Nowadays, the climate mitigation policies of EU promote the energy production based on renewable resources. Anaerobic digestion (AD) constitutes a biochemical process that can convert lignocellulosic materials into biogas, used for chemical products isolation or energy production, in the form of electricity, heat or fuels. Such practices are accompanied by several economic, environmental and climatic benefits. The method of AD is an effective method of utilization of several different low-value and negative-cost highly available materials of residual character, such as the lignocellulosic wastes coming from forest, agricultural or marine biomass utilization processes, in order to convert them into directly usable energy. Lignin depolymerization remains a great challenge for the establishment of a full scale process for AD of lignin waste. This review analyzes the method of anaerobic digestion (biomethanation), summarizes the technology and standards involved, the progress achieved so far on the depolymerization/pre-treatment methods of lignocellulosic bio-wastes and the respective residual byproducts coming from industrial processes, aiming to their conversion into energy and the current attempts concerning the utilization of the produced biogas. Substrates’ mechanical, physical, thermal, chemical, and biological pretreatments or a combination of those before biogas production enhance the hydrolysis stage efficiency and, therefore, biogas generation. AD systems are immensely expanding globally, especially in Europe, meeting the high demands of humans for clean energy.

In this study, the quality of wood fuel pellets, commercially available in the Greek market, was evaluated using the ISO 17225 Standard Requirement Thresholds as a benchmark. The examined quality criteria were calorific value, ash content, mechanical durability, bulk density and moisture content. The reliability of the information on packages was evaluated. Meanwhile, the potential correlation between the most crucial qualitative properties of pellets was investigated to elucidate their potential contribution to pellets’ quality estimation. Most of the pellet brands showed low moisture and ash content and acceptable calorific values for residential use—although the quality of half of the pellet brands was found to be lower than that reported, mainly with regard to the mechanical durability and bulk density. The application of two different collection periods highlighted a stability in quality over time. Higher calorific value seemed to be provided by pellets which had low ash and low moisture content and were mechanically durable. As regards the specific samples, a dark colour and high roughness were correlated with lower fuel quality (impact of 56.2% and 43.6%, respectively).

Wood of black pine and poplar species were subjected to thermal modification under variant conditions, while subsequently, a number of the thermally-modified black pine specimens were subjected to surface modification with organosilane solutions, and the biological resistances of the different materials were examined using laboratory agar block tests against the action of basidiomycetes and microfungi. Thermally-modified pine specimens were exposed to the brown rot fungi Coniophora puteana and Oligoporus placenta, whereas poplar wood was exposed to the white rot fungus Trametes versicolor and O. placenta. Regarding the biological durability of thermally-chemically-treated pine wood with organosilanes, it was tested against the action of C. puteana. Additionally, both of the thermally-treated wood species, as well as thermally-chemically-treated pine wood were exposed to a microfungi mixture, so that the wood treatments efficacy would be evaluated through a visual assessment of fungal growth on the specimen’s surface The thermal treatments seem to increase the biological resistance of black pine against C. puteana by 9.65–36.73% compared to unmodified wood. The most significant increase in biological durability among all the thermally-treated wood categories was recorded by O. placenta, with 28.75–68.46% lower mass losses in treated pine specimens and 31.98–64.72% in thermally-treated poplar, respectively, compared to unmodified wood. The resistance of treated poplar against T. versicolor was also found increased (13.25–46.08%), compared to control. Thermal modification affected positively the biological resistance of both species, though it did not manage to protect effectively pine and poplar wood from the microfungi action. The combination of thermal and organosilanes treatment revealed a significant improvement of the durability of pine wood compared to? control (45.68–87.83% lower mass losses against C. puteana), as well as against the microfungi action, with the presence of benzin to have a positive effect on the silanes solutions performance and protective action.