Manure-eating worms could be the dairy industry’s climate solution

With 6,000 dairy cows, 5,000 beef cattle and thousands of tons of apples, potatoes and cherries produced each year, Royal Dairy in Royal City, Washington uses hundreds of millions of gallons of water annually . All of this water, when used, carries animal waste, pathogens and environmentally harmful chemicals, such as nitrate, which can contaminate groundwater and contribute to greenhouse gas emissions.

To prevent this from happening, Royal Dairy cleans and reuses its water more than 10 times before the water leaves the farm. The dairy has also reduced its nitrate pollution and lowered its greenhouse gas emissions, all thanks to a new type of worm-powered wastewater filtration system.

Every day, half a million gallons of agricultural wastewater are pumped through a gigantic bed of worms. The worms, writhing in wood chips and sawdust, feast on liquid manure and sewage, washing away harmful nutrients and chemicals from the stream. The water then seeps through a layer of crushed rock, collects at the bottom of the worm bed, and exits through an outlet pipe for Austin Allred, the farm owner, to use again on the closed.

Allred is one of two dairy producers 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 a solution to agricultural pollution problems, especially as states require dairies to implement better water management plans and remove nitrates from their wastewater.

Some scientists even claim that vermifiltration could reduce greenhouse gas emissions from dairy farms by preventing the production of methane, a potent greenhouse gas. As such, vermifiltration could be a possible alternative to manure digesters, controversial technologies that capture the methane produced by manure ponds and then sell that methane as a fuel source.

The dairy industry is a “significant contributor” to groundwater nitrate pollution 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 considered carcinogenic in drinking water and has been studied 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 condition that affects the blood’s ability to deliver oxygen to the body.

Droughts fueled by climate change could also worsen the nitrate pollution problem, as the state experiences its second extreme drought in a decade.

Such a severe drought reduces the snowpack in the Sierra Nevada mountains. As a result, much less water flows into the central valley. Without the irrigation provided by this water, farmers must rely more on wells that access groundwater. As farmers and towns in the Central Valley increasingly pump from these wells, they may also begin to pump nitrate-contaminated water. Think of it like drinking through a straw – nitrate-contaminated groundwater sits on top of cleaner, deeper groundwater. As the water below depletes, nitrate begins to seep into the well.

“We are actually seeing a change in groundwater quality, which is quite surprising,” said Zeno Levy, a research geologist with the United States Geological Survey. Levy was the first author of a 2021 study showing how drought can introduce nitrate into groundwater.

According to the National Drought Mitigation Center, most of California is currently experiencing a “severe” to “exceptional” drought, and in April officials in Southern California 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 the Central Valley Water Board, requires dairies to submit nitrate management plans for their facilities and all croplands where wastewater are applied.

Vermifiltration systems like those from BioFiltro can be part of these nitrate management plans because they reduce nitrates in water before the water is applied to crops. While the percentage of nitrate reduction depends on a number of different factors, such as temperature, pH and the types of microbes living in the system, a study, funded by BioFiltro, found that it removed 84% of total nitrogen (a precursor to nitrate). used waters. A 2022 study of a vermifiltration system by researchers at the University of Nebraska-Lincoln found reductions in total nitrogen between 53 and 61 percent.

The poop the worms generate, called casings or vermicompost, is a very valuable soil additive that farmers can either use on their own farms or sell. Vermicompost contains microbes that help fix nitrogen in the soil, making fertilizer applications more effective and efficient, said Mai Ann Healy, BioFiltro’s chief sustainability officer.

The worms, she says, can also help a dairy use less energy in its wastewater treatment. Typical wastewater management requires dairies to add oxygen to wastewater. This aeration, if done by pumping air into the water, consumes energy. When the worms burrow into the sewage, however, the worms do the aeration instead.

Vermifiltration has also been shown to reduce methane emissions on dairy farms in some cases. Methane, a much more potent greenhouse gas than carbon dioxide, is a byproduct of cow manure and burps. On dairy farms, methane is released into the atmosphere or captured by a manure digester. The BioFiltro study, for example, found that the system reduced the dairy’s methane emissions by 97% compared to a dairy without an emissions containment system. A 2022 study from Washington State University found similar results.

Using vermifiltration instead of digesters has a particular climate benefit: while digesters capture the methane produced by manure, vermifiltration prevents that methane from existing in the first place. That’s good news for some community advocates, who fear digesters aren’t a foolproof climate solution and want dairies to reduce — not just capture — their methane emissions.

Digester developers are prioritizing dairies closer to existing gas pipelines, so the captured biogas can be sent elsewhere in the state. Healy said BioFiltro’s system is a good alternative to digesters for farms that aren’t near an existing pipeline network. BioFiltro is also more economically feasible on small farms that don’t have enough cows to make a digester profitable, she said.

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Allred said the system has helped Royal Dairy move closer to its goal of developing sustainability. Although there are many farms that use sustainable management methods, these farms are often smaller, serve niche markets, and sell their products at a higher price. Allred’s goal is to prove that sustainability can be a realistic option for large-scale operations like its own.

“[We’re] taking regenerative agriculture and the concepts we’ve learned from these small farms and exploding them, so we can feed the masses,” Allred said.

Allred estimates the cost of the BioFiltro system for his farm at about $25 to $30 per acre. This cost, for him, is not even “in the same field” as what it would cost to build a digester. With the clean water he’s able to reuse, the carbon credits he gets, and the soil additives the system produces, he said the vermifiltration system has a “pretty good” return on investment.

Recently, the BioFiltro system was approved to be part of the California Department of Food and Agriculture’s Alternative Manure Management Program, which provides grants to farmers to install sustainable greenhouse gas reduction projects. tight. Even with these incentives, however, digester projects receive higher grants from CDFA – this year, CDFA limits grants for digesters to $1.6 million, while grants for the alternative manure management program are capped at $750,000.

Dairy farmers with large enough herds could then make a potentially more profitable choice for their manure management, Allred said, by installing a digester. California, for example, has invested millions in the development of digesters, and other states are following suit. The state’s low-carbon fuel standard gives dairy farmers credits for producing biogas with manure digesters that they can sell or trade. Depending on their agreement with the developer of the digester, some dairies also get a share of the profits from the sale of the biogas.

Sabina Dore, lead author of the BioFiltro study, said low adoption is also due to the system being newer and not on many dairy farmers’ radar. However, she said, BioFiltro competes with digesters, which generally receive more financial support. “There is a lot of money behind [digesters]“, said Allred. Royal Dairy does not have a digester.

Genevieve Amsalem, director of research and policy at the Central California Environmental Justice Network, agrees. “I think the incentives are designed to promote the development of transport fuels, rather than agro-ecological solutions,” she said.

Allred is happy that Royal Dairy has taken the plunge and hopes the practice will grow. “Farmers are looking to purify their water and retain nutrients on their farm as best they can, in forms that support our soils,” he said.

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