Page 214 - Materials Chemistry, Second Edition

Ch005-P373623.qxd 3/22/07 5:34 PM Page 193
193
Sustainability of Municipal Solid Waste Management
(nitrogen:phosphorous:potassium) is adjusted with natural rocks (El-Haggar
et al., 2004a).
Advantages

• Natural convection
• Low running cost
• Less maturation time
• Odor can be controlled by adding a top layer of finished compost

Disadvantages

• Relatively high cost compared with natural aeration

Forced aeration
Forced aeration works like the previous system except that the ends of plas-
tic pipes are connected to blowers that force (or suck) the air through the
compost at a specific rate and velocity. Otherwise if the air rate exceeded a
certain limit, the temperature inside the compost pile decreases affecting
the microbial activity. Also, the air velocity during the day should always be
higher compared with the air velocity at night. This system needs higher
technology with air velocity control and more energy consumption, which
is why it is less economic compared to the other two systems and it is not
recommended for rural or developing countries that want to make a profit
out of all recycling processes. This method needs capital investment, skilled
workers, and has high running costs.

Advantages

• Odor can be controlled by adding a top layer of finished compost
• Less maturation time compared with natural aeration

Disadvantages

• Needs electrical source near compost
• High capital cost and velocity control
• Requires skilled workers

Vermi-composting
Vermi-composting is an ecologically safe and economic method that depends
on worms’ characteristic of transforming the organic wastes to fertilizers
that are extremely beneficial to the earth. There are two types of earth-
worms that are used due to their insensitivity to environmental changes:

the red wiggler (Eisensia foetida) and
the Red Worm (Lumbricus rebellus).