I’ll admit it: As editor of this magazine I have paid attention to treatment technology at the expense of a highly cost-effective alternative for improving water quality.

I’m talking about nutrient trading, often called water quality trading. It’s a way for clean-water agencies to meet increasingly strict permit limits on nitrogen and phosphorus without spending multimillion dollars on new treatment processes.

Let’s say a regulatory agency decides that a stream is impaired and that phosphorus inputs need to be reduced. One way to do that is to ratchet down the phosphorus limits in clean-water plants’ effluent permits. Yet often those plants are not, by far, the biggest phosphorus contributors to the stream; inputs from stormwater and farm runoff are much greater.

Another problem is that removing phosphorus from effluent runs smack into the law of diminishing returns: wringing out the last milligrams per liter can cost tons of money, for not much benefit.

Looking elsewhere

So, why not work on those big sources where a far lower investment can make a lot more difference? That’s where nutrient trading comes in. It creates market-based financial incentives for all who affect the stream to work together on nutrient reduction.

For example, the clean-water agency, instead of spending millions on a new process, can invest a fraction of that to help farmers adopt best practices that curtail runoff and keep the phosphorus on the land.

Suppose that a utility pays a farmer to plant cover crops and improve fertilizer management, leading to nutrient reductions greater than required. That utility then would earn credits (generally measured in pounds of nutrient) that could be sold to another source, such as a treatment plant faced with difficulty meeting nutrient discharge limits on its own.

These programs require the nutrient reductions achieved through trading to result in water quality as good as or better than what would be achieved through more intensive treatment. 

A practical example

The easiest way to understand how this works is to look at an actual project.[1] MSA Professional Services undertook nutrient trading with the small Wisconsin city of Brodhead. To meet strict new water-quality-based effluent limits in discharge to a creek, engineers and city leaders saw that a treatment plant upgrade (estimated cost $4.2 million) was not the optimal solution.

In response, the city wastewater team, MSA engineers and farmers worked together to reduce phosphorus inputs from the land. One project component was to stabilize stream banks against erosion because sediment washed into the water naturally contains phosphorus.

Workers stabilized 62 actively eroding banks in cooperation with two landowners. They deployed practices including vegetative reinforced soil slopes, root wads and backwater refuges to bolster and protect aquatic life along the creek. Custom flood gates made of vertical hanging PVC pipe were installed in sensitive areas to keep cattle from crossing the stream, yet allow canoeists and kayakers to pass through.

The team also helped a dairy farmer modernize manure handling and curtail runoff. This included building a 2.2 million-gallon manure tank with six months of storage, installing roof covers and gutters, adding waste transfer channels to collect runoff and manure from barnyards and transport it to the storage tank.

The farmer also improved nutrient management in crop fields. Runoff to the creek from animal production area was essentially eliminated. The storage tanks enabled the farmer to apply manure to the fields at the optimal times and places.

The payoff

In the end, through the water quality trading program, the city reduced its total phosphorus load by 1,090 pounds per year, versus about 190 pounds that would have been removed by the $4.2 million treatment upgrade. The city achieved more than five times the required phosphorus reduction and earned 390 pounds per year of water quality trading credits. In the bargain, 1.2 miles of the creek was rehabilitated. The total capital cost was just $932,256.

So clearly, reducing nutrients isn’t all about more and better treatment technology. Sometimes it’s about looking to the land and assembling a team to approach the reductions holistically. That’s something I need to remember in reporting on treatment facility operations.

Reference:

[1] Water Quality Trading Flips the Script on Phosphorus Compliance, Andrew Skog, MSA Professional Services, June 14, 2022, https://www.acecwi.org/news/water-quality-trading-flips-the-script-on-phosphorus-compliance.