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Sustainable Industrial Design and Waste Management
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fermentation (biogas), vermi composting, and co-composting processes. Com-
posting is the most commonly used method to recycle organic wastes from
technical, economical, and environmental points of view as will be explained
later in this chapter.

5.3 Recycling of Waste Paper
The earth has limited natural resources, which must be conserved for future
generations – “sustainable development”. The scale of consumption of raw
materials from forest and crop planting is very large in paper manufacturing.
Hence one of the solutions to this problem is to recycle existing products’
waste. Recycling may enable the recovery of primary material for reuse in
the paper manufacturing process.
Paper is a “pliable material used for writing, packaging, and a variety of
specialist purposes” (Biermann, 1993). Paper materials are classified as paper
or paperboard. Paper includes newsprint, stationery, tissue, and many others
while paperboard includes linerboard, corrugating media, milk cartons, etc.
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Kraft paperboards are any of the heavyweight papers generally above 134 g/m ,
used in packaging. Bleached paperboards are made from bleached kraft pulp
and are used in folded milk cartons, cups, and plates. Unbleached paper-
boards are used in linerboard and corrugating media for the production of
corrugated boxes for example. Recycled fiber is being used in larger amounts
in the production of unbleached paperboards (Biermann, 1993).
There are four main categories of paper: high-grade printing and writ-
ing paper, newsprint, corrugated/paperboard (including packaging), and tis-
sue/towel products. The overall recycled content in each category varies,
with tissue/towel containing the highest percentage of recycled material and
printing and writing paper the lowest. So far, all pulp used for tissue/towel
products as well as newspaper is imported in most developing countries.
These products could be produced in developing countries very easily through
simple recycling technologies with high return because they do not require
high technologies or good quality (El-Haggar et al., 2001; El-Haggar, 2001a).

Pulping processes
Paper consists of a web of pulp fibers normally made from wood or other lig-
nocellulosic materials that is produced by physical or chemical means for
separating the fibers to be used for paper production. In general, there are three
processes for pulping, these are: mechanical, semi-chemical, and chemical
pulping.

Mechanical pulping
Mechanical pulping is a process used for separating fibers without the addition
of any chemicals. The process gives a pulp that is generally characterized by