Dauphin, MB meets its cold weather ammonia level requirements

Dauphin, MB meets its cold weather ammonia level requirements using a new technology

By Patrick D. Hill

Winters in Dauphin, Manitoba, like much of northern Canada, are bitterly cold. Between December and February, temperatures routinely sink to an average low of -20°C. During this time, the city’s wastewater treatment lagoon is typically engulfed in almost a metre of ice.

That’s a problem, says Jeff Hume, utility foreman for Dauphin’s Utility department. Extremely low lagoon temperatures affect the microorganisms that keep ammonia levels in check. Come spring, when it’s time to start releasing eight months of effluent into the Vermillion River, Hume has been hard pressed to control ammonia levels.

“We are on a seasonal discharge schedule and only discharge four months out of the year, starting in April. The rest of the time, we store our influent. The challenge is our lagoon becomes anaerobic over the winter; our microorganisms freeze and are inactive. So, when we go to start releasing, ammonia is an issue,” Hume explains. “We definitely want and need to protect the local ecosystem.”

Dauphin is known for its many national and provincial parks and lakes. Manitoba's highest point, Baldy Mountain, is located here. While the local economy is largely based on farming and ranching, Dauphin attracts a significant number of tourists. So, it’s important to protect the local splendour.

Dauphin Utility is responsible for maintaining the city’s wastewater operation for a local population of about 8,000 year-round residents. The facility consists of one lagoon with seven cells and three lift stations with a processing capacity of 3.8 MLD.

For aeration, the facility employs three blowers and static tube aerators that release coarse bubbles. Dauphin’s aeration equipment is roughly 50 years old and there are breaks in the submerged aeration pipes. This means aeration across the lagoon is inconsistent. The equipment is also very energy intensive compared to newer technologies.

Energy use and staying within regulated ammonia levels is always on Hume’s mind. “Our system is so antiquated, it’s costing us a lot of money. Taxpayers want our facility to be more cost-effective, so we are looking at doing a big upgrade.”

REDUCING AND STABILIZING AMMONIA LEVELS

Dauphin’s wastewater plant is regulated by Manitoba Conservation under the Environment Act of 1987. The Water and Wastewater Facility Operators Regulation of 2003 sets the standards for classification of water treatment and distribution systems. The average allowable level of ammonia in effluent is 4 mg/L.

During the spring/summer discharge season of 2019, Dauphin was having difficulty meeting this number, experiencing an unacceptable range of 6-15 mg/L

Although planning for a future upgrade of its wastewater treatment facility, ammonia removal took on a new urgency. Hume began researching options. He met Patrick Hill of Triplepoint Environmental at a wastewater conference and decided to get information from him on the company’s NitrOx® lagoon ammonia removal system. The system excels at cold water ammonia removal, achieving an average effluent of 0.03 mg/L, well below Dauphin’s requirements.

“What I liked about the NitrOx system was the small footprint. Other solutions were quite large and choosing one of them would require us to purchase additional land. The NitrOx is compact and fits our current space, avoiding a capital expense,” Hume says. “We were assured

The pilot system was housed in a small building. Winter temperatures in Dauphin routinely sink to an average low of -20°C.

that NitrOx would work in our lagoon throughout the winter, so ammonia levels in our spring release would be a non-issue.”

THE ULTIMATE COLD WEATHER CHALLENGE

The city and Triplepoint agreed to a two-year pilot of the NitrOx system, beginning in the fall of 2019 and concluding in the spring of 2021. The pilot required the installation of two 500litre tanks, each with an air compressor, for predetermined mixing, aeration and biomass. The plant’s microorganisms responsible for consuming organic waste, resided in the controlled environment of the tanks. Influent temperature would be thermally regulated when needed to ensure biological nitrification.

During the first winter of the pilot program, Triplepoint heated the water to 15°C to ensure the microorganisms made it through the winter and continued to process waste. In the spring of 2020, the plant’s ammonia level was below 2 mg/L, which is half of the required level.

Buoyed by the results, it was decided not to heat the water during the second winter of the pilot. It was speculated that the insulating properties of the ice and snow on the lagoon would keep the water in the tanks warm enough to sustain the microorganisms, regardless of the outside temperature.

It was a big risk, but on February 28, 2021, the plant’s ammonia level was 2 mg/L. The system had beaten the cold weather and avoided the cost of heating the tanks.

“Going into the second winter with no heat, I had my doubts,” Hume says. “But we achieved the same results. I was amazed it worked.”

WHAT NEXT?

Dauphin is in the process of identifying funding to upgrade their wastewater treatment plant. The city’s engineer did a cost analysis of NitrOx versus a competing system and determined that with NitrOx the city would achieve a savings of $3 million on the system and installation.

It is also projected that Dauphin would realize a 30% savings in energy costs. With the NitrOx system requiring just three hours of maintenance per year, those costs would be lower as well.

One of the two 500-litre tanks used during the pilot program.

Patrick D. Hill is with Triplepoint Environmental. Email: patrick@lagoons.com