Air district considers alternatives to open burning of ag waste
Almost five years have passed since regional air quality regulators undertook a comprehensive analysis of pollution created by open burning of agricultural waste. What that means, under state law, is that it’s time to do it again.
But what’s going to be different this time? What more can the regulatory agency responsible for overseeing the process — the San Joaquin Valley Air Pollution Control District — do to minimize such pollution in an economically feasible way?
Not surprisingly, changes in technology and business are likely to be the biggest determinants going forward. And while some old problems remain, there’s also hope that new approaches might pan out to the benefit of every breathing human in the region.
For years the state’s favored practice was to have local farmers gather up their woody waste, such as prunings, old almond trees and former vineyards, and haul it to a biomass plant equipped to take in the material and burn it to create energy. Some of these facilities have also generated steam for the benefit of local oil production.
It wasn’t a perfect alternative, in that the process still emits particulate matter. But in the end market forces, and some say lack of support from policy-makers, led to the shutdown of several biomass plants around the Central Valley.
Since then, district officials say, open ag burning has been unavoidable at times, leading farmers to apply for permission to rake up their waste into a pile and light it on fire. That option, allowed only when weather conditions permit, only exacerbates some of the worst air quality in the country.
There are alternatives — several, actually — but
they’re not equally attractive. In some cases the technology isn’t as refined as it ought to be; in others the technology is there but it hasn’t been commercialized to the degree necessary to make it economically viable.
Jon Klassen, the district’s director of air quality science and planning, said this year’s assessment will likely focus on options known as soil incorporation, pyrolysis, composting and air curtain burners, as well as biomass incineration when possible and open burning in situations where no feasible alternatives exist.
Soil incorporation refers to the process of chipping and shredding ag waste that is then buried in ag fields where it is left to decompose.
There are benefits, including the sequestration of carbon that contributes to global warming. Since late 2018 the air district has invested $8 million in creating incentives that resulted in 17,000 acres worth of waste being plowed back into the ground.
But some say ag waste is being generated more quickly than farmers can bury it.
“Typically, there’s too much orchard waste to be incorporated back into the soil,” Karen Norene Mills, director of legal services for the California Farm Bureau Federation, said by email.
Klassen added that soil incorporation “may work for some (farmers) and not for others.”
Pyrolysis, or gasification,
is another option. It involves heating up ag waste without actually burning it. The process creates a gas that can be sold, as well as a byproduct called biochar that can also be used or stored efficiently.
For all its potential, however, Klassen said pyrolysis is not yet widely available.
“This is kind of a developing area,” he said.
Composting is another alternative available to farmers. Klassen said the air district has looked at it in the past and found there are a number of limitations in local and state regulations.
It’s still not very widely used, he added, but it’s something the district does plan to review as it considers the whole range of viable options to open burning.
A process he said does seem to hold considerable potential is what’s called air curtain burners. It’s a technology that blows and recirculates hot air over a closed box.
The result is a cleaner burn, but the drawback is cost: Klassen said farmers generally have to pay someone to come perform the service, which can be prohibitively expensive.
Mills, at the farm federation, said the group sees biomass plants as a strong option but that more such facilities are needed to handle the volume of waste being generated.
“We hope the consideration of the double value of biomass energy, in improving air quality and adding another source of renewable energy, could help stabilize California energy supplies,” she wrote.
The president of the Kern County Farm Bureau, John C. Moore III, said by email the valley’s agriculture community is interested in new ways to incorporate or reduce ag waste. But an important consideration is timeliness. When farmers need to dispose of wood they generally need to do it quickly to make room for something else.
Given the shortage of biomass plants, he said, soil incorporation might be a good option to open burning. “At the end of the day,” he wrote, “we all breathe the same air.”