Development of a Conceptual Model to Explain Apparent Free Ammonia Inhibition in Wastewater Systems (WEFTEC 2006)

Abstract

The common consensus among researchers and practitioners alike is that high free ammonia concentrations cause nitrite oxidizer inhibition in wastewater treatment systems. The work of Anthonisen et al. (1976), who produced an operational chart providing guidance on the free ammonia concentrations most likely to produce nitrite oxidizer inhibition, is considered by many to be the definitive work that established the inhibitory nature of free ammonia in wastewater treatment systems. Over the past three decades several investigators have reported discrepancies in the range of inhibitory free ammonia concentrations. Anthonisen et al. (1976) reported inhibition of nitrite-oxidizers at free ammonia concentrations of 0.1 to 1 mg/L, Turk and Mavinic (1986) reported no significant nitrite-oxidizer inhibition for free ammonia concentrations below 10 mg NH 3 -N/L, whereas Mauret et al. (1996) concluded that free ammonia inhibits Nitrobacter, in the range of 6.6 to 8.9 mg NH 3 -N/L. On the other hand, Gieseke et al. (2003) state that it is not known whether bacteria of the genus Nitrospira, now believed to be the most prevalent nitrite oxidizer in wastewater systems, are inhibited by free ammonia.Some investigators have called into question the true cause of observed nitrite oxidizer inhibition. For example, Cecen and Ipek (1998) suggested that the dissolved oxygen to free ammonia ratio and not the free ammonia concentration itself is important, when attempting to induce nitrite accumulation. The work of others (Stuven et al. 1992;Yang and Alleman 1992;and Hyungseok Yoo et al. 1999) has suggested that hydroxylamine -an intermediate in the ammonia oxidation process -may be the true cause of nitrite oxidizer inhibition and therefore of nitrite accumulation. Many authors agree; however, that selective inhibition of nitrite oxidation via apparent free ammonia inhibition would allow direct oxidation of ammonia to nitrite and denitrification to dinitrogen gas with the inherent benefits of reduced aeration and carbon requirements. The starting point to designing such a process is the development of a clearer understanding of the mechanism(s) associated with nitrite oxidizer inhibition and nitrite accumulation. This paper describes the results of exploratory work conducted to both confirm the results of mixed culture batch tests suggesting free ammonia may not be inhibitory to nitrite oxidizers as commonly reported and elucidate the likely mechanism(s) responsible for observed phenomenon. Free ammonia inhibition trials were undertaken using pure cultures of Nitrospira moscoviensis, since Nitrospira spp. were the predominant nitrite-oxidizers in the systems studied for this research program. The results of these experiments support the conclusion that free ammonia is probably not inhibitory to nitrite-oxidizing organisms in wastewater systems. 6548 WEFTEC®.06Copyright 2006 Water Environment Foundation. All Rights Reserved © Several long-term reactor perturbation studies were conducted with mixed microbial cultures to identi...

Gaseous Nitrogen and Carbon Emissions from a Full‐Scale Deammonification Plant

“…There were approximately ten full-scale deammonification plants in operation in 2007 (Jardin et al, 2006;Wiebe et al, 2007). Substantial research has been conducted on resourcesaving alternative nitrogen elimination routes (e.g., Anthonisen et al, 1976;Fux et al, 2002;Hellinga et al, 1999;Strous et al, 1999), and several mechanisms, such as inhibition by process intermediates and inorganic carbon limitation, are under discussion (Guisasola et al, 2007;Kampschreur et al, 2007;Simm et al, 2006;Wett and Rauch, 2003). However, little is known about the gaseous intermediates from the deammonification systems.…”