Designers facing many challenges with creating largest waste water treatment plant in north

Designers facing many challenges with creating the largest WWTP in Canada’s north

By Ken Johnson, Stantec Consulting, Edmonton

Iqaluit wwtp with Koojesse Inlet in the background (high tide) In spite of being a modest community of only 7,000 people, the City of Iqaluit has a considerable stature because it is the Capital City of Nunavut, and regularly hosts prime ministers and the occasional world leader.

The City is embarking on its latest notable endeavour with the development of the largest wastewater treatment plant in the Canadian north. Larger northern cities, like Yellowknife, and Whitehorse, can boast larger wastewater facilities, but these are lagoon systems, which demand considerably less technology and attention for the design, construction, and operation and maintenance. The feasibility study associated with this latest endeavour was awarded to Stantec in January, 2015 Wastewater management in Iqaluit dates back to 1964, when a sanitary sewer outfall consisting of five pipes, discharged raw sewage directly onto the beaches of the community of Frobisher Bay, as it was called back then. Shoreline discharge of raw sewage was maintained for 12 years until the construction of several lift stations provided the means to pump sewage to a macerator system at the head of Koojesse Inlet.

Concurrent with the construction of the macerator station in Frobisher Bay, was the construction of a holding pond built on the tidal plain at the head of Koojesse Inlet.

This facility operated successfully for several decades. However, several overflow and breaching events demanded improvements in the earth structures, and the perimeter drainage to the facility. The lagoon performed well as a primary treatment facility, with a continuous discharge. Effluent quality from the lagoon systems varied significantly over the course of the year because the only process at work in the winter months was sedimentation. Biodegradation enhanced the process performance during the summer months.

In the early 90's, expectations to improve the primary treatment system prompted the Town to complete an engineering feasibility study. This included a rotating biological contactor (RBC), an extended aeration system (EA) and a sequencing batch reactor (SBR). These options were evaluated against nine lagoon options, which included relocating the lagoon facility to other areas on the perimeter of the community.

The highest rated scenario from a decision analysis evaluation was the construction of a new facility. This consisted of a detention lagoon (primary treatment), and the construction of an outfall into the deeper water of Koojesse Inlet. Capital cost of this option was estimated to be $5.7 million (1994 dollars). However, none of these options advanced beyond the feasibility stage.

Regulatory pressure was placed upon Iqaluit in the mid 1990’s to have a system capable of producing secondary treatment effluent quality.

One of the primary reasons for this demand was that sewage discharge into Koojesse Inlet was subject to limited dispersion because of the action of the 11 metre tides in the 4 kilometre long inlet. Several studies have concluded that primary sewage discharge was having a considerable impact on organisms in the tidal flats, because of limited dispersion.

The first attempt at secondary treatment for Iqaluit was a design-build contract that was awarded in 1998 to a contractor that selected a membrane bioreactor (MBR) process. Unfortunately, the inexperience of the design builder in northern wastewater treatment became evident by mid 1999. Significant problems began to arise, due to the placement of concrete within the aeration basins. Upon filling the basins, major leakage was observed, along with deflections in the walls due to insufficient structural strength. Remedial work was completed, and the basins were determined to be waterproof and structurally sound. At this juncture, the design builder effectively abandoned the project. Iqaluit subsequently became aware of additional design and construction problems with the facility.

An evaluation of the un-commissioned sewage treatment plant was completed in 2002. This included an accounting of all the electrical, instrumentation, mechanical, structural, and architectural equipment or features found within the plant. These were compared to the equipment and features presented in the design documents. This accounting identified significant deficiencies in both the design and construction.

Further remedial work was designed to change to conventional wastewater treatment, and abandon MBR technology.

Phase 1 of the remedial work involved building the primary treatment system which was completed in 2006. This work consisted of an auger screen, and a primary screen (Salsnes Filter) housed in an addition to the original building envelope.

Phase 2 of the project was to include design and construction of a secondary clarifier to match the hydraulic capacity of the aeration basins to be converted from the MBR process.

Unfortunately, funding for the project was only sufficient for Phase 1. Nine years after completion of Phase 1 in 2006 , the project is once again proceeding.

Stantec is in a unique position to assist the City of Iqaluit with the current feasibility study, and possibly into the detailed design, with a project team that has been associated with Iqaluit's wastewater treatment challenges for over 20 years. In 1994, team member Ken Johnson completed the first engineering study to provide secondary treatment in Iqaluit, and 10 years later, team member Glenn Prosko completed the assessment of the uncommissioned facility, as well as the engineering associated with the Phase 1 and Phase 2 of the remedial work.

An important consideration for facility performance is the influence of septage or trucked sewage, which still accounts for about 25% of the load into the facility. The concentrated nature of septage along with the high degree of debris in the loads has the tendency to negatively impact the performance of preliminary and primary treatment (Salsnes filter) processes, and increase the maintenance requirements of these systems. The addition of a septage receiving process train, which removes sand, grit and coarse material, benefits the front end, as well as the overall facility performance.

As a capital city, Iqaluit is moving forward with the water and sanitation infrastructure that is appropriate to this status. The path to achieving secondary treatment in Iqaluit has encountered considerable "hiccups" over the past 20 years, but the "time is right" and the "team is right" for the work to proceed to a successful conclusion.

Septage dump station – wwtp in the background

Ken Johnson is an environmental engineer and planner with almost 30 years of experience in the Canadian arctic.

E-mail: kenneth.johnson @stantec.com