Aerated static pile composting
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Aerated Static Pile (ASP) composting, or tunnel composting systems include both passive and active methods. Sandwiched somewhere between windrow and in-vessel technologies with regard to complexity and cost, aerated systems are most commonly used by larger, professionally-managed composting facilities.
There are also hybrid windrow and in-vessel systems incorporating features of ASP.
Aerated static piles don't need as much space as a windrow operation, but offer rapid biodegradation and process control similar to in-vessel composting, and work well for facilities processing wet materials or a wide variety of feedstocks. ASP facilities can be outdoor operations, under roof, or totally enclosed.
As the name implies, static piles are not turned, rotated, or otherwise manipulated during primary composting. Instead, the blended admixture is placed on perforated piping, improving air circulation.
A passive ASP system relies on natural air currents. An active system uses fans to pull or push air through the composting mass. Rigid or flexible perforated piping, connected to fans, delivers the air. The pipes can be installed in channels, on top of a floor, or along the ground.
This assisted aeration method is also known as forced aeration and may be augmented with a computerized monitoring system responsible for controlling the amount of air delivered to the composting mass. Meters and manual monitoring techniques may also be used.
Positives of using this composting method include the ability to maintain sufficient oxygen levels for the microbial populations and the removal of excess heat, which can kill desirable microbes and crash the system. Aerated systems also facilitate the use of biofilters to treat process air (remove particulates and mitigate odors) prior to venting.
However, aerated systems dry out quickly and must be monitored closely to maintain desired moisture levels.
