It’s amazing what creative thinking can do for clean-water facilities. That’s notably true in dealing with ever-stricter phosphorus limits.
When tighter effluent P permits began hitting a decade or two ago, utilities faced what looked like horrendously expensive plant upgrades that would drive up sewer rates — always a big hit with residential and industrial customers.
But then along came a variety of innovations that today give operators choices other than spending big on new concrete and machinery. This edition of TPO highlights one of those choices: water-quality trading. In particular, we feature a trading clearinghouse in our home state of Wisconsin that is the only one of its kind in the nation.
A challenge with water-quality trading (sometimes called nutrient trading) is putting trade partners together. The clearinghouse makes those connections easier.
A related approach is adaptive management, which acknowledges that reducing a clean-water plant’s discharges often is not the most cost-effective way to remove phosphorus from a stream or watershed.
Here the answer, at least in part, is for the clean-water utility to help a nonpoint source of phosphorus — often a farm — install best practices to help keep that nutrient on the land and out of the water. That’s usually much less costly than a treatment process upgrade, and in the bargain usually removes more phosphorus.
And then, back at the plant level, there are process innovations that can remove at least part of the effluent phosphorus load without a major upgrade. One practitioner of this approach is Grant Weaver, P.E., of Grant Tech in New London, Connecticut.
Weaver helps plant teams treat phosphorus biologically with process adjustments such as changing aeration sequences — shutting off and turning on the air at prescribed intervals to let the microbes do their work optimally.
Some plants (usually smaller ones) have used this basic method to meet their phosphorus limits at extremely affordable cost. In other cases, the process adjustments alone aren’t quite enough. And that’s where the real creativity can come in for plants regardless of size.
Often, it’s a combination of approaches that gets the job done. A story in last month’s TPO included insights on Preduction from Pat Morrow of MSA Professional Services. In his view, as regulators drive phosphorus limits down to extremely low levels, it doesn’t make economic sense to rely solely on multi-million-dollar engineered solutions.
He advocates first treating to a reasonable level, whether by process adjustments, chemical addition or some form of plant upgrade, and then looking to alternatives like adaptive management or water-quality trading to address the issue at the watershed level.
Strict phosphorus limits aren’t going away. Many clean-water plants have new permits coming down the pike that will push those limits even lower than they are now. Operators can take comfort in knowing they can comply without breaking ratepayers’ backs — as long as they’re willing to engage in some outside-the-basin thinking.
