Environmental Engineering FOURTH EDITION

Reuse, Recycling, and Resource Recovery 291

Figure 14-14. Windrow composting.

Compost pile

Figure 14-15. Static pile composting.

Temperatures within a windrow approach 140"F, entirely because of biological
activity. The pH will approach neutrality after an initial drop. With most wastes, addi-
tional nutrients are not needed. The composting of bark and other materials, however, is
successful only with the addition of nitrogen and phosphorus. Moisture must usually
be controlled because excessive moisture makes maintenance of aerobic conditions
difficult, while a dearth of moisture inhibits biological life. A moisture content of
40 to 60% is considered desirable.
There has been some controversy over the use of inoculants, freeze-dried cul-
tures used to speed up the process. Once the composting pile is established, which
requires about two weeks, the inoculants have not proved to be of any significant value.