Under-the-counter reverse osmosis units continue to show promise as an added defense mechanism against the most common form of algal toxin found in western Lake Erie, known as microcystin-LR.
For as little as $200 for the machine and roughly the same amount for labor, if a plumber installs it, homeowners can get the satisfaction of knowing their tap water is pretty much free of that particular type of microcystin, Glenn Lipscomb, a University of Toledo chemical engineering professor, said during a 30-minute Freshwater Science webinar hosted Tuesday by Ohio Sea Grant and Ohio State University’s Stone Laboratory.
Microcystin-LR is believed to be one of about 200 known congeners, or varieties, of that algal species. But it is so common that it is the basis for nearly all microcystin research, on this and other issues.
More research is needed on the other forms of microcystin, Mr. Lipscomb said.
Reverse osmosis units weren’t created to remove microcystins, but the same concept applies: Strong, reverse pressure is used to force water through an extremely tight membrane filter that leaves impurities behind.
“These do reject salt, so they have some promise for rejecting microcystin,” Mr. Lipscomb said.
Tests on three brands of reverse osmosis units commonly sold by major home improvement chains differed slightly, but were overall effective at removing residual microcystin particles in tap water, he said.
“They were able to do what we hoped they would do,” Mr. Lipscomb said. “They were able to take microcystin out of the water.”
It should be noted, however, that tests were done on residuals found in ordinary tap water. The machines are not expected to purify raw lake water, Mr. Lipscomb said.
He also said during the question-and-answer session that most homeowners installing the devices will likely see a reduction in faucet flow rate when the units are operating.
“It’s going to be reduced significantly,” Mr. Lipscomb said, adding that there can be a storage tank option to help get around that.
In general, those machines that are most effective as removing salts tend to be more effective at removing microcystins, he said.
Reverse osmosis is a technology pioneered in the 1960s to take salt out of seawater.
Mr. Lipscomb’s research is supported by Ann Arbor-based NSF International, which specializes in science for testing standards at water-treatment plants.
On its website, NSF said it is “important to understand that not all filters can reduce all contaminants.”
“Based on the water report or your water testing results, you can decide what contaminants you want to reduce in your drinking water,” the company states.
During a 2016 presentation at OSU’s Stone Laboratory on Gibraltar Island, near Put-in-Bay, Mr. Lipscomb said reverse osmosis technology came of age in the 1960s in parallel with desalination, the process by which salt is removed from seawater. The technology became much more fine-tuned about 1980, he said.
Reverse osmosis is a process that goes against the natural tendencies that solvent, water-based molecules have to mix together and equalize.
Instead, water is pushed under intense pressure through a semi-permeable membrane so fine that it can filter out impurities down to the molecular level. The water on the other side that has been squeezed through the membrane is free of impurities.
Microcystin-LR particles are often 1 to 1.5 nanometers in size, Mr. Lipscomb told webinar attendees.
A nanometer is one-billionth of a meter.
“The holes are small enough we’re filtering molecules,” Mr. Lipscomb said.
There are at least two downsides: Reverse osmosis is incredibly energy-intensive because of the amount of pressure required. And there can be as much or more wastewater generated as good water from the technique.
In industrial uses, some minerals actually have to be added back in to stabilize water that has gone through a reverse osmosis treatment; otherwise, it would corrode pipes.
First Published February 23, 2022, 2:00 p.m.
