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Biological pretreatment of waste from the leather industry to obtain biogas through anaerobic co-digestion processes - A review

The leather industry produces a relatively high amount of hard degradable waste, with a negative impact on the environment. This waste usually contains two major categories of residues, namely animal fat and residues containing mostly proteins, suitable for biogas conversion. Obtaining biogas from leather waste by co-digestion with vegetable waste can be a sustainable and eco-friendly alternative to conventional energy from fuels. Anaerobic co-digestion is now considered to reduce waste from various sources and turn it into energy, generating in addition a digestate used as fertilizer in agriculture. This waste is relatively resistant to transformation into an easily fermentable substrate for anaerobic digestion to produce biogas. Thus, the methane yield can be significantly improved by biological treatments with enzymes and enzyme complexes, with microorganisms selected and used as inoculum or by mixed methods, which include other physical or chemical treatments. This paper aims to show the main methods of biological treatment of leather industry waste, in order to increase the yield of biogas by co-digestion with plant materials.