Microbiological aspects of ammonia oxidation of swine waste

Abstract

Ammonia-oxidizing bacteria were present at 102 MPN/mL (most probable number per millilitre) in swine waste, and they were outnumbered by a factor of 105 by the heterotrophs of the indigenous flora. To study these ammonia-oxidizing bacteria we attempted to isolate them in pure culture. We succeeded in increasing the concentration of these bacteria by successive transfers to an inorganic medium, but the heterotrophs were always dominant. To overcome this problem Nitrosomonas europaea ATCC 19718 was adapted to grow in stabilized swine waste. With this adapted strain it was shown that the number of cells inoculated into swine waste rapidly decreased both under the aerobic conditions used to oxidize the organic matter of swine waste and under the anaerobic conditions found in stored swine waste. Ammonia oxidation was delayed when adapted N. europaea was inoculated into a partially stabilized swine waste as compared with results in a completely stabilized waste. A biofilm of 107 MPN/cm2 of N. europaea was developed after 114 days of incubation at 29 °C on polyvinyl chloride discs covered with geotextile in a rotating biological contactor using an inorganic medium. This biofilm was gradually adapted to stabilized swine waste and the rate of disappearance of ammonia reached 270 mg∙L−1∙day−1 in the compartment of the reactor containing 2.5 L of waste. Key words: amonia-oxidizing bacteria, swine waste, ammonia oxidation, biofilm, most probable number.