REDUCTION OF NITRATE AND NITRITE IN A CYCLICALLY OPERATED CONTINUOUS BIOLOGICAL REACTOR

Biological reduction of nitrate and nitrite was studied with a continu ously operated cyclic reactor. The medium was fed to the reactor durin g the first phase of the cycle, and the effluent was drawn from the re actor during the third phase of the cycle; reaction occurred throughou t the cycle. The process was described mathematically based on kinetic expressions revealed in an independent study. The model equations wer e subjected to detailed analysis with numerical codes based on the bif urcation theory for forced systems. The analysis has shown that in the operating parameter space there are extensive regions where the syste m can reach up to three different periodic states. The results of this analysis are shown in the form of two-dimensional operating diagrams. Numerical results have also shown that under certain operating condit ions nitrate can be completely eliminated, while nitrite remains pract ically untreated. An experimental unit was designed, constructed, and used in experiments with a strain of Pseudomonas denitrificans [Americ an Type Culture Collection (ATCC) 13867] under different operating con ditions. The experimental results confirmed the theoretical prediction s both qualitatively and quantitatively. Conditions under which comple te reduction of both nitrate and nitrite is achieved, were found and e xperimentally verified. The results of this study suggest a methodolog y for analysis and design of cyclically operated bioreactors employed in denitrification of wastewaters. (C) 1995 John Wiley and Sons, Inc.