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Applying Molecular Tools for Monitoring Inhibition of Nitrification by Heavy Metals
Citation:
Kapoor, V., X. Li, C. Impellitteri, K. Chandran, AND J. Santodomingo. Applying Molecular Tools for Monitoring Inhibition of Nitrification by Heavy Metals. Presented at WEFTEC 2015, Chicago, IL, September 26 - 30, 2015.
Impact/Purpose:
We applied molecular methods to measure the degree of nitrification inhibition in wastewater treatment systems, and to study the bacterial composition and dynamics of a nitrifying bioreactor.
Description:
The biological removal of ammonia in conventional wastewater treatment plants (WWTPs) is performed by promoting nitrification and denitrification as sequential steps. The first step in nitrification, the oxidation of ammonia to nitrite by ammonia oxidizing bacteria (AOB), is sensitive to various inorganic contaminants such as heavy metals (e.g., Cu2+, Zn2+, Cd2+) that enter WWTPs via industrial discharges or stormwater runoff (Kim et al., 2008; Jönsson et al., 2000; Grüttner et al., 1994). Nitrification inhibition is commonly assessed by specific oxygen uptake rates (sOUR) of bacterial pure cultures (i.e., Nitrosomonas sp) exposed to several metal concentrations (Chandran and Love, 2008; Park and Ely, 2008). Chemical methods are relatively cumbersome, time consuming, and are not amenable to automation and simultaneous processing of multiple samples. Moreover, respirometry methods alone do not always provide sufficient information for accurate assessment of nitrification rates in wastewater treatment systems and do not help us understand how the composition and physiology of the microbial community affects nitrification pathways. To circumvent these limitations we applied molecular methods to measure the degree of nitrification inhibition in wastewater treatment systems, and to study the bacterial composition and dynamics of a nitrifying bioreactor. Specifically, we extracted RNA and DNA from nitrifying enrichment samples and determined the presence and relative activity of genes coding for ammonia oxidation (amoA), hydroxylamine oxidation-reduction (hao), nitrite reduction (nirK), and nitric oxide reduction (norB) after samples were exposed to copper (Cu2+) under starving conditions.
