Increased Methane Production Research Articles

The role of sulfidated zero-valent iron in enhancing anaerobic digestion of waste activated sludge.

Zero-valent iron (ZVI) has been confirmed in enhancing methane production by improving interspecies electron transfer during anaerobic digestion (AD) of waste activated sludge (WAS). In this study, we suppose that sulfidated zero-valent iron (S-ZVI), a semiconductor material, has better property of electron transfer in AD process. Based on two-phase anaerobic digestion process, nitrite and S-ZVI were used separately for improving acidogenic phase and methanogenic phase of anaerobic sludge digestion. Based on XRD and XPS, Fe(Ⅱ)-O and Fe(Ⅲ)-O were substituted by Fe(Ⅱ)-S and Fe(Ⅲ)-S after ZVI sulfidation, which increased the electric conductivity of S-ZVI. Nyquist plot and Tafel corrosion curve showed that the sulfidation treatment can reduce impedance of electronic transmission. The results showed that the addition of S-ZVI increased methane production by 24.22% compared with ZVI alone. The addition of S-ZVI increased the relative abundance of Actinobacteria in R3(Raw+S-ZVI) and R6(NO2-+S-ZVI), enhancing the activity of microbial in anaerobic sludge digestion. The relative abundance of Acidobacteriota, Synergistota, WPS-2, Firmicutes, Caldisericota, and Gampylobactenota have changed markedly, and facilitated the activity of acidogenic microbes to produce more biodegradable organic matter, further boosting methane production. The findings of in-situ formation of S-ZVI in R5 anaerobic digestion saves the economic cost of S-ZVI preparation, which will be helpful for the extensive application of this technology.

Increased methane production associated with community shifts towards Methanocella in paddy soils with the presence of nanoplastics

BackgroundPlanetary plastic pollution poses a major threat to ecosystems and human health in the Anthropocene, yet its impact on biogeochemical cycling remains poorly understood. Waterlogged rice paddies are globally important sources of CH4. Given the widespread use of plastic mulching in soils, it is urgent to unravel whether low-density polyethylene (LDPE) will affect the methanogenic community in flooded paddy soils. Here, we employed a combination of process measurements, short-chain and long-chain fatty acid (SCFAs and LCFAs) profiling, Fourier-transform ion cyclotron resonance mass spectrometry, quantitative PCR, metagenomics, and mRNA profiling to investigate the impact of LDPE nanoplastics (NPs) on dissolved organic carbon (DOC) and CH4 production in both black and red paddy soils under anoxic incubation over a 160-day period.ResultsDespite significant differences in microbiome composition between the two soil types, both exhibited similar results to NPs exposure. NPs induced a change in DOC content and CH4 production up to 1.8-fold and 10.1-fold, respectively. The proportion of labile dissolved organic matter decreased, while its recalcitrance increased. Genes associated with the degradation of complex carbohydrates and aromatic carbon were significantly enriched. The elevated CH4 production was significantly correlated to increases in both the PCR-quantified mcrA gene copy numbers and the metagenomic methanogen-to-bacteria abundance ratio. Notably, the latter was linked to an enrichment of the hydrogenotrophic methanogenesis pathway. Among 391 metagenome-assembled genomes (MAGs), the abundance of several Syntrophomonas and Methanocella MAGs increased concomitantly, suggesting that the NPs treatments stimulated the syntrophic oxidation of fatty acids. mRNA profiling further identified Methanosarcinaceae and Methanocellaceae to be the key players in the NPs-induced CH4 production.ConclusionsThe specific enrichment of Syntrophomonas and Methanocella indicates that LDPE NPs stimulate the syntrophic oxidation of LCFAs and SCFAs, with Methanocella acting as the hydrogenotrophic methanogen partner. Our findings enhance the understanding of how LDPE NPs affect the methanogenic community in waterlogged paddy soils. Given the importance of this ecosystem, our results are crucial for elucidating the mechanisms that govern carbon fluxes, which are highly relevant to global climate change.

Anaerobic wastewater treatment containing sulfate enhanced by N-acyl homoserine lactones: Microbial insights as deciphered by metagenomics

Addressing the challenge of enhancing anaerobic wastewater treatment containing sulfate is a pressing concern. Adding quorum sensing signaling molecule N-acyl-homoserine lactones (AHLs) is beneficial for improving anaerobic treatment performances. Previous studies focused on the impact of AHL addition on microbial communities, the role of AHL addition in functional metabolism and interspecies electron transfer (IET) is poorly understood. This study delved into the roles of AHLs in anaerobic wastewater treatment containing sulfate. AHLs expedited COD degradation and improved methane production, with a 15.49 % increase in methane production with 20 μM AHL addition. AHL addition enhanced electron transport system activity by 28.02 % and specific methanogenic activity by 22.61 %, suggesting an enhancement in microbial activity and methanogenic capability. Taxonomic analysis revealed the facilitation of AHL addition on symbiotic relationships between acidifying bacteria and methanogens. KEGG annotations highlighted upregulation of genes associated with key enzymes in acidification, sulfate reduction, and methanogenesis with AHL addition. AHLs also bolstered syntrophic metabolism by upregulating genes involved in IET processes, including H2 production and utilization, riboflavin synthesis and secretion, and conductive pili assembly and synthesis. This study bridges gaps in understanding the influence of AHL addition on microbial metabolism and electron transfer.

A novel tubular single-chamber microbial electrolysis cell for efficient methane production from industrial potato starch wastewater

The integration of microbial electrolysis cells (MEC) with anaerobic digestion (AD) shows great promise for enhancing methane production from high-COD wastewater. However, an efficient MEC-AD reactor design remains elusive. Here, a novel tubular single-chamber MEC-AD reactor was constructed to treat potato starch wastewater (COD over 20,000 mg/L). The concentric and compact design of the stainless-steel cathode and anode reduced internal resistance, resulting in enhanced methane production. Applying −0.2 V vs. Ag/AgCl to the anode increased methane production by 1.73 times compared to the open circuit and halved hydraulic retention time. Moreover, the reactor achieved an average methane content of 82.57 %, which was 23.89 % higher than the open circuit. The reactor showed a total COD removal of 92.2 %, which was 24 % higher than the open circuit. Additionally, base consumption to maintain pH was reduced to one-sixth of that in conventional AD, preventing volatile fatty acid accumulation. Microbial analysis showed Geobacter (63.4 %) and Methanobacterium (96.8 %) were highly enriched in the anode and cathode biofilms, respectively. The proportion of fermentative bacteria also increased in the MEC-AD system. These results demonstrate the effectiveness of the tubular single-chamber MEC-AD reactor in enhancing methane production from potato starch wastewater, with strong potential for scale-up applications.

The intriguing effect of CO2 enrichment in anaerobic digestion

This study explores carbon dioxide enrichment in anaerobic digestion to boost biomethane production and assess degradation kinetics and methanogenic pathway evolution. Carbon dioxide enrichment was found to improve inoculum digestion, supplying additional energy for methanogenic archaea. The methane yield of blank inocula increased by 53 % to 77 % after carbon dioxide enrichment. Although further digestion of inoculum residues took longer, rapid adaptation led to an increased methane production rate that surpassed the lag phase. No antagonistic effects were observed with carbon dioxide enrichment after applying the feedstocks. Increased methane production, along with a significant reduction in chemