Ohio University is home to the largest in-vessel composting system at any college or university in the nation.
Facts about composting at OU:
About the In-Vessel Composting Machine:
- Ohio University elected to employ this type of in-vessel composting system for management of all its food waste for several reasons: the system features a highly efficient contained system, which has the capacity to manage all forms of organic waste (including meat, dairy, biodegradable service-ware and landscape waste); it speeds the processing of waste into usable soil; it controls odors, vectors and leachates; and minimizes staff time needed for operation.
- The tunnel optimizes the natural composting process by controlling airflow, moisture levels and temperatures thereby accelerating the decomposition cycle of organic wastes. Composting material is moved in a plug flow fashion through the tunnel in the designated number of retention days. Material is supported on a series of stainless steel perforated trays that form the tunnel floor.The trays are pushed forward as a continuous unit by an external hydraulic ram. When the ram is moving an empty tray into the tunnel, all trays within the tunnel are moving forward. As an empty tray is being inserted, compost from a single tray is being unloaded at the tunnel discharge end using a series of vertical breaker bars and a discharge auger. The auger discharges the compost from the unloading tray onto a conveyor and the empty tray emerges from the tunnel ready for inspection and re-use.
- Surges of waste quantities or changes in composition can be accommodated by inserting and filling more trays than the number required on a typical loading day.
- The tunnel is controlled for air supply and temperature using dedicated control proves, a supply and exhaust fan and an air circulation system with associated air plenums. Composting material then moves through a set of spinners that act to invert, homogenize, agitate and stack the material into the next zone. Water is added during material cross-mixing (if needed) to re-establish proper moisture levels. Material remains in the second zone for an additional number of days equivalent to the retention time in Zone 1 (e.g. 7 days in Zone 1 and 7 days in Zone 2 equals 14 retention days) while significant stabilization occurs through control of air supply, water and temperature.
- The tunnel is equipped with a series of probes that monitor temperatures. These temperatures, in relation to control panel set points, are used to operate supply fans. The optimum temperature range for composting organic waste is 50 degrees Celsius to 65 degrees Celsius. The temperature set point in the first composting zone is typically set between 58 degrees Celsius and 60 degrees Celsius for greater than three days to ensure pathogen reduction. A set point between 52 degrees Celsius and 54 degrees Celsius is used in the second zone to maximize conversion of putrescible materials. Any moisture that drains out of the composting material flows into the plenums that run along the base of the tunnel and from the plenums to sump boxes through pipes located at the sides of the tunnel. Leachate is pumped back onto the composting materials from the sump boxes through pipes located at each sump box. Some leachate is released to the on-site septic system when the overall water balance is positive inside the machine.
- Once removed from the system, the compost needs to cure for at least 90 days.The windrows are turned regularly to offer a more homogenous mix to the compost. The 2012 expansion project included the purchase of a Windrow Turner which is expected to streamline this turning process.
- The resulting nutrient-rich soil is used on-campus (intramural athletic fields, gardens used by Plant Biology students, Ecohouse community garden, etc.).
- The University has spent several years testing out a variety of biodegradable/compostable service-ware (plates, cups, forks, etc.).
It was discovered that certain products, particularly those that are potato starch-based, do not break down quickly enough to be used with our system.We have had recent success in PLA (polylactic acid) service-ware. During our transition from a 2-ton daily load to 6+-ton
daily loads, the use of service-ware as a bulking agent slowed. Now that our new system is running (as of Fall 2012), we are hopeful that we can reintroduce service-ware as a primary bulking agent in the compost recipe.
- Note: Details regarding the "compost recipe" are not provided here since it can be a temperamental process depending on individual
batches of organic matter, among other things. This is a learning process that can only be mastered by experiencing it first-hand. Typically, we strive for 60% food waste and 40% bulking agents.
- The compost staff was trained by Wright Environmental following the installation of each facility.
- Additionally, various other staff members at the institution have completed trainings for successful operation of the facilities.
While composting is an excellent way to divert waste from the landfill, Ohio University is also excited to be able to use this project as a way to promote student engagement and academic programs while improving the efficacy and sustainability of our program.The opportunities for research studies and programming surrounding soil analysis, PLA testing, sociological impacts, behavior change, etc. is at the heart of what we hope to offer.Students are encouraged to contact the Office of Sustainability with research requests as they relate to the Compost Facility.