Phosphates are added to public water systems to keep our drinking water safe by controlling the corrosion of copper and zinc-coated pipes. However, if large amounts of phosphorus ends up in our freshwater, it can cause eutrophication, leading to the development of harmful algal blooms, also known as “dead zones.”
What’s more, high amounts of phosphorus in wastewater treatment can also lead to struvite creation, a crystalline mineral compound made up of magnesium, ammonium, and phosphate.
Struvite can build up in pipes, pumps, and other equipment, leading to an operational and costly maintenance nightmare.
These factors make phosphorus recovery not just an important step but a critical requirement in any wastewater treatment process.
This blog explores how Metro Water Recovery in Denver, Colorado, the largest wastewater treatment provider in the Rocky Mountain West, successfully implemented the Centrisys/CNP MagPrex™ system to enhance its phosphorus removal process and control struvite formation.
Watch our on-demand webcast where Gerhard Forstner, President of CNP, and Rudy Maltos, Ph.D., P.E., Staff Engineer at Metro Water Recovery, discuss the successful implementation of the MagPrex™ system for phosphorus recovery.
Keeping Up With Phosphorus Recovery Demands
Metro Water Recovery’s Robert W. Hite Treatment Facility serves around 2.2 million people. The facility treats and reclaims about 130 million gallons of water daily, of which roughly 85 percent is discharged into the South Platte River.
In the mid-2010s, the facility recognized the need to optimize its phosphorus recovery due to new stringent regulatory phosphorus discharge limits. This project was initiated in response to mandates such as Reg 85, which requires phosphorus discharge limits of 1.0 mg/L in the effluent, and the Voluntary Incentive Program (VIP), which sets an even stricter target of 0.7 mg/L.
Overcoming Phosphorus and Struvite Challenges: Implementing The MagPrex Reactor Solution at Metro Water Recovery
The challenge: Phosphorus, initially accumulated in the biological phosphorus removal (BNR, EBPR, or Bio-P) process, is released when the waste activated sludge (WAS) enters an anaerobic digester. The aim of these processes is to transfer phosphorus from the liquid stream into the solid stream (WAS). However, in the anaerobic environment of the digester, phosphorus is released and combines with magnesium (from drinking water) and ammonia (produced by organic decomposition) to form struvite. If this process is uncontrolled, struvite can scale, and any phosphorus not captured as struvite remains in the liquid phase, returning to the front of the plant. This return of soluble phosphorus makes it more challenging to remove it from the effluent at the back end of the plant.
The Solution: Metro Water Recovery implemented the MagPrex reactor between the anaerobic digester and the dewatering equipment in its wastewater treatment process to improve phosphorus recovery and control struvite formation.
Was MagPrex Successful for Phosphorus Recovery? Results and Performance Metrics
Since its implementation, the MagPrex system has delivered impressive results and an invaluable return on investment (ROI). The system consistently achieves over 90% transformation of soluble phosphorus to particulate phosphorus, often reaching up to 95%. This has significantly reduced phosphorus levels in the effluent, consistently staying below the VIP target of 0.7 milligrams per liter.
Additional benefits of implementing MagPrex include:
- Reduced Polymer Consumption and Costs: The MagPrex reactor has significantly contributed to reducing the need for polymer in the dewatering process, providing substantial chemical cost savings.
- Reduced Struvite in Pipes: By capturing struvite (and manipulating its formation) before it can build up in pipes and equipment, the facility has significantly reduced maintenance hassles and costs.
- Improved Dewatering of Biosolids: The presence of magnesium in the MagPrex reactor plays a crucial role in binding particles together during the dewatering process, which has helped improve the overall process efficiency.
- Enhanced Operational Performance: With fewer pipe blockages from struvite build-up, the facility has seen an improvement in its overall performance and system reliability.
These benefits prove the MagPrex system was well worth the investment. It has significantly helped Metro Water Recovery lower its phosphorus levels and improve its process flow, contributing to environmental sustainability and operational efficiency.
A Unique Approach to Struvite Formation
While minimizing phosphorus levels is a primary goal of the MagPrex system, Metro Water Recovery has a unique struvite objective: not only to manage but also maximize and harvest struvite formation.
Unlike most phosphorus recovery systems that aim to minimize struvite, the MagPrex reactor at Metro Water Recovery is specifically configured to effectively capture and harvest it. This innovative approach opens up possibilities for repurposing struvite as a valuable resource. By recovering the struvite, the facility can explore potential markets for this byproduct in the Denver area, turning a maintenance challenge into a potential economic opportunity.
Learn everything you need to know about MagPrex, including how it limits struvite build-up in pipes and minimizes maintenance issues, here!
Struvite Harvesting Challenges and Finding the Best Solution
While phosphorus recovery at Metro Water Recovery has met and exceeded expectations, the facility faced challenges with the struvite harvesting process. Initially, the goal was to harvest around 2,000 pounds of struvite per day using the MAGPEX system. However, the actual harvest ranged from 200 to 400 pounds per day.
The primary issue was the particle size and settling of the struvite crystals. The crystals were often too fine to settle efficiently, resulting in lower-than-expected recovery rates. To address this, Metro Water Recovery made several operational adjustments:
- Continuous Operation of the Classifier: Initially operated intermittently, the classifier was switched to continuous operation, significantly improving struvite capture.
- Dilution of the Struvite Stream: Diluting the stream entering the classifier helped separate small particles more effectively, increasing the recovery rate.
- Recycle of Overflow: Implementing a system to recycle the overflow from the classifier back into the reactor allowed for the growth of larger crystals, further enhancing struvite capture efficiency.
By fine-tuning the MagPrex reactor's conditions, Metro Water Recovery increased its struvite harvest to about 1,000 pounds per day, achieving just over 50% of its target. The engineers at Metro Water Recovery continue to collaborate with research teams and system operators to better understand the dynamics of struvite formation, allowing for continual process improvement.
Check out our top 4 maintenance tips on how you can reduce struvite formation in your decanter centrifuge here!
Conclusion and Future Outlook
Metro Water Recovery's implementation of the MagPrex reactor system has proven to be a significant step forward in phosphorus recovery and struvite management. The system not only helped the facility meet stringent regulatory targets for phosphorus levels but also addressed the operational challenges associated with struvite buildup.
By strategically placing the MagPrex reactor between the anaerobic digester and the dewatering system, the facility has been able to optimize phosphorus recovery, improve dewatering efficiency, reduce polymer consumption and costs, manipulate struvite formation, and reduce struvite build-up maintenance costs.
The success of the MagPrex reactor at Metro Water Recovery highlights the importance of innovative solutions in wastewater treatment. For more information about the MagPrex reactor and how it can benefit your wastewater treatment facility, visit our MagPrex product page.
