192 COMPOSTING
causal relationship between compost operations and the
disease. 31,32 With background levels of this ubiquitous
fungus found in most households and backyards in the
country, compost proponents state unswervingly that there
has never been a case of a. fumigatus infection associated
with composting facilities, either in workers or in the sur-
rounding public.^33 By way of caution, however, it should
be noted that any microorganism can become an invading
opportunist given the right circumstances; and immuno-
compromised individuals, the elderly and workers with
unprotected wounds should not risk exposure to microbial
infection where microbiological processes are taking place.
Though the odors that can be generated during com-
posting are more likely to be nuisance problems than health
risks, offensive odors from poorly controlled compost opera-
tions have resulted in the closing of more facilities than any
other health or environmental factor. The groups of odorous
compounds that have been identified at composting facilities
are reduced sulfur compounds, ammonia and amine com-
pounds, fatty acids, terpenes, acetone, phenol and toluene.^34
The most common odors are for the most part the result of
the formation, release and reactivity of hydrogen sulfide
(i.e., a reduced sulfur compound), a natural end product
of anaerobic decomposition. Hydrogen sulfide in itself is
fairly malodorous, but in its reactions with available organic
matter, a class of compounds are formed, called mercaptans
or thioorganics, that are even more disagreeable. Typical
mercaptans are dimethylsulfide (DMS) and dimethyldisul-
fide (DMDS). These compounds can then further combine
with the natural odors of composting such as ammonia, or
the alcohols, acids and aldehydes associated with fermen-
tation, or with other vegetable-based hydrocarbons such as
limonene to produce serious odor problems.
Odor control now plays a significant role in large and
small composting operations alike. Aeration systems, dis-
cussed previously, are in use in many facilities, and the newer,
enclosed facilities have odor control/treatment systems in
place. The most common and effective treatment systems are
multistage chemical scrubbers and biofilters. Both packed-
tower adsorption and misting are operated in stages to allow
different chemical reactions to remove different groups of
compounds from the air stream. Gaining in popularity, bio-
filters are now used in over two dozen biosolids and MSW
composting facilities in the U.S.^34 It should be noted that, in
the near future, facilities’ air treatment technology may have
to have the capacity control VOC emissions. With the enact-
ment of 1990 Clear Air Act Amendments, regulations are
being developed to limit VOC emissions in nonattainment
areas for the pollutant ozone, and such regulations would
most likely have an impact on the operations of large scale
MSW compost facilities.^34
While virtually all land application of mature compost
supports plant growth and improves soil properties, environ-
mental concerns specific to compost use in field and horti-
cultural crops have been raised by industry researchers and
farmers. These concerns involve the cumulative loading of
trace amounts of heavy metals to soils, the cumulative effect
of nitrate leachate on ground water,^35 and to a lesser degree,the potential presence of lawn-care pesticide residues in fin-
ished yard waste compost.^36
Despite the use of top quality compost and standard agri-
cultural practices, trace amounts of heavy metals can accu-
mulate in field soil if compost is applied at rates high enough
to supply fertilizer requirements. After a 3–5 year period, the
concentration of a specific metal in the soil could be toxic
to certain agricultural or horticultural crops. It is interesting
to note that some fruit tree farmers can repeatedly use com-
post with higher metal concentrations with benefits from the
cumulative effect, for the longevity of some species of fruit
trees depletes the surrounding soil of the necessary inorganic
trace nutrients. Research into the concerns of nitrate-N con-
tamination of ground water from compost amended field test
plots indicates that after three consecutive years there is a
cumulative effect in the soil. Because of the effect, it is sug-
gested that lower rates should be applied in subsequent years
to lessen nitrate leaching.^35 However, to date, there has been
no indication of ground water contamination. Samples ana-
lyzed beneath several different test sites were in one case, well
below 10 ppm drinking water standard, and in another case,
showed no significant difference from ground water flowing
under control plots.^37
It is generally agreed that with rigorous monitoring, qual-
ity assurance and pH management to limit bio-availability,
the use of compost containing low levels of trace minerals
can be safely applied for an indefinite period of time with-
out risk to agriculture or the environment. These concerns
underscore the push for quality and utilization guidelines in
the composting industry.CONCLUSIONWith the potential to divert millions of tons of MSW from land-
fills and incinerators and to provide beneficial end-products for
horticultural and agricultural uses, composting is an obvious
and natural method for recycling, reusing and conserving the
organic fraction of the solid waste stream.REFERENCES- Finstein, M.S. and M.L. Morris, “Microbiology of Municipal Solid
Waste Composting,” Advances in Applied Microbiology, D. Perlman, ed.;
Vol. 19, Academic Press, Harcourt Brace Jovanovich, New York, 1975. - Anonymous, “Composting Basics,” Composting Council Fact Sheet,
The Composting Council, a compost industry association, Alexandria,
VA, 1994. - Tchobanoglous, G., H. Theisen and S. Vigil, Integrated Solid Waste
Management, McGraw-Hill, Inc., 1993. - Anonymous, “Cleaning Our Environment—The Chemical Basis,”
Amer. Chem. Soc., Washington, D.C., 1969. - Diaz, L.F. and C.G. Golueke, “Composting of MSW in the USA,”
Proceedings from the Recycling and Composting Sessions of the First
United States Conference on Municipal Solid Waste Management,
Washington, D.C., June 1990. - Adams, N.E., “Composting Food Wastes on the Farm,” BioCycle, June,
1993. - Rockwell, F., “Supermarket Stream Added to Composting Mix,”
BioCycle, Oct. 1994. - Goldstein, N. and R. Steuteville, “1994 Biocycle MSW Survey—Solid
Waste Composting Seeks Its Niche,” BioCycle, Nov. 1994.
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