Variable persistence of artificial sweeteners during wastewater treatment: Implications for future use as tracers.

For more than a decade the artificial sweeteners acesulfame (ACE) and sucralose (SUC) have been applied as tracers of the input of wastewater to environmental waters. Recently concerns have been raised that degradation of ACE during treatment may hinder or restrict its use as a wastewater tracer. In this study the value of ACE and SUC as tracers was reassessed based on samples of wastewater at 12 municipal wastewater treatment (MWWT) plants and from 7 septic systems and associated septic plumes in groundwater. The results indicated stability of SUC during MWWT at most plants, and variable removal of both sweeteners during some MWWT and in the septic wastewater systems. However, the residual concentrations of ACE and SUC in municipal effluent and in septic plumes indicate that both sweeteners remain valuable wastewater tracers. The mass ratio SUC/ACE was found to be a useful parameter for examining the relative persistence of these sweeteners.

Pyrite Oxidation Halts Migration of a Phosphorus Plume.

We have established a monitoring record of phosphate (PO4 3- ) migration in the Long Point, ON campground septic system plume that now spans 26 years. Previously, at year 16 (2006), a P plume 16 m in length was documented and provided a good fit with an analytical advection dispersion model when a P migration velocity of 0.8 m/yr was used (retardation factor of 37) and when P behaved in an otherwise conservative manner (sorption only). However, between years 16 and 26 (2016), the P plume length expanded by only 2 m (0.2 m/yr) and increased in depth by only 0.5 m. The zone of abrupt P depletion at depth occurs close to the zone where SO4 2- concentrations increase in response to NO3 - oxidation of pyrite. Scanning electron microscope images of sand grains from the nose of the P plume reveal abundant authigenic mineral coatings of considerable thickness (∼5 to 20 µm), with Fe as the dominant cation and containing 1 to 3 wt % P. This evidence suggests that P is now being attenuated along a reaction front that coincides with the zone where pyrite oxidation is occurring. P migration may now be controlled by the rate of migration of the pyrite oxidation front and this is several times slower than the previously indicated rate in the shallower, sorption-controlled portion of the plume. Monitoring at Long Point has demonstrated the danger of embracing an overly simplistic conceptual model when attempting to predict wastewater P migration in groundwater and also highlights the unique insight provided by a long-term monitoring record.