Aerated Static Pile (ASP)

Design Report for Grimm’s Fuel Aerated Static Pile

General Description of Proposed Facility

The composting site for Grimm’s Fuel is in the south end of the Portland Metro Region. This site is a well-established composting site consisting of about 11.5 acres of industrial land along Highway 99, with a long history of receiving and processing yard debris for compost in large static piles for four to eight months at a time. It also has a recent history with malodors impacting the neighbors to the site. Yard debris volumes have increased significantly over the past 10 years in the local area, and the regional solid waste planners want to keep the existing composting capacity at Grimm’s and find ways to expand capacity to keep up with the growing population.

The site is currently limited to its existing operational area for receiving and processing yard debris, and doing active composting, curing and bio-filtration. The office, shop, scales, fuel and landscaping sales yards are also within this area. There is a substantial limitation on layout and operational flow. As such, Green Mountain Technologies (GMT) and Grimm’s Fuel have a significant challenge to design a composting system that will control composting odors and expand the current capacity of the site.

The goal for Grimm’s Fuel is to build an Aerated Static Pile system (ASP) which receives organic waste from two grinding and mixing operations, one ASP system to the north being fed with a portable horizontal grinder and one in the center being fed with the fixed vertical grinder and screening system. The ASP composting system is an aeration floor designed to be filled with fresh yard debris in multiple 27.5-foot-wide by 110-foot-long 13-foot piles. The pile is then covered with a bio-cover of 6-12 inches of finished compost or one-foot of compost overs to adsorb odors. After controlled composting for two to three weeks, the pile will be turned into the adjacent aeration zone alongside it for an additional 2 to 3 weeks, again with a bio-cover over the top.

Strategically there are challenges in bringing one composting system off line while building and bringing a new system online while receiving incoming wastes. This requires a step-wise and phased-in operational and construction approach to keep all activities happening simultaneously. Currently finished materials from the large static pile are being screened and removed to an adjacent product storage yard, and a portion (400 cubic yards per week) of the fresh received yard debris is now being placed in three temporary ASP bins for a month with one turn. Grimm’s needs to proceed immediately with the construction of the permanent ASP solutions described in detail below to keep the incoming wastes managed in continuous aerobic conditions.

 The North Pit Aeration System has the supply manifolds go to the center of the pile and then move air both east and west from the center to assure that the pipes drain along the existing grade. The air supply manifolds are the low point of the aeration system. These manifolds are drained into the existing leachate collection and treatment and reuse system.

Fresh compostable yard debris is placed on the aerated floor for about 15 days, and then is flipped into another aerated floor area and watered as needed to maintain proper moisture control. At the end of a month of aerated composting, the pile is removed and screened with the trommels of the processing plant, which sends the overs back into the composting system, and the fines are placed in the curing pile.  In a future phase of construction, the curing compost will undergo an additional 36 days on air for curing. After curing, the product ready for sale or storage as a finished product.

The composting systems will be built in three phases. This will preserve the current capacity, make room for the new ASP modules and allow the static pile system to finish up composting.

Phase One

The First Phase provides a significant change in on-going operations. During this construction period, the overall volumes received will be maintained but composting time will shorten as additional material is processed by ASP.  The first phase of development is in the northern pit area below the unloading zone It encompasses an existing paved area just under 1 acre. This includes the two compost aeration modules that hold 5,800 yd³ each, shown in green, and the bio-filters that are shown in tan behind the two blowers. There are 4 aeration zones per module. Each aeration zone is 1,476 cubic yards – 110 feet long by 27.5 feet wide and 13 feet tall. The primary and secondary zones are next to each other to minimize material handling as they are flipped over to the side as they are re-watered. After 30 to 36 days the compost is screened, pulling out materials 5/8-inch or greater.  With the completion of Phase One, Grimm’s will have 50-60% of composting material on ASP.

Phase Two

The second phase of the facility development is the center composting modules. Two additional modules plus another two blower and bio-filter systems just like the northern modules.

The completion of Phase Two will allow the facility to process an average of 100,000 tons per year of yard debris with ASP.  The last of the old static pile composting system will be phased out as the material is screened and the southern area cleared and readied for the development of an aeration module for curing.  There is a seasonal peaking factor of 1.2x built into the site capacity calculations to handle spring and fall surges.

Future Phase

A future phase of development will be grading and adding pipes for the curing aeration on the south end area of the central modules. Blocks and grading will provide the storage locations for the bio-cover and the fresh ground and mixed material that comes off the conveyor system. There will be just one large aerated pile for material curing at the aeration rate of up to 1.75 cfm per cubic yard for a volume of 10,900 cubic yards. This is a pile 167 feet wide by 126 feet long by 14 feet. The curing module will use the same pipe at grade aeration system.   

Project Schedule

  • Concept Design Completion               March 19th 2019
  • Construction Drawing package          March 22nd  2019
  • Project bid package to contractor       April 1st 2019
  • Equipment order to vendors               April1st 2019
  • Construction commences                    May 1st 2019
  • Equipment delivery to site                  July 1st  2019
  • Installation of ASP equipment            July 7th  2019
  • Startup and training                             Sept 15th 2019