Cold climate municipal wastewater treatment lagoons upgraded with SAGR post-lagoon nitrification, SAGR Recycle for denitrification, and dosing for phosphorus removal

Project Background & Challenges

Back in 2014, Pilot Butte’s population had just climbed past 2,500, and with several developments in progress, the Saskatchewan municipality needed to upgrade their two-cell facultative lagoon system to allow for more treatment capacity. Around the same time, the creek into which the lagoons seasonally discharged that had been classified as “fish bearing” by regulators, and thus the upgraded treatment system would need to meet Canada’s strict Wastewater Systems Effluent Regulations (WSER).

Before the project was finalized, in addition to the common cBOD₅ and Total Suspended Solids (TSS) treatment targets of <10 and <15 mg/L, respectively, and the WSER-inspired non-toxicity requirements of <0.019 mg/L of un-ionized ammonia, it was determined the system would need capacity to treat 3,550 m³/day (0.94 MGD) to Total Nitrogen of <10 mg/L and Total Phosphorus of <1 mg/L as well. The unique challenge at Pilot Butte was the limited property boundary. Setback requirements from existing wells in the area dictated the available footprint. Early design solutions considered raising the lagoon berms and increasing lagoon slopes to squeeze as much treatment volume as possible into the small available footprint; however, it was not possible to gain enough volume in the lagoons while staying within the property boundaries and site setback constraints.


The Nexom Answer

Working with engineers from B&L Engineering in Saskatoon, Nexom’s lagoon process experts helped design a solution that would enable the Pilot Butte community to maximize the use of their existing lagoon infrastructure without sacrificing the operations and maintenance (O&M) simplicity that makes it ideal for a small municipality.

Achieving cold water ammonia removal

Before the advent of Nexom’s proprietary SAGR®, removing ammonia has been a challenge for cold water lagoons. Bacteria that removed ammonia via the process of nitrification (turning ammonia into nitrates) would be crowded out of lagoons as the water cooled, the biomasses’ metabolism slowed and the more hardy cBOD₅-removing heterotrophic bacteria took over. The SAGR would address this by providing the ideal bacterial climate that would pre-grow multiple nitrifying biomasses to be capable of fully removing the ammonia to <1 mg/L even in freezing water as cold as <1°C.

Removing nitrates via lagoon-based denitrification

Converting ammonia to nitrates does little to address Total Nitrogen compliance, which encompasses both nitrogen bound up in ammonia, nitrites, and nitrates. For this, denitrification is required, a similarly challenging process to accomplish in cold lagoons. It requires the same heterotrophic bacteria that consume cBOD₅ to turn to nitrates (in place of the often much-more plentiful dissolved oxygen) as fuel. To accomplish denitrification in this lagoon setting, Nexom turned to its proprietary SAGR Recycle process, whereby a portion of the SAGR effluent rich in nitrates is recycled to the front of the plant—the lagoons’ influent point—where the heterotrophic bacteria feasting on cBOD₅ is plentiful. Not only does this allow for partial denitrification as the heterotrophs turn to nitrates as an oxygen alternative, it serves a dual purpose of reducing the demands on the subsequent optAER® lagoon aeration.

Meeting <1 mg/L Phosphorus with minimal O&M

There are many ways to remove phosphorus from the waste stream; however, many biological and/or filtration-based systems would dramatically increase the complexity of lagoon-based systems originally chosen for their unmatched simplicity. To address the need to meet the <1 mg/L Total Phosphorus limit most simply, influent phosphates need to be bound into flocs and removed from the waste stream. At Pilot Butte, a specially-designed, simple chemical dosing and mixing process was introduced, whereby a bench scale-tested ratio of chemical is introduced to the influent in a rapid mix tank to achieve full contact and reaction with the phosphates, is subsequently mixed in a slow mix tank to allow the phosphates to flocculate, and is discharged into the primary lagoon where the flocs settle.

Site Construction


Upgraded System Performance

After two full years of operation, the system has exceeded expectations: it has yet to produce a detectable level of Total Ammonia-Nitrogen (all samples reporting below 0.04 mg/L), and has averaged 4.2 mg/L of Total Nitrogen, less than half its limit.

In addition, lending credence to the significant (and still growing) evidence that a SAGR-equipped system provides sufficient disinfection performance, the 10/19/21 sample from Pilot Butte showed effluent <10 and 20 MPN/100 mL of E.coli and Total Coliform, respectively.

Project Information

Project Type: Municipal wastewater treatment
Completion Date: 2021

Treatment Objectives

Design Flow:
• <3,550 m³/day (0.94 MGD)
Effluent Objectives:
• <0.5 mg/L Total Ammonia-N
• <0.019 mg/L Un-ionized Ammonia
• <10 mg/L cBOD5
• <15 mg/L Total Suspended Solids
• <10 mg/L Total Nitrogen
• <1 mg/L Total Phosphorus

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