Page 79 - Solid Waste Analysis and Minimization a Systems Approach

FUNDAMENTALS OF RECYCLING PROCESSES 57

make bottles or jars. Recycled glass is melted at a lower temperature than virgin glass,
which saves 30 percent of the energy used.

2.8.5 PAPER RECYCLING

Collected paper must be sorted and graded before being recycled. The recycling
process itself can be separated into eight steps

1 Sorting
2 Baling
3 Pulping
4 Screening
5 De-inking
6 Pouring
7 Rolling
8 Packing

This section provides a brief overview of each of these steps. Paper recycling can be
challenging because there are over 50 grades of waste paper. The main four groups are

1 Low grade (mixed paper, corrugated board)
2 De-inking grade (newspapers, magazines, office paper)
3 Kraft grade (unbleached brown backing)
4 High grade (printer cut-offs and unprinted paper)

Large amounts of paper, including shredded paper, are baled before being trans-
ported to a paper mill. Once at the paper mill, the paper is placed into a large vat and
mixed with water. The process breaks down the paper into tiny strands of cellulose
fibers. Eventually, this turns into a mushy mixture called pulp.
The pulp is then filtered and screened. The screens are made of a series of holes and
slots of different shapes and sizes, and remove any remaining contaminants such as
bits of plastic of glue. For certain uses, pulp must also be de-inked. There are two main
methods of de-inking

1 Washing—Chemicals can be used to separate the ink from the paper and then washed
away with water. Although this process requires the use of chemicals and waster the
quantities used are much less than the manufacture of new paper and the water can
often be cleaned and reused.
2 Floatation—Air can be passed through the pulp to produce foam. The foam holds
at least half of the ink and can be skimmed off.

Pulp is poured into a huge flat wire screen. On the screen, water starts to drain from
the pulp and the recycled fibers quickly begin to bond together to form a watery sheet.
The sheet, which now resembles paper, passes though a series of heavy rollers, which