Name: Sludge Densification with Sidestream Enhanced Biological Phosphorus (S2EBPR) Removal at Ashbridges Bay Wastewater Treatment Plant (WWTP)
Start: 2026-09-17T13:30:00-0600
End: 2026-09-17T14:00:00-0600

Sludge Densification with Sidestream Enhanced Biological Phosphorus (S2EBPR) Removal at Ashbridges Bay Wastewater Treatment Plant (WWTP)

Thursday September 17, 2026 1:30pm - 2:00pm MDT

Lombardy

Ashbridges Bay WWTP in Toronto is anticipated to reach an average daily flow of 818 megalitres per day (ML/d) in 2054. Due to space limitation for future expansion, intensification of existing secondary treatment is required.
Different technologies were explored to intensify the existing trains, including S2EBPR. S2EBPR would intensify secondary treatment through promoting enhanced biological phosphorus removal (EBPR); the process increases readily biodegradable substrate to enhance floc-forming microorganisms such as phosphate accumulating organisms (PAOs). The facility typically achieves phosphorus removal through chemical precipitation in grit and primary treatment with dosing ferrous chloride.
The City of Toronto along with Jacobs has piloted S2EBPR in an existing secondary treatment train. One of the existing eleven activated sludge aeration tanks is modified to evaluate the potential for secondary treatment intensification by S2EBPR to increase the process capacity.
Multiple modifications were completed on Aeration Tank 2 (AT2) to achieve required operational conditions for S2EBPR:

Converting upstream passes of the AT2 to fermentation cells
Extending return activated sludge (RAS) distribution system from the main RAS header to distribute RAS flow between the fermentation and anaerobic cell appropriately
Converting underflow to overflow baffles between the fermentation and anaerobic cells to retain sludge in the fermentation cells and direct supernatant flow from fermentation to the next cells
Installing mixers and oxidation-reduction potential (ORP) probe in the fermentation cells to enhance and monitor fermentation

An intense sampling program was conducted from February to September 2025 to evaluate the process performance. Three testing periods were performed with intense substrate/nutrients profile and settling testing to evaluate the impact of S2EBR implementation on process performance and capacity. Flow to AT2 was increase from approximately 10% of total plant influent in Phase 1 to approximately 16% of total plant influent in Phase 3.
The trial results show that fermentation and EBPR began developing about one month into Period 1. S2EBPR performance improved in Period 2 due to higher solids retention in the fermentation cells from increased RAS flow; this produced higher rbCOD concentrations and greater phosphorus release, indicating stronger PAO activity. Effluent ortho‑phosphate remained below 0.5 mg‑P/L in Periods 1 and 2, supported in part by ferrous dosing. In Period 3, phosphorus release increased further, suggesting enhanced PAO activity after ferrous dosing to AT2 stopped. Although effluent phosphorus rose slightly, it generally remained below 0.5 mg‑P/L.
A key objective of the trial was to assess process intensification potential. Settling tests showed clear shifts in sludge characteristics, including formation of dense sludge (>3 m/h) and partial granulation (>9 m/h). Granule fractions peaked at 35% in July when SVI was 82 mL/g, then declined in August due to increased flow and no ferrous dosing. S2EBPR significantly reduced AT2 SVI (80–105 mL/g) compared to a control train (AT6), where SVI ranged from 110–180 mL/g at similar or higher flows. Ferrous dosing strongly improved AT6 settleability but had a weaker effect on AT2.
Overall, the trial demonstrated that S2EBPR promotes dense sludge formation, increases secondary treatment capacity, and reduces reliance on costly ferrous chemicals. With appropriate bioreactor design and operational adjustments, process intensification can be achieved with S2EBPR.

Speakers

Roya Pishgar

Process Engineer, Jacobs

Roya is a process engineer with Jacobs, focusing on wastewater treatment and biosolids management solutions. She has 10+ years of experience in consulting and academia and has worked on wastewater and biosolids projects for municipal clients. Roya is interested in biological wastewater... Read More →

Thursday September 17, 2026 1:30pm - 2:00pm MDT
Lombardy 2nf Floor, Delta Hotel

Wastewater Treatment, Plant optimization, tiral of S2EBPR

WCW26

Roya Pishgar

Attendees (1)

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WCW26

Roya Pishgar

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