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Design Variations in Aerated Static Pile Composting Systems
Scott Gamble, P.Eng.
Compost Council of Canada 2014 Annual Conference
Halifax, Nova Scotia
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• ASP composting originated at the USDA research facility in Beltsville, MD in the early 1970’s.
• ASP’s have remained a mainstay for composting dewatered biosolids.
• There were many “departures” in SSO composting technologies in the 1980’s and 1990’s.
• ASP systems are the building block from which many of the common higher tech systems have evolved (e.g. channels, tunnels, static containers).
• During the past ten years we have seen a revival of ASP systems.
What are Aerated Static Piles?
Beltsville ASP circa 1975
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Where Do ASP’s Fit in the
Technology Spectrum?
Passively Aerated Systems Actively Aerated Systems
Passively Aerated Static Piles
Passively Aerated Windrows
Bunker
Windrow
Turned mass bed
Aerated Static Piles
(uncovered and covered)
Tunnels
Static Containers
Agitated Containers
Channels
Agitated beds
Rotating drum
Environment Canada Technical Document on MSW
Organic Processing, 2013
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Advantages Disadvantages
• Pile configurations and height reduce
the space requirements of the facility.
This can translate into lower land costs
and civil development costs.
• Positive aeration provides better odour
control than passively aerated systems.
Negative aeration with biofilters
provides even better odour control.
• Smaller surface area (relative to
windrows) reduces the impacts of cold
weather and rain infiltration.
• Significantly shorter active composting
times than passively aerated systems.
• Capital cost of forced-aeration
equipment.
• Over-aeration can remove moisture and
slow biological decomposition process.
• Feedstock preprocessing requires a
higher degree of care; feedstocks must
be properly sized, well mixed, and
moistened.
• More operator skill is required to
manage the aeration systems.
• Aeration systems generally require
three-phase electrical supply.
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What Feedstocks can be Handled?
• Leaf and yard waste (Harvest
Power pre 2008)
• Food waste (Jepson Prairie)
• Biosolids (Clearwater, Kelowna)
• Digestate (Harvest Power)
• Abattoir waste (Spa Hills)
• Specified Risk Materials
(Lethbridge Research Station)
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Basic ASP Components
Aeration Header
Centrifugal Fan
Biocover (e.g. compost, screening overs)
or Fabric Cover
Aeration Lateral
• Pile Configurations
• Aeration Laterals
• Fan Controls
• Aeration Method
(air direction)
• Aeration Zoning
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Common ASP Design Variations
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Discrete Piles
Pile Configurations
Bunker Systems
Extended Piles.
Pile heights typically
range from 6 to 11
feet high.
Aeration Laterals - Above Grade
Aeration Laterals - Below Grade
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• The simplest way to controls aeration fans is
on an intermittent basis using a timer. A typical
timer cycle involves 2 to 5 minutes of run time
during each 15 to 20 minute cycle.
• Fans can also be operated on an intermittent
basis using temperature feedback. Fans turn
on when temperatures reach a high level set
point, and off when a low level set point is
reached
• Fans can also be operated on an intermittent
basis using temperature feedback. Fans turn
on when oxygen reaches a low level set point,
and off when a high level set point is reached.
Fan Control – Intermittent Aeration
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• Aeration fans operated on a
continuous basis are normally
controlled using a VFD.
• The fan speed can be set
manually on the VFD keypad,
or remotely via a PLC.
• Fans/VFD’s wired to a PLC can
also be programmed to ramp
up and down “automagically” in
response to temperature or
oxygen readings.
Fan Control – Continuous Aeration
Basic Aeration Methods
Positive Aeration
Negative Aeration
Bidirectional Aeration
Control Dampers
Dual Fan System
Single Fan System
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Aeration Zoning
It is important for operators to
understand the air flow limits of
their fans/ ducting system, and
how their PLC logic distributes
air between zones.
• In a multi-zone system, each
aeration fan supplies air to two or
more compost piles or zones.
• Fans typically operate continuously
and air flow to/from each zone is
controlled with dampers.
• Dampers can be controlled
manually or “automagically” with a
PLC.
• Systems can be positively or
negatively aerated, or bidirectional.
Basic Multi-zone Aeration
Positive Aeration
Negative Aeration
Bidirectional Multi-Zone Aeration
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• Pile configuration (length, width) is a balance between
available space and site traffic/layout, duct and fitting
costs (for headers and laterals) and fan costs.
• Pile sizing should also consider daily/weekly feedstock
quantities, delivery schedules, and site operational
schedules.
• In bunker systems, end wall vs side wall lengths should
be optimized. Roof truss lengths and column locations
are a factor when enclosing ASP piles in buildings or
pole barns.
• Longer piles (e.g. > 100ft) may require a special lateral
designs (e.g. varying diameter and/or perforation
pattern).
ASP Size Considerations
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• Ducting materials must match the anticipated air temperatures. Ducting
designs must account for expansion/contraction, fan vibration, and
construction tolerances.
• Duct sizes, fittings and transitions must be appropriate to the air volumes
so that system pressures are reduced.
• Condensate and leachate drainage must be considered in the ducting
design and aeration fan selection. The ducting design should also allow
for easy maintenance and cleanout of ducting runs.
• Ducting and fans in negative and bidirectional aeration systems must be
designed to resist corrosion.
• Aeration fans must provide appropriate aeration rates and meet pressure
requirements of the system.
Aeration Design Considerations
