A NOVEL METHOD TO DETERMINE MAXIMAL NITRIFICATION RATES BY SEWAGE-SLUDGE AT A NONINHIBITORY NITRITE CONCENTRATION APPLIED TO DETERMINE MAXIMAL RATES AS A FUNCTION OF THE NITROGEN LOAD

A new method was developed to determine the maximal nitrification capa city of sewage sludge. Samples of sludge were taken from two domestic waste water treatment plants and were chemolithotrophically grown in r ecycling reactors. The experimental duration was typically in the orde r of hours. The maximal nitrification rates were estimated from the co ncentrations of nitrogen compounds in effluents. These rates could be easily determined by first order kinetics, since substrates were suppl ied in excess and growth was generally negligible. However, accumulati on of nitrite affected the ammonia oxidation rates. At 3-5 mM nitrite these rates were halved as compared to 0-1 mM. Since the accumulated n itrite is continuously diluted without loss of sludge, recycling react ors are especially suitable to study nitrification. Subsequently, this method was applied to investigate the development of the maximal nitr ification capacity as a function of the nitrogen load. For this purpos e, sludge was subcultured with synthetic waste water in recycling reac tors. Since heterotrophic ammonium assimilation was negligible, the fi nal capacities were proportional to the nitrogen load. However, these capacities were lower than expected. Since the numbers of protozoa had increased, predation might have reduced the nitrifying population.