Monitoring and troubleshooting a POTW's nitrification process was examined by monitoring total ammonia oxidizing bacteria (AOB 16S rDNA gene), β-subclass of AOB (amoA gene) and total bacteria (bacterial 16S rDNA gene) using quantitative PCR and correlating these biological
variables with operating parameters to establish baseline conditions in activated sludge of a wastewater treatment plant. Phylogenetic analyses of the amoB sequences, obtained from the sludge samples, grouped with those belonging to the Nitrosomonas clad. Total bacterial, AOB,
and β-subclass AOB cell concentrations ranged from 2.1 × 1014 to 9.5 × 1015, 2.04 × 1012 to 6.8 × 1014, and 6.4 × 109 to2.4 × 1014 cells l−1, respectively. Over the three
month study, ammonia removal ranged from 61% to 98%, which were categorized into 3 conditions: normal (>90%), stressed (85 – 89%), and inhibited (<80%). Mixed liquor suspended solids and dissolved oxygen (DO) correlated with total bacterial and
total AOB population, and β-subclass AOB. Flow negatively correlated with total bacteria and β-subclass. The study's results showed these molecular indicators of ammonia oxidation were useful tools for predicting, troubleshooting, and improving the nitrification process in the
WWTP through adjustments of MLSS, DO, and flow.
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