Could charcoal filters be used to help clear up Lake Okabena?
Aug. 4—WORTHINGTON — Drawing on the academic background and experience of one of its advisers gave the Okabena-Ocheda Watershed District's Board of Directors insight Tuesday on a proposal to use biochar filters in Lake Okabena.
The filters would remove phosphorus and nitrogen from water either before it enters the lake or directly from the lake, eliminating the excess nutrients that fuel algae blooms. Excess algae can deplete the oxygen available for supporting other aquatic life, harm water quality and kill aquatic plants, according to the Minnesota Department of Natural Resources.
The proposal, from Eden Lakes Inc., of Spring Lake, Michigan, would include installation of nine filter arrays in various locations around the lake and in ponds that feed into the lake, as well as supply of 309 filters to be installed by dock owners on the lake and 30 anchor arrays each for Sunset Bay and Sailboard Beach.
The cost estimate is $80,487, or $62,123 if the watershed provides the labor. Removing the filters prior to winter, as well as replacing some filters, would be an additional cost of $33,575.
"This is outside of my area of expertise, but I was able to look up a couple of literature review publications and try to learn a little bit more about this biochar technology," said Tyler Wadzinski, who teaches chemistry at Minnesota West Community & Technical College and serves on the Watershed District's advisory board. "It is a legitimate, real thing. It's an active research area."
While research on the topic has increased, particularly in the past 10 years, results of biochar treatment have varied significantly, depending on both the specific type of biochar product used and its setting, he explained.
"...really, my takeaway from it was this — if a proposal like this would be done with rigorous testing — you know, sampling to figure out which biochar ingredients, what preparation techniques would work best in our setting — it could work," Wadzinski said. "But I didn't get any indication from this proposal that they would do that, and they didn't really give any details about how they prepare their biochar."
The proposal did not seem rigorous enough to him, though he said he would not rule it out either.
He also cautioned the board that biochar is more useful for some contaminants than others, and that the research seems to indicate it needs to be customized for its setting.
"Generally speaking, when people are using charcoal filters, they're removing pharmaceuticals and poisons and heavy metals rather than phosphorus," said Okabena-Ocheda Watershed District Administrator Dan Livdahl.
Because Steve Bousema, a member of the watershed board, was not present at Tuesday's meeting, the group agreed to table the matter for further dialogue at a later meeting.
In other news Tuesday, the board:
* Received drafts of two easement agreements for the pond on District 518 property near Crailsheim Road, one for building and one for maintaining it. The pond would prevent phosphorus and sediment from reaching Lake Okabena, where it negatively impacts water quality.
* Discussed the appearance and testing of some algae blooms in area lakes. Some testing has proven difficult due to algae being too thick for the tests to work, and because moving the algae aside or filtering it somewhat could potentially impact test results, the issue isn't easily resolved. Algae testing will continue.
* Continued to consider possible solutions for its Prairie View project, where sand filters that remove silt and nutrients from the water have been plugging up. Erosion around the filters has led to soil from the pond's banks being deposited on the filter, where it turns into rock-like chunks of dirt that water can't easily penetrate.
* Agreed to set a preliminary levy of $253,000 — the same as last year and the past several years.
