Renjie Dong

The anaerobic digestion performance of straw silage was influenced by the fermentation profiles and environment during ensiling process. This study examined how pentoses (xylose, arabinose), hexoses (glucose, fructose), and a disaccharide (sucrose) affect maize straw ensiling to maximize methane yield. The organic dry matter (ODM) loss was reduced by carbon sources added, decreasing from 9.1% to below 3.0%. Arabinose caused a high ODM loss (7.8%), attributable to the selective pressure its metabolic properties exerted on the microbial community. This pressure enriched functional taxa such as Clostridium and Sporolactobacillus. Consequently, mixed-acid fermentation emerged, characterized by lactic and butyric acids. The resulting mildly acidic environment (pH approximately 4.7) enhanced acid‑microbial synergy, which in turn improved the efficiency of lignocellulose degradation. Consequently, arabinose treatment achieved the highest methane yield (309.6 m³/t) and net energy gain (8.4%). For practical application, arabinose riched additives are recommended to steer fermentation toward butyrate production and maximize methane output.

The substantial discharge of vinasse biogas slurry (VBS) from anaerobic digestion poses significant environmental risks, while microalgae could recover nutrient for biomass production from VBS treatment. This study comprehensively investigated the bio-remediation potential of microalgae via rotating biofilm reactor, focusing on microalgae species and inoculation ratios, as well as VBS dilution ratios. The results revealed that Desmodesmus sp. had a better performance in biomass productivity (0.62 g/L), and total phosphorus (TP) removal efficiency (77.03%) than the other two microalgae (p < 0.05). The low VBS proportion (≤30%) obtained a higher biomass accumulation of 0.87–0.89 g/L than groups of high VBS proportion of 50%. These growth inhibition in high VBS proportion groups were attributed to high ammonium nitrogen (NH₄⁺-N) toxicity and elevated turbidity of biogas slurry. Both the total nitrogen (TN) removal of 34.11–36.48% and NH₄⁺-N removal of 83.63–97.38% revealed ammonium assimilation during the treatment of VBS via microalgae. Inoculum optimization demonstrated that reduced initial inoculation ratio (10% v/v) obtained highest TN removal efficiency of 46.52% and biomass growth rate of 0.04 g/(L·d), likely through alleviated light limitation. In the rotating biofilm reactor, treatment with 50-time diluted VBS achieved the highest biomass growth rate of 1.60 g/(m2·d), and the removal of TN, NH₄⁺-N, and TP was 74.93%, 93.94% and 98.01%, respectively. Moreover, coarse ribbed fiber fabric (CRFF) exhibited higher attached biomass (48.76 g/m2) and NH₄⁺-N removal efficiency (76.30%) than other attached materials. The research offered insights into trade-offs between the nutrient recovery and accumulating microalgae biomass during biogas slurry treatment.

This work aimed to conduct a kinetic study of cotton stalks (CSs) through TGA to examine the impact of reaction conditions on bio-oil yield derived from CS slow pyrolysis using a tube furnace lab-scale reactor, as well as a characterization of bio-oil and biochar products. The iso-conversional approaches of Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were applied to estimate kinetic parameter activation energy (E_a) for the range of conversion degrees (α = 0.1–0.9). The kinetic results demonstrated that the average values of E_a for secondary pyrolysis were lower compared to those of primary pyrolysis; this could be explained by the fact that mainly cellulose degrades during primary pyrolysis, which requires more energy to be degraded. The pyrolysis findings indicated that the highest yield of bio-oil was 38.5%, which occurred at conditions of 500 °C and 0.5–1 mm size, while retention time showed an insignificant effect on pyrolysis oil. GC–MS analysis demonstrated that bio-oil is dominated by phenol compounds, which account for more than 40% of its components. SEM and XRD analyses emphasized that biochar is porous and has an amorphous shape, respectively. It can be concluded that these outcomes confirm that CSs have the potential to be a good candidate for a feedstock material for bioenergy production via the pyrolysis process.