Composting 117Figure 3.12 Chinese composting pile covered with rice straw
Forced-air aeration composting
A more efficient composting method which ensures temperatures in the upper
thermophilic range and provides an effective inactivation of pathogen is called
the Beltsville aerated rapid composting (BARC) method. Developed by Epstein
et al. (1976), this method involves placing a mixture of sludge and wood chips
over a base (consisted of compost and chips) and aeration piping system (Figure
3.13). The approximate size of each pile is 12 x 6 x 2.5 m (length x width x
height) and is connected to a centrifugal blower to draw air through the pile
(sucking) or to blow air into the pile (blowing) according to the pre-determined
aeration requirements (section 3.4.4). The gases drawn into the pipe are
deodorized by passing them into a pile of screened compost (Figure 3.14). The
entire pile is covered with a 30 cm layer of the screened compost to minimize
odors and to maintain high temperatures in the compost pile.
As shown in Figure 3.15, a rapid temperature rise to within 60-80 °C was
achieved in 3-5 days of composting, and these temperatures continued for about
10 days. The distribution of temperature in a compost pile for both blowing and
sucking types is shown in Figure 3.16 (Stentiford et al. 1985). There appeared to
be uneven temperature distribution in the compost pile, with higher temperature
developed at the inner part and lesser temperature at the outer portion. This
uneven temperature distribution is a typical drawback of the static, non-pile-
turning composting method in which pathogens present at the outer portion of
the compost pile may not be effectively inactivated by the biologically produced
heat.