urease so that urease is expressed regardless of ammonia or nitrogen compound concentration. Such organisms include the following bacteria: Sporosarcina pasteurii and Sporosarcina ureae. Other microorganisms suitable for the method of the invention are non-pathogenic bacteria in which urease is expressed only in the presence of urea.