Mixing characteristics of submerged and surface wastewater outfalls at McMurdo Station

Abstract

AbstractThe mixing characteristics of the existing surface wastewater discharge and a proposed submerged wastewater outfall at McMurdo Station, Antarctica, are compared. The wastewater is a combination of sanitary sewage and brine from a desalination plant. Dispersion from a proposed submerged (15 m-deep) outfall was simulated using the CORMIX1 computer model. The mixing characteristics of the surface discharge were estimated from visual observations and a conceptual analysis. The wastewater was found to be less dense than ambient seawater. From the submerged outfall, the effluent is predicted to be diluted by ratios ranging from 80:1 to 450:1 between the point of discharge and the point where the effluent plume begins to spread out underneath the sea ice. The variation in dilution depends mostly on tidal current speed, and dilution of the wastewater with desalinator brine is predicted to provide only minor reductions in concentrations of the effluent. The heat content of the discharge plume from a submerged outfall is expected to cause at least partial melting of the sea ice from underneath. A surface discharge provides much less mixing with ambient water before the effluent spreads along tidal cracks and underneath the sea ice. The submerged discharge is expected to confine settleable wastewater solids to a benthic area near the outfall, but a surface discharge allows solids to settle over a wider area.