Vermifiltration: Worm biofilters cut manure pollution in

Alberto Dairy began using a vermifiltration system in October 2024, installing long beds of wood chips and crushed river rock populated by red earthworms that act as a biofilter to treat dairy wastewater. The farm’s three-foot mounds stretch across the equivalent of six football fields, and the water takes about four hours to percolate through the beds and drain to the end, according to farmer Anthony Agueda.

How does vermifiltration work?

Vermifiltration routes slurry through mechanical screens to remove most solids, then sprinkles the remaining liquid over a worm-populated biofilter where worms and microbes consume remaining solids as the water percolates through. At Alberto Dairy, pumps send flushed manure through V-shaped metal screens on a concrete pad; a conveyor removes solids for composting and the liquid moves to settling ponds and an irrigation system that waters the tubular structure running over the vermifiltration mounds. The worms and microbes in the wood-chip beds break down organic material; the system’s inventor, the Chilean company BioFiltro, says that the biofilter then reduces methane, nitrous oxide, and water pollution generated by the manure. Agueda reports the percolation cycle takes about four hours from start to finish.

Why is California pushing alternatives to anaerobic digesters?

California’s 2016 law requires dairies, landfills, and other businesses to cut methane emissions 40% below 2013 levels by 2030. The state estimates the dairy sector is on track to reduce annual methane emissions by the equivalent of 5 million metric tons of carbon dioxide by 2030, but that still leaves it about 4 million tons short of the law’s goal. The bulk of the state’s methane reductions so far have come from anaerobic digesters, which capture biogas from slurry, clean it, and convert it into pipeline gas. Since 2020, those programs have produced more than $1 billion for farms, Cal Poly researchers noted. Digesters can be expensive and are generally viable only for farms with about 2,000 cattle or more, a limitation that has driven interest in lower-cost alternatives.

What alternatives exist and where does vermifiltration fit?

Alternatives aim to reduce methane formation or to expose waste to oxygen so methanogens cannot thrive. Solid separation, which uses screw presses to remove water from slurry so remaining solids dry in open air, has been widely adopted. Other tactics include increasing lagoon acidity, bubbling air through storage, or adding methane-eating microbes. The state set up the Alternative Manure Management Program and the Dairy Plus Program to help smaller farms adopt such options. California has provided more than $18 million to support 15 vermifiltration projects, and Alberto Dairy has received nearly $2 million from those two programs. BioFiltro says Alberto Dairy was among the first U.S. adopters; the company reports eight of its systems are already operating on U.S. dairies, with another 16 under construction or due next year, nearly all in California.

Why it matters

Manure management is a nontrivial slice of greenhouse-gas emissions: the World Resources Institute estimates manure management on dairy and swine farms accounts for 1.6% of U.S. greenhouse-gas emissions, and globally manure storage and processing makes up about 10% of the livestock industry’s contribution to climate change. California’s dairy industry produces about 45% of the state’s methane pollution, with more than half of that coming from manure, so even incremental reductions matter for meeting state targets. Vermifiltration and other lower-cost options could expand viable choices for smaller operations that cannot afford digesters, and they also address water-quality risks that digesters often do not.

What to watch

Track whether the 16 BioFiltro systems listed as under construction or scheduled for next year are completed and begin operating, and whether state funding priorities shift beyond the $18 million already assigned to vermifiltration projects. Observers should also watch comparative, long-term studies that measure methane and nitrous oxide reductions alongside water-quality outcomes under real farm conditions.