BioFiltro's worm beds cut ammonia from dairy wastewater ~90%, but methane data conflict

At the Alberto Dairy in Hickman, California, third-generation farmer Anthony Agueda has used a vermifiltration system from Chilean company BioFiltro since October 2024. Manure is flushed into a pit, pumped through mechanical screens that remove most solids (composted for bedding or fertilizer), and the liquid goes through settling ponds to an irrigation rig that sprinkles it over beds of wood chips and crushed river rock, about three feet deep and spread over the equivalent of six football fields. The water percolates through in about four hours.

MIT Technology Review reports that BioFiltro says eight more such systems operate on US dairies and 16 are under construction or due next year, nearly all in California. UC Davis professor Frank Mitloehner was skeptical of BioFiltro's claims, so he studied a similar system at the Fanelli Dairy in Hilmar; his 2018 paper found it cut ammonia emissions from the treated water by about 90%. BioFiltro says it removes up to 99% of wastewater contaminants, and a 2022 study funded partly or fully by BioFiltro and a regional distributor found the filter removed nearly 85% of the nitrogen.

Mitloehner doubts how much the worms matter. His view is that the porous bed replaces a lagoon's oxygen-free conditions with oxygen-rich ones, so microbes convert nitrogen compounds into nitrogen gas instead of ammonia, which can become groundwater-polluting nitrates. Methane is where the evidence splits: studies supported by the company and its partner found the filter eliminated most methane pollution, while Mitloehner's independent study found methane emissions nearly 85% higher than the lagoon's.

Swap the oxygen-free manure lagoon for an oxygen-rich bed of wood chips and river rock, where worms and microbes turn nitrogen into harmless gas.

A manure lagoon is an oxygen-free slurry where methane-producing microbes thrive; the bed swaps it for an aerobic, porous filter.

Mechanical screens take the solids out first, so the beds only have to treat the liquid.

Agueda chose it because it is simple and relatively cheap next to higher-tech options, as environmental rules tightened.

Anaerobic digesters, the state's main methane tool, suit only farms with about 2,000 cattle or more, leaving most dairies to find another fix.

A simpler, cheaper fix can attract subsidies and adopters while the evidence is still split; the useful read is what was actually measured, such as ammonia and nitrogen, not the tagline.

Alberto Dairy has received nearly $2 million from two California manure programs, which have put more than $18 million into 15 vermifiltration projects, though most of the programs' money went to solid-separation systems. Researchers told the magazine much more work is needed on trade-offs and long-term performance under real farm conditions.