Composting Inside? The Earth Flow Shows You How

The thought of composting indoors may sound daunting to many folks. For some, it could seem like an excellent way to invite unwanted guests and foul odors into your home or business but, for others it sounds like a great challenge to take on to create further opportunities to divert organic waste from landfills, especially in urban settings. Composting indoors has gained lots of traction to apartment dwellers by way of vermicomposting, the process of composting with organic materials with worms. Here at GMT, we’re going even further with our in-vessel Earth Flow systems to make hot composting a safe and viable option on a larger scale.

The first key to composting inside a building is composting “in a box”. In-vessel composting allows the gasses produced during the compost process to be captured. Otherwise, those compost gasses could potentially accumulate in the space, creating a health and safety hazard.Here is one of our first Earth Flow installations way back in 2010 at Battery Park City Parks in New York City.  This Earth Flow custom vessel system was installed in the basement of a high rise in lower Manhattan. This system operates in a large basement warehouse which utilizes a carbon filter for odor control.  An exhaust blower negatively pressurizes the air space above the compost in the vessel and this pulls the compost through the filter.

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A hot composting process produces heat, moisture, and compost gasses, particularly CO2 (carbon dioxide). In order to compost effectively inside, those compost gasses and moisture need to be effectively ventilated to the outdoors. It would not be beneficial for that CO2 and other compost gasses to accumulate inside an interior space.

The way this is most typically done is with a biofilter. A biofilter is a simple odor filter that uses a biological media, such as large wood chips to filter the odors from compost. The gasses from the compost process are mechanically evacuated out of the compost vessel and routed to the appropriate location via ductwork and then inserted into the base of the biofilter, embedded in the wood chip media. When the warm, moist air containing those compost gasses encounters the colder wood chips, the moisture in the air condenses onto the wood chips. In this process, the compost gasses that create odors are captured as well. Biofilters are more than 90% effective at capturing odor compounds, especially if they are kept moist.

When a composting system is installed inside a building, it is often ideal for the biofilter to be located outside so the CO2 can easily escape to the atmosphere after passing through the biofilter.

Here is an example of an indoor Earth Flow installation with an exterior biofilter. This is our client ENSO, a cannabis waste composter in Oklahoma. This is a 20’ Intermodal Earth Flow, which uses a repurposed shipping container, installed inside of a warehouse. 

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As pictured above, the exhaust blower and biofilter piping extend horizontally from the vessel and penetrate the wall on the building. The piping then directs into the base of the biofilter housed within a wooden box on the exterior of the building. A large container of wood chip is used as the filtration media.

Our next example is the Earth Flow installation at Northland College in Wisconsin. This is a 20’ x 10’ Site-Built Earth Flow built into a custom constructed wooden vessel with a stainless lining.

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Northland also employs an external biofilter. As shown above, the two horizontal ducts exiting the head space of the vessel. These continue to the biofilter outside. In this case, the exhaust blowers are located outside.

This image outside shows the exterior of the building with the white ducting extending into the exhaust blowers and then into the wooden biofilter box. Here, students are shown loading wood chips into their biofilter.

Our next example is with Camphill Soltane in Pennsylvania. This is a 20’ x 8’ Site-Built Earth Flow installed inside of a growing greenhouse.  This system employs an external biofilter as well. You can see the green ductwork exiting the building through the wall at the left of the picture.

This Earth Flow is also designed to help heat the greenhouse in the winter using residual heat from the composting process.

As you can see, large scale composting inside a building is an absolutely viable option. However, it is important to correctly design the system to effectively manage the gasses generated by a hot composting process and direct these gasses safely to the building exterior, ideally using a biofilter for odor filtration.

If you are interested in composting, whether indoors or out, we can help you ensure safety and success. Please contact us at [email protected].

Written by Van Calvez, System Designer, Engineer, Sales & Customer Service