Aerated static pile composting

Aerated Static Pile compost facility located in the City of Hutchinson

Image showing the blowers located behind the push wall in the above image

Aerated static pile (ASP) composting refers to systems using forced aeration to keep compost material aerobic without physical manipulation. This is typically done by placing mixed feedstocks on perforated piping where air is then either pushed up (positive aeration), sucked down (negative aeration), or pushed and pulled (reversing aeration) through the material. If air is pulled through the material (negative and reversing aeration) it is typically then run through a scrubber like a biofilter to remove odor and emissions

ASP's are typically constructed outdoors in mass beds or bunker configurations (see image for example of bunker style ASP). They can also be constructed within open-sided buildings, enclosed bunkers known as tunnels, or windrows. Many ASPs are protected from rain and precipitation with a roof, reducing leachate generation and allowing operators to evaporate detained water through biodrying.

When properly designed and operated, aerated composting facilities have 95% less odor/emissions and 25% of the footprint of a comparable windrow facility. For these reasons, ASP's are typically implemented at sites composting putrescible feedstocks (manures, biosolids or food waste) with a higher potential for adverse environmental impact. They are also used at sites that are land constrained or managing wet dense feedstocks.

Aeration

Aeration system for a closed chamber composting facility

The aeration system uses fans to push and/or pull 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 included throughout the pile during buildup.

In large-scale systems, forced aeration is accompanied with a computerized monitoring system responsible for controlling the rate and schedule of air delivery to the composting mass, although meters and manual monitoring techniques may also be used in smaller scale operations.

Advantages of this composting method include the ability to maintain the proper moisture and oxygen levels for the microbial populations to operate at peak efficiency to reduce pathogens, while preventing excess heat, which can crash the system. Aerated systems also facilitate the use of biofilters to treat process air to remove particulates and mitigate odors prior to venting. However, aerated systems can dry out quickly and must be monitored closely to maintain desired moisture levels.

In Thailand this system has been used by 470 farmer groups. (May, 2008). The process required 30 days to finish without turning, with 10 metric tons of compost (10 piles) obtained each time. A 15-inch squirrel-cage blower was used to force the air through 10 static piles of compost, one at a time, for 15 minute periods twice a day. The raw materials consisted of agricultural wastes and animal manure in the ratio of 3:1 by volume.

See also

• List of composting systems
• Anaerobic digestion
• In-vessel composting
• List of solid waste treatment technologies
• Windrow composting