The use of Mn2O3 nanoparticles (NPs) is growing since they are known as environmentally friendly catalysts in removing carbon monoxide and nitrogen oxides from waste gases. Thus, the release of these materials into the environment as well as wastewater stream is evident. The entry of Mn2O3 NPs into the wastewater treatment plans (WWTPs) can affect nitrification performance. Nitrification is a key process for biological nitrogen removal in nitrogen cycle and WWTPs in which ammonia is converted to nitrite by ammonia oxidizing bacteria (AOB), and nitrite is converted to nitrate by nitrite oxidizing bacteria (NOB). Thus, the studies on impact of Mn2O3 NPs on nitrifying bacteria are crucial. To date, most batch studies on the impact of nanoparticles to nitrifying bacteria have been employed without aeration (low DO) which can be seen as a model for several environmental conditions such as river or stream sedimentation. Herein, in accordance with traditional batch studies, we also set up a matrix of low DO batch tests along with aerated (high DO) batch tests with difference concentrations of Mn2O3 NPs exposed to nitrifying bacteria, which can be seen as a model for nitrification in WWTPs. Here, we investigate the physiological and transcriptional responses of the nitrifying bacteria due to the presence of Mn2O3 NPs based on the specific oxygen uptake rate (sOUR) tests and gene expression. The most sensitive step in nitrification is conversion of ammonia to nitrite by ammonia oxidizing bacteria (AOB). Two genes ammonia monooxygenase (amoA) and hydroxylamine oxidoreductase (hao) are linked to this biochemical step and they are considered as targets to study nitrification inhibition due to their sensitivity to environment. Thus, with the same sample for sOUR test, we examined the transcriptional response of these two genes. Our results showed that there was increase in nitrification inhibition as determined by sOUR with increasing dosages of Mn2O3 NPs for both cases- low DO and high DO. There was notable reduction in the transcript levels of amoA and Hao for increasing Mn2O3 NPs dosage for the case of high DO and 3 h exposure, which corresponded well with sOUR. In addition, we observed gene expression stimulation after 3 h in low DO mode and 1h in high DO mode due to detoxification mechanism.

Impact of Mn2O3 nanoparticles on nitrification under low and high dissolved oxygen conditions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.