Composting is a form of recycling that mimics
nature’s recycling of nutrients—one of the four
scientific principles of sustainability. It involves
allowing decomposer bacteria to recycle yard trimmings,
food scraps, and other biodegradable organic
wastes. The resulting organic material can be added
to soil to supply plant nutrients, slow soil erosion, retain
water, and improve crop yields. Homeowners can
compost such wastes in simple backyard containers, in
composting piles that must be turned over occasionally,
or in small composting drums (Figure 21-10) that
can be rotated to mix the wastes and to speed up the
decomposition process. Over 6 million homes in North
America compost their organic wastes and the number
is increasing. For details on composting, see the website
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