In the aftermath of the 2014 harmful algal bloom (HAB) in Lake Erie, which left residents in the city of Toledo without drinking water, there’s been a lot of activity around making sure something similar doesn’t happen again. Water treatment plants have added additional testing for the algal toxin microcystin that caused Toledo’s water shutdown, scientists are monitoring HABs as they develop, and backup intakes let larger plants avoid pulling in potentially contaminated water altogether.
But remembering the news reports of people stuck without water for days, some concerned citizens may still wonder “what if?”
Dr. Glenn Lipscomb at the University of Toledo will address just that question. As a chemical engineer, one of his focus areas is membrane separation, where thin filter membranes are used to separate very small particles or even molecules – oxygen from the nitrogen and gases that make up the air we breathe, for example.
“When this incident we had two years ago occurred, it was a natural fit,” Lipscomb said. “It was obvious that a reverse osmosis membrane would take out the microcystin in the water, and it was just a question of coming up with a way to provide some certainty to the fact that it’ll do that.”
Reverse osmosis (RO) occurs when water is pushed through a semipermeable membrane with “holes” that are too small for anything but the water molecules themselves. The process is commonly used in drinking water purification, as it removes minerals and particles that can cause undesirable flavors.
Partnering with NSF International (formerly the National Sanitation Foundation), Lipscomb’s research focuses on the reverse osmosis systems commonly sold at home improvement stores and installed under kitchen sinks in a number of homes. The goal is to develop a certification process for these home membrane systems that shows that they remove microcystin from drinking water.
RO membranes are essentially sheets of very thin plastic, and include a layer with pores so small that contaminants like mineral salts, organic contaminants and viruses can’t pass through them. Microcystin is a peptide – essentially a very small protein molecule – that is much larger than a water molecule, so it should be filtered out quite effectively.
With the project just getting underway after receiving funding from the Ohio Department of Education’s Harmful Algal Bloom Research Initiative (HABRI), the final certification protocol should be complete in early 2018.
Before assessing the full systems, the researchers will work with Dow Water & Process Solutions, a division of the Dow Chemical Company, to characterize different system components straight from the manufacturer.
“One of the things that we’re really concerned about is how effective the systems retain their ability to filter out microcystin over time,” Lipscomb explained. “So we’ll be developing some accelerated aging protocols for testing. Chlorine is added to water to help protect us, and it turns out that for the membranes that are used in these home systems, the chlorine can attack the membrane and reduce the ability to filter out toxin. So we’re going to be accelerating that effect and look at how the system responds.”
Reverse osmosis membranes are made up of three distinct layers: a coarse fibrous mat comparable to a furnace air filter that provides the primary strength and support for the membrane, a second thinner layer that acts as a secondary support structure, and the membrane itself, which is the thinnest layer and has the very smallest pores that would filter out microcystin.
“When chlorine attacks that very top layer, it basically eats it up,” Lipscomb explains. “It degrades the material into smaller particles that lift right off the surface and reveal the larger-pored support underneath. And that larger-pore support is not capable of filtering out the microcystin.”
This process takes a long time at the chlorine levels found in drinking water, but it does occur and needs to be addressed. Studies have shown that increasing chlorine concentration above normal drinking water levels is an effective way of demonstrating chlorine’s effect on membranes over time in a much shorter timeframe. Applying those findings to actual membrane systems will be an important data point for the certification Lipscomb and his partners plan to develop.
“Our goal is to demonstrate how a manufacturer would go through this process, and then NSF International would ultimately be responsible for doing the certification or identifying third parties that would do it,” Lipscomb said. “But what this would show is how to certify a system, and then everybody can compete on price and quality, on how often you have to change the units out, and so on, under the same set of guidelines.”
While the home membrane systems Lipscomb is testing are relatively affordable at $250-300, some people may not be able to install an under-sink water filter system – they may rent an apartment, or the upfront cost of the system may strain their budget too far. For them, the natural next question is “will my Brita pitcher filter out microcystin?”
It’s a question Stone Lab research coordinator Dr. Justin Chaffin hears a lot at outreach events. “I didn’t know how to answer that question at first,” Chaffin said. “So we wrote a proposal to the Lake Erie Protection Fund and got funded, and now I know the answer.”
That answer, as with so many things in science, is “maybe.”
Read the rest of the story in the Fall 2016 issue of Ohio Sea Grant’s Twine Line magazine.