Ex-situ biomethanation for CO2 valorization: State of the art, recent advances, challenges, and future prospective.

Ex-situ biomethanation is an emerging technology that facilitates the use of surplus renewable electricity and valorizes carbon dioxide (CO2) for biomethane production by hydrogenotrophic methanogens. This review offers an up-to-date overview of the current state of ex-situ biomethanation and thoroughly analyzes key operational parameters affecting hydrogen (H2) gas-liquid mass transfer and biomethanation performance, along with an in-depth discussion of the technical challenges. To the best of our knowledge, this is the first review article to discuss microbial community structure in liquid and biofilm phases and their responses after exposure to H2 starvation during ex-situ biomethanation. In addition, future research in areas such as reactor configuration and optimization of operational parameters for improving the H2 mass transfer rate, inhibiting opportunistic homoacetogens, integration of membrane technology, and use of conductive packing material is recommended to overcome challenges and improve the efficiency of ex-situ biomethanation. Furthermore, this review presents a techno-economic analysis for the future development and facilitation of industrial implementation. The insights presented in this review will offer useful information to identify state-of-the-art research trends and realize the full potential of this emerging technology for CO2 utilization and biomethane production.

Mitigation of benzoic acid-driven autotoxicity in waste nutrient solution using O3 and O3/H2O2 treatments: Seed germination and root growth of Lactuca sativa L.

Benzoic acid (BA), a secondary metabolite released through root exudates, is considered to be the most common inhibitor that leads to plant autotoxicity, even at low concentrations in closed hydroponic systems. In this study, to mitigate BA-driven autotoxicity, the effects of O3 and O3/H2O2 oxidation treatment (O3 concentration: 1, 2, 4, 8 mg L-1, H2O2 concentration: 4, 8 mg L-1) on waste nutrient solution (WNS) were investigated in terms of BA degradation, the rate of germination inhibition (GI), and the rate of root growth inhibition (RI). In the case of O3 treatment, the BA degradation rate improved up to 14.1% as the O3 concentration increased, while alleviation of GI was insignificant (94.6-100%), confirming that a single O3 treatment was unsuitable for mitigating autotoxicity. On the other hand, O3/H2O2 treatment increased BA degradation by up to 24.8%, thereby significantly reducing GI (up to 7.69%) and RI (up to 0.88%). Both the highest BA mineralization rate and phytotoxicity mitigation was observed at BA125 (4-4) (BA mineralization: 16.7%, GI: 12.82%, RI: 11.69%) and BA125 (1-8) (BA mineralization: 17.7%, GI: 7.69%, RI: 0.88%) at each H2O2 concentration. In addition, the operating costs were evaluated by a chemical and electricity cost analysis at the different treatments. As a result, the operating costs of BA125 (4-4) and BA125 (1-8) were calculated to be 0.40 and 0.42 $ L-1 mg-1 of mineralized BA, respectively. After consideration of the mineralization rate, autotoxicity mitigation, and operating cost, BA125 (1-8) was suggested for the optimal treatment condition and our findings would contribute to the alleviation of BA-driven autotoxicity.

Elucidation of microbial interactions, dynamics, and keystone microbes in high pressure anaerobic digestion.

High-pressure anaerobic digestion (HPAD) is a promising technology for producing biogas enriched with high methane content in a single-step process. To enhance HPAD performance, a comprehensive understanding of microbial community dynamics and their interactions is essential. For this, mesophilic batch high-pressurized anaerobic reactors were operated under 3 bars (H3) and 6 bars (H6). The experimental results showed that the effect of high-pressure (up to 6 bar) on acidification was negligible while methanogenesis was significantly delayed. Microbial analysis showed the predominance of Defluviitoga affiliated with the phylum Thermotogae and the reduction of Thiopseudomonas under high-pressure conditions. In addition, the microbial cluster pattern in H3 and H6 was significantly different compared to the CR, indicating a clear shift in microbial community structure. Moreover, Methanobacterium, Methanomicrobiaceae, Alkaliphilus, and Petrimonas were strongly correlated in network analysis, and they could be identified as keystone microbes in the HPAD reactor.

A critical review on biomass-based sustainable biorefineries using nanobiocatalysts: Opportunities, challenges, and future perspectives.

Biocatalysts, including live microbial cells/enzymes, have been considered a predominant and advantageous tool for effectively transforming biomass into biofuels and valued biochemicals. However, high production costs, separation, and reusability limit its practical application. Immobilization of single and multi-enzymes by employing different nano-supports have gained massive attention because of its elevated exterior domain and high enzymatic performance. Application of nanobiocatalyst can overcome the drawbacks mainly, stability and reusability, thus reflecting the importance of biomass-based biorefinery to make it profitable and sustainable. This review provides an in-depth, comprehensive analysis of nanobiocatalysts systems concerning nano supports and biocatalytic performance characteristics. Furthermore, the effects of nanobiocatalyst on waste biomass to biofuel and valued bioproducts in the biorefinery approach and their critical assessment are discussed. Lastly, this review elaborates commercialization and market outlooks of the bioconversion process using nanobiocatalyst, followed by different strategies to overcome the limitations and future research directions on nanobiocatalytic-based industrial bioprocesses.

Developing Microbial Co-Culture System for Enhanced Polyhydroxyalkanoates (PHA) Production Using Acid Pretreated Lignocellulosic Biomass.

In the growing polymer industry, the interest of researchers is captivated by bioplastics production with biodegradable and biocompatible properties. This study examines the polyhydroxyalkanoates (PHA) production performance of individual Lysinibacillus sp. RGS and Ralstonia eutropha ATCC 17699 and their co-culture by utilizing sugarcane bagasse (SCB) hydrolysates. Initially, acidic (H2SO4) and acidified sodium chlorite pretreatment was employed for the hydrolysis of SCB. The effects of chemical pretreatment on the SCB biomass assembly and its chemical constituents were studied by employing numerous analytical methods. Acidic pretreatment under optimal conditions showed effective delignification (60%) of the SCB biomass, leading to a maximum hydrolysis yield of 74.9 ± 1.65% and a saccharification yield of 569.0 ± 5.65 mg/g of SCB after enzymatic hydrolysis. The resulting SCB enzymatic hydrolysates were harnessed for PHA synthesis using individual microbial culture and their defined co-culture. Co-culture strategy was found to be effective in sugar assimilation, bacterial growth, and PHA production kinetic parameters relative to the individual strains. Furthermore, the effects of increasing acid pretreated SCB hydrolysates (20, 30, and 40 g/L) on cell density and PHA synthesis were studied. The effects of different cost-effective nutrient supplements and volatile fatty acids (VFAs) with acid pretreated SCB hydrolysates on cell growth and PHA production were studied. By employing optimal conditions and supplementation of corn steep liquor (CSL) and spent coffee waste extracted oil (SCGO), the co-culture produced maximum cell growth (DCW: 11.68 and 11.0 g/L), PHA accumulation (76% and 76%), and PHA titer (8.87 and 8.36 g/L), respectively. The findings collectively suggest that the development of a microbial co-culture strategy is a promising route for the efficient production of high-value bioplastics using different agricultural waste biomass.

Lignin-Mediated Silver Nanoparticle Synthesis for Photocatalytic Degradation of Reactive Yellow 4G and In Vitro Assessment of Antioxidant, Antidiabetic, and Antibacterial Activities.

This study explored the potential of abundantly available sodium lignosulfonate (LS) as a reducer and fabricating agent in preparing silver nanoparticles (LS-Ag NPs). The operational conditions were optimized to make the synthesis process simpler, rapid, and eco-friendly. The prepared LS-Ag NPs were analyzed via UV-Vis spectroscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy. Results demonstrated that LS-Ag NPs were of crystalline structure, capped with LS constituents, and spherical in shape with a size of approximately 20 nm. Under optimized conditions, LS-Ag NPs exhibited significant photocatalytic activity in Reactive Yellow 4G degradation. The effects of photocatalyst (LS-Ag NPs) dosage, dye concentration, and its reusability for dye degradation were studied to make the process practically applicable in textile wastewater treatment. Additionally, the synthesized LS-Ag NPs displayed significant free radical scavenging against 2-diphenyl-1-picrylhydrazyl (DPPH) with an IC50 value of (50.2 ± 0.70 µg/mL) and also exhibited antidiabetic activity in terms of inhibition in the activity of carbohydrate-degrading marker enzyme α-glucosidase with an IC50 value of (58.1 ± 0.65 µg/mL). LS-Ag NPs showed substantial antibacterial potential against pathogenic strains, namely E. coli and S. aureus. In conclusion, LS-Ag NPs can be a reliable and eco-friendly material for their possible application in the treatment of dye-containing wastewater and have a great perspective in the biomedical and pharmaceutical sectors.

An Overview of Recent Advancements in Microbial Polyhydroxyalkanoates (PHA) Production from Dark Fermentation Acidogenic Effluents: A Path to an Integrated Bio-Refinery.

Global energy consumption has been increasing in tandem with economic growth motivating researchers to focus on renewable energy sources. Dark fermentative hydrogen synthesis utilizing various biomass resources is a promising, less costly, and less energy-intensive bioprocess relative to other biohydrogen production routes. The generated acidogenic dark fermentative effluent [e.g., volatile fatty acids (VFAs)] has potential as a reliable and sustainable carbon substrate for polyhydroxyalkanoate (PHA) synthesis. PHA, an important alternative to petrochemical based polymers has attracted interest recently, owing to its biodegradability and biocompatibility. This review illustrates methods for the conversion of acidogenic effluents (VFAs), such as acetate, butyrate, propionate, lactate, valerate, and mixtures of VFAs, into the value-added compound PHA. In addition, the review provides a comprehensive update on research progress of VFAs to PHA conversion and related enhancement techniques including optimization of operational parameters, fermentation strategies, and genetic engineering approaches. Finally, potential bottlenecks and future directions for the conversion of VFAs to PHA are outlined. This review offers insights to researchers on an integrated biorefinery route for sustainable and cost-effective bioplastics production.

Efficient bioconversion of sugarcane bagasse into polyhydroxybutyrate (PHB) by Lysinibacillus sp. and its characterization.

In this study, Lysinibacillus sp. RGS was evaluated to synthesize polyhydroxybutyrate (PHB) from a broad range of pure carbon sources and residual sugars of chemically pretreated sugarcane bagasse (SCB) hydrolysates. Effects of supplementation of nutrients and various experimental variables to enhance PHB accumulation were investigated. Results of optimized parameters were identified as 48 h, 37 °C, pH 7; inoculums concentration (2.5% v/v) and shaking condition (100 rpm). Growth kinetics and bioprocess parameters of Lysinibacillus sp. using SCB hydrolysates with corn steep liquor (2%) accounted for the maximum cell growth (8.65 g/L) and PHA accumulation (61.5%) with PHB titer of (5.31 g/L) under optimal conditions. The produced biopolymer was studied by Fourier Transform Infrared (FTIR) spectroscopy and the results revealed the obtained to be PHB. Thus Lysinibaciluus sp. exhibits high potential in industrial scale manufacture of PHB using SCB as an inexpensive substrate.

A comprehensive overview and recent advances on polyhydroxyalkanoates (PHA) production using various organic waste streams.

Polyhydroxyalkanoates (PHA) are appealing as an important alternative to replace synthetic plastics owing to its comparable physicochemical properties to that of synthetic plastics, and biodegradable and biocompatible nature. This review gives an inclusive overview of the current research activities dealing with PHA production by utilizing different waste fluxes generated from food, milk and sugar processing industries. Valorization of these waste fluxes makes the process cost effective and practically applicable. Recent advances in the approaches adopted for waste treatment, fermentation strategies, and genetic engineering can give insights to the researchers for future direction of waste to bioplastics production. Lastly, synthesis and application of PHA-nanocomposites, research and development challenges, future perspectives for sustainable and cost-effective PHB production are also discussed. In addition, the review addresses the useful information about the opportunities and confines associated with the sustainable PHA production using different waste streams and their evaluation for commercial implementation within a biorefinery.

Utilization of Noxious Weed Water Hyacinth Biomass as a Potential Feedstock for Biopolymers Production: A Novel Approach.

This study aims to utilize a noxious weed water hyacinth biomass (WH) for polyhydroxybutyrate (PHB) production. Alkaline and peracetic acid pretreatment was employed for the hydrolysis of WH and consequently enzymatic saccharification to produce fermentable sugars for PHB production. The pretreatment competence was determined using various operational parameters. By applying ambient conditions, alkaline pretreatment gave higher lignin removal of 65.0%, with 80.8% hydrolysis yield, and on enzyme hydrolysis (40 FPU/g of dry WH), produced total reducing sugar of about 523 mg/g of WH. The resulted WH enzymatic hydolysates were evaluated for the production of PHB by Ralstonia eutropha (ATCC 17699). The WH hydrolysates cultivation was compared to synthetic hydrolysates that contain a similar carbon composition in terms of bacterial growth and PHB synthesis. The effects of various supplements to enhance PHB production were estimated. Supplementation of corn steep liquor (CSL) as a cheap nitrogen source with WH hydrolysates favored a higher amount of PHB synthesis (73%), PHB titer of 7.30 g/L and PHB yield of 0.429 g/g of reducing sugar. Finally, using standard analytical tools, the physical and thermal characteristics of the extracted PHB were evaluated. The findings revealed WH was a promising and technically feasible option for transforming biomass into sustainable biopolymer conversion on a large scale.

Synergistic effect of Cu loading on Fe sites of fly ash for enhanced catalytic reduction of nitrophenol.

A novel Cu catalyst was developed using water-washed coal fly ash (WFA) as a support material for catalytic reduction of p-nitrophenol (p-NP) in the presence of NaBH4. Cu/WFA showed ~ × 105 times higher estimated rate constant kobs-p-NP/CCu (L min-1 gCu-1) compared with Cu/SiO2, Cu/Al2O3, and other Cu catalysts previously reported. Surprisingly, we obtained a significant lower price value (Price'/K) (0.027-0.068 USD/L min-1) for Cu/WFA in comparison with other Cu catalysts and precious metallic catalysts (Pd, Au, Ag, and Pt). Various surface analyses and additional experiments using Fe/SiO2, Cu/Fe2O3/SiO2, and Cu/HCl-treated WFA demonstrated that Cu(0) nanoparticles were well loaded on the surface of WFA, where Fe elements were abundant, resulting in a dramatic enhancement of the Cu/WFA catalytic activity. Particularly, X-ray photoelectron spectroscopy revealed the abundance of Cu(0)/Fe(III) and Cu(0)/Fe(II) in the WFA surface. This indicates that Cu(0) was the main driving force for the activation of Had molecule, and that the reduction of Fe(III) to Fe(II) by NaBH4 can accelerate the reduction of Cu(II) to Cu(0). Recycling and phytotoxicity tests showed that Cu/WFA can be applied as a reusable catalyst with low environmental impact, revealing the remarkable potential of non-precious metal/WFA catalyst in the field of environmental remediation.

Pretreatment of kenaf (Hibiscus cannabinus L.) biomass feedstock for polyhydroxybutyrate (PHB) production and characterization.

Kenaf biomass (KB) was employed as feedstock for the synthesis of polyhydroxybutyrate (PHB) using Ralstonia eutropha to replace conventional petroleum-derived polymers. Various pretreatments followed by enzymatic saccharification were applied to release monomeric sugars from KB for PHB production. The effects of increasing concentration of Na2CO3 + Na2SO3 (NaC + NaS) pretreated KB hydrolysates (20-40 g/L) on PHB production were investigated. NaC + NaS pretreated KB hydrolysates (30 g/L) exhibited maximum 70.0% PHA accumulation, with PHB titers of 10.10 g/L and PHB yields of about 0.488 g/g of reducing sugar produced within 36 h of fermentation. PHA accumulation, PHB yield and R. eutropha growth performance using KB hydrolysates were found to be comparable with those of synthetic sugar mixture. Characterization of the produced PHB in terms of crystalline structure, and thermal properties was done using various analytical techniques and results coincide with standard PHB. Thus, green liquor pretreated KB hydrolysates deliver a promising and economically feasible carbon substrate for PHB production.

Dispersion aided tenside disintegration of seagrass Syringodium isoetifolium: Towards biomethanation, kinetics, energy exploration and evaluation.

In this study, an attempt was made to enhance the biomethanation potential of seagrass (Syringodium isoetifolium) by the aid of disperser-tenside (polysorbate 80) disintegration for the first time in literature. A disperser rpm of 10,000 for 20 min and PS 80 dose of 0.000864 g/g TS were selected as ideal parameters for effectual seagrass biomass disintegration. Dispersion aided tenside disintegration (DTD) with a disperser energy consumption of 349 kJ/kg TS, was observed to be efficacious with a biomass lysis rate of 25.6%. The impact of DTD on bioacidification and biomethanation assay with respect to volatile fatty acids concentration (1100 mg/L) and methane generation (0.256 g/g COD), was greater than dispersion disintegration (DD) (800 mg/L; 0.198 g/g COD). Thus, S. isoetifolium is considered as a promising substrate to attain the third generation biofuel goals in the near future.

Wheat straw extracted lignin in silver nanoparticles synthesis: Expanding its prophecy towards antineoplastic potency and hydrogen peroxide sensing ability.

Lignin, is the most abundant, renewable and degradable biopolymer available in the nature. The present study exploited purified lignin from wheat straw as reducing, capping and stabilizing agent for the green synthesis of silver nanoparticles (Li-AgNPs) under optimized conditions. The analytical studies revealed synthesized Li-AgNPs having a face centered cubic crystalline structure, size ranging ~15-20 nm and the biomolecules comprising majorly phenolic, hydroxyl and carboxylic group of lignin coated on the surface of AgNPs. Li-AgNPs showed significant antimicrobial efficacy against human pathogens namely; Staphylococcus aureus and Escherichia coli and also determined their minimum inhibitory and minimum bactericidal concentration (MIC and MBC). Li-AgNPs also displayed substantial antioxidant activity in terms of well-known enzyme marker viz.; ABTS and DPPH free radical scavenging assay relative to commercial AgNPs. In vitro cytotoxicity assay of Li-AgNPs demonstrated dose-dependent toxicity effects in SKOV3 ovarian cancer cell line (LD50; 150 µg/mL) indicative of promising anticancer agent. Further, H2O2 sensing ability of stabilized Li-AgNPs exhibited its vital role in determining reactive oxygen species. Synthesis of Li-AgNPs is a cheap green technology and could exhibit its commercial use in biomedical, cosmetic, and pharmaceutical industry.

Photocatalytic activity of CuO/Cu(OH)2 nanostructures in the degradation of Reactive Green 19A and textile effluent, phytotoxicity studies and their biogenic properties (antibacterial and anticancer).

In this study, CuO/Cu(OH)2 (denoted as CuONs) nanostructures were synthesized relying to a cheap and rapid chemical co-precipitation method using copper sulfate and liquid ammonia as precursors. Results obtained from X-ray diffraction, and field emission scanning electron microscopy analysis revealed the crystalline nature of synthesized CuONs. Fourier transform infrared spectroscopy and energy dispersive spectroscopy studies showed interactions between copper and oxygen atoms. Synthesized CuONs showed the size in the range of 20-30 nm using high resolution transmission electron microscopy analysis. The photocatalytic degradation performance of Reactive Green 19A (RG19A) dye using CuONs was evaluated. The results showed that CuONs exhibited 98% degradation efficiency after 12 h and also complete mineralization in form of reducing chemical oxygen demand (COD) (84%) and total organic carbon (TOC) (80%). The nanocatalyst was recovered from the dye containing solution and its catalytic activity can be reused up to four times efficiently. CuONs was also able to decolorize actual textile effluent (80% in terms of the American Dye Manufacturers' Institute (ADMI) value) with significant reductions in COD (72%) and TOC (69%). Phytotoxicity studies revealed that the degradation products of RG19A and textile effluent were scarcely toxic in nature, thereby increasing the applicability of CuONs for the treatment of textile wastewater. Additionally, the CuONs showed a maximum antibacterial effect against human pathogens which also displayed synergistic antibacterial potential related to commercial antibiotics. Moreover, CuONs displayed strong antioxidant activity in terms of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (IC50: 51 µg/mL) and DPPH (1,1-diphenyl-2-picrylhydrazyl) (IC50: 60 µg/mL) radical scavenging. The CuONs exhibited dose dependent response against tumor rat C6 cell line (IC50: 60 µg/mL) and may serve as anticancer agents.

Effects of changes in temperature on treatment performance and energy recovery at mainstream anaerobic ceramic membrane bioreactor for food waste recycling wastewater treatment.

An anaerobic ceramic membrane bioreactor (AnCMBR) has been attracted as an alternative technology to co-manage various organic substrates. This AnCMBR study investigated process performance and microbial community structure at decreasing temperatures to evaluate the potential of AnCMBR treatment for co-managing domestic wastewater (DWW) and food waste-recycling wastewater (FRW). As a result, the water flux (≥6.9 LMH) and organic removal efficiency (≥98.0%) were maintained above 25 °C. The trend of methane production in the AnCMBR was similar except for at 15 °C. At 15 °C, the archaeal community structure did not shifted, whereas the bacterial community structure was changed. Various major archaeal species were identified as the mesophilic methanogens which unable to grow at 15 °C. Our results suggest that the AnCMBR can be applied to co-manage DWW and FRW above 20 °C. Future improvements including psychrophilic methanogen inoculation and process optimization would make co-manage DWW and FRW at lower temperature climates.

Biohydrogen production from food waste: Current status, limitations, and future perspectives.

Among the various biological routes for H2 production, dark fermentation is considered the most practically applicable owing to its capability to degrade organic wastes and high H2 production rate. Food waste (FW) has high carbohydrate content and easily hydrolysable in nature, exhibiting higher H2 production potential than that of other organic wastes. In this review article, first, the current status of H2 production from FW by dark fermentation and the strategies applied for enhanced performance are briefly summarized. Then, the technical and economic limitations of dark fermentation of FW are thoroughly discussed. Economic assessment revealed that the economic feasibility of H2 production from FW by dark fermentation is questionable. Current efforts to further increase H2 yield and waste removal efficiency are also introduced. Finally, future perspectives along with possible routes converting dark fermentation effluent to valuable fuels and chemicals are discussed.

Bacterial community analysis in upflow multilayer anaerobic reactor treating high-solids organic wastes.

A novel anaerobic digestion configuration, the upflow multi-layer anaerobic reactor (UMAR), was developed to treat high-solids organic wastes. The UMAR was hypothesized to form multi-layer along depth due to the upflow plug flow; use of a recirculation system and a rotating distributor and baffles aimed to assist treating high-solids influent. The chemical oxygen demand (COD) removal efficiency and methane (CH4 ) production rate were 89% and 2.10 L CH4 /L/d, respectively, at the peak influent COD concentration (110.4 g/L) and organic loading rate (7.5 g COD/L/d). The 454 pyrosequencing results clearly indicated heterogeneous distribution of bacterial communities at different vertical locations (upper, middle, and bottom) of the UMAR. Firmicutes was the dominant (>70%) phylum at the middle and bottom parts, while Deltaproteobacteria and Chloroflexi were only found in the upper part. Potential functions of the bacteria were discussed to speculate on their roles in the anaerobic performance of the UMAR system. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1226-1234, 2017.

Low-strength ultrasonication positively affects methanogenic granules toward higher AD performance: Hydrolytic enzyme excretions.

In our previous studies, enhanced methane (CH4) production using low-strength ultrasonication was achieved and the results were evidenced by physico-chemical and molecular biological approaches. As a final continuation study, the effects of low-strength ultrasonication on the activities of hydrolytic enzymes (amylase, cellulase, and protease) were investigated on methanogenic granules given that hydrolysis regulates the whole anaerobic digestion (AD) process. Up to 213% enhanced hydrolytic enzyme activities were observed, and they seem to be highly related to the enhanced CH4 production. However, the effects of ultrasonication on the distribution (liquid- and solid-phases) of hydrolytic enzymes were negligible. Enzymatic activation by low-strength ultrasonication was hypothetically caused by acoustic streaming, presumably enabling to overcome the masking effect, substrate inhibition and spatial constraint.

Low-strength ultrasonication positively affects methanogenic granules toward higher AD performance: Implications from microbial community shift.

To elucidate the enhanced methane yield from organic wastes, the effects of low-strength ultrasonication on the microbial community structures in upflow anaerobic sludge blanket reactors were for the first time analyzed using pyrosequencing. Interestingly, a more even microbial community was observed in the ultrasonicated granules than in the control, which could compensate for the decreased richness and resulted in comparable (archaea) or even higher (bacteria) diversity. The ultrasonicated granules contained higher levels of δ-Proteobacteria, of which many are reportedly potential syntrophs, as well as methanogenic genera Methanosaeta, Methanotorris, and Methanococcus. The increased presence of syntrophic bacteria with their methanogenic partners was discussed with respect to hydrogen flux; their selective proliferation seems to be responsible for the enhanced anaerobic performance. This study is the first research shedding light on the novel function of low-strength ultrasound shifting the microbial structure towards better biogas production performance, and will facilitate application of low-strength ultrasound to other bioprocesses.