With 26 power-generating dams over its length, the Wisconsin River lives up to its billing as one of America’s hardest working rivers.
However, there is growing concern about algal growth — specifically green and blue-green algae — in Wisconsin’s waterways.
Much of the algal growth is attributed to high nutrient levels in the water. The vast majority of these nutrients come from nonpoint sources, such as fertilizer runoff from agriculture and contamination from developed urban areas, that eventually reach the river. This is the opposite of a point source, such as our Nekoosa Mill, which returns effluent (or treated wastewater) into the river via a large pipe.
While the regulatory path to control nonpoint sources is unclear, Wisconsin has strict regulations that apply to point sources. As concern over algal growth increases, the state has proposed a requirement for point sources to reduce phosphorous levels in effluent by 80 percent or more. That is where our ‘bugs’ come in.
Microorganisms Help Clean Our Water
Like all of our mills, the Nekoosa Mill’s effluent treatment plant relies on microorganisms (affectionately called ‘bugs’) to naturally break down dissolved contaminants in wastewater before being discharged to the river. Because our effluent lacks sufficient nutrients to support this crucial biological system, we add nutrients, such as phosphoric acid and ammonia, into the wastewater to feed the bugs and keep them healthy. In return, the bugs clean the effluent from the mill.
“The whole process is biologically driven,” says Dave Orcutt, environmental manager for the mill. “You have whole organisms that treat and remove contaminants from the water. We may refer to them as bugs, but in reality they are microorganisms, and just like any living creature you have to feed them vitamins and nutrients to help fuel their metabolic processes.”
While essential, this process can also have the unintended consequences of increasing nutrient levels in the mill’s effluent and exceeding the phosphorous limits allowed by the state of Wisconsin. Excess phosphorous can lead to increased algal growth.
In 2015, the mill devised a plan that would enable it to feed the microorganisms a balanced amount of phosphorous, keeping the bugs healthy enough to do their work without overloading the mill’s effluent with excess nutrients.
Under the new approach, the mill’s technical services team takes daily measurements at several points in the effluent treatment process. The data helps the team monitor the amount of dissolved materials in the system that the bugs have to digest and adjust the amount of nutrients the bugs need to do that work.
As a result of this environmental control innovation, Nekoosa has successfully reduced phosphorous discharges by 65 percent. This puts the mill on track to meet the state’s future permit limit — all while maintaining the bugs’ biological health and stability, as well as the efficiency of the effluent treatment plant. At the same time, the mill’s water management costs — for buying chemical nutrients and for paying the state’s fees for discharging phosphorous — have decreased, improving Nekoosa’s bottom line.
Thanks to a little innovation by our mill staff and a lot of help from our smallest coworkers, we’re helping to reduce algal growth in the Wisconsin River.
Source: Domtar Newsroom