Investigation of different pre-treatments of chromium leather shavings to improve biogas production

Abstract

Abstract Chromium shavings are wet by-products of the leather industry, of which thousands of tons accrue worldwide during leather manufacture. Due to their chromium content, chromium shavings are responsible for the most important ecological challenges caused by the leather industry. They are stable towards temperatures of up to 110 °C and enzymatic degradation. This high stability is caused by the three-dimensional native structure, typical for collagen, and additional chemical cross-links between the collagen fibres achieved by Cr3+ salts in the tanning process. Therefore, hitherto chromium shavings are not utilized industrially to produce biogas. In order to generate biogas, this stable structure has to be denatured. Chromium shavings were pre-treated by extrusion and hydrothermal methods. To prove the enzymatic degradability, the different pre-treatments were evaluated by differential scanning calorimetry (DSC), enzymatic assays, and by measuring the solubility in water. The biogas production potential was investigated using batch trials to examine feasibility. Results demonstrated that both pre-treatments allowed enzymatic attack and increased degradability of the chromium shavings reducing the lag-phase of biogas production and the remaining waste. Graphical abstract