Unlocking the potential of sugarcane leaf waste for sustainable methane production: Insights from microbial pre-hydrolysis and reactor optimization.

Sugarcane leaf waste, a byproduct of the growing global sugar industry, challenges agricultural waste management. This study explores its potential for methane production via anaerobic digestion. A microbial pre-hydrolysis, using lignocellulose-degrading bacteria, enhanced soluble chemical oxygen demand at an optimal initial substrate concentration of 40 g-volatile solid/L. Comparative analysis with untreated and bioaugmented leaves revealed the pre-hydrolyzed leaves achieved the highest methane production rate (MPR) at 14.0 ± 0.5 mL-CH4/L·d, surpassing others by 1.47 and 1.67 times. Two continuous stirred tank reactors were employed to assess the optimal hydraulic retention time (HRT). Results showed a stable methane production with an HRT of 25 days, yielding high MPRs: 88.70 ± 0.63 mL-CH4/L·d from pre-hydrolyzed sugarcane leaves and 82.57 ± 1.22 mL-CH4/L·d from microbial consortium-augmented leaves. A 25-day HRT fosters high microbial diversity with Bacteroidota, Firmicutes, Chloroflexi, and Verrucomicrobiota dominance, indicating favorable conditions. Conversely, a 20-day HRT results in lower diversity due to unfavorable factors like low pH during organic overloading, leading to increased concentrations of volatile fatty acids and lactic acid, with Firmicutes as the predominant phylum. This study highlights sugarcane leaf waste's potential as a valuable resource for sustainable methane production.

Valorization of spent coffee grounds through integrated bioprocess of fermentable sugars, volatile fatty acids, yeast-based single-cell protein and biofuels production.

Recovering nutrients from waste for biological processes aligns with sustainability principles. This study aimed to convert spent coffee grounds (SCG) into valuable products, including fermentable sugars, volatile fatty acids (VFAs), yeast-based single-cell protein and biofuels. Alkaline pretreatment was conducted before enzymatic hydrolysis, in which the pretreated SCG was hydrolyzed with varying enzyme loadings (20-60 filter paper units (FPU)/g-solid) and solid loadings (3-15 % w/v). The hydrolyzed slurry was utilized for VFAs and hydrogen production, yielding high values of 0.66 g/g-volatile solids (VS) and 109 mL/g-VS, respectively, using an enzyme loading of 50 FPU/g-solid and a solid loading of 3 % (w/v). The derived VFAs were used to cultivate a newly isolated yeast, Candida maltosa KKU-ARY2, resulting in an accumulated protein content of 43.7 % and a biomass concentration of 4.6 g/L. This study highlights the conversion of SCG into essential components, emphasizing the benefits of waste utilization through cascade bioprocesses.

Influences of size reduction, hydration, and thermal-assisted hydration pretreatment to increase the biogas production from Napier grass and Napier silage.

Pretreatment of lignocellulose materials prior to biogas production is required to minimize biomass recalcitrance and increase biomass digestibility. In this study, the effects of particle size reduction, hydration, and thermal-assisted hydration on Napier grass and silage for methane production were evaluated. Compared to the 4.75-mm particle size Napier grass and silage, 0.425-mm Napier grass and silage showed 72% and 46% increases in methane yield, respectively, whereas hydration pretreatment using hydrogenic effluent increased the methane yields from Napier grass and silage by 23% and 56%, respectively. Superior effects were observed when Napier grass and silage were pretreated with thermal-assisted hydration using hydrogenic effluent for 60 and 15 min, respectively, resulting in methane yields of 385 and 331 mL CH4/g substrateadded. The results indicate that size reduction accompanied by thermal-assisted hydration using hydrogenic effluent as a hydration medium significantly improved the biodegradability of Napier grass and silage.

Membrane bioreactor-assisted volatile fatty acids production and in situ recovery from cow manure.

Cow manure (CM) generation in large volumes has for long been considered a waste management challenge. However, the organic content of CM signals opportunities for the production of value-added bioproducts such as volatile fatty acids (VFAs) through anaerobic digestion (AD). However, a robust VFAs fermentation process requires effective methane formation inhibition and enhance VFAs recovery. In this study, thermal pretreatment was applied to inhibit methanogens for enhanced VFAs production and an immersed membrane bioreactor (iMBR) for in situ recovery of VFAs in a semi-continuous AD. Maximal VFAs yield of 0.41 g VFAs/g volatile solids (VS) was obtained from thermally-treated CM without inoculum addition. The CM was further fed to the iMBR operating at organic loading rates of 0.8-4.7 gVS/L.d. The VFAs concentration increased to 6.93 g/L by rising substrate loading to 4.7 g VS/L.d. The applied iMBR set-up was successfully used for stable long-term (114 days) VFAs production and recovery.