Improvement of anaerobic degradation by white-rot fungi pretreatment of lignocellulosic biomass: A review

Anaerobic digestion of lignocellulosic biomass appears to be an efficient process for the production of energy whilst answering present-day environmental challenges. However, lignin contained in lignocellulosic biomass is hardly biodegradable, thus representing a major obstacle for maximum methane production. Consequently, although pretreatments need to be considered, their cost is a limit for their full-scale use. Biological pretreatments are a cheaper alternative in this context. Several biological pretreatments have been studied for anaerobic digestion: ensiling, partial composting, specific microbial consortia, enzymes and fungi. Simple, inexpensive and efficient pretreatments can be obtained using fungi. White-rot fungi (WRF), have been considered as most capable of delignifying a substrate. However, their use in the pretreatment of substrates for anaerobic digestion is quite recent and still needs to be investigated. This review compares fungal pretreatment with other biological treatments for anaerobic digestion of lignocellulosic biomass. Enzymatic mechanisms for WRF pretreatments are then exposed. The literature data regarding the improvement of anaerobic digestibility with WRF pretreatment are summarized (anaerobic digestion and in vitro digestibility with rumen microorganisms). Finally, lignocellulosic biomass features allowing the improvement of anaerobic digestion are exposed (porosity, cellulose crystallinity, etc.). The possible effects of WRF on these characteristics are discussed and industrial perspectives for WRF pretreatments are presented.