Natural Attenuation of Septic System Nitrogen by Anammox

Abstract

On-site disposal of sewage in septic systems can lead to groundwater plumes with NO(3)(-)-N concentrations exceeding the common drinking water limit of 10 mg/L. Currently, denitrification is considered as the principal natural attenuation process. However, at a large seasonal-use septic system in Ontario (256 campsites), a suboxic zone exists where nitrogen removal of up to 80% occurs including removal of NH(4)(+)-N. This zone has both NO(3)(-)-N and NH(4)(+)-N at >5 mg/L each. In the distal NH(4)(+)-rich zone, NH(4)(+)-N concentrations (8.1 ± 8.0 mg/L) are lower than in the proximal zone (48 ± 36 mg/L) and NH(4)(+)-N is isotopically enriched (concentration-weighted mean δ(15)N of +15.7‰) compared to the proximal zone (+7.8‰). Furthermore, δ(15)N-NH(4)(+) isotopic enrichment increases with depth in the distal zone, which is opposite to what would result if nitrification along the water table zone was the mechanism causing NH(4)(+) depletion. Bacterial community composition was assessed with molecular (DNA-based) analysis and demonstrated that groundwater bacterial populations were predominantly composed of bacteria from two Candidatus genera of the Planctomycetales (Brocadia and Jettenia). Together, these data provide strong evidence that anaerobic ammonium oxidation (anammox) plays an important role in nitrogen attenuation at this site.

Wastewater Effluent Impacts Ammonia-Oxidizing Prokaryotes of the Grand River, Canada

“…The prevalence of "Ca. Brocadia"-like sequences in this study is consistent with that in other freshwater environments, such as river sediment (26), lake (27), and groundwater (18,57). Although anammox communities in the water column were not assessed explicitly in this study, their communities in water column and sediment samples were analyzed previously (64).…”

Isotopic overprinting of nitrification on denitrification as a ubiquitous and unifying feature of environmental nitrogen cycling

“…Thus, in the absence of any O 2 -requiring transformations, it is likely that any return of NO 2 − to the NO 3 − pool in anaerobic aquifers is associated with anammox, the anaerobic oxidation of NH 3 coupled to reduction of NO 2 − , which yields NO 3 − (as well as N 2 ) as a metabolic product (24,42). Indeed, recent studies suggest that a substantial fraction of N 2 production in aquifers originates from anammox (63)(64)(65), rivaling N 2 production by canonical denitrification in some instances (45).…”

Persistence of artificial sweeteners in a 15-year-old septic system plume

“…Groundwater ages in the proximal plume zone were estimated previously from seasonal breakthrough of EC peaks and from two NaBr tracer tests (Robertson et al, 2012) and vary from about 7 days in the shallow water table zone below the tile bed (during heavy sewage loading) to about 1 year, 17 m down gradient from the edge of the tile bed. There is also a strong vertical component of flow below the tile bed (up to $10 cm/day, Robertson et al, 2012) as a result of the high sewage loading rate.…”

“…Groundwater monitoring in the Tile Bed 2 area ( Fig. 1) has been ongoing since it was commissioned in 1990 and the fate of a variety of constituents in the groundwater plume have been reported previously including; NO À 3 and NH þ 4 (Aravena and Robertson, 1998;Robertson et al, 2012), PO 3À 4 (Robertson, 2008); pharmaceutical compounds (Carrara et al, 2008;Sabourin et al, 2010) and the artificial sweeteners, cyclamate, saccharin, sucralose and acesulfame (Van Stempvoort et al, 2011b). Several pharmaceutical compounds including carbamazapene and ibuprofen and several of the sweeteners, particularly acesulfame, which was approved for use in Canada in 1988 (Gougeon et al, 2004), persist in the plume, but the monitoring network used previously only extended 17-25 m from the tile bed and only intercepted the portion of the plume that was about 1 year old.…”