FULL-SCALE FIELD TRIALS IDENTIFY SULFATE DISCHARGE LIMITS FOR MUNICIPAL WASTEWATER ODOR AND CORROSION CONTROL

The Massachusetts Water Resources Authority (MWRA) owns and operates one of the largest wastewater collection and treatment systems in the U.S. serving 45 member communities and operating the 1.2 billion gallon-per-day Deer Island Wastewater Treatment Plant in Boston Harbor. The MWRA has very few odor and corrosion problems so it was unusual when the MWRA encountered a high incidence of localized hydrogen sulfide related odor complaints and severe concrete corrosion in one trunk sewer called the Framingham Extension Sewer (FES). As part of a periodic review of the MWRA Industrial Discharge Limitations, it was proposed to limit sulfide discharges into the FES because of the historic odor and corrosion problems. Member discharging communities were required to use chemicals or other methods to reduce the concentration of sulfide entering the MWRA system to 0.5 mg/l or less. However, the MWRA did not notice a reduction in downstream odor complaints and corrosion following these sulfide discharge controls. Further review of sulfide generation patterns in the FES revealed several local industries which discharge high concentrations of BOD5 and sulfate into the FES, with one industry discharging over 25,000 mg/l sulfate on a regular basis. An extensive sampling and monitoring program showed a direct cause-and-effect mechanism between high sulfate discharges, high BOD5 discharges and hydrogen sulfide generation in the FES itself. A full-scale field analysis was performed during an industry shutdown which showed a 10-fold increase in sulfide due to industrial discharges alone. Discharge permits were revised to include sulfate as a controlled parameter.