Clay Township Regional Waste District recently underwent a plant expansion, adding biological phosphorus removal to its treatment train. |
However, with BPR, alum is no longer added to the VLR. Instead, the VLR’s anaerobic zone was increased to facilitate BPR. While chemical treatment is still used with the Orbal oxidation ditch, the overall amount of added alum has been significantly reduced. The team decided to forgo adding BPR to the Orbal oxidation ditch, as the expansion plan already called for construction on the VLR.
Thus, the team was able to add a cost-effective treatment alternative without additional construction. In addition, the VLR and Orbal oxidation ditch use a single sludge system where the RAS is mixed prior to returning to the respective tanks and the BPR process should promote enough PAO growth for the reactors.
While outfitting the VLR for the new treatment represented a higher preliminary investment than just keeping with the traditional chemical addition, the cost of adding BPR to the $5.3 million expansion project was only 2 percent of the total project cost. Also, the long-term maintenance of BPR is more cost effective since the process continues to recycle itself again and again without the need for additional materials. With the addition of BPR, CTRWD has been able to reduce the amount of alum added by more than 70 percent.
Many factors made the plant a prime candidate for BPR. For one thing, the incoming wastewater was conveyed through long force mains, giving the organic materials more time to ferment and develop VFAs. Increasing the amount of VFAs increased the amount of available carbon or “food” for the PAOs, thereby, enhancing the organisms “training.” In addition, the plant’s influent wastewater strength was higher than normal, which, again, promoted the amount of microorganisms available to facilitate BPR.
The project was completed in 2014, with a corresponding expansion of the aerobic digesters completed in 2015, and has fulfilled CTRWD’s primary goal of expanding the design average flow of the plant from 2.55 to 3.05 mgd and the peak hourly flow from 8.1 to 15.3 mgd to more effectively handle wet weather flow.
By embracing forward-thinking treatment options and answering the call of opportunity, CTRWD has not only expanded its plant but also welcomed a viable, cost-effective treatment option. CTRWD’s expansion project took the opportunity to break away from tradition and embrace cost-effective measures that can now serve as a model for future BPR installations throughout Indiana.
Established in 1946, Strand Associates is a dynamic, multidisciplinary engineering firm serving the needs of public and private sector clients throughout the United States. To learn more, visit www.strand.com.
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