‘Dairy digesters’ drastically reduce emissions: study

University of California, Riverside – Dairy digesters can reduce atmospheric methane emissions by roughly 80 per cent, said a new study from the University of California, Riverside, by trapping methane into tightly sealed manure ponds.

The findings, published in Global Change Biology Bioenergy, come as California ramps up investment in methane control technologies to meet its goal of cutting emissions 40 per cent below 2013 levels by the end of the decade. More than 130 of these systems are now operating across California dairies, but until now, their real-world performance hadn’t been verified this rigorously.

“The digesters can leak, and they sometimes do,” said UCR climate scientist Francesca Hopkins who led the study. “But when the system is built well and managed carefully, the emissions really drop. That’s what we saw here.”

Methane is more than 80 times as potent as carbon dioxide at warming the atmosphere over a 20-year time frame. In California, much of the methane comes from dairy cows. The gas is not just from the burps they emit after eating, but from the way their manure is stored. When manure is held in open, water-filled pits, it breaks down without oxygen and emits methane into the air.

Covering those pits with gas-tight membranes allows the gas to be trapped, cleaned and piped into fuel systems that often replace diesel in long-haul trucks.

While the study affirms the potential of dairy digesters, they do not address other emissions common to dairy operations, such as ammonia or airborne particles that affect local air quality. Building the digesters is also no small task as it requires permits, capital investment and long-term maintenance.

“They’re not for every farm,” Hopkins said. “But for dairies that can make it work, this is one of the most cost-effective ways we have to cut these greenhouse gas emissions.”