Aerated static pile composting

From Wikipedia, the free encyclopedia

At this facility, the channeled, concrete floor of the composting pad protects perforated piping so it can be reused many times to deliver oxygen to the composting mass.

Aerated Static Pile (ASP) composting, or tunnel composting systems include both passive and active methods. 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. 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. Features of ASP are also incorporated into some hybrid windrow and in-vessel systems.

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.

[edit] Aeration

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.

Example of a motor-blower unit supplying air in a forced aeration composting system

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.

In Thailand, May 2008, this system has been used by farmer groups for more than 445 sites. The process needs only 30 days to be finished and 10 metric tons of compost is obtained each time. A blower (15 inch squirrel-caged blower with 3 hp motor) is needed to force the air through 10 piles of compost twice a day and 15 minutes each. The raw materials consist of agricultural wastes and animal manure in the ratio of 3 : 1 by volume. For more information please visit www.compost.mju.ac.th/eng