Misipawistik Cree Nation, ManitobaRemote, northern lagoon upgraded for year-round ammonia and phosphorus compliance.
Project Background & Challenges
First Nations communities in Canada are faced with many obstacles when it comes to building and maintaining water and wastewater treatment facilities. Geography and cold climate conditions create challenges for existing and proposed treatment facilities, and often limited road access presents the initial roadblock to bring in construction equipment and trained personnel, even as high population growth puts more and more loading on these aging wastewater facilities.
The Misipawistik Cree Nation (MCN) in Manitoba, Canada, is descended from ancestral indigenous peoples who have populated the Canadian Shield region for over 10,000 years. Once known as Grand Rapids First Nation, for the four miles of turbulent rapids through which the Saskatchewan River drains into Lake Winnipeg, this close relationship to water meant the stakes for the performance of their wastewater treatment system were clearly higher than simply regulatory non-compliance.
In 2012, their existing wastewater treatment facility—a two-cell facultative lagoon—had proved incapable of achieving updated BOD, TSS, phosphorus, and ammonia limits. The community sought a new solution to upgrade their wastewater facility from a facultative seasonal discharge lagoon to a continuous discharge facility that would be reliable, simple and cost effective to operate, while also meeting meet Canada’s Wastewater System Effluent Regulations (WSER) of 2012, which specified effluent un-ionized ammonia cannot be acutely lethal for aquatic life and cannot exceed 1.25 mg/L.
The Nexom Answer
Working with engineers from Nexom, MCN’s chosen solution would use and revitalize the existing lagoons system.
An aluminum sulfate (alum) addition system prior to water entering the first lagoon cell would provide phosphorus removal via settling within the primary (Cell #1) lagoon. Upgrades were conducted on the secondary lagoon (Cell #2) with the addition of Nexom’s optAER® aeration system for secondary treatment. Finally, SAGR® post-lagoon cold-water nitrification beds were added for ammonia removal and final BOD/TSS polishing. The chosen solution could then reliably and safely discharge into Lake Winnipeg via the Saskatchewan River.
Upgrading the existing lagoons:
The goal at Misipawistik Cree Nation was to create a process that was cost effective and simple to operate, while also providing consistent performance in winter water temperatures (November through April) that can fall below 1°C.
Biological wastewater treatment using lagoons has been a common answer for communities seeking low operations and maintenance (O&M) solutions. But they come with significant challenges for cold climates. In a typical unaerated lagoon, once ice forms on the surface, the ability of oxygen from the air to dissolve into the water and reach the nitrifying (ammonia-removing) bacteria disappears. Even when lagoons are aerated, near-zero water temperatures slow bacterial metabolism down to a fraction of summer rates.
Working with MCN, Nexom utilized the existing facultative lagoons for primary treatment, upgraded with an optAER aeration system for enhanced BOD and TSS removal. Aeration provides oxygen, residence and contact time for the natural bacteria, which ultimately convert the wastewater contaminates (BOD, ammonia, and TSS) to carbon dioxide, water, inert ash and nitrates. It also provides effective odor control.
The optAER aeration system at MCN consisted of floating laterals and a pair of positive displacement blowers. With floating laterals, lagoon cells don’t need to be dewatered or taken out of service for installation or maintenance – all maintenance work can be completed from a boat, using a 2-person crew. In comparison to conventional mechanical treatment facilities, optAER-enhanced lagoons maintain the simplicity of a lagoon system for a fraction of the costs to construct and operate.
The two blowers provide the necessary air supply during normal system operations, in a duty/standby configuration. The benefits of using positive displacement blowers include consistent flow of air to the lagoon regardless of discharge pressure, as well as simple operation and maintenance. Each blower included a sound-reducing enclosure.
Implementation of a two-cell aerated horizontal flow SAGR:
At Misipawistik Cree Nation, the team at Nexom planned two SAGR beds for post-lagoon secondary treatment. The two cells were constructed in parallel, with water from the lagoons divided and distributed evenly between cells before recombining at the end for final discharge.
