Anaerobic co-digestion of marine macroalgae waste and fruit waste: Effect of mixture ratio on biogas production

Metagenomic characterization of the enhanced performance of multicomponent synergistic thermophilic anaerobic co-digestion of food waste utilizing kitchen waste or garden waste as co-substrate

Food waste (FW) single-substrate anaerobic digestion usually suffers from rapid acidification and inhibition of oil and salt. To overcome these problems and improve the process efficiency, supplementing other substrates has been used in FW anaerobic digestion. This study investigated the biogas production potential through co-digestion of FW with kitchen waste (KW) or garden waste (GW) in different ratios under thermophilic conditions. The results showed that the optimal ratios were FW:KW=60:40 and FW:GW=80:20 which biogas production improved 73.33% and 68.45% compared with single FW digestion, respectively. The organic matter removal rate of co-digestion was 84.46% for FW+KW group (RFK) and 65.64% for FW+GW group (RFG). Co-digestion increased the abundance of the dominant hydrolytic bacteria Defluviitoga and Hydrogenispora and hydrogenotrophic methanogen Methanoculleus. Furthermore, glycoside hydrolases (GHs), vital carbohydrate-active enzymes (CAZymes), were improved by co-digestion. Co-digestion could also effectively promote the function of cellulase and hemicellulose. This strategy for utilizing different organic wastes together as co-substrate provides a new avenue for bioenergy production.

Effect of acidic pretreatment on the microstructural arrangement and anaerobic digestion of Arachis hypogea shells; and process parameters optimization using response surface methodology

Enzymatic hydrolysis of lignocellulose feedstocks has been observed as the rate-limiting stage during anaerobic digestion. This necessitated the need for pretreatment before anaerobic digestion for an effective and efficient process. Therefore, this study investigated the impact of acidic pretreatment on Arachis hypogea shells, and different conditions of H₂SO₄ concentration, exposure time, and autoclave temperature were considered. The substrates were digested for 35 days at a mesophilic temperature to assess the impact of pretreatment on the microstructural organization of the substrate. For the purpose of examining the interactive correlations between the input parameters, response surface methodology (RSM) was used. The result reveals that acidic pretreatment has the strength to disrupt the recalcitrance features of Arachis hypogea shells and make them accessible for microorganisms' activities during anaerobic digestion. In this context, H₂SO₄ with 0.5% v. v^-1 for 15 min at an autoclave temperature of 90 °C increases the cumulative biogas and methane released by 13 and 178%, respectively. The model's coefficient of determination (R²) demonstrated that RSM could model the process. Therefore, acidic pretreatment poses a novel means of total energy recovery from lignocellulose feedstock and can be investigated at the industrial scale.

Research on Biogas Yield from Macroalgae with Inoculants at Different Organic Loading Rates in a Three-Stage Bioreactor

Macroalgae can be a viable alternative to replace fossil fuels that have a negative impact on the environment. By mixing macroalgae with other substrates, higher quality biogas can be obtained. Such biogas is considered one of the most promising solutions for reducing climate change. In the work, new studies were conducted, during which biogas yield was investigated in a three-stage bioreactor (TSB) during the anaerobic digestion of Cladophora glomerata macroalgae with inoculants from cattle manure and sewage sludge at different organic loading rates (OLR). By choosing the optimal OLR in this way, the goal was to increase the energy potential of biomass. The research was performed at OLRs of 2.87, 4.06, and 8.13 Kg VS/m³ d. After conducting research, the highest biogas yield was determined when OLR was 2.87 Kg VS/m³ d. With this OLR, the average biogas yield was 439.0 ± 4.0 L/Kg VS_added, and the methane yield was 306.5 ± 9.2 L CH₄/Kg VS_added. After increasing the OLR to 4.06 and 8.13 Kg VS/m³ d, the yield of biogas and methane decreased by 1.55 times. The higher yield was due to better decomposition of elements C, N, H, and S during the fermentation process when OLR was 2.87 Kg VS/m³ d. At different OLRs, the methane concentration remained high and varied from 68% to 80%. The highest biomass energy potential with a value of 3.05 kWh/Kg VS_added was determined when the OLR was 2.87 Kg VS/m³ d. This biomass energy potential was determined by the high yield of biogas and methane in TSB.