Abstract
The inhibition of free ammonia (FA) on nitrite-oxidizing bacteria (NOB) was investigated using an enriched NOB community with high nitrifying performance. A continuous-flow reactor was operated for the enrichment of the bacterial community. High-throughput sequencing analysis showed that Nitrospira (NOB) using in batch experiments was extended from 4.78% to 12.08% during the under continuous-flow operation for 27 days. For each batch experiments, an ammonia injection at the start-up resulted in the desired initial FA concentration (at pH = 8.1–8.2, T = 25 °C), and a continuous ammonia feeding stream allowed for a relatively stabilized FA levels as much as the initial one. Results indicated that FA inhibition on NOB was not instantaneous but occurred gradually at a certain reaction time. Low concentrations of FA (18.08–24.95 mg L−1) had a limited inhibition on NOB with increasingly high nitrate production rates, whereas high FA levels (36.06–50.66 mg L−1) exerted a significant negative impact on the NOB. Also, strong adaptation happened in these high levels of FA inhibition on NOB, which resulted in an overall low NOB activity during the whole aerobic operation.
Highlights
Traditional nitri cation is a two-step process commonly utilized in wastewater treatment plant (WWTP)
The feasibility of a continuous- ow con guration was demonstrated for the enrichment of nitrite-oxidizing bacteria (NOB) with high performance by conducting a series of experiments of free ammonia (FA) inhibition
Highthroughput sequencing implied that Nitrospira (NOB) used in the batch experiments increased from 4.78% to 12.08% during the continuous- ow operation period corresponding to the high nitrate production rate from 72.04 to 154.06 mg (L h)À1
Summary
Traditional nitri cation is a two-step process commonly utilized in wastewater treatment plant (WWTP). These steps are performed by two different autotrophic bacterial population. Partial nitri cation (ammonia oxidation to nitrite) has drawn much attention as it could reduce the oxygen and organic compound demand by 25% and 40%, respectively, compared with nitri cation and denitri cation.[1] The success of the process depends on the elimination of NOB, thereby resulting in nitrite as the primary nal product.[2] attempts have been made to devise a microbiological method for AOB enrichment and NOB washout to enable optimal partial nitri cation.[3,4]
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