The disposal of leather products16 June 2003
The consumer has a responsibility not to use the simplest method of disposal - unfortunately still in common practice - that is, just throwing refuse away. Campaigns to collect used and unwanted products and sporadic recycling initiatives go some way towards improving the situation. However, the best solution would be to make new material or products from recovered leather. The second best way to dispose of used leather is by incineration, because leather provides considerable amounts of energy. But this leaves the problem of dealing with the ash and slag. Nature of the problem The simplest method of disposal is to return the used natural product leather to nature, eg to compost it. TFL are therefore studying this carefully. Some initial progress has been achieved. We have ascertained that organic materials such as dyes or pigments, retanning agents or fatliquors may degrade under certain biological conditions. However, chrome tanned leather is hard to compost and the reaction of the remaining metal, which includes some inorganic pigments and metals from complex dyes, is not known in detail. Therefore, at the present time, composting trials are mostly performed with metal-free shavings or leather waste. The composition of a typical wet-white shaving waste is shown in Table 1. Composting method Compost, normally placed in a shady corner, is the heart of a biological garden. It requires heat, moisture and oxygen in order to react aerobically (oxidatively). The compost shown in Table 2 was used in a field test. The compost behaved like natural garden compost. The reaction process is triggered by micro-organisms and takes place in three stages (heating, hot stage, cooling) at different temperatures over a total period of about approximately 6 months. The reaction mass heats up to a maximum of 70-80°C, harmful biological substances thereby being destroyed. The earth organisms then require nitrogen in order to build up their own protein. In biological enterprises, especially in autumn, when foliage, wood and shrub waste occurs, there is often too little nitrogen present, and it frequently has to be added. We have seen that metal-free shavings or metal-free leather, added at the beginning of the composting process, can provide this additional nitrogen. However, every compost composition shown behaves differently. Therefore, the general guideline shown in Table 3 should be followed for composting leather waste and in selecting chemicals used for producing metal-free leather. Results The results of various studies carried out show that excellent compost with a high nutrient content is obtained by this method. The assumed average analysis of compost including leather waste is shown in Table 4. Field tests with this compost revealed that nitrogen was released to the soil at a slow rate. Therefore, this compost has to be classified as a long-term nitrogen fertiliser. This is a very clear indication that leather is (and should be) a highly stable material. Too much leather in the compost can slow down the fertilising effect. The heavy metal content should be low to meet the strict limits set by experts and authorities. Conclusion Experience to date indicates that on the strength of these results, we can feel justified in hoping to have found an environmentally acceptable disposal procedure for chrome-free shavings and leather. In principle, metal-free shavings and leather have been found not to inhibit the biological process of composting and can be used as fertiliser. However, it must be borne in mind that leather is often produced with unknown chemicals, which may slow down the composting and fertilising behaviour. For every type of leather, trials should be carried out and be verified by drawing up integral environmental balance sheets. The author would like to say thank you to the many contributors who have helped in the writing of this paper.