TherRNAt/rDNA ratio as a measure of nitrite oxidizing activity.

摘要

A bench scale nitrification reactor (BSNR) containing the genus Nitrobacter (1 x 1010/L; 5 to 20% of bacteria) was used to assess the ribosomal RNA transcript (rRNAt) to ribosomal RNA gene (rDNA) ratio as a nitrite oxidizing activity metric. Upper (1.8) and lower (0.69) prediction intervals were established for the ratio in the BSNR during 10 consecutive weeks of high nitrification efficiency. It was hypothesized that during NOB inhibition the ratio would decline below 0.69 and during unlimited nitrite oxidation exceed 1.8. When the ratio was measured in a batch nitrite oxidation experiment, the value increased monotonically from less than 0.10 during nitrite starvation to more than 3.0 eight hours after unlimited nitrite oxidation began. The metric declined monotonically back to 0.10 within 4 hours of nitrite exhaustion. The response was mediated by rRNAt abundance that varied as the growth prospect changed from unfavorable (nitrite starvation: 5 x 108 copies/L), to favorable (excess nitrite: 3 x 10 10 copies/L), and back to unfavorable (nitrite starvation: 5 x 10 8 copies/L). Batch inhibition experiments supported a hypothesized negative monotonic correlation between the ratio and the inhibitor concentration and fraction inhibition level. For all inhibitors studied, the ratio was significantly reduced ( 0.69) after 4.5 hours of exposure to concentrations that extensively inhibited nitrite oxidation, though the response varied at the same inhibition level for different inhibitors and was absent after a sudden pH change to 4.5. Despite being widely reported in the literature, free ammonia did not significantly reduce nitrite oxidation rates if ammonia oxidizing bacteria (AOB) were inhibited; however, the metric reflected ( 0.69) the virtual absence of nitrite oxidizing activity at low free ammonia concentrations when the AOB activity level was high. In a staged BSNR inhibition experiment, the ratio dropped significantly ( 0.69) 22 hours before the nitrification efficiency fell below 90%. When nitrite oxidizing activity was later recovered, the ratio increased significantly (> 0.69) before this was apparent in soluble nitrogen data. In summary, a range of experiments suggested the rRNAt/rDNA ratio was an effective monitor for nitrite oxidizing activity that could feasibly identify and forecast wastewater treatment instability.