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

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 Cr 3+ 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 pretreatments allowed enzymatic attack and increased degradability of the chromium shavings reducing the lag-phase of biogas production and the remaining waste.

The effect of various pre‐treatment methods of chromium leather shavings in continuous biogas production

“…Consequently, chromium shavings are more easily accessible to enzymatic degradation. This is explored in more detail in a previous work .…”

“…The organic matter present in the final biomass is formed from organics from the inoculum and intermediate products from the hydrolysed substrate, such as volatile fatty acids, amino acids, and peptides. In a previous work , it was shown that the anaerobic digestion of inoculum without adding substrate leads to a final biomass of about 40% of organic content from which the conclusion can be drawn that part of the initial organic matter will remain unprocessed. The increase in organic matter content along the digestion is a consequence of the accumulation of unprocessed substrate in the form of intermediate products, which are not transformed into biogas probably due to inhibition of the anaerobic bacteria.…”

“…Hence, it is necessary to denature the collagen fibres present in chromium leather waste to enable the anaerobic microorganism to degrade this solid waste . A pre‐treatment can be used to denature the collagen and enable degradation in order to reduce the digestion time and increase the biogas yield .…”

“…While some studies treated chromium leather waste under batch conditions , there is no published work on continuous reactors for this material. Continuous tests simulate long‐term process conditions and are essential for adapting the method in the industry since most large‐scale industrial digesters work in continuous mode as this allows the digester to continually produce biogas .…”

Production of Agglomerates, Composite Materials, and Seed Coatings from Tannery Waste as New Methods for Its Management

“…Moreover, the authors of papers [22][23][24][25][26] developed a model for simulating and predicting the pyrolysis behavior of chrome shavings. A pretreatment can increase the feasibility of producing energy with chromium leather waste [27] and can reduce the costs of energy consumption, waste disposal, eliminate solid waste, and reduce greenhouse gas emissions from microbiological degradation of tannery waste [28,29]. The removal and recovery of heavy metals from tannery sludge subjected to a plasma pyro-gasification process was described in [30].…”