An Efficient, Optimized System To Increase Solids Content From Dewatering 

For the past 50 years, the City of Westminster’s Big Dry Creek Wastewater Treatment Facility has processed wastewater from the city’s northern two thirds. While the goal is to land apply as much of the biosolids as feasible, weather and nitrogen limits sometimes prohibit it. During these times, the city stockpiled biosolids and hauled them to third-party composting facilities. Although this still produces byproduct synergy, it’s not a sustainable or cost-effective solution. 

The Solids Dewatering and Campus Wide Improvements project is the city’s first Envision® project. The new centrifuge process removes excess water from the biosolids, increasing the solids concentration from 6% to 20%. This reduces volume for hauling to application sites, and subsequently truck trips, by 60%. 

The operations and maintenance friendly design includes flexibility for Westminster’s booming population, projected flow increases, new regulations and expansion options to add revenue streams. Though the project was wholly contained within the secure BDCWWTF, the team and City coordinated to engage with the community — holding meetings, sending mailings, maintaining a project website and celebrating project completion with an open house and ribbon cutting. 

If not for this project, the city’s anticipated biosolid production would significantly increase composting expenditures. Instead, this project will lead to $100,000 in savings annually, reducing the burden on ratepayers in the future. At the same time, the project reduced the nitrogen content in the biosolid byproduct by 30%. 

In comparison to the previous gravity belt thickeners, the new system uses 97% less water, equivalent to 8.5 million gallons of water. However, the team also repurposed the old equipment, part of an overall value engineering effort that saved $800,000. 

The team optimized the building footprint, constructing a new structure that matches the existing campus and maintaining operations throughout. When faced with spiking ammonia and phosphorus loads from the new dewatering system, they devised a unique storage system — using a tank no longer required for liquid storage — to capture and hold the centrate and equalize the feed rate back into the front of the treatment system. 

Completed on schedule and on budget, the project provides an efficient, optimized system to increase the solids content from the dewatering process.