We are excited to divert organic waste from landfill because it seems like the right thing to do in our pathway to zero waste. There needs to be a home for this material – what is it going to get changed into, and where is it going to go? I have discussed the need for maintaining our soil organic matter, and that our organic waste should be recycled back to maintain our soil organic matter for healthy soils.
But what about the process of the change – the composting process itself? How are we going to do this in a manner that is economically viable, environmentally sustainable and socially acceptable? By the term “socially acceptable”, I am refering most specifically to odor control. It also refers to public and worker safety which I will discuss in a later blog.
As we begin to include more foodwaste into our composting process, the potential for odor production increases logarithmically. We are seeing this trend throughout the world, and increasingly in North America as we begin to divert foodwaste into our yardwaste composting processes. Vancouver is beginning to understand this as well, as it now implementing an odor bylaw (http://www.vancouversun.com/technology/Metro+Vancouver+tries+diffuse+potential+stink+over+food+waste+odours/6873635/story.html)
How do we as the composters respond? First of all, we need to understand the potential sources of odor before we can make a plan to reduce the risk of odor formation and emission. The most important point to understand is that most odor causing compounds are produced by microbes under anaerobic conditions (when they don’t have enough oxygen). The potential sources of odor at a composting facility are:
1. Incoming material – composters have no control over the odor level of the incoming material, but can design strategies to mitigate further odor emission as soon as it arrives at the site. Strategies include immediate blending and incorporation into the composting process, or simply covering the material with bulking agent until it is able to be blended.
2. Active composting process – odor from the active composting process seems to receive the most attention. Controlling moisture content, ensuring adequate oxygen concentrations in the composting material, and providing biofiltration (either on top of the composting material or an external biofilter in a negatively ventilated building) are important strategies to reduce odor.
3. Leachate collection areas – leachate from composting material can cause some of the most serious odor concerns at a composting site. This is because leachate may contain high concentrations of biologically active material, and oxygen doesn’t diffuse very well into liquids, meaning that odorous compounds are being produced.
4. Curing areas can be the most significant source of odor, particularly if the material is not thoroughly composted and stabilized, and if the moisture content of the compost increases to more than 60%. For us in British Columbia where we have significant rainfall, managing our curing piles to minimize odor potential is important.
A number of communities are implementing composting bylaws that define how composting needs to be done in order to reduce the potential for odor emission. In some cases, this includes receiving and composting the organic material in an enclosed and negatively ventilated building. Its a great idea and has been implemented very successfully throughout North America. I support this type of regulation, but we must also understand that controlling odor is in many cases more about management than about specific technology requirements. We need to give our industry and our communities the tools to manage odors so that we can be a socially acceptable industry.