Faced with the one of the most stringent nutrient limits in Minnesota and seven years to comply, the City of Detroit Lakes is making long-range plans for their wastewater treatment facilities. Find out what they are planning to do and why.
Like many cities, the City of Detroit Lakes is negotiating a complex nexus of aging infrastructure, population growth, new regulations, funding concerns and environmental considerations.
It’s not easy.
“Finding the best solution for any given challenge has more variables than a generation ago,” says wastewater engineer Susan Danzl. “The truth is, everything is connected. We have a responsibility, and an opportunity, to plan infrastructure that positively impacts current and future citizens — and the world.”
For Detroit Lakes, this means developing a long-term wastewater facilities plan that addresses aging infrastructure and accommodates growth throughout the next few decades, while considering user rates and available funding.
It also means further protecting the local water’s beneficial uses — like fishing and swimming — by reducing nutrient loads to extremely low levels.
In 2013, a regulatory agency dedicated to protecting Minnesota’s many water resources, the Minnesota Pollution Control Agency (MPCA), directed the City to decrease the phosphorus content of the wastewater effluent in order to preserve area water quality.
Specifically, a study conducted by the MPCA revealed phosphorus levels from various sources were affecting a nearby body of water, Lake St. Claire, that was placed on the impaired list due to high levels of excess nutrients. The nutrients were causing algal blooms.
As a result, the City of Detroit Lakes was faced with a new Total Maximum Daily Load (TMDL), a regulatory term describing the maximum amount of a pollutant that a body of water can receive while still meeting water quality standards.
The City would need to reduce the phosphorous entering Lake St. Claire. Not by just a little, in fact, but by 94 percent — from 1 milligram per liter to .066 milligrams per liter, which is the concentration equivalent to the mass load limit the City received in their discharge permit at future projected flows.
“There are other cities in Minnesota facing similar limits, but this is one of the lowest in the state,” says Jessica Hedin, PE, who assisted in developing the long-range wastewater facilities plan.
The low limit comes from guidelines established at a national level by the EPA. These guidelines are currently being handled by each state individually. In Minnesota, this took the form of two key regulations.
Arriving first, in 2008, were the Lake Eutrophication Standards. Then, in 2014, an additional regulation came into effect, called the River Eutrophication Standards. Combined, these standards are driving change in the wastewater treatment industry and others.
In fact, efforts were made to overturn these significantly low nutrient limits, but were recently denied by the Minnesota Court of Appeals.
“The question now is, how do we find the most sustainable, most reasonable way to comply?” says Hedin.
What could the City of Detroit Lakes do to meet the stringent wastewater regulation and, while they are at it, serve the community far into the future?
SEH wastewater professionals assisted the City in looking at the options and identifying the most cost-effective approach to meet the limits. Alternatives included:
Looking at the alternatives side by side, they discovered that costs associated with moving the facilities or discharge were high. The proposed long-range plan involves leaving the plant and discharge where they currently are, but getting more serious about treatment.
How do you move from one milligram per liter to .066 milligrams per liter?
To meet the extremely stringent nutrient limit at the current location, the City would have to incorporate a range of new and emerging technologies.
“However the City decides to approach the solution, technology will play a key role in meeting a reduction of this magnitude,” says Danzl.
According to Danzl, a combination of innovative wastewater technologies and processes can be implemented in tandem in order to reduce nutrient load to low levels, including enhanced tertiary processes coupled with biological nutrient removal.
As it progresses with its wastewater treatment facilities and prepares for the next few decades, the City of Detroit Lakes Public Utility will continue to serve as a role model for other communities affected by extremely stringent nutrient load regulations.
Jessica Hedin, PE*, is a wastewater engineer with experience in planning and design of industrial and municipal wastewater treatment facilities. Her experience with wastewater treatment includes anaerobic and activated sludge systems, headworks, ultraviolet disinfection and biosolids handling. Contact Jessica
Susan Danzl, PE**, is a wastewater engineer with experience in planning, evaluation, design and construction of wastewater treatment facilities. Her experience with wastewater treatment encompasses small and large facilities, including retrofits as well as new treatment facilities. Contact Susan