COMPOSTING 191
While compost maturity is a key parameter for end
use applications, it is important to note that unlike other
parameters, standard testing methods for stability and
maturity do not yet exist.^19 Efforts by compost produc-
ers and scientists to devise a standard measurement for
compost maturity are underway in a number of countries
including the United States, Japan and Italy. Areas of con-
sideration include a measure of the degree of humification
via fractionation of organic carbon (i.e., the ratio between
humified fractions—humic and fulvic acid—and total
extractable carbon),^22 magnetic resonance scanning and
kinetic modeling of the composting process.
Recent work on a kinetic model for commercial yard waste
composting has enabled researchers, with some limitations, to
better predict the biochemical behavior of different waste mix-
tures. With a further researched kinetic model in hand, produc-
ers will be able to adapt processes for a seasonally changing
waste stream and design systems which reduce odor release,
leachate production and other localized environmental prob-
lems. By optimizing the process, operators can produce a higher
quality, more marketable finished product (e.g., a product that
is more likely to function as a substitute for peat moss—a non-
renewable resource) 23,24 and, avoiding nuisance problems, gain
greater public acceptance for the facility.ApplicationTop quality composts from a variety of feedstocks are
marketed to the agricultural, horticultural and landscaping
industries as a soil amendments and low grade fertilizers
for use in row crops, nursery stock, container plants, com-
mercial sod production, tree farms, etc. Lesser quality com-
posts (i.e., with some contamination by inerts or borderline
heavy metal concentrations) are used for excavation and
forest reclamation, hazardous waste bioremediation, DOT
landscaping and landfill cover. Such composts are often
products of co-composting facilities where an MSW waste
stream is combined with biosolids (waste water sludges).
It is widely known that in some MSW, as well as in bio-
solids from urban areas (i.e., where automotive contami-
nants enter waste water facilities through run-off into storm
drains) heavy metal concentrations in the finished product
will exceed unrestricted use criteria, limiting application to
land reclamation and landfill cover.
Using compost to suppress soilborne plant diseases may
be one of the most valuable, beneficial effects of compost
application.^24 Agricultural scientists, plant pathologists
and compost operators are currently field testing composts
as biocontrol agents with specific applications in the nurs-
ery container plant and tree-farming industries.^25 Research
over the past two decades has identified large numbers of
microorganisms, isolated from mature composts, that induce
suppression to soil-borne disease. There is now sufficient
information available on compost’s disease-suppressive
properties that predictable, effective biological control can
now be practiced. The mechanics of suppression, in the sim-
plest terms, can be described as a competition between ben-
eficial microbes and their disease-causing counterparts forthe nutrients delivered to the soil by the plant’s root system.
In mature compost with a robust microbial population, the
beneficial microbes dominate the nutrient source; biological
control prevails; the disease is suppressed. 26,27
Compost with its resident microorganisms is also useful
for bioremediation of hazardous wastes ( in situ as well as
off-site). Recent tests and pilot programs have found that
composts successfully degrade pesticide-contaminated soils^28
and crop residues; remediate oil field wastes (benzene, tolu-
ene, xylene) and petroleum sludges;^29 and detoxify other
hydrocarbon pollutants such as PCBs and chlorinated ali-
phatic solvents. Composting hazardous wastes has distinct
advantages to incineration: lower capital and operating
costs, and it’s safer in terms of impact on water, land and
air resources. However, there are disadvantages as well: for
instance, the preparatory work and precautionary measures
(e.g., enclosing the site or facility) that might be required to
compost a particular hazardous material can be economically
prohibitive.^30Public Health Concerns/Environmental ImpactAs composting gains wider acceptance, and becomes a part
of more communities’ integrated solid waste management
plans, certain health and environmental issues have been
raised and will continue to be raised by concerned facility
neighbors and end users. The most common concerns are
the fate of pathogenic organisms, bioaersol exposure, odors
and cumulative loading of contaminants to soil groundwater.
To ensure a continued role for composting in MSW disposal,
producers are currently addressing, monitoring and manag-
ing these concerns more aggressively than ever before.
Questions often arise about the survival or reproduction
of pathogenic organisms shown to be present in some MSW
and waste water sludges: what happens to microorganisms
such as Salmonella, enteric bacteria, flagellated and amebic
protozoans and enteric viruses at a composting facility; can
compost produced from the other pathogenic microorgan-
isms do not compete well in enriched environments such
as soil or waste water sludges, nor can they withstand for
even short periods of time the elevated temperatures (140F
to 160F) produced during the composting process. Under
existing Federal regulations for handling sludges—and con-
sidering the temperature reached in composters for extended
periods of time wastes can be safe for agricultural uses. In
general, these from finished compost, is negligible. To meet
EPA top quality, Class A criteria, compost must be main-
tained at 55C (130F) for three days. This is referred to
as PFRP (process to further reduce pathogens). The second
EPA category, Class B, requires that compost be kept at 40C
for five days or 55C for three hours. Class B is referred to as
PSRP (process to significantly reduce pathogens).
Another public health concern often linked to compost
facilities is aspergillosis, an infection of the lung caused
by an invading fungus of the same genus name, mostly
Aspergillus fumigatus. Although this organism is common
in composting materials—its spores are small, buoyant
bioaerosols—investigators have been unable to establish aC003_003_r03.indd 191C003_003_r03.indd 191 11/18/2005 1:00:20 PM11/18/2005 1:00:20 P