optAER-Martensville-Saskatchewan

PROJECT BACKGROUND & CHALLENGES

The town of Martensville, Saskatchewan, is less than 300 KM (173 M) from provincial capital Regina but less than 20 minutes north of Saskatoon. It can be found roughly halfway between the North and South Saskatchewan Rivers, where it inhabits a region of aspen parkland – the transitional zone between the expected prairie grasses of the south and the rugged boreal forest in the north. North of Saskatoon, the Martens family had originally purchased a plot of land in 1939. Sections of this land were later sold to other families also wishing to live in a small community, eventually resulting in the community of Martensville. First incorporated as a town in 1969, it would gain sewer and water systems in 1976 as more and more people began to move into the area.

Officially granted city status in 2009, many people who work in Saskatoon choose to live in Martensville, given its proximity and the ability to retain close connections within the community. In fact, the most recent Canadian census places the population of Martensville at nearly 10,000 people - making it the 11th largest city in the province. Starting first in 2004, Martensville sought to upgrade their wastewater treatment facility. Faced with a rapidly expanding population and a pair of facultative lagoons, city engineers turned to a combination of our optAER® fine-bubble lagoon aeration with patented Float-Sink headers, to ultimately create a solution.

THE NEI ANSWER

The original treatment system (facultative ponds) had been adequate for wastewater treatment until the area began experiencing rapid population growth. In 2004, the existing system was no longer able to maintain permit levels of Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). Additionally, facultative (or passive) wastewater storage ponds are well known for producing odors, particularly during spring break up.

One option for increasing capacity, without constructing additional lagoons or expanding existing ones, is to aerate the lagoons. Aerated treatment cells greatly reduce the footprint of the treatment upgrade as compared to installing additional facultative cells.

Working with Catterall & Wright Consulting Engineers, we proposed upgrading the existing lagoons using the our optAER system, enabling Martensville to both deal with its odor issues and also meet its permit limits for Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) year-round.

Solving the capacity problem:

The initial upgrade was created in two phases. By pre-planning for greater needs in the future, the system was designed so additional diffusers and piping wouldn’t be required to upgrade the system for higher flow, as the projected increase in oxygen demand could be met easily by increasing the speed of the existing blowers. The first phase was designed to handle the 2004 population of 6,000 people, at a flow rate of 1,800 m3/day.

Two new optAER aerated lagoons were constructed, and the existing facultative lagoons were converted to storage cells. By doing this, we were able to address increased loading and rapid community growth in a way that made use of previous treatment infrastructure investments. Additional modifications were also completed at this time in preparation for the second phase. Headers were added around both the new aerated lagoons and the existing storage cells, which would allow for further expansion of treatment plant capacity in the future and enable the addition of aeration to the storage cells in the future.

Air was provided to the system via one 75 hp positive displacement blower, with a second blower on standby. This allowed for redundancy in the system in the case of regular maintenance or repairs to the primary blower. It also provided room to expand system capacity in the future. Both blowers are housed inside a precast concrete building to provide protection from the elements, and came with full sound enclosures, which effectively reduce the noise level within the blower building to below 73 dBA.

During both phases, the fine-bubble aeration diffusers pivotal to the optAER system provide excellent operational flexibility, operating in an airflow range of 5-20 SCFM. The airflow can be adjusted to accommodate variable load conditions while also providing cost effective future upgrades to increase capacity. Fine bubbles also mean greater surface area and a slower rise rate when compared to traditional “coarse bubbles”. This increases the overall oxygen transfer efficiency of the system, and effectively mixes the water to ensure aerobic conditions throughout the pond.

The diffusers are placed at the bottom of the pond, suspended from air distribution floating laterals on the surface of the pond. This provides a level surface, meaning diffusers can be installed at consistent depth regardless of the condition of the bottom of the pond. Equal diffuser submergence allows for even distribution of air, providing consistent mixing and prevents the formation of localized anaerobic zones, which can create odor issues.

The second phase would allow the WWTF to accommodate the needs of a future population of 8,000, with a flow rate of 2,400 m3/day. In 2008, the storage cells were aerated with the optAER aeration system, using the headers pre-installed during the initial construction of the new lagoons in 2004. Linear aeration tubing was installed in the shallow storage cells to provide gentle mixing and maintain aerobic conditions in order to minimize odor generation, as aerating the water throughout the winter is very effective for minimizing “spring turnover” odors.

Growing with the community:

Unexpectedly rapid population growth saw the community of Martensville hit its 20-year population projection within ten years. In 2013, the town reached out again to us, seeking a solution. In order to gain additional capacity from the current structures, a third aerated storage cell was constructed in order to accommodate the increase in flow. The blower servicing the storage ponds was also replaced with a larger one to supply the required oxygen.

Implementation of the SAGRs:

At Doaktown, two SAGR beds were constructed after the lagoons for tertiary treatment, providing additional BOD and TSS polishing. The SAGR consists of an aerated submerged aggregate bed, with a horizontal flow distributing influent wastewater across the bed.

With the SAGR, the only moving parts are the blowers supplying oxygen to the lagoons and SAGR. A simplified control scheme manages the day-to-day operation of the blowers, maintaining the simplicity of a lagoon-based system while still meeting effluent limits. This simple process allows nitrification and polishing to be accomplished following any aerated or facultative lagoon.

One concern during the design of the Doaktown facility was low influent alkalinity, which is required for complete nitrification. However, following additional testing, it was determined that no alkalinity addition was necessary to meet the effluent limits. Operational data over the past 9 years has confirmed that the system meets the required nitrification levels reliably despite low alkalinity.

UPGRADED SYSTEM PERFORMANCE

Following the successful completion of system construction, the upgraded WTTF at Doaktown was commissioned in December 2010, with operator training on December 20th. Since commissioning, the Doaktown facility has exceeded all effluent requirements - consistently producing low effluent concentrations for BOD, TSS and TAN.

The system was designed with simplicity in mind. The O&M requirements of the process are similar to the operation of a conventional diffused air aerated lagoon, but with no solids return to monitor and adjust, sludge management and disposal becomes a non-issue. Since commissioning, it is estimated operators of the Doaktown facility spend (an average) 30 minutes per day doing a systems check and maintenance.

One of the considerations while designing the treatment facility was the temperature of the effluent discharging from the lagoon, as warm water entering the Miramichi River was having an adverse effect on the salmon population. The system’s long retention time allows the temperature of the effluent time to drop to match environmental conditions, ensuring a safe breeding ground for the salmon.

The upgraded system in Doaktown is an example of a cost-effective and efficient solution for small and mid-sized communities. These communities face the same effluent challenges as larger communities and are now able to keep the low operational complexity and costs associated with their existing lagoon systems.