TEMPORAL VARIATION OF MERCURY IN EFFLUENT FROM MUNICIPAL WASTEWATER TREATMENT PLANTS IN SOUTHWEST OHIO

Effluent from wastewater treatment plants (WWTPs) can be a significant source of mercury (Hg) to receiving waters; however, little is known about the temporal variability of Hg in WWTP effluent. We quantified concentrations and fluxes of Hg in effluent from two WWTPs in southwest Ohio over a 13-month period with weekly sampling. Preliminary results suggest that there is little temporal variability in effluent Hg concentrations throughout the year. However, there is a substantial difference of Hg concentrations in effluent between the two WWTPs, with the larger Dayton facility (~60 million gallons per day; 0.72 ± 0.39 ng/L) having a lower mean measured concentration than that from the smaller Xenia plant (~2 million gallons per day; 4.30 ± 1.10 ng/L). Estimated fluxes of Hg are 60 ± 32 g/y from the Dayton plant and 12 ± 3 g/y from Xenia. At the point of discharge, effluents from the Dayton and Xenia WWTPs increase Hg loadings to the Great and Little Miami Rivers by about 8% and 4%, on an annual basis, but can be a much greater fraction of total fluvial Hg loadings (up to 40%) during periods of low river flow. Effluent from these two WWTPs is a relatively constant and significant source of Hg to their receiving waters.