Of the
470,000 tons of organic waste produced in the U.S. each year, less than 3
percent is composted. Odors and
public perception are often cited as one of the primary reasons that composting
sites are not approved or are closed. The
GORE Cover system can significantly reduces odors by the controlled use of a
PTFE membrane that is permeable to oxygen but impermeable to large molecules.
In addition to the membrane, which covers the organic material during
composting, the system includes a concrete floor and wall, blowers for aeration,
and a winder for efficient movement of the cover.
The system also requires consistent management including preparation of
materials to achieve a homogenous mixture with moisture content of 55-60 percent
and monitoring of temperature and oxygen levels.
With this system, the composting process takes eight weeks.
The “heap” of organic material is covered by the membrane, which is
secured to the ground, allowed to compost for four weeks, then moved and
re-covered for two weeks for stabilization.
During the final two weeks of curing, the heap is uncovered.
Discussion:
Harry
Hoitink (OSU) asked if freezing were a problem.
Sheremeta responded that the heat produced by the heap prevents freezing
of the membrane except where it is in contact with the ground.
Placing 2-3 inches of porous material beneath the cover’s edge
minimizes the freezing.
Bob Shanz (Garik
Corp.) asked how moisture that condenses on the underside of the cover is
returned to the pile. Also, does it
tend to run down the sides, leaving the center dry?
Sheremeta indicated that it is not a problem but that the specifics are
confidential.
Jerry
Richter (Garden Ridge Nursery) requested cost information for the system. Sheremeta noted that costs are expected to be available by
the end of March 2003. Currently,
the system is being used in seven reference facilities in the U.S. which GORE is
using to collect cost data and to demonstrate its effectiveness.
The system is not turnkey and everything but the site preparation, which
must meet specs, is provided by GORE. The
system has been used in Europe since 1994 and meets Germany’s stringent
requirements.
Hoitink
suggested that other than the cover, the basics of the system are standard.
Sheremeta replied that GORE’s insistence on providing the entire system
is based on their desire to control all details so the success is ensured.
Hoitink
noted that the cover should be needed only for the first four weeks as most odor
compounds will be decomposed by then. Sheremeta
agreed but explained that the end market may have an impact. If a finer product is required, the grinding that is done
after the four weeks will expose fresh surface area and there will be a sharp,
though brief, increase in the composting rate.
Bob Page (Farmore
Farms) asked what GORE supplied for the price paid.
Sheremeta replied that most materials are provided including precast
trenches (for aeration), steel trench covers, water traps, pipes, blowers,
wiring and fiber optics with conduit blowers, mechanical winder and track for
movement, GORE covers, oxygen and temperature sensors, PC with software and
training.
Dave Ertl (OSU)
asked for specifics of what is not supplied.
Sheremeta responded that the installation and cost of the civil work,
including a cement or asphalt base and a cement wall with embedded steel to
support the winder railing, are the responsibility of the buyer and must be
installed according to GORE specifications.
Hoitink
asked if GORE is partnering with a large dairy facility in the western U.S. as a
reference site. Sheremeta noted
that there have been conversations but no commitment.
GORE is still looking for an agricultural site as they intend for
references sites to illustrate the system for different climates and feedstocks.
Notes
by Mary Wicks