By Grace van Deelen
With 6,000 dairy cows, 5,000 beef cattle and thousands of tons of apples, potatoes and cherries produced annually, Royal Dairy in Royal City, Washington, uses hundreds of millions of gallons of water per year. All that water, once used, carries animal waste, pathogens and environmentally harmful chemicals, like nitrate, that can contaminate groundwater and contribute to greenhouse gas emissions.
To prevent that from happening, though, Royal Dairy cleans and reuses its water more than 10 times before the water leaves the farm. The dairy has also cut its nitrate pollution and lowered its greenhouse gas emissions, all thanks to a new kind of wastewater filtration system powered by worms.
Every day, half a million gallons of farm wastewater is pumped through a gigantic bed of earthworms. The worms, wiggling in wood chips and shavings, feast on the liquid manure and wastewater, removing nutrients and harmful chemicals from the stream. The water then percolates through a layer of crushed rock, collects at the bottom of the worm bed, and travels out an exit pipe for Austin Allred, the farm’s owner, to use on the farm once more.
Allred is one of two dairy farmers in the United States currently using such a system, called a vermifiltration system, to manage wastewater. The system, installed by a company called BioFiltro, could be one solution to agricultural pollution problems, especially as states require dairies to implement better water management plans and eliminate nitrate from their wastewater.
Some scientists even say that vermifiltration could reduce greenhouse gas emissions from dairy farms by preventing the production of methane, a powerful greenhouse gas. As such, vermifiltration could be a possible alternative to manure digesters, controversial technologies that capture methane produced by manure ponds, then sell that methane as a fuel source.
The dairy industry is a “significant contributor” to nitrate pollution in the groundwater in agricultural regions like California, said Clay Rodgers of the Central Valley Water Board. Nitrate, a chemical found in most fertilizers, manure and human sewage, is thought to be carcinogenic in drinking water, and has been investigated as a risk factor for pregnancy complications. Drinking water with high nitrate levels can be a factor in the development of methemoglobinemia, sometimes called “blue baby syndrome,” a disease that affects the ability of blood to deliver oxygen to the body.
Climate change-fueled droughts could be worsening the nitrate pollution problem, too, as the state is experiencing its second extreme drought in a decade.
Drought so severe makes for a smaller snowpack in the Sierra Nevada mountains. As a result, far less water flows into the Central Valley. Without the irrigation provided by this water, farmers are left to rely more heavily on wells that access groundwater. As farmers and towns in the Central Valley pump more and more from these wells, they can begin to pump up nitrate-contaminated water, too. Think of it like drinking through a straw—the nitrate-contaminated groundwater sits on top of cleaner, deeper groundwater. As the water below is depleted, nitrate begins to seep into the well.
“We’re actually seeing a change in groundwater quality, which was quite surprising,” said Zeno Levy, a United States Geological Survey research geologist. Levy was the first author on a 2021 study showing how drought can introduce nitrate into groundwater.
According to the National Drought Mitigation Center, most of California is currently experiencing “severe” to “exceptional” drought, and in April, Southern California officials declared a water shortage emergency.
California has made reducing nitrate pollution a requirement for agricultural producers. CV-SALTS, a collaborative water quality effort of the California State Water Board and Central Valley Water Board, requires dairies to submit nitrate management plans for their facilities and any cropland where wastewater is applied.
Vermifiltration systems like BioFiltro’s can be part of these nitrate management plans, as they reduce nitrate in the water before the water is spread on crops. While the percent reduction in nitrate depends on a number of different factors, like temperature, pH, and the types of microbes living in the system, one study, funded by BioFiltro, found that it removed 84 percent of total nitrogen (a nitrate precursor) from the wastewater. A 2022 study of a vermifiltration system done by researchers at the University of Nebraska-Lincoln found reductions of total nitrogen between 53 and 61 percent.
The poop that the worms generate, called casings or vermicompost, is a highly valuable soil additive the farmers can either use on their own farms or sell. The vermicompost contains microbes that help fix nitrogen to the soil, making fertilizer applications more effective and efficient, said Mai Ann Healy, BioFiltro’s sustainability officer.
The worms, she said, can also help a dairy use less energy in its wastewater treatment. Typical wastewater management requires dairies to add oxygen to the wastewater. That aeration, if done by pumping air into the water, takes energy. When worms burrow through the wastewater, though, the worms do the aeration instead.
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