Putting the Operator in Charge; Improved Human Machine Interface Leads to Significant Centrifuge Operation Savings

Metropolitan Wastewater Treatment Plant
St. Paul, Minnesota

All plants have an obligation to ratepayers to deliver the best wastewater treatment service at the lowest cost. As polymer prices started to soar even faster than energy costs, plants have needed to find new ways to reduce its dewatering polymer use. Some improvements are capital intensive, such as installing newer equipment. Others cost very little; they are simply improving the way we do things, such as putting the operators in charge. Most plants change operating goals passed down to operators intermittently as specific directives: “Try not to use more than 15 GPM of polymer, and keep the cake at least 27%.” This sort of instruction is OK, but usually not done often enough to account for changes in the dewatering processes. In the Minneapolis-St Paul Metro Plant the control system displays, operators are empowered to make changes independently, hour by hour, so the dewatering costs can be constantly minimized. We are looking into on line analyzers, to continuously monitor the blend ratio. The instruments for continuous solids measurement were unreliable ten years ago, but are now proven. Since polymer has now surpassed electricity as the largest expendable for solids processing (Table 1), another enhancement will be to combine energy and polymer costs on a real-time solids management screen. This would be incorporated into the already developed energy cost/conservation screen (Figure 8). MCES is also investigating ways to reduce the sludge yield in the winter (when most of the secondary sludge is produced). A 25 dryton-per-day reduction of secondary sludge production could save $400,000 in polymer while costing $200,000 in extra energy netting a savings of about $200,000 per year. Source: WEFTEC 2008 Proceedings

Metric Used:
Posted: August 27th, 2010 | Filed under: >1M, Waste Water Treatment | Tags: Cost Savings, Improved Organization, Plant Optimization | No Comments »

---