Aerated Composting System | UW Farm

Hello everyone! My name is Ross. I am a student farmer working on a research project at the farm that I would like to tell you all about! My project was to design and build an aerated composting system that would improve composting efficiency while eliminating the need to turn a compost pile. Does it work? The short answer is, we're not sure yet. I had some issues getting the compost piles to heat up and we had to rebuild them. We will continue to take data over spring quarter and keep you posted on the results! Still, I would like to share my project because it leaves a lot of room for further experimentation and data collection. The following describes the aerated system, which was constructed from mostly donated materials. Before I proceed, I must give a HUGE thank you to Beth Wheat, Doug Ewing, Keith Possee, Tom Hinckley, and all the student farmers who helped greatly in constructing the aerator and compost piles. Thank you all so much!! the Aerating System The aerator sits at the base of a compost pile. I found that many farmers using an aerated composting system were composting on a large scale. These piles were often in wind-rows and consisted of one to three perforated pipes at the base of the pile, which blew air at scheduled intervals. Smaller scale aeration systems had difficulties heating the sides of the piles. So when designing our aeration system, I decided to use three perforated PVC pipes in hopes that- if the system is effective, the sides of the piles will warm up as well. The system can easily be altered to test the effectiveness of using only one pipe in the pile as well. The aerator was built by farm interns and dirty dozen volunteers. farmer Oli drills holes in the PVC pipe to allow air to push through the compost pile. Air holes at the top of PVC pipe Doug Ewing supplied the PVC and allowed us to drill a hole into the shed behind the compost pile to allow us to keep the blower indoors. click to enlarge A blower that sits in the shed behind the compost pile connects to the three-pronged aeration system. We are using an air mattress blower as the primary source of air running through the pile. The blower was donated by Beth Wheat, and we hope that this blower is powerful enough to make a significant difference in composting efficiencies. Our current experiment has the blower running on 15 minute intervals during the afternoon, when it is "warmer" than the rest of the day. This is to help ensure we are aerating the pile when the pile itself is the hottest. In total, the air runs for an hour a day for the current experiment. Further experimenting with this system allows for great variation in the amount of air running through the pile. We will keep you posted! The blower is hooked up to a timer which allows a farmer to manipulate the period and frequency that the blower is on. Building the Compost Piles Our initial experiment with the aerating compost system is to test if there is a difference between using the aerator and manually turning piles. Two compost piles were built: a control and a pile over the aerator. To make sure the air holes in the PVC pipe would not be clogged by the compost, we first put down a layer of wood chips over the aerator. Wood chips are very porous, allowing air from the PVC pipe to push through and hopefully move through the entire pile. wood chips make up the first layer of compost over the aerator Next, we layered the essential elements of a compost pile: Carbon leaves are a great source of carbon Nitrogen fresh greens are a great source of nitrogen for your compost pile that is one big pile of horse manure The horse manure was donated to us from a local horse farm who consistently supply our farm with manure, which we turn into great soil! Manure is not only rich in nitrogen, it is also a great source of organic matter, which increases nutrient availability for plants. At the UW Student Farm, we use a general rule for mixing our compost piles: 1 part nitrogen for 3 parts carbon. This ensures a healthy carbon-nitrogen ratio ideal for bacteria and microorganisms that break down our compost and turn it into fantastic soil. When building a compost pile, an easy way to visualize this ratio it to build the pile in layers. That way, you can make a clear estimate about the amount of carbon vs. nitrogen you need in your pile. click to enlarge After building two compost piles and taking temperature measurements for a week, it was clear that both piles were not heating up. The picture above illustrates one reason why this might have happened. Whenever adding fresh greens to your compost pile, chop up your greens into small pieces, creating a larger surface area for your material. This is important because when microorganisms decompose particles, air must be present. The greater the surface area of the material, the more air that is present, allowing for more digestion of material, causing more rapid growth rates of microorganism, which heat up the compost pile. After a week of little heat coming from our piles, Julia Reed and I tore down the piles, chopped up the material and put them back together. Two days ago, the aerated pile had reached 95ºF at the center, where the control pile had only reached 85ºF. We do not have enough data to determine if there is a significant difference between the piles yet, or if that difference is due to the aeration system. Further experimentation must be conducted. Starting in spring quarter, we will turn the control pile while leaving the aerated pile alone. We will keep measuring temperature and decomposition rates and determine if there was a difference between the two piles. If you are at all interested in experimenting with the aeration system, I strongly encourage you to get involved! Whether it be simply helping take data, designing your own experiment for future quarters, or if you simply have any questions about this research, please feel free to contact me at: rover[dot]ross[at]gmail[dot]com. Thank you! Happy farming.

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