New Sidestream Process Removes Ammonia and Provides Total Nitrogen Removal while Saving Energy
Written By: Bradley Lake, PE and Randy Wirtz, PhD, PE, ENV SP, Strand Associates Inc.
Many communities face the pressures of increased nutrient removal requirements, increased loadings, and constrained wastewater treatment plant sites, while also needing to maintain treatment performance and manage tight budgets. The City of Fond du Lac project is an excellent example of how to successfully addresses all these issues. Many communities face the pressures of increased nutrient removal requirements, increased loadings, and constrained wastewater treatment plant sites, while also needing to maintain treatment performance and manage tight budgets. The City of Fond du Lac project is an excellent example of how to successfully addresses all these issues.
Wastewater treatment plants typically use biological processes to remove excess nutrients from wastewater. One of these nutrients is ammonia, which if left untreated and returned to the environment can either be toxic or take oxygen from streams, rivers, and lakes, resulting in the proliferation of algae and compromised water quality. The conventional processes used to remove ammonia require significant energy and require substantial infrastructure.
New technologies have been developed to remove ammonia using less energy and employing fewer facilities. These technologies use naturally occurring bacteria – termed “Anammox”, which stands for Anaerobic Ammonia Oxidation – that have unique metabolism applied to the wastewater treatment process. This new Anammox process results in total nitrogen control with more than 90 percent of the original ammonia being converted to nitrogen gas and the remaining percentage converted to nitrate. The Anammox or deammonification process has only recently been commercialized in the United States.
Benefits of the Anammox technology include:
- Reduced energy use
- Smaller facility footprint
- Improved quality of effluent discharged into the environment
- 90 percent total nitrogen removal • Improved operations, including minimal carbon usage, which is necessary for the Biological Phosphorus Removal Process
Fond du Lac Implements First Sidestream Deammonification Process in the State
The City of Fond du Lac designed and recently started up a sidestream deammonification process – the first in Wisconsin, the second in the Midwest, and the first in the United States to use the Paques AnammoPAQTM process.
The City’s Wastewater Treatment and Resource Recovery Facility (WTRRF) treats an average of approximately 8 million gallons per day (MGD) of wastewater from about 65,000 customers, including residents in the city, surrounding municipalities, and local industry. The influent loadings to the WTRRF have increased and high ammonia loadings from industrial wastes and recycled flows at the WTRRF would have required significant expansion of the facility in the near future.
Excess biosolids are wasted from the biological treatment process and digested anaerobically. The facility also receives and treats high-strength wastes from industrial customers (metered slowly and directly into the digesters) to increase digester biogas production so the facility can operate a 450 kW biogas co-gen system to off-set electrical demands at the plant. The digested sludge is dewatered in centrifuges for approximately 7 hours per day, which produces dewatered sludge cake and centrate high in ammonia. Since the centrate ammonia mass (pounds per day) is similar to the mass of influent ammonia the WTRRF receives in the raw wastewater, the centrate is equalized to spread the recycle ammonia load over a full day to avoid erratic influent loading to the biological processes. The ammonia is then nitrified through the traditional process and converted to nitrate to meet discharge permit effluent ammonia requirements. Planning for the WTRRF identified the need for a full aerobic treatment train expansion in order to continue meeting these effluent ammonia requirements. The sidestream deammonification concept was identified as an alternative during planning for treating the highly concentrated centrate ammonia before it was recycled back to the raw wastewater entering the WTRRF. Ultimately, the sidestream ammonia concept was selected and implemented at the WTRRF.
The sidestream project involved the construction of a new treatment tank adjacent to the existing pumping and equalization facilities, which were reused. The footprint of the new deammonification tanks was minimized by installing the new solids removal pretreatment equipment on top of the new deammonification tank, all resulting in a very compact layout and conserving as much of the WTRRF site as possible for future expansion. Additionally, the project’s budget was met, and the start-up time for the biological process was significantly less than the anticipated 4 months, requiring less than 1 month for actual process startup.
Compared to the alternative of expanding the WTRRF aerobic treatment train to continue the traditional nitrification process, the implementation of the Annamox sidestream deammonification technology saved an estimated $3 million in capital costs. This project also reduces energy costs due to the lower oxygen requirement associated with the deammonification process along with an innovative settling device that avoids traditional return activated sludge pumping. The deammonification process has also been shown to improve the performance of the biological phosphorus removal process at the WTRRF, which has been in-service for several years.
More conventional treatment options would have resulted in approximately double the project costs and higher customer rate increases. With the application of the sidestream deammonification process, ammonia loadings were significantly reduced, resulting in a multi-year delay in the need for a facility expansion.
Performance Is Exceeding Expectations
The process has been highly successful, currently exceeding the guaranteed ammonia removal efficiency of 83 percent on a mass basis. Since startup, the system typically achieves more than 90 percent removal. Furthermore, the process can receive more loadings as the WTRRF grows, which will allow the City to meet its needs without expanding the deammonification system for many years.
With the successfully implementation of this sidestream deammonification project, Fond du Lac has shown a way for other communities to address increased nutrient removal requirements, increased loadings, and constrained treatment facility sites, while also maintaining treatment performance and managing tight budgets.
About the Guest Bloggers
Bradley Lake, PE, of Strand Associates, Inc.® (Strand), served as Primary Design Engineer for the Fond du Lac Wastewater Treatment and Resource Recovery Facility Sidestream Deammonification project. Brad earned his Bachelor of Science degree in Civil/Environmental Engineering and his Master of Science degree in Civil/Environmental Engineering from the University of Iowa. He has been with Strand for nearly 30 years.
Randy Wirtz, PhD, PE, ENV SP, of Strand Associates, Inc.® (Strand), served as Project Manager for the Fond du Lac Wastewater Treatment and Resource Recovery Facility Sidestream Deammonification project. Randy earned his Bachelor of Science degree in Civil/Environmental Engineering at the University of Wisconsin-Platteville and his Master of Science degree in Civil/Environmental Engineering and his Doctorate degree in Civil/Environmental Engineering from Iowa State University. He has been with Strand for 25 years.
Strand has been providing exceptional civil and engineering service to clients since 1946 and is a long-time ACEC Wisconsin member.