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Best Practices in Wood Waste Recycling Click here for printable PDF version Quality
Specification
for
Composting
Applications
Material: Wood Waste Issue: A clear understanding of the desired specification is necessary for wood waste processors to produce a feedstock suitable for composting, whether that material is to be used by the processor themselves or sold to another company. For composting, the critical characteristics may include:
Failure to comply with specifications for utilization of wood waste in this application will lead to performance problems and dissatisfied customers.
Best Practice: This best practice recommends that suppliers (processors) of wood waste and potential end-users come to a clear understanding of quality requirements for compost feedstocks. Written specifications should be developed and made available to purchasers of the compost feedstocks, or developed cooperatively with potential customers.
The appropriate specification for compost feedstocks will vary significantly depending on the actual application and mix of materials. Research into local needs and applications is absolutely necessary to ensure an acceptable feedstock product. In some cases, trial and error may be necessary to determine optimal chip size and other characteristics. Bearing in mind the need to tailor compost feedstocks for each application, wood waste feedstocks can generally be placed into one of two broad applications: bulking agents and carbon sources.
Provided below are general specifications for the two primary compost feedstock applications. The use of wood waste derived feedstocks for a bulking agent requires a coarser grade of material that will be screened out after composting and reused. In this case, the size and other characteristics of the wood chip must be tailored to the aeration system and other operational parameters. As a carbon source, the primary purpose of the wood waste feedstock is to break down during the composting process, and thus a finer grade of material is required. Hybrid applications, with wood waste feedstock used for both purposes, are also possible.
Wood
Species There are typically no limits on the acceptable types
of
tree
species
or
on
the
softwood-hardwood
mix
for
this
product. However, substantial amounts of certain varieties
should
be
avoided.
Species
that
should
be
avoided
include
Black
Walnut
and
some
Cedars,
as
these
contain
compounds
that
inhibit
plant
growth
or
may
not
be
completely
broken
down
in
the
composting
process.
Cedars
and
certain
other
species
are
also
more
resistant
to
being
composted
and
so
could
be
less
effective
as
a
carbon
source,
although
small
amounts
of
these
species
have
not
been
shown
to
be
a
problem. Size Distribution
Bulking
Agent
Carbon
Source Length:
2
-
8”
(50-200
mm)
max.
1”
(25
mm) Overs:
Varies (> 1”), max. 15% Thickness: Not
critical
Not
critical Width: Not
critical
Not
critical Fines
under
0.25
in.
(6
mm)
Varies* Not critical *
more
or
less
fines
would
be
desirable
depending
on
the
extent
to
which
the
wood
waste
is
also
intended
to
act
as
a
carbon
source.
Acceptable
Geometry A coarse/shredded material is typically acceptable
instead
of
a
chipped
material.
Maximum
Allowable
Contamination
Levels **
Bulking
Agent
Carbon
Source Rot:
5% Not critical Bark
Not
critical
10% Dirt,
rock,
sand
10% 10% Metals
0.25% 0.25% Plywood
5% 0.5% Particleboard
5% 0.5% Wood
with
laminates
2% 0.1% Plastics
Trace
Trace Painted
wood
0.1% 0.1% Treated
wood
0.1% 0.1% Other
non-wood
materials
Trace Trace ** Contamination limits are highly variable depending
on
the
compost
facility’s
operating
conditions,
end-markets
for
the
finished
compost,
and
other
factors.
Color/Brightness Color and brightness are generally not important.
Moisture Moisture requirements will vary depending on the facility,
in
particular
depending
on
the
moisture
content
of
other
feedstocks.
Implementation: In the course of adapting processing systems to produce a feedstock for composting purposes, wood waste processors should work with each potential buyer to determine optimal specifications for their application. Wood waste processors should then monitor their compliance with the developed specifications through a consistent QA/QC program that controls incoming material before processing, tests the finished compost feedstock that is produced after processing, and also occasionally tests the performance of the feedstock by examining the finished compost.
Benefits: Providing a consistent and high-quality feedstock for composting will improve the marketability of the processor’s product or the success of in-house composting operations, potentially increasing both the price and volume of the material sold. Application
Site:
This
Best
Practice
applies
to
wood-waste
processing
facilities. Contact:. For more
information
about
this
Best
Practice,
contact
CWC,
(206)
443‑7746,
e-mail
info@cwc.org.
References: 1. Hoeck, Jack. Rexius Forest Products, Eugene, OR. 2. Hlavka, Rick. Green Solutions, South Prairie, WA.. 3. Sargent, Bob. Rainier Wood Recyclers, Kent, WA.
Issue Date /
Update: March 1997
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