White rot fungi using P. sajor-caju and T. versicolor was examined to pretreat raw champost (lignin-rich) and oyster champost (cellulose-rich) for enhancement of fermentative volatile fatty acid (VFA) production. Results showed that the efficiency of pretreatment and VFA production was influenced by the fungal strains and substrates. P. sajor-caju pretreatment showed preferential lignin degradation on raw champost and obtained the maximum VFA yield (203 ± 9 mg COD/g VS_added), which increased by 60% and 74% compared to that of control and unpretreated champost, respectively. For cellulose-rich oyster champost, however, fungal pretreatment decreased VFA yield compared to unpretreated champost. Further mechanisms analysis demonstrated the two strains grow and secreted ligninolytic enzymes, which substantially influenced the characteristics of two champosts such as cellulose/lignin ratio and morphology in different extents. P. sajor-caju was highly efficient to lignin-rich champost on selectively degrading lignin and further enhancing digestibility such as VFA production.

Anaerobic digestion has been widely applied throughout the world for lignocellulosic biomass treatment and energy recovery. However, the solid digestate from anaerobic digestion still contains a rather large fraction of poorly anaerobic degradable lignocellulosic fibers due to inhibition of lignin, which deeply limits the bioenergy production from lignocelullosic biomass. Therefore, a novel fungal pretreatment method using P. sajor-caju and T. versicolor was investigated to advance the solid-state fermentation of solid digestate and improve the production of fermentative volatile fatty acids (VFAs). The results showed that a maximum VFA yield of 240 mg COD/g VS was obtained from solid digestate pretreated by P. sajor-caju in 6 weeks, which was 1.17-fold and 1.24-fold higher than that of the autoclaved group and raw substrate, respectively. The mechanisms indicated that these fungal strains could grow on the solid digestate and secrete ligninolytic enzymes such as laccase and manganese peroxidase to degrade lignin in different extents. Besides, fungal pretreatment substantially changed the solid digestate characteristics such as cellulose/lignin ratio and the presence of specific functional groups. Moreover, fungal pretreatment using P. sajor-caju effectively damaged the structure and increased surface area and pore size of the solid digestate, which is beneficial to further VFA production.

In order to improve the efficiency of anaerobic sludge digestion, alkaline and high pressure homogenization (HPH) were combined to pre-treat the excess activated sludge. The effect of HPH operating parameters, including homogenization pressure and cycle number, on the performances of anaerobic sludge digestion was studied. The results demonstrated that the performances of sludge disintegration and anaerobic digestion were markedly enhanced by increasing the homogenization pressure. After pretreatment at a homogenization pressure of 60 MPa with one homogenization cycle combined with an alkaline dosage of 0.04 mol/L, the sludge TCOD, VS removal and cumulative biogas production in a mesophilic anaerobic digestion system increased by 24.68%, 18.95% and 95.81%, respectively, in comparison with that with the alkaline pretreatment alone. But the sludge disintegration and biogas production only slightly increased with the increase of homogenization cycle. Considering biogas production and energy-saving, the suitable homogenization operation was selected as homogenization pressure of 60 MPa with once cycle. Relationships between methane yield and sludge disintegration showed that the improved methane production was mainly attributed to the sludge disintegration resulted from combined sludge pretreatment.