16.5 Tannery Waste Treatment Technologies
Generally, various physico-chemical and biological methods or combination of both
are used for treatment of tannery waste effluent. Tannery waste can be treated by
various methods. In general practice, individual tannery applies only to
pre-treatment or a part pre-treatment, and sometimes there is no treatment, and
they simply send the effluent to a centralist treatment plant, but a treatment is
necessary due to toxicity of the effluent at each and every level (Midha and Dey
2008). Generally, for treatment of tannery effluent, physical and chemical methods
are generally employed, but they often are unable to remove the contaminants, and
they are found to be costly in comparison to biological methods. That is why
biological methods are more favorable and cost-effective for treatment of tannery
effluents. A group of organisms work together in the presence or absence of oxygen
to carry out decomposition of pollutants, as they utilize them as a source of energy or
nutrients (Buljan and Kral 2011). Many research works have reported that tannery
effluent can be treated by using activated sludge process (Ahmad 2002, Srivastava
and Thakur 2006). By using activated sludge process, BOD 5 removal of tannery
effluent can be attained to 90–97% as suggested by these studies, which indicate that
this process of treatment is highly efficient. We have already discussed the necessity
of removal of chromium and other heavy metals from industrial waste effluent not
only due to its toxicity to human beings but also its adverse effect on soil fertility. For
carrying out removal of heavy metals, a number of physico-chemical methods have
been employed, such as precipitation by hydrolysis, use of ion-exchange resins,
carbonates and sulphides, membrane separation, adsorption on activated carbon, and
bioremediation, despite that effluents emerging out of leather industries (Spiegel
et al. 2012).
In recent times, low-cost industrial proven advanced methods have been applied
which includes hair-save liming, salt-free preserved raw hides and skins, advanced
chrome management system, ammonia free or low ammonia bating, deliming
methods and many more. By using above mentioned methods, it is possible to
reduce pollution load significantly as BOD5 and COD by more than 30%, ammonia
nitrogen by 80%, sulphides by 80–90%, total kjeldahl nitrogen (TKN) by 50%,
sulphates by 65%, chlorides by 70%, and chromium by up to 90%.
Generally, in the following different phases, treatment of tannery effluents takes
place:
16.5.1 Preliminary Treatment
It is often used in developing countries where common effluent treatment plants is
used for examining the tannery clusters and for removal of not only sand/grit, grease,
and large particles but also helps in the reduction of sulphides and chromium before
the effluent gets discharged into the collection tank.
588
N. Patel et al.
Generally, various physico-chemical and biological methods or combination of both
are used for treatment of tannery waste effluent. Tannery waste can be treated by
various methods. In general practice, individual tannery applies only to
pre-treatment or a part pre-treatment, and sometimes there is no treatment, and
they simply send the effluent to a centralist treatment plant, but a treatment is
necessary due to toxicity of the effluent at each and every level (Midha and Dey
2008). Generally, for treatment of tannery effluent, physical and chemical methods
are generally employed, but they often are unable to remove the contaminants, and
they are found to be costly in comparison to biological methods. That is why
biological methods are more favorable and cost-effective for treatment of tannery
effluents. A group of organisms work together in the presence or absence of oxygen
to carry out decomposition of pollutants, as they utilize them as a source of energy or
nutrients (Buljan and Kral 2011). Many research works have reported that tannery
effluent can be treated by using activated sludge process (Ahmad 2002, Srivastava
and Thakur 2006). By using activated sludge process, BOD 5 removal of tannery
effluent can be attained to 90–97% as suggested by these studies, which indicate that
this process of treatment is highly efficient. We have already discussed the necessity
of removal of chromium and other heavy metals from industrial waste effluent not
only due to its toxicity to human beings but also its adverse effect on soil fertility. For
carrying out removal of heavy metals, a number of physico-chemical methods have
been employed, such as precipitation by hydrolysis, use of ion-exchange resins,
carbonates and sulphides, membrane separation, adsorption on activated carbon, and
bioremediation, despite that effluents emerging out of leather industries (Spiegel
et al. 2012).
In recent times, low-cost industrial proven advanced methods have been applied
which includes hair-save liming, salt-free preserved raw hides and skins, advanced
chrome management system, ammonia free or low ammonia bating, deliming
methods and many more. By using above mentioned methods, it is possible to
reduce pollution load significantly as BOD5 and COD by more than 30%, ammonia
nitrogen by 80%, sulphides by 80–90%, total kjeldahl nitrogen (TKN) by 50%,
sulphates by 65%, chlorides by 70%, and chromium by up to 90%.
Generally, in the following different phases, treatment of tannery effluents takes
place:
16.5.1 Preliminary Treatment
It is often used in developing countries where common effluent treatment plants is
used for examining the tannery clusters and for removal of not only sand/grit, grease,
and large particles but also helps in the reduction of sulphides and chromium before
the effluent gets discharged into the collection tank.
588
N. Patel et al.