Evaluation of Dental Clinic Mercury Contributions to Wastewater Treatment Plant Biosolids

A study was conducted to quantify the impact of dental wastewater discharges on Metropolitan Council Environmental Services (MCES) wastewater treatment plant (WWTP) mercury loadings. This was accomplished by an intensive biosolids sampling and analysis program in two Minnesota communities, Hastings and Cottage Grove. The sampling was conducted at the community WWTPs before and during the time period amalgam removal equipment was operated at the dental clinics upstream of each WWTP.During the study dental amalgam removal equipment was installed in the communities' dental clinics for at least a three-month period for data collection. The dental amalgam removal equipment performed as anticipated in the dental clinics. No significant problems were encountered with the amalgam removal equipment or the associated dental clinic vacuum systems. During the study, a 44 % reduction in mercury loading to the Hastings WWTP was measured while the amalgam removal equipment was installed in the Hastings dental clinics. The corresponding mercury reduction for Cottage Grove was found to be 29%.