Page 211 - Materials Chemistry, Second Edition

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Sustainable Industrial Design and Waste Management
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biological decomposition of organic matter, under controlled conditions,
into soil conditioner (El-Haggar et al., 1998). Aerobic fermentation is the
decomposition of organic material in the presence of air. During the com-
posting process, microorganisms consume oxygen, while CO 2 , water, and
heat are released as result of microbial activity as shown in Figure 5.23.

Factors affect the composting process
Four main factors control the composting process: moisture content, nutri-
tion (carbon:nitrogen ratio of the material), temperature and oxygen (aeration).

Moisture content: The ideal percentage of the moisture content is 60%
(El-Haggar et al., 1998). The initial moisture content should range from 40 to
60% depending on the components of the mixture. If the moisture content
decreases less than 40%, microbial activity slows down and becomes dor-
mant. If the moisture content increases above 60%, decomposition slows
down and odor from anaerobic decomposition is emitted.

Carbon to nitrogen ratio: Microorganisms responsible for the decomposition
of organic matter require carbon and nitrogen as a nutrient to grow and
reproduce. Microbes work actively if the carbon:nitrogen ratio is 30:1. If the
carbon ratio exceeded 30, the rate of composting decreases. Decomposition
of the organic waste material will slow down if C:N ratios are as low as 10:1
or as high as 50:1.

Additives

Air

Water

Odor
Organic
wastes

CO 2

Compost
(soil conditioner/
Hot organic fertilizer)

FIGURE 5.23 Composting process