614 - Maximize the Effectiveness of Existing Wet-Weather Infrastructure through Operational Optimization

Many collection system networks are operated passively during wet-weather and miss opportunities to capture additional flow and improve receiving water quality through more effective use of existing system capacity. However, implementing new operational strategies can be daunting for utilities without proper evaluation of the benefits and risks. Using hydraulic optimization, a range of control strategies can be evaluated offline to identify an operational strategy that improves collection system performance while meeting a utility’s constraints and preferences regarding operational complexity, maintenance and risk.
For both St Louis Metropolitan Sewer District (MSD), Missouri, USA and SEVESC, France, an offline optimization analysis was performed to evaluate modifications to existing CSO diversion structures, such as static weir crest increases, simple gate control logic based on existing local sensors and more complex gate control logic based on a regional sensor network that would require additional investment.
The first step for both systems was to define the range of potential system changes. Existing control rules were reviewed, and alternative control strategies defined. Next, performance criteria were defined for characterizing system benefits. For the both examples, these criteria included CSO volume reduction, interceptor surcharging, and cost of operational changes. Optimization analysis evaluates over 300,000 unique control strategies. Through simple local control, for MSD, CSO can be reduced by over 4% at the same level of risk as the baseline operations, which translates to approximately 200 MG of typical year CSO, while investing in a more complex regional control strategy could provide an additional 1.7% reduction. MSD is moving forward with local control changes and piloting regional control at one location to better quantify any additional complexity, cost and reliability concerns. Similar to St Louis MSD, SEVESC were able to more effectively utilize existing infrastructure to exceed in their target CSO reduction goal of 15%.
For both use cases, the offline evaluation of operational alternatives increased the utility’s level of comfort with modified operations and offered a phased implementation route to reach additional water quality benefits with minimal capital expenditure.