SENTRY monitoring toxic impact of free nitrous acid: Hydrogen sulfide implications.

There are a number of applications in which free nitrous acid (FNA), the protonated form of nitrite (HNO2), is used as an antimicrobial agent due to its bacteriostatic and bactericidal effects on a range of microbes. FNA has been shown to be the factor in inhibiting denitrifying and phosphorus uptake processes. The impact of FNA on the nitrite oxidizing bacteria has been characterized and demonstrated more than 700 days of inhibition during SBR operation. In relation to the inhibition of hydrogen sulfide generation FNA has been demonstrated as a suitable inhibitory compound at bench-scale and more recently in commercial demonstration applications. For bench-scale studies FNA levels succeeded in suppressing sulfide production and methane production.

In this study we characterized the impact on SENTRY sensors installed in a demonstration wastewater treatment system. The sensors were dosed with three cycles of FNA and the bio-electrode response was noted.

SENTRY added to municipal wastewater stream to monitor impact of free nitrous acid addition

The use of SENTRY technology as a real-time sensor to control the dosing of FNA was considered in this study to determine its suitability in

(1) Characterizing impact of dosing on embedded microbial communities

(2) Understanding the response time of communities to FNA dosing

Impact of free nitrous acid dosing on SENTRY output

CONCLUSIONS:

· Free nitrous acid dosing caused a major - 92% drop in SENTRY output (MET) and repeatable response on the SENTRY sensors.

· Output from SENTRY sensors recovered after dosing events.

· This SENTRY bio-electrode information could be tied to understanding when and how often to dose the free nitrous acid (FNA) for optimized hydrogen sulfide inhibition.