[USCC] Ventilation for Aerobic Composting

[Tim Howard]

I work for Poly-Flex Composting in support of the Husky Ecopod
composting system.  In our system a 200 foot long tube is filled with
mixed material to be composted.  Both ends of the tube are sealed and
approximately (12) 2" diameter vents installed near the top of the tube
as it lays on the ground.  In the process of filling (2) 4": perforated
tubes are imbedded near the bottom of the bag for the length of the
tube, coupled at one end and connected to a Y at the other end.  The
third leg of the Y is brought outside the tube and attached to a blower.
The blower operates on a timed basis to bring fresh air into the tube,
venting to the outside through the 2" vents installed near the top of
the tube.

 

The blower forces approximately 400 CFM per minute into the tube at
about 2" of static pressure.  Usually the blower is set to 10 minutes on
and 10 minutes off after the bag is filled.  The time may be adjusted as
needed based on the measured temperature in the composting material.
Usually the temperature will show a steep rise over the first 48-72
hours from ambient to 150 to 160F.   Usually the blower on time would be
reduced to lower the temperature to 130-140F to prevent drying the
material excessively and stopping the composting process.

 

Blower operation will continue for the next 4 to 8 weeks.  The
temperature will generally stay at 140F for 7-10 days and gradually
taper down.  When the temperature reduces to 100-110F the material is
removed from the bag and windrowed or piled for curing.  It would be
normal for the material to reheat to 130F once and possible twice after
turning in the curing piles, at which time the compost is usually ready
for use.  When the bag is opened the moisture will have migrated toward
the outer perimeter and the center of the matrix will be thoroughly
composted but relatively dry.  There will be some condensation of
moisture on the plastic tube itself.  Depending on ambient conditions it
may be desirable to add water when curing.

 

The assumptions are that the material going into the Ecopod will have a
good C:N ratio, enough bulking materials to allow airflow through the
matrix and a moisture level of 50-65 percent.  Casual calculations show
the blower gives a complete air change about every 80 minutes based on
50 per cent run times.  The material quickly composts near the vents
forming small biofilters at each vent controlling odor, odiferous
volatiles condense on the inside of the tube and are contained in the
matrix until they can be completely composted and the matrix is not
exposed to ambient precipitation or objectionable vectors. 

 

While the Ecopod process does not lineup well with Mr. Crocker's
ventilation requirements, given a proper mix and moisture level it works
well and successfully produces high quality compost.

 

Tim Howard

Poly-Flex Composting

9480 Jamaica Avenue 

Cottage Grove, MN 55406

Desk Phone: 651-734-6237

Direct Fax: 651-734-6537

Email: tim at upnplastics.com

Cell: 612-616-0759