Riverbend Water Reclamation Plant Expansion

The Upper Trinity Regional Water District (UTRWD) serves communities within Denton County, a rapidly growing area within North Texas. As part of their 2016 master-planning efforts, the utility contracted Carollo to re-evaluate the capacity of the Riverbend Water Reclamation Plant, a critical wastewater treatment facility whose sequencing batch reactor process was struggling to meet increased flows.

Through modeling, Carollo determined that, to stay ahead of the region’s growth without compromising water quality, the plant should be expanded from 2 million gallons per day (mgd) in capacity to 4 mgd. Because the project’s design phase was allotted a nine-month timeframe, Carollo and UTRWD collaboratively decided to perform the project under the construction manager at-risk (CMAR) delivery method, an alternate project delivery method that accommodates an accelerated construction schedule.

With $30 million in funding assistance from the Texas Water Development Board, the project team began designing the expanded plant, which incorporated a new influent pump station, headworks, return activated sludge (RAS)/waste activated sludge (WAS) building, secondary clarifiers, expanded ultraviolet disinfection, and aeration basins modified from the former sequencing batch reactors. The new plant also boasts improved odor control to minimize disturbances to local neighborhoods and businesses.

However, the design’s main feature was the implementation of BioMag^®. This activated-sludge technology utilizes magnetite to ballast biological floc, not only improving settling in the plant’s secondary clarifiers but also enhancing the UV transmissivity of the clarifiers’ effluent. It is also known to increase concentrations of mixed liquor suspended solids (MLSS) in the aeration basins, thereby reducing the required aeration volume.

Although well-established and proven, the BioMag^® process was new to UTRWD as well as the entire state of Texas. The novelty understandably caused some hesitancy amongst the project team, including the plant staff who would come to operate and maintain this unfamiliar technology. To earn confidence in the technology, Carollo worked with the manufacturer, CMAR, and UTRWD in robustly pilot-testing BioMag^®’s application at the Riverbend Water Reclamation Plant. This opportunity allowed the operations team to freely ask questions and familiarize themselves with the new equipment and process in a controlled and supportive environment.

The successful two-month-long pilot-testing helped the process earn the Texas Commission on Environmental Quality’s (TCEQ) approval. This process helped save approximately $4.5 million in construction cost from reduced treatment basin volume requirements.