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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:8073 |
| Date | 05 February 2009 |
| Creators | Hooghiemstra, Carol |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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