Green Mountain Technologies is in the business of manufacturing technologies that help organizations compost. In this business, we often find ourselves in the position of advocating for aerobic composting as a beneficial process and an intelligent way to recycle nutrients. Aerobic composting is a natural process where bacteria, fungal organisms and other creatures do the work of decomposing organic compounds such as food scraps, garden scraps, wood fiber, etc.. These microbes have been doing this work for hundreds of millions of years and have evolved a very efficient and reliable process. They provide this ecosystem service for “free” (well, they do get room and board). One thing we know is that these organisms take a certain amount of time to do their work.
We find that the initial (mesophilic and thermophilic) stages of composting require a minimum of 10-20 days to complete, even under optimum conditions (here is one reference from Cornell University). And those are really just the initial stages. After these microbially dominated stages, fungal organisms go to work and this curing phase can take several months or more.
Why Composting Takes Time
When we hear equipment vendors claim to complete a composting process and/or produce a compost product in 24 hours (or 3 days or 5 days), we are naturally skeptical. Based on everything we know in our 25+ years of experience in composting, the microorganisms just don’t work that fast.
While it is possible to use vasts amount of heat energy to dehydrate food waste in a short period of time, this is not a composting process and the product is not compost. A dehydration process produces dehydrated food. When that food is reconstituted with water, it produces food again, albeit ground up food. As it turns out, dehydration is a very effective method of food preservation.
Pre-Treatment vs Composting
We want to be clear that a commercial food waste dehydrator is not the same thing as an aerobic composting system. The US Composting Council (USCC) refers to systems such as commercial food waste dehydrators (FWD) as a type of pre-treatment system. CalRecycle also publishes an informative web page on this topic.
Loyola Marymount University (LMU) published an interesting study in Biocycle that shows what happens when dehydrated food waste (DFW) is mixed with mulch in various proportions and applied to the landscape. Basically, they learned that that, once the food waste rehydrates, it then begins a composting process in place on the ground.
Here is their finding:
Ultimately, the study revealed that the unprocessed dehydrated food waste samples were not suitable as a soil amendment on LMU’s campus. Rehydration of DFW produced large quantities of fungus, an outcome not acceptable on LMU’s grounds. Although dehydrated, the material is not decomposed to a stable state. This is a key distinction. While dehydrating LMU’s preconsumer food waste is a good first step towards sustainability, further processing of this material is needed before it is suitable to be used as a soil amendment or for another purpose.
Why We Prefer Composting
We certainly understand the value of a food waste dehydrator to reduce the weight and volume of food waste in a short period of time. This can be beneficial in specific applications.
However, we have several criticisms with these types of systems:
- Higher Carbon Footprint. It takes a significant amount of energy to rapidly dehydrate a feedstock that is at 70-90% moisture in 1-5 days. This energy typically comes from the burning of fossil fuels. With natural composting, the microbes provide this heating at no extra charge, no fossil fuels required.
- Higher System Costs. In part because of the external heating and fine grinding of the food scraps, the costs of a dehydration system on a per ton basis are typically higher than a comparable composting system.
- Dubious Claims. We have a beef with equipment vendors who claim that a dehydration process is a composting process. This, in our opinion, is deceptive. This sounds like a classic case of greenwashing. We would really appreciate it if the vendors of food waste dehydrators would refer to their systems as food waste dehydrators and not pretend that they are composting systems. If it sounds too good to be true, it probably is too good to be true.
So, if you are shopping for a composting technology and you actually want to produce compost, we encourage you to be wary of vendors that claim they can complete an aerobic composting process in 1-7 days. These claims are at odds with the biology of composting. We put our trust in the microbes that have hundreds of millions of years of R&D under their belts.