Advanced Biomethane Production from Biologically Pretreated Giant Reed under Different Harvest Times

Increasing energy demands and fossil fuel consumption causing global warming has motivated research to find alternative energy sources such as biofuels. Giant reed (<i>Arundo donax</i> L.), a lignocellulosic, perennial, rhizomatous grass has been proposed as an important bioenergy crop for advanced biofuel in the Mediterranean area. Anaerobic digestion for advanced biomethane seems to be a promising approach. However, the presence of lignin in lignocellulosic biomass represents the main obstacle to its production (due to its recalcitrance). Thus, to use effectively lignocellulosic biomass in anaerobic digestion, one or more pretreatment steps are needed to aid microorganisms access to the plant cell wall. To this end, the present study investigated the effect of fungal pretreatment of giant reeds obtained from two different harvesting time (autumn and winter) on biomethane production by anaerobic digestion using two white rot fungi (<i>Pleurotus ostreatus</i> and <i>Irpex lactus</i>, respectively). The highest biomass lignin degradation after 30 days incubation with <i>P. ostreatus</i> in both autumn (27.1%) and winter (31.5%) harvest time. <i>P. ostreatus</i> pretreatment showed promising results for anaerobic digestion of giant reed achieving a cumulative yield of 130.9 NmL g⁻¹ VS for the winter harvest, whereas <i>I. lacteus</i> showed a decrease in methane yield as compared with the untreated biomass (77.4 NmL g⁻¹ VS and 73.3 NmL g⁻¹ VS for winter and autumn harvest, respectively). <i>I. lacteus</i> pretreatment resulted in a loss of both holocellulose and lignin, indicating that this strain was less selective than <i>P. ostreatus</i>. Further studies are necessary to identify white rot fungi more suitable to lignocellulosic biomass and optimize biological pretreatment conditions to reduce its duration.