MUNICIPAL SOLID WASTE MANAGEMENT AND DISPOSAL - Environmentally Conscious Materials Handling - page 150

minimal labor. These equipments are not weather sensitive because the
temperature, moisture and aeration are closely controlled. They vary in
size and capacity although and they are usually used for handling small
volumes of material. It only takes several weeks to produce the com-
post but takes several weeks to stabilize the compost. The initial cost of
equipment setup may be high compared to other methods.
For small amount of household organic waste, two additional small-scale com-
posting methods can be employed: backyard composting or vermicomposting.
Backyard or onsite composting can take between one to two years to complete
the composting process. However, occasional turning can improve the efficiency
and reduce the composting period to six months. Vermicomposting uses red
worms to mix with organic waste in composting bins to break down the organic
wastes into a high-value compost called castings .
Several factors that influence the composting process include: carbon (C) to
nitrogen (N) ratio, oxygen concentration, moisture content, particle size, temper-
ature, and pH of the composting materials. Carbon and nitrogen are essential
nutrients for the microorganisms to function properly in the composting process.
The ideal C:N ratio should be 30:1. This ratio is important because a high C:N
ratio could slow or halt the composting process. A low ratio, by contrast, could
cause the organics to degrade too rapidly and use too much oxygen, causing
unpleasant odors due to anaerobic conditions. It has been found that green, wet
plant materials have a low C:N (high N), and brown, dry materials have a high
C:N (high C). A proper blending of materials is thus necessary to achieve an
appropriate ratio for the composting process.
Oxygen is needed for aerobic biodegradation, wherein microorganisms use
oxygen to effectively degrade organic materials into carbon dioxide, humus, and
inert mineral compounds. Without oxygen, the process becomes an anaerobic
degradation process. In the anaerobic process, organic materials will still be
degraded, but the process is relatively slow compared to the aerobic process, and
it also causes unpleasant odors due to the presence of methane and noxious sulfur
compounds. Water is an essential element for the composting process, helping to
dissolve the organic and inorganic nutrients present in the compostable materials
and making them available to soil microorganisms and their metabolic processes.
The ideal moisture content of the compost pile should be between 40 and 60
percent by weight.
The surface area of organic materials exposed to soil organisms affects the rate
of composting. The more finely ground a material, the higher the surface area
per unit weight. Hence, large materials should be ground and shredded to smaller
sizes. A mixture of materials should be used. When bulky materials are shred-
ded in size, the decomposition rate increases while the porosity of the material
decreases, resulting in anaerobic conditions. Ideal temperatures vary between 90 ◦
and 140 ◦ F. Maintaining high temperatures is necessary for rapid composting and