Combined sewer overflow control using storage in seawater

This paper describes the flow balance method facility (FBM) used to control a combined sewer overflow (CSO) and a statistically based efficiency evaluation for the system. The FBM uses containment within a receiving water body (in this case seawater) to store CSO followed by pumpback to the wastewater treatment plant for treatment. The efficiency evaluation uses a mass balance incorporating measured specific conductivity and flow volumes with their probability distributions in a Monte Carlo model to calculate probable volumes of seawater in the pumpback and hence efficiency of the system. The methods described in the paper refer to phase 1 and form the basis for monitoring phase 2 of the project. Important aspects of this analysis for phase 2 of the FBM demonstration included: confirmation of the reliability of specific conductivity to determine the volume of seawater in the pumpback; an indication of the sensitivity of the predicted efficiency to variation in the parameters used; and therefore, identification of the relative importance of the different data distributions to allow more effective data collection in phase 2.