• Solubilisation and removal of non-collagen protein
• Reduced time of soaking and faster opening of the fibre structure
• Production of leather with less wrinkled grain
• Improves softness and elasticity of the leather
• Increases the yield of hair, wool, scales and fur
• Reduces the amount of water used and wastewaters generated
• Energy efficient
7.2.2 Enzymatic Dehairing
Dehairing is the main and most polluting operations in the beam house. The aim of
dehairing is to remove the hair, scales, epidermis and to some extent the interfibrillary
proteins from the skin. Five methods of dehairing are generally used, i.e. (1) clipping
process, (2) scalding process, (3) sweating process, (4) chemical process and (5) enzymatic process [3]. Clipping process is achieved by cuttings the wool of the sheep
when the animal is either alive or dead. Scalding is the process of treating carcasses or
skin with hot water or steam to loosen the hair or feather (of birds) in the follicle to aid
their removal. Pork and poultry carcasses are both commonly subjected to a scalding
operation during processing [39]. Sweating process is applied if the wool is of greater
value than the skins and it involves hanging up soaked skins in dark humid rooms or
in piles inside suitable chambers under controlled conditions of temperature and
humidity for about 4–5 days where bacteria attacks keratin cells of hair and epidermis,
until wool is loose. Sweating process may result in serious damage to the raw hide
surface [40].
Of these, the most commonly practiced method of dehairing of hides or skins is
the chemical process using high concentration of lime and sodium sulphide which
creates extremely alkaline environments which result in pulping of hair and its
subsequent removal. High alkalinity also helps in opening the fibre structure and
hide plumping. The time span of the process may fluctuate from 18 to 168 h
depending on the method used [41]. Even though this process is very efficient in
hair removal, its inherent drawback has to be taken into account, noteworthy
amongst these are:
• High concentration of lime blended with sodium sulphide accounts for generation
of 70–80% of the total BOD and COD of effluent from all the leather-making
processes. About 75% of the organic waste from a tannery is from the beam house
and 70% of this waste is from dissolved hair rich in nitrogen [3].
• Sodium sulphide and hydrogen sulphide generated is highly toxic with extremely
unpleasant odour. It can cause major health and pollution problems in the sewers
if left untreated.
• Long processing time compromises the quality of the final leather and affects the
costs.
• The process yields greenhouse and toxic gases such as carbon dioxide, hydrogen
sulphide, ammonia and organic solvents.
Alkaliphilic Enzymes and Their Application in Novel Leather Processing. . .
207
• Reduced time of soaking and faster opening of the fibre structure
• Production of leather with less wrinkled grain
• Improves softness and elasticity of the leather
• Increases the yield of hair, wool, scales and fur
• Reduces the amount of water used and wastewaters generated
• Energy efficient
7.2.2 Enzymatic Dehairing
Dehairing is the main and most polluting operations in the beam house. The aim of
dehairing is to remove the hair, scales, epidermis and to some extent the interfibrillary
proteins from the skin. Five methods of dehairing are generally used, i.e. (1) clipping
process, (2) scalding process, (3) sweating process, (4) chemical process and (5) enzymatic process [3]. Clipping process is achieved by cuttings the wool of the sheep
when the animal is either alive or dead. Scalding is the process of treating carcasses or
skin with hot water or steam to loosen the hair or feather (of birds) in the follicle to aid
their removal. Pork and poultry carcasses are both commonly subjected to a scalding
operation during processing [39]. Sweating process is applied if the wool is of greater
value than the skins and it involves hanging up soaked skins in dark humid rooms or
in piles inside suitable chambers under controlled conditions of temperature and
humidity for about 4–5 days where bacteria attacks keratin cells of hair and epidermis,
until wool is loose. Sweating process may result in serious damage to the raw hide
surface [40].
Of these, the most commonly practiced method of dehairing of hides or skins is
the chemical process using high concentration of lime and sodium sulphide which
creates extremely alkaline environments which result in pulping of hair and its
subsequent removal. High alkalinity also helps in opening the fibre structure and
hide plumping. The time span of the process may fluctuate from 18 to 168 h
depending on the method used [41]. Even though this process is very efficient in
hair removal, its inherent drawback has to be taken into account, noteworthy
amongst these are:
• High concentration of lime blended with sodium sulphide accounts for generation
of 70–80% of the total BOD and COD of effluent from all the leather-making
processes. About 75% of the organic waste from a tannery is from the beam house
and 70% of this waste is from dissolved hair rich in nitrogen [3].
• Sodium sulphide and hydrogen sulphide generated is highly toxic with extremely
unpleasant odour. It can cause major health and pollution problems in the sewers
if left untreated.
• Long processing time compromises the quality of the final leather and affects the
costs.
• The process yields greenhouse and toxic gases such as carbon dioxide, hydrogen
sulphide, ammonia and organic solvents.
Alkaliphilic Enzymes and Their Application in Novel Leather Processing. . .
207