Date of Award
Master of Science
Nitrification, a key step in biological nitrogen removal processes, is the oxidation of ammonia into nitrate performed by ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) under aerobic condition. Researchers have focused on factors affecting the performance of nitrification for decades, but the inorganic carbon limitation on nitrification had been neglected. However, the increase in nitrogen in wastewater has increased the need to evaluate and improve our understanding of this limitation. In a previous research, the hypothesis that different inorganic carbon concentrations would enrich different AOB populations has been examined. In this study, the focus was on the effect of inorganic carbon concentration on NOB, which has a close relationship with AOB. Two 5L lab–scale continuous–flow stirred tank reactors (CSTR) were operated to evaluate the nitrification performance and microbial ecology of nitrifier populations acclimated under inorganic carbon sufficient (high–IC) and limited (low–IC) conditions for approximately 700 days. During the operation period, both bioreactors were able to maintain satisfactory nitrification efficiency higher than 95% at an influent ammonium concentration of 250 mg–N/L. Nitrate was the major end product and no significant nitrite accumulation was observed. To evaluate the effects of inorganic carbon on NOB community structures, cloning/sequencing and real–time PCR were applied to target and quantify the two common NOB genera, Nitrospira and Nitrobacter, as no molecular probe targeting all known NOB is available presently. The results showed that these two genera were both found in the two reactors. Nitrospira was the dominant NOB population in the high–IC bioreactor, while Nitrobacter was dominant in the low–IC one after one year acclimation. Kinetic analysis revealed that NOB enriched in the two reactors have different kinetic performances. However, IC concentration did not show a significant impact on the nitrite oxidizing kinetics of NOB in the batch tests.
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