Page 256 - Materials Chemistry, Second Edition

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Composting MSW 227

FIGURE 8.9 A cured pile ready to go to market.

Since curing piles undergo slow decomposition, monitoring is important during this period so that
piles do not become anaerobic.
The curing piles should be small enough to permit adequate natural air exchange. A maximum
pile height of 2.4 m (8 ft) is suggested. If compost is intended for high-quality uses, curing piles
should be limited to 1.8 m (6 ft) in height and 4.8 to 6.1 m (15 to 20 ft) in width (Rynk, 1992).
The C:N ratio of finished compost should not exceed 20:1. As mentioned earlier, C: N ratios that
are too low can result in the production of phytotoxins within the pile, which are dispersed into the recip-
ient soil when the compost is land-applied. One group of phytotoxins is produced when microorgan-
isms are not capable of utilizing all the excess nitrogen. The free nitrogen is biologically transformed,
resulting in the release of NH and other chemicals that are toxic to plant roots and inhibit growth.
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8.8 ENVIRONMENTAL CONCERNS DURING COMPOSTING

Composting at the municipal level involves the treatment of tons of potentially odoriferous and wet
material containing a wide range of microorganisms. Homes and businesses may be located near
the facility. It is therefore essential to control carefully the composting process at all times in order
to limit or prevent environmental concerns such as air and water pollution, odor, noise, vectors,
fires, and litter. These concerns can be minimized through proper design of the facility and consci-
entious daily operations.

8.8.1 AIR QUALITY

Air pollution is typically not a major concern at composting facilities, with the exception of natu-
ral odor problems. Dust can be a problem, particularly in the dry summer months. Dust is gener-
ated from dry, uncontained organic materials, especially during screening and shredding operations
and from vehicle traffic. Dust carries bacteria and fungi that can affect facility workers and possi-
bly facility neighbors. Dust may also clog certain equipment and filters.

8.8.2 ODOR
Most stages of the composting process can release odors. The feedstock itself will contain odorous
compounds; odors can be produced during collection, transport, and storage of the feedstock.
Improper composting procedures, for example, not providing adequate O and allowing anaerobiosis,
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