Composting Mill Waste Wins Blue Ribbon for the Climate


Martha Walden, Wendy Ring

for 11th Hour

H.S.U. Spring 2020 Capstone Class on Alternative Biomass Uses: Compost, Gasifcation, Wood Pellets, and Particle Board. Photo source: Redwood Coast Energy Authority Biomass Webpage.

Each year, Environmental Science and Management students at Humboldt State University tackle a local environmental challenge. Last spring semester they were enlisted by Redwood Coast Energy Authority (RCEA) to investigate better uses for the mountains of sawdust and wood chips at Humboldt Redwood’s lumber mill. Currently this waste stream is incinerated at the biomass plant next door where it generates nearly a quarter of our electricity. Burning wood pollutes the air and emits as much carbon as coal. The resulting power is more expensive than clean energy, such as wind and solar.

Two teams chose gasification, burning the wood waste with restricted oxygen to produce syn-gas, and then burning that for electricity. This would reduce air pollution by 90% and cut carbon emissions by up to 27%, but the cost of building gasification plants is high ($100 million to $270 million). 

Two teams chose conversion to wood pellets.  One pro-pellet team proposed torrefaction — heating waste at low temperatures with no oxygen to produce a clean-burning, low carbon fuel at a cost of $54 million. However, it would need to be co-fired with coal. The other team wanted to make the type of pellet burned in pellet stoves. Although making them would indeed emit less carbon, actually burning them would double the emissions of the Scotia plant. 

The emissions of burning the pellets were simply not counted. That was not an oversight. California has designated burning biomass as carbon neutral — despite its carbon-intensity — because trees are renewable, unlike fossil fuels. This argument strikes many climate activists as well past its prime, considering the rapid and urgent decarbonizing we must accomplish. 

The two remaining teams chose composting the mill waste. Based on expense — $3 to $5 million — and sheer amount of reduced emissions, this was the winning solution. Although composting does emit some carbon, the net emissions are estimated to be 200% less than those of incineration because of how much is sequestered in the soil along with the carbon subsequently absorbed by enhanced photosynthesis of future growth. Lifecycle analyses conducted by UC Berkeley, HSU and California Air Resource Board all agree that composting is net carbon negative. 

Large scale compost application on Humboldt County’s working lands has great potential to sequester carbon. It also creates income for farmers and ranchers. The state of California provides financial incentives for applying it to farm and ranch lands, and markets for agricultural carbon credits are taking off.  Humboldt Waste Management Authority pays a million dollars a year to haul compostable waste to a landfill in Oregon. Much of this is the kind of nitrogen-rich waste needed to compost mill waste. If we compost here, that money — and the resource — stays local. 

Cow manure is another waste product / potential resource that currently does nothing but emit methane. It too could aid in composting mill waste. Granted, it’s much more convenient to not disturb it, ship compostable waste to Oregon, and burn mill waste at the 32 year-old, inefficient biomass plant. By paying more than competitive rates for biomass electricity, RCEA ratepayers incentivize Humboldt Redwood Company to keep things the way they are for as long as possible. 

Composting our waste would achieve a major reduction of emissions here in Humboldt county. It’s a goal we all believe in.