COMPETITION IN DENITRIFICATION SYSTEMS AFFECTING REDUCTION RATE AND ACCUMULATION OF NITRITE

During the process of denitrification of wastewater nitrite has often been observed to accumulate, most probably because of the nitrite reduction rate falling behind the rate of nitrate reduction. The hypothesis to be investigated in this study was that microbial communities could be enriched for facultative anaerobes capable of reducing nitrate, but only to nitrite. A mathematical model was developed, and experiments were conducted to study results of enhanced proliferation of facultative anaerobes, on the expense of true denitrifiers, in activated sludge biocommunities. A lab-scale sequencing batch reactor system was employed for the studies. As predicted, the rate of nitrite reduction progressively decreased whereas the nitrate reduction rate remained almost unaffected, when fermentation conditions were introduced into the process schematic. Implications in design and operation of wastewater treatment plants are discussed.