Biological nutrient removal continues to gain momentum as utilities look for ways to meet tightening effluent limits while reducing chemical reliance and long-term operating costs. Among these innovations, side stream enhanced biological phosphorus removal (S2EBPR) is emerging as a promising alternative to chemical phosphorus removal and conventional enhanced biological phosphorus removal (EBPR), particularly at facilities where tankage, site footprint, or readily available carbon are constrained.
In a recent episode of the PARC Innovation Flow Podcast, Carollo Principal Technologist Bryan Coday discussed how S2EBPR works, why interest in the approach is accelerating, and what utilities can learn from a recent pilot project at South Platte Renew.
Rethinking Phosphorus Removal Without Chemicals
Phosphorus plays a complicated role in wastewater treatment. While excess phosphorus in receiving waters contributes to eutrophication and hypoxic zones, it is also a finite resource with growing interest in recovery and reuse. Traditionally, some facilities have relied on chemical dosing to meet phosphorus limits, but that approach comes with long-term costs and downstream impacts.
“There are opportunities to reduce effluent phosphorus discharges, but also opportunities to recover it for beneficial use,” Bryan explained. Biological phosphorus removal creates that opportunity by shifting phosphorus capture into the biomass, where it can later be managed or recovered in the side stream.
How Side Stream EBPR Improves Reliability
Conventional EBPR in the mainstream process can be difficult to sustain. Phosphorus-accumulating organisms require readily biodegradable carbon, which many facilities do not consistently have. Seasonal variability and existing tank configurations can also limit performance or reduce plant capacity.
S2EBPR addresses these challenges by moving the anaerobic conditioning step out of the mainstream process. “By moving that anaerobic zone to the side-stream, you can ferment carbon internally and be less reliant on influent wastewater quality,” Bryan said. “That presents the opportunity to make biological phosphorus removal much more resilient than it has been historically.”
This approach enables facilities to preserve secondary treatment capacity by relocating the anaerobic zone to the side stream, while enhancing phosphorus removal performance – particularly at plants that were not originally designed to support biological phosphorus removal.
Lessons From the South Platte Renew Pilot
The pilot project at South Platte Renew provided an opportunity to test S2EBPR within a complex, legacy facility configuration. By repurposing an existing tank to function as a side-stream fermentation zone, the team evaluated whether biological phosphorus removal could reduce reliance on current chemical dosing.
One challenge encountered during the pilot was the need to route 100 percent of the return-activated sludge through the side-stream zone, which reduced retention times to levels below ideal conditions for S2EBPR. Even with those constraints, the results were encouraging. “We did see a significant shift in the phosphorus accumulating organisms and an appreciable increase in phosphorus removal,” Bryan noted.
While the pilot did not yet achieve full regulatory targets, it demonstrated proof of concept and justified further testing and refinement.
Water Innovation Starts with Operations
As innovation accelerates across the wastewater industry, approaches like S2EBPR demonstrate how biology, piloting, and collaboration can help utilities meet today’s challenges without overreliance on chemicals.
To hear Bryan Coday’s full discussion on S2EBPR, pilot testing, and innovation in wastewater treatment, watch the complete PARC Innovation Flow Podcast episode: