Pretreatment of polysaccharidic wastes with cellulolytic Aspergillus fumigatus for enhanced production of biohythane in a dual-stage process

Value addition through biohydrogen production and integrated processes from hydrothermal pretreatment of lignocellulosic biomass

Bioenergy production is the most sought-after topics at the crunch of energy demand, climate change and waste generation. In view of this, lignocellulosic biomass (LCB) rich in complex organic content has the potential to produce bioenergy in several forms following the pretreatment. Hydrothermal pretreatment that employs high temperatures and pressures is gaining momentum for organics recovery from LCB which can attain value-addition. Diverse bioprocesses such as dark fermentation, anaerobic digestion etc. can be utilized following the pretreatment of LCB which can result in biohydrogen and biomethane production. Besides, integration approaches for LCB utilization that enhance process efficiency and additional products such as biohythane production as well as application of solid residue obtained after LCB pretreatment were discussed. Importance of hydrothermal pretreatment as one of the suitable strategies for LCB utilization is emphasized suggesting its future potential in large scale energy recovery.

Advances in physicochemical pretreatment strategies for lignocellulose biomass and their effectiveness in bioconversion for biofuel production

The inherent recalcitrance of lignocellulosic biomass is a significant barrier to efficient lignocellulosic biorefinery owing to its complex structure and the presence of inhibitory components, primarily lignin. Efficient biomass pretreatment strategies are crucial for fragmentation of lignocellulosic biocomponents, increasing the surface area and solubility of cellulose fibers, and removing or extracting lignin. Conventional pretreatment methods have several disadvantages, such as high operational costs, equipment corrosion, and the generation of toxic byproducts and effluents. In recent years, many emerging single-step, multi-step, and/or combined physicochemical pretreatment regimes have been developed, which are simpler in operation, more economical, and environmentally friendly. Furthermore, many of these combined physicochemical methods improve biomass bioaccessibility and effectively fractionate ∼96 % of lignocellulosic biocomponents into cellulose, hemicellulose, and lignin, thereby allowing for highly efficient lignocellulose bioconversion. This review critically discusses the emerging physicochemical pretreatment methods for efficient lignocellulose bioconversion for biofuel production to address the global energy crisis.

Integrative biohydrogen- and biomethane-producing bioprocesses for comprehensive production of biohythane

The production of biohythane, a combination of energy-dense hydrogen and methane, from the anaerobic digestion of low-cost organic wastes has attracted attention as a potential candidate for the transition to a sustainable circular economy. Substantial research has been initiated to upscale the process engineering to establish a hythane-based economy by addressing major challenges associated with the process and product upgrading. This review provides an overview of the feasibility of biohythane production in various anaerobic digestion systems (single-stage, dual-stage) and possible technologies to upgrade biohythane to hydrogen-enriched renewable natural gas. The main goal of this review is to promote research in biohythane production technology by outlining critical needs, including meta-omics and metabolic engineering approaches for the advancements in biohythane production technology.

Integrated hydrothermal and deep eutectic solvent-mediated fractionation of lignocellulosic biocomponents for enhanced accessibility and efficient conversion in anaerobic digestion

Effective fractionation of lignocellulosic biocomponents of lignocellulosic biomass can increase its utilization in anaerobic digestion for high yield biomethane production. A hydrothermal process was optimized and integrated with a deep eutectic solvent (DES) pretreatment to preferentially fractionate hemicellulose, cellulose, and lignin in rice straw. The optimized hydrothermal process resulted in 96% hemicellulose solubilization at moderately low combined pretreatment severity (log S = 2.26), allowing increased hemicellulosic sugar recovery with minimal formation of inhibitory byproducts. Subsequent DES pretreatment resulted in highly bioaccessible cellulosic pulp, removing 81.3% of lignin that can be recovered and converted into value-added products. Anaerobic digestion of hemicellulosic fraction and cellulosic pulp using a microbial methanogenic consortium seed acclimatized to the lignocellulosic inhibitors resulted in a 33.4% higher yield of methane (467.84 mL g^-1 VS_initial) than with anaerobic digester sludge seed. This integrated approach can facilitate and maximize the targeted utilization of different biocomponents through sustainable biorefining.

Influence of confectionery wastewater pretreatment in vortex layer apparatus on its physical and chemical properties

The paper studies the effect of pretreatment of highly concentrated wastewater from confectionery production in a vortex layer apparatus (VLA) on its physical and chemical properties, with the aim of its further use as a substrate for dark fermentation with the production of biohydrogen. Pretreatment in VLA resulted in a 2.6-fold increase in the iron content and 6.5% increase in soluble chemical oxygen demand after 3 minutes of exposure. After pretreatment in VLA, an increase in the content of acetic acid and a decrease in the contents of propionic, butyric and caproic acids were observed. An increase in the content of mono- and disaccharides was registered, and the effect of the VLA exposure time of confectionery wastewater on its physicochemical properties was studied. An increase in the concentration of iron and simple sugars in wastewater makes the use of VLA promising for improving the process of its subsequent dark fermentation.

Methane Generation from Anthracite by Fungi and Methanogen Mixed Flora Enriched from Produced Water Associated with the Qinshui Basin in China

Biogenic coalbed methane (CBM) is generally believed to be formed by anaerobic bacteria and methanogens, while a few studies took fungi into account. Here, the microflora consisting of fungi and methanogens was enriched from the produced water associated with the Qinshui Basin using anthracite as the only carbon source. The maximum methane yield of 231 μmol/g coal was obtained after 22 days of cultivation under the optimum temperature of 35 °C, pH of 8, salinity of 0-2%, particle size of 0.075-0.150 mm, and the solid-liquid ratio of 1:30. It could remain active even after exposure to air for 24 h. Miseq results showed that the archaea were mainly composed of Methanocella, a hydrogenotrophic methanogen, followed by acetoclastic methanogen Methanosaeta and Methanosarcina, which could use various methanogenic substrates. The fungal communities mainly included Amorphotheca, Alternaria, Aspergillus, and Penicilium, which are all able to degrade complex organics such as aromatics and lignin. After cultivation, the crystal structure of anthracite became looser, as shown by XRD results, which might be due to the swelling effect caused by the destruction of the aromatic ring structure of coal under the function of fungi. The stretching vibration intensity of each functional group in coal decreased with cultivation, as revealed by FTIR. The GC-MS results showed that the concentration of alkanes and alcohols decreased significantly, which are the products of ring-opening of aromatics by fungi. These results suggested that fungi and methanogens in the coalbed also can syntrophically degrade coal effectively, especially for aromatics in coal.

Anaerobic co-digester microbiome during food waste valorization reveals Methanosaeta mediated methanogenesis with improved carbohydrate and lipid metabolism

This study determines the optimum food waste (FW) loading in an anaerobic digester for methane production. Interrelation between the degradation mechanism and microbial community composition was assessed through in-depth metabolic pathway analysis and gene quantification. Higher methane production and short lag phase were observed in the FW reactors with low substrate loadings (<4% v/v) while extended lag phase and incomplete substrate utilization were observed in the reactors fed with higher substrates (>6% v/v). The long-chain fatty acids (LCFAs) degradation was influenced by initial FW loading, and up to 99% LCFA degradation occurred at 4% FW reactor. The addition of 8 to 10% FW substrate inhibited methanogenesis due to the accumulation of volatile fatty acids (VFA) and low LCFA degradation. Under optimal conditions of substrate loading, Methanosaeta and Methanosarcina were abundant, indicating their role in methanogenesis and syntrophic acetogenesis, along with enhanced metabolic pathways specific for carbohydrate and lipid metabolism.

Rapid recovery of methane yield in organic overloaded-failed anaerobic digesters through bioaugmentation with acclimatized microbial consortium

Acidification during anaerobic digestion (AD) due to organic overloading is one of the major reasons for process failures and decreased methane productivity in anaerobic digesters. Process failures can cause the anaerobic digesters to stall completely, prolong the digester recovery period, and inflict an increased operational cost on wastewater treatment plants and adverse impacts on the environment. This study investigated the efficacy of bioaugmentation by using acclimatized microbial consortium (AC) in recovering anaerobic digesters stalled due to acidosis. Overloading of digesters with food waste leachate (FWL) led to the accumulation of volatile fatty acids (11.30 g L^-1) and a drop in pH (4.67), which resulted in process failure and a 22-fold decline in cumulative methane production compared to that in the initial phase. In the failure phase, the syntrophic and methanogenic activities of the anaerobic digester microbiota were disrupted by a significant decrease in the abundance of syntrophic populations such as Syntrophomonas, Syntrophorhabdus, Sedimentibacter, and Levilinea, and the phylum Euryarchaeota. Bioaugmentation of the failed digesters by adding AC along with the adjustment of pH resulted in the prompt recovery of methane productivity with a 15.7-fold higher yield than that in unaugmented control. The abundance of syntrophic bacteria Syntrophomonas and phylum Euryarchaeota significantly increased by 29- and 17-fold in the recovered digesters, respectively, which showed significant positive correlations with methane productivity. Methanosarcina and acetoclastic Methanosaeta played a major role in the recovery of the digesters; they were later replaced by hydrogenotrophic Methanoculleus. The increase in the abundance of genes associated with biomethanation contributed to digester recovery, according to the functional annotation of 16S rDNA amplicon data. Thus, bioaugmentation with AC could be a viable solution to recover digesters experiencing process failure due to organic overloading.