Measuring nitrification inhibition by metals in wastewater treatment systems: Current state of science and fundamental research needs

Abstract

Wastewater treatment is an important step within the water continuum as it reduces the risks associated with microorganisms as well as organic and inorganic compounds. From a chemical standpoint, treatment effectiveness is generally linked to carbon and nutrient (e.g., nitrogen, phosphorus) removal. A critical step in nitrogen removal is initiated by the conversion of ammonia to nitrate, a process that is carried out by nitrifying microorganisms. Nitrification is considered a key step as it removes the toxic effect of ammonia, while the resulting nitrate can be further converted into N₂ gas (by autotrophic or heterotrophic nitrifying bacteria), which is not harmful to the environment. As nitrification is susceptible to a wide range of inhibitory substances, measuring the effect of potential inhibitors on nitrification rates is relevant to maintaining the performance of treatment plants. In this review we discuss the primary methods used to measure nitrification inhibition, their applications, and potential limitations. The authors also identify the research gaps that need to be addressed to better assess inhibition, with special attention on the effect of metals on nitrification in engineered wastewater treatment systems.

KEYWORDS:

• nitrification inhibition
• wastewater
• heavy metals
• ammonia oxidation

Acknowledgments

The authors thank Michaek Elovitz for critically reviewing this manuscript. Any mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Funding

Drs. Li and Kapoor were supported by ORISE-EPA Research Fellowship. Dr. Chandran was supported by the Water Environment Research Foundation. The U.S. Environmental Protection Agency, through its Office of Research and Development, funded and managed, or partially funded and collaborated in, the research described herein. This work has been subjected to the agency's administrative review and has been approved for external publication. Any opinions expressed in this paper are those of the authors and do not necessarily reflect the views of the agency; therefore, no official endorsement should be inferred.