Green disposal of a green menace
By Leslie Mertz
Great Lakes beachgoers want sand underfoot, not the inches-thick mats of slimy Cladophora algae that can wash onto shorelines throughout the summer.
Truckloads of the stuff are hauled to landfills every week or so, but beach managers want a greener and cheaper method of disposal.
“Algae removal is sort of a routine beach-grooming thing that we do, but because it’s wet and heavy, it can be expensive to dispose of,” said Cathy Breitenbach, director of Green Initiatives for the Chicago Park District, which is responsible for 26 miles of lakefront in the city. She’s hoping to find an alternative that saves taxpayers money and is more sustainable than taking it to the dump like the district does now.
Composting may seem like an obvious solution, but it’s not as simple as it sounds, say algae experts. Cladophora mats can harbor large concentrations of bacteria, including some potentially dangerous varieties.
“We have evidence to show that E. coli bacteria are found in very high densities in Cladophora mats,” said Murulee Byappanahalli, a research microbiologist at the U.S. Geological Survey’s Lake Michigan Ecological Research Station in Porter, Ind.
“Sometimes the numbers can be much higher (in the mats) than what you find in raw sewage, when you look at a volume-by-volume basis for comparison purposes,” Byappanahalli said.
While most E. coli strains are harmless, some are human pathogens, he said. “And there is some evidence that pathogenic E. coli strains, and also the bacteria Shigella, Campylobacter and Salmonella, are often found in the algal mats. If these bacteria are present, there is a greater chance for human swimmers coming into contact with these bacteria and perhaps getting exposed.”
These pathogens can lead to such symptoms as diarrhea and stomach pain.
Cladophora, is about 90 percent water and would have to be dried for composting, said Richard Whitman, chief of the Lake Michigan Ecological Research Station. “You couldn’t do it on the beach,” he said, citing both the potential pathogens that would flourish in the sunbaked and moist mats, as well as “all of the flies that would come in.
“It’s unsightly, and it smells just terrible,” he said. “It smells like rotten eggs.”
Nonetheless, composting can be done, according to Mary Seaman, senior lecturer in the biology department at the University of Wisconsin Oshkosh.
She and her students studied how best to compost Cladophora mats for use in flower beds in Door County on the west shore of Lake Michigan.
“The people in (the town of) Bailey’s Harbor actually harvested the Cladophora off of the beach and then trucked it over to me at the Ephraim Wastewater Treatment Plant,” she said. She and her students found that a mix of 75 percent algae and 25 percent wood chips is best for composting. Mixes with other organic waste, such as grass clippings, might also work well, she said.
The students tracked moisture, temperature, pH, nitrogen, phosphorus and potassium content as it decomposed. “We determined that this composted material would be good for flower gardens, but since we didn’t test for bacteria, I would not suggest using it on a vegetable garden,” Seaman said.
Byappanahalli and Whitman are a little more cautious.
“Definitely through composting, we can reduce the microbial load, but there are still some nasty organisms that might persist,” Byappanahalli said. “Usually with composting, most bacterial vegetative cells die off, but spore-forming bacteria, such as Clostridium botulinum, can survive.”
That bacteria is responsible for avian botulism, a paralytic disease that has killed thousands of birds in the Great Lakes over the past few years.
And there are other problems. Extremely toxic methylmercury has been found in high concentrations in Cladophora mats.
In typical garden or farm applications, it probably wouldn’t be an issue in the compost, said Dave Krabbenhoft, research hydrologist and geochemist at the USGS Wisconsin Water Science Center in Middleton, Wis. In gardens and farm fields, soil microbes would likely break down methylmercury.
“And from what we know, terrestrial plants don’t accumulate methylmercury from the soil anyway, so produce grown with the compost would not likely pose a health risk to eat,” he said.
One important exception: Unlike terrestrial plants, aquatic plants such as rice can take up methylmercury, which can then get into the grain, he said. “In much of China, for instance, the biggest source of methylmercury exposure is actually not from consuming fish (which do accumulate methylmercury), but from the very large amounts of rice they eat.”
Overall, however, Cladophora compost would work well, he said. “So long as it’s being tilled into the gardens or agricultural fields, I can’t see where there would be much concern over the mercury and methylmercury content.”
It would just take a little more investigation to give Cladophora compost a thumbs up or thumbs down, Whitman said. “There is definitely potential for using decomposed mats as a biofertilizer, but first we need to know if there are any chemicals and pathogens that are dangerous.
“It wouldn’t be a big investment in time and research. We’re talking about two or three years of work. We’re not alarmists. We’re just saying that we’ve got to do some experiments.”
Other researchers are studying whether Cladophora can be use for fuel, said Julie Peller, associate professor of chemistry at Indiana University Northwest. “Certainly, macroalgae such as Cladophora has oils that are important, and there are research groups out there that have shown that you can extract these particular compounds and then make simple chemical transformations to turn them into biofuels,” Peller said.
Back in Chicago, the Cladophora-disposal quandary looms. “We are looking into options for composting, but I can’t tell you that we’ve figured out anything yet,” Breitenbach said. “In concept, we’d love to be able to find a way to divert this waste stream from the landfill. Everybody wants to be green, but there has to be a place to take it that is a reasonable distance and there’s no commercial facility in Chicago where we could take it.
“It has to make economic sense.”