Page 253 - Materials Chemistry, Second Edition

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224 Waste Management Practices: Municipal, Hazardous, and Industrial
decomposition of materials. Using the turned pile method, the composting process is completed in
approximately 2 months to 1 year.
Turned piles are constructed outdoors; however, piles can also be situated under shelters. Such
a cover will prevent saturation with the consequent production of anaerobic conditions as well as
leachate generation. Leachate problems are further addressed by constructing piles on firm surfaces
(preferably paved) surrounded by berms or trenches to collect runoff. This is discussed below.
Turning frequencies range from twice per week to once per year. The more frequently that piles
are turned, the more quickly the composting process is completed. Where odor control and com-
posting speed are a high priority, oxygen monitoring equipment can be installed to alert operators
when oxygen levels fall below 10 to 15%, which is the minimum oxygen concentration required for
aerobic decomposition and to minimize odor problems (Richard, 1992). Simple portable oxygen
meters and long-stem thermometers can be inserted within the pile to assess these conditions.

8.6.2 TURNED WINDROWS
Turned windrows are elongated compost piles that are turned frequently to maintain aerobic condi-
tions (Figure 8.5). Forming windrows of the appropriate size helps in maintaining the desired tem-
perature and oxygen levels. Windrows operate most effectively at a height of 1.5 to 1.8 m (5 to 6 ft)
(CRS, 1989). This height allows the feedstock to be insulated but prevents the buildup of excessive
heat. Windrow heights vary, however, based on the feedstock (e.g., the tendency to compact), sea-
son, local climate, and turning equipment used. Windrow widths generally are twice the height of
the piles. Land availability, operating convenience, type of turning equipment, and desired end-
product quality also affect the windrow width (U.S. EPA, 1994).
If the windrow resembles a triangular shape, the volume can be determined by the equation
1

2 (WHL) (8.5)
where W is the average width at the bottom, H the average height of the pile, and L the length of
the windrow.
For a trapezoidal shape, volume is determined by
1
(W W )HL (8.6)
2 1 2
where W is the average width at the bottom, and W average width at the top.
2
1

FIGURE 8.5 Composting of MSW using the windrow system.