Low-Odor Composting: How to Keep the Smell in Check

Blog ECS Staff 12/03/2021

Successfully composting food waste or other types of waste for an entire population, all while adhering to multiple regulations and meeting strict air emissions standards is no small feat. There’s a tricky, delicate science to industrial composting—even the smallest change in temperature can lead to a smelly disaster.

Engineered Compost Systems has many years of experience developing low-odor composting operations all over the world, and has the process down to a science—literally.

What’s needed to ensure low-odor composting?

The first few days and weeks of composting is the most critical time for a compost pile, especially when composting food waste. Before the pile has a chance to heat up (can start happening within 24-72 hours, depending on the feedstock energy and ambient conditions), it must be highly aerated to transition the pH level from acidic (4-6) to neutral (>6.5). This transition is critical for ensuring both low-odor and rapid composting. 

It’s not that passively aerated piles—that is, turned windrow and/or unaerated static pile systems—do not make compost; they are just far less efficient (much slower), and generate significantly more odorous gasses. Unaerated or poorly aerated systems starve the microbes of oxygen and create anaerobic conditions. A forced aeration composting system is the ticket when air emission standards must be strictly adhered to.

Impact of Temperature Control on Compost pH and emissions

With an early mesophilic stage (high aeration, well controlled temperatures), the mesophilic microbes help raise the feedstock pH. This enables subsequent thermophilic microbes to work very efficiently. Teamwork!

The graphs on the left show a small initial spike in volatile organic compounds (VOC), which correlates to odor, followed by almost negligible levels. In addition, we see a very high sustained CO2 release (sign of rapid bio-oxidation!)

Conversely, the graphs on the right shows material that heats up quickly and skips the mesophilic stage. The pH remains acidic, which inhibits the thermophilic microbes. This results in sustained VOCs/Odors. In addition, we see very little CO2 activity. While this pile may be ‘cooking’, it is NOT composting. The resulting product will stink, have a very low pH, and will have achieved very little stability (commonly measured by CO2 respiration).

Graphs showing the impact of temperature on the odor of a compost pile
Impact of temperature on the odor of a compost pile

pH and Odor

pH has been shown to be the key process indicator in predicting lifecycle odors when composting acidic feedstocks. As measured in work by Cecilia Sundberg , we consistently see sites with low pH achieving a 20-100x higher rate of odor generation than sites with neutral pH feedstock. The highly aerated mesophilic stage is the key to neutralizing the pH and avoiding excessive odors.

Again – the key to low odor commercial composting: manage the composting process conditions!

Graph showing odor concentration as a function of pH at IVAR, NSR and in the reactor runs at SLU.
Odour concentration as a function of pH at IVAR, NSR and in the reactor runs at SLU. Sundberg, Cecilia (2005)

What’s the best composting system for minimizing odors? (hint: in-vessel composting!)

A well-designed forced aeration composting system does wonders when it comes to keeping odors in check. A forced aeration system provides adequate cooling to maintain temperatures throughout the majority of a compost pile, enabling aerobic bacteria to efficiently bio-oxidize feedstocks while minimizing the creation of odorous compounds.

ECS offers the only In-Vessel Tunnel-type composting system developed and built in North America. The sealed, well-drained, and highly controlled aeration allows in-vessel composting systems to reliably manage less-than-ideal feedstock mixes without creating nuisance odors—truly the ultimate in process and environmental control for facilities that are odor-sensitive.

In-vessel composting system
In-Vessel composting sytem.

Is my composting system meeting air emissions standards?

Engineered Compost Systems has a unique set of scientific skills, air emissions data, and sampling and analysis tools to allow operators to comprehensively manage air emissions. Our systems have been recognized for their superior odor control, and we have the ability to  quantify emissions by conducting sampling at a facility’s current process, or from a pilot facility. 

Not up and running yet? If your facility is only in the planning phase, ECS has an extensive database to provide a most likely range of emissions to help remove the guesswork. We can provide odor analysis and dispersion modeling to quantitatively predict the odor impact from operations.

Sample odor modeling of a compost facility
Sample odor modeling of a compost facility.

Need help determining what type of composting system you’ll need to meet local air emissions regulations? Wondering if what you’re planning to build will pass the sniff test? Contact us today.  

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