ASP Project

The Aerated Static Pile (ASP) describes the composting method utilized. Transitioning to an Aerated Static Pile process refers to making large, compact piles of compostable material instead of long, narrow rows. This results in the more efficient use of the compost pad. 

Polk County’s compost facility currently utilizes a low-tech but very common composting process referred to as a Static Windrow composting process. Long rows of compostable materials are formed in which moisture and heat are managed to promote the composting process. When composting activity slows, and heat drops, the windrow is mixed to reintroduce air and moisture to the material to re-activate the composting process. A specialized compost turner is utilized to mix these materials until the composting process is completed.

Timeline

Regional County representatives visited Western Lake Superior Sanitary District (WLSSD) in Duluth, MN, in September 2024. WLSSD operates a regional compost facility, which accepts SSOM. WLSSD’s facility utilizes a hybrid composting system, which is low-tech but effective, combining the windrow system, which utilizes forced aeration at the bottom of the windrow. While not efficient in utilizing the compost material footprint, the aeration speeds the compost process faster and with less resources than does a static windrow operation.  

Polk County Landfill Complex received its permit from the MPCA on September 29, 2025. This is the satisfaction of the conditions placed on the 2017 Landfill permit, and removes the restrictions for compost use for only on-site purposes (i.e. Alternate Daily Cover – or ADC – on the MSW Landfill).  It also approves the 2020 Major Permit Modification request to accept certain SSOM’s for inclusion in its composting operations. This includes animal carcasses, pet wastes, fish cleaning wastes, processed animal carcasses, and unrecyclable organic materials (i.e. wet cardboard/paper). It also includes the testing protocols required to certify compost produced, which is a requirement of many markets.

Project Updates

10/24/25: 

Polk ordered 165 linear feet of concrete panels from Precast Systems to construct a compost bunker system. The concrete L-panels and T-panels needed to build the aerated static pile (ASP) bunker began arriving on October 24^th. The use of bunkers in lieu of windrows allow for more compostable materials to be composted on a smaller footprint.  The ability to make multiple bays within that bunker system allows for a more efficient processing, which requires less fuel and labor to process.   

11/06/25: 

Assembly of the ASP bunker was completed on November 6. One large bay is located in the center, but the walls of each side of the bay are two-sided, allowing for up to four piles to be constructed for material processing, which may be at various stages in the composting process. The bunker system is modular, so the divider walls can be moved along the back wall as needed, and additional panels can be ordered to lengthen the walls or expand the bays in the future. Once the perforated thick-walled HDPE blower pipes, connectors, and blower system are delivered, the ASP system will go into operation.