Abstract
M.Sc.
Waste generation and waste disposal forms part of our everyday lives, even more so for a tanning
facility. This mini dissertation discusses the delisting of waste generated at a tanning facility.
This facility produces crust leather from partially tanned hides received from other tanneries in
the Mpumalanga province. Crust leather is the product in the penultimate process before it
attains its desired leather like properties. The crust leather is sent to a finishing plant for the final
process of painting before it is supplied to the automotive industry for upholstery purposes.
Large volumes of raw materials including chemicals, water and hides are used in the retanning
process to produce crust leather. During the production of this leather various waste streams are
generated including effluent, solid waste and tanning sludge. The tanning sludge is classified in
terms of the Department of Water Affairs and Forestry’s Minimum Requirements for Handling,
Classification and Disposal of Hazardous waste as a possible or potentially hazardous waste.
Hazardous waste must be disposed of to a permitted hazardous waste landfill site which has a
significant cost implication for the tanning facility. This mini-dissertation focuses on the attempt
to delist the tanning sludge.
This mini-dissertation highlights the problems associated with hazardous waste disposal in the
form of sludge from the tannery. This disposal is expensive because there is only one permitted
hazardous waste landfill site in the Gauteng and Mpumalanga provinces. This site is called
Holfontein and is situated approximately 200 km from the tanning facility. The high disposal
cost encountered is owing to the specialist management required because of the environmental
risks involved in operating this waste disposal site.
However, an option to delist the hazardous tanning sludge waste is available to the tanning
facility, which could mean that the hazard rating is reduced from extremely hazardous to a lower
rating or even to general waste. Delisting the tanning sludge will allow it to be disposed of to a
general landfill site. Previous attempts to delist the tanning sludge were not successful as the
presence of hexavalent chromium (Cr (VI)) and cyanide (CN) in the tanning sludge caused it to
remain classified as extremely hazardous waste.
Due to the increasing waste disposal cost the tanning facility once again engaged in the processes
to delist the tanning sludge. The personnel of the tanning facility is of the opinion that
hexavalent chromium (Cr(VI)) and cyanide (CN) should not be present in the tanning sludge as
these substances are not used generally in the tanning industry. Therefore, the main aim of this
mini-dissertation is to delist the tanning sludge to general waste thus allowing it to be disposed of
to a general landfill site, which in turn will result in a reduction in the waste disposal costs.
Delisting of hazardous waste produced in a tannery
In order to achieve the main aim, the study entailed a literature review of the retanning process
explaining the generation of the various waste streams, the possible presence of chromium (Cr)
and hexavalent chromium (Cr(VI) in the process, and a review of the environmental legislation
that will determine the waste disposal options. To delist the tanning sludge the tanning facility
followed a defined procedure as determined by the Department of Water Affairs and Forestry.
The tanning sludge was assessed using analytical procedures as specified. The objective was to
characterise the leachability of the tanning sludge, as well as to verify the presence of any
hazardous substances which prevent the tanning sludge from being delisted. Leachability is the
potential mobilisation of substances from the sludge under circumstances similar than that of the
waste disposal sites. This includes the presence of hexavalent chromium (Cr(VI)) and cyanide
(CN) in the tanning sludge.
In an approach to verify the presence of hexavalent chromium (Cr(VI)) and cyanide (CN) in the
tanning sludge the composition of the raw materials (chemicals and hides) were evaluated and
samples were taken from the various effluent streams. The tanning sludge was sampled
separately to determine the leachability characteristics. No hexavalent chromium (Cr(VI)) and
cyanide (CN) were found to be present in the raw materials or in any of the waste effluent
streams. However, small quantities of cyanide (CN) and hexavalent chromium (Cr(VI)) were
found to be present in the tanning sludge. The reason for the presence of these constituents could
not be determined as it was proved that hexavalent chromium (Cr(VI)) and cyanide (CN) do not
enter the process through the raw materials. It was further proved that the process does not
support circumstances to oxidise trivalent chromium to hexavalent chromium (Cr(VI)). Further,
the presence of cyanide (CN) cannot be explained since it is not a substance that is generally used
in the tanning industry.
Part of the study included determining treatment options for the tanning sludge. It was found that
treating the tanning sludge with lime reduced the concentration of heavy metals such as
hexavalent chromium (Cr(VI)).
However, after analysis and classification of the tanning sludge it was found that it was not the
hexavalent chromium (Cr(VI)) and cyanide (CN) that prevented the tanning sludge from being
delisted to a lower hazard rating but rather the presence of small quantities of cadmium (Cd).
Cadmium (Cd) is classified as extremely hazardous and therefore it is this substance that is
responsible for the high hazard rating classification of the sludge.
Although the objective to delist the tanning sludge was not achieved, it was determined that the
waste can be disposed of to a general waste landfill site permitted to accept a certain amount of
waste containing heavy metals (such as chromium and manganese). The reduction in the waste
disposal cost will therefore be achieved and the tanning facility will dispose of their waste in a
Delisting of hazardous waste produced in a tannery
sound and environmentally responsible method ensuring it will not have a significant impact on
the environment.