Page 68 - Energy from Toxic Organic Waste for Heat and Power Generation

56 Energy from Toxic Organic Waste for Heat and Power Generation

and more than 60% as solid and liquid waste including the highly carcino-
genic heavy metal “chromium” [2,4].

5.2 LEATHER PRODUCTION PROCESSES

The process of leather manufacturing is subdivided into three basic processes
namely, (i) preparatory stage or beam house stage, (ii) tanning stage, and
(iii) crusting stage [5,6]. Surface coating is also employed as an additional
setup in leather processing. In the preparatory stage or beam house stage, the
skin of the animal is prepared for tanning. This stage involved the following
operations, namely, preservation, soaking, liming, unhairing, fleshing, splitting,
reliming, deliming, bating, degreasing, bleaching, pickling, and depickling [7].
Tanning is the stage in which the raw skin is converted into a stable mate-
rial. The stable material is dried to a flexible form where the skin does not pu-
trefy or decay and this stable form is suitable for a wide range of applications.
Tanning process is carried out in two methods namely, (i) vegetable tanning
and (ii) chrome tanning. The leather produced by the chrome tanning method
is much better to vegetable-tanned leather as it is less time- consuming, soft
with high thermal and water stability. The majority of leather produced from
the skin of goats, lambs, sheep, and pigs are chrome-tanned [8].
The next process after tanning is known as “Crusting” of the skin. In this
process, dye and chemicals are added to the tanned skin. Crusting involves
several steps like wetting back, sammying, splitting, shaving, re-chroming,
neutralization, re-tanning, dyeing, fat liquoring, filling, stuffing, stripping,
whitening, fixating, setting, drying, conditioning, milling, staking, and buff-
ing [9]. Finally, the finishing process involves surface coating comprising the
following processes, namely, oiling, brushing, padding, impregnation, buff-
ing, spraying, roller coating, curtain coating, polishing, plating, embossing,
ironing, combing (for leather with hair), glazing, and tumbling [10].
Thus, leather industry involves the usage of raw skin of animals and
many chemicals to convert the raw material into finished product. These
chemicals are discharged into the environment as solid and liquid wastes
leading to harmful effect on the environment.

5.3 POLLUTION FROM LEATHER INDUSTRY
In the manufacture of leather goods, especially footwears, solid wastes are
produced which contribute to 15%–20% of the raw material used, that
is, skin of the animals. These wastes of leather processing industry are not
capable of reuse and lost its utility.