Anthony Agueda, a third-generation California dairy farmer, recently gave a tour of his family's land in Hickman, population 604, where he proudly revealed a clump of muck teeming with red earthworms. There are likely hundreds of thousands more wriggling beneath a three-foot mound of wood and crushed river rock that stretches across the equivalent of six football fields. This biofilter is the centerpiece of a vermifiltration system, developed and patented by the Chilean company BioFiltro, that promises to dramatically cut methane, nitrous oxide, and water pollution from the massive amounts of manure produced by the farm's Holstein cows.

Vermifiltration is just one of several methods farmers are adopting as the livestock industry faces growing pressure to address its environmental footprint. California, the nation's largest milk producer, has funneled more than a billion dollars into programs promoting these technologies. The Alberto Dairy was one of the first cattle operations in the state to adopt vermifiltration; eight more such systems are already operating on US dairies, and another 16 are under construction or planned, nearly all in California.

Manure is a significant source of climate pollution. The World Resources Institute estimates that manure management on dairy and swine farms accounts for 1.6% of US greenhouse-gas emissions. Globally, it makes up about 10% of the livestock industry's climate contributions. Traditionally, manure is sprayed into lagoons where methanogens thrive in low-oxygen conditions, producing methane - a gas with 30 times the warming power of carbon dioxide over a century. The slurry is often spread on fields, leading to water pollution from nitrates, pathogens, and drug residues.

California has been particularly aggressive in targeting livestock methane. In 2016, the state enacted a law requiring dairies to cut methane emissions 40% below 2013 levels by 2030. Most reductions so far come from anaerobic digesters, which capture methane from covered lagoons and convert it into natural gas. But digesters are expensive - viable only for farms with about 2,000 cattle or more - and do little to address water pollution. Critics say the rich revenue stream from California's Low Carbon Fuel Standard program has diverted attention and resources from alternatives like vermifiltration.

Enter the worms. The vermifiltration system at Alberto Dairy, which began operating in October 2024, uses a flush system to wash manure into a collection pit, where solids are separated. The liquid then flows through pipes to irrigation systems suspended above vermifiltration beds. The worms and microbes in the biofilter consume much of the remaining solid material. According to UC Davis professor Frank Mitloehner, who studied a similar setup at a nearby farm, the system can nearly eliminate nitrogen and associated pollutants like ammonia and nitrates. “Once the water is sprinkled on top, it takes about four hours from beginning to end for it to percolate through and drain to the end,” Agueda explains.

California has provided more than $18 million to support 15 vermifiltration projects, including nearly $2 million for the Alberto Dairy. As Agueda puts it, “This makes me excited, because it shows how we are part of the solution.” The state estimates the dairy sector is on track to reduce annual methane emissions by the equivalent of 5 million metric tons of CO2 by 2030 - though that still falls about 4 million tons short of the target. But with worms on the job, maybe they'll get there yet.