From the leather industry to building sector: exploration of potential applications of discarded solid wastes

Abstract The leather industry is an example of circular economy, as it uses meat industry wastes (hides and skins) as raw materials. However, the process of tanning also produces a substantial amount of organic waste. This research project studies the case of a tannery located in Navarra, in the North of Spain, committed to a circular economy and environmental protection, which produces around 2 tons per day of leather shavings and buffing dust and 10 tons per day of discarded bullock hair. The study tackles the challenge of whether the discarded waste material might be used as a new resource for products or processes related with the building sector. Three different types of solid wastes (chromium free tanned shavings, chromium buffing dust, and discarded hair) were categorized and analyzed. The paper examines two proposals to reuse the weekly tons of leftovers (both shavings and hair) produced by the tannery, instead of taking them to an external composting plant or to the landfill. The first exploration path proposed to use the discarded material to obtain biomass for the company’s thermal production plant. After establishing the calorific values of the discarded hair and the shavings, these were found to offer competitive value in comparison with the biomass products used at present, such as wood pellets. The second approach to the waste upcycling involved seeking new products in the building sector, acoustic panels in this case. After a mechanical behavior analysis, different binders were blended with diverse proportions and particle sizes of shavings to obtain samples for a sound absorption coefficient determination. The results show coefficients close to those of cork panels or carpets. This experimental experience serves as a preliminary study for the use of leather industry wastes in the construction sector.