The SAGR is a patented process providing full nitrification as well as BOD and TSS polishing in cold to moderate climates. Presently installed at more than 70 locations across North America, with an additional 15 systems currently being installed, the SAGR features a clean gravel bed with evenly distributed wastewater flow across the width of the cell, and a horizontal collection chamber at the end of the treatment zone. Linear aeration throughout the floor of the SAGR provides the aerobic conditions that are required for nitrification. The gravel bed is covered with a layer of wood chips or mulch for insulation.
The only moving parts are the blowers supplying air to the system, making the O&M requirements like that of an aerated lagoon. Process control requirements are limited to seasonal (twice a year) manipulation of the influent control valves. Additional benefits of the SAGR system include low capital and operation costs, full nitrification in all seasons, compatibility with existing facultative lagoons, and fecal and total coliform removal.
The SAGR consistently reduces Total Ammonia-Nitrogen (TAN) in near-freezing water to levels less than 1 mg/L, safely meeting the non-toxicity requirements of WSER. Nexom’s patented Step-Feed process nurtures the nitrifying bacteria needed to meet these requirements at temperatures less than 1.0°C. At MCN, the SAGR also polishes the effluent, providing BOD5 and TSS levels less than 10 mg/L and significantly reduces coliform bacteria (>99% reduction), resulting in no need for additional disinfection.
Treating for Phosphorus:
In total phosphorus (TP) removal, a metal salt such as aluminum sulfate (alum) is brought into contact with the soluble phosphorus to form a solid floc. The design of a TP removal system is dependent on numerous factors including wastewater characteristics, the chemical feed point, metal salt quantity, the method of addition and the time after addition. Following testing, Nexom engineers determined alum dosing into the primary influent lift station would reduce the TP levels in the system to less than 1 mg/L.
At Misipawistik Cree Nation, the alum was dosed near the intake of the primary lift station pump via an insulated feed line. The dosing pumps deliver a flow of up to 125 mL/min of alum and have the ability for turn-down during initial operation. The lift station pump creates a rapid mix zone, ensuring the alum is distributed evenly within the wastewater to maximize reaction with the dissolved phosphorus. Slower mixing within the 800m forcemain to the lagoon allows the alum and phosphorus to bind together into flocs. The forcemain has a 50-minute retention time for floc formation prior to settling in the primary lagoon (Cell #1). The wastewater then continues through the aerated lagoon (Cell #2) and SAGRs on its way to the Saskatchewan River.
Location: Misipawistik Cree Nation, Manitoba
Project Type: Municipal Wastewater Treatment
Completion Date: October 2013
408 m3/day (0.108 MGD)
- Non-Toxic Effluent
- 1 mg/L Total Ammonia-Nitrogen (Summer)
- 7 mg/L Total Ammonia-Nitrogen (Winter)
- 20 mg/L cBOD5
- 25 mg/L Total Suspended Solids
- 1 mg/L Total Phosphorus
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The lagoon aeration upgrades and SAGR installation were commissioned successfully by Nexom staff on October 30th, 2013. The operation of the system was explained and demonstrated to the operators with both theoretical and hands-on instruction. Both the lagoon and SAGR aeration systems were left in operation, with one blower running and one on standby for each system. The alum dosing system was commissioned in November 2013.
Due this late start-up date, the SAGR system was unable to produce the expected nitrification targets during the first winter of operation. Cold water temperatures during system start up prevented the SAGR system from growing enough biomass within the bed to provide full nitrification at startup. Nexom staff and engineers worked with the team at MCN to support and overcome this challenge, providing three additional training sessions with WWTP operators. Once water temperatures increased in the spring, enough biomass was established to allow the SAGR system to fully nitrify secondary treated lagoon effluent to less than 1 mg/L.
Misipawistik Cree Nation now has a technologically advanced wastewater treatment system that is simple to both operate and maintain, while also being capable of growing with the community to accommodate a growing population. Since its first winter of operation, the system has reliably met federal wastewater regulations, and in doing so, MCN has become an example for small rural and remote Canadian communities looking to achieve full wastewater effluent quality compliance without giving up on their existing infrastructure.