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Sustainable Industrial Design and Waste Management
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Under suitable aeration, humidity, and temperature, worms feed on
organic wastes and expel their manure (worm castings) that break up soil
providing it with aeration and drainage. The process also creates an organic soil
conditioner as well as a natural fertilizer. Worm castings have more nutrients
than soil conditioner in terms of nitrogen, phosphorus, etc.
A mature worm will produce a cocoon every 7 to 10 days which contains
an average of seven baby worms that mature in approximately 60 to 90 days,
and in one year each 1,000 worms produce 1,000,000 worms (El-Haggar, 2003a).
Vermi-composting can be used internally easily by using a special con-
tainer (worm bin) that can be placed in any place that is not subjected to
light such as a kitchen, garage, or basement. The organic waste is put in this
container with the worms. The worms are odorless and free from disease.

5.13 Rejects
The rejects problem starts at the municipal solid waste sorting stage where
recyclable wastes can be collected leaving unrecyclable wastes (rejects) with-
out collection to be disposed off. The plastic bags that are contaminated with
organic material are not collected because cleaning them is very costly and
recycling of such waste is not cost effective. Also items such as small pieces
of glass can be harmful to workers during manual sorting, so they are not
collected. In a typical municipal solid waste composting plant, the incoming
raw materials are food waste mixed with contaminated plastic bags and
other impurities. The compost piles, after reaching maturation stage, are
driven by a conveyor belt to a drum-like machine that separates the organic
material from the rejects as shown in Figure 5.26. This drum rotates com-
post inside and the cutting tools located at the inner surface decompose the
organic material further. As the drum rotates the organic material pene-
trates through the openings along the body of the drum while the rejects,
shown in Figure 5.27, that rotate and move along the axis of the drum pass
by an exit at the end of the drum (Sawiries et al., 2001). Figure 5.26 shows
a drum in a typical composting plant in Egypt, with the piles of compost at
the front and the rejects at the other end. Figure 5.27 shows the rejects accu-
mulated at the side of the composting plant. These rejects represent 20–25%
of the total solid waste generated (El-Haggar and Toivola, 2001). Rejects can
be disposed of using incineration, landfills, or recycling if possible.

Incineration
Rejects can be incinerated to be converted into ash. Incineration is the
process of thermally combusting solid waste using a thermal treatment
process. There are various types of incinerators as discussed in Chapter 1
and the type used depends on the type of waste to be burnt. Conceptually,
incinerators are not recommended for sustainable development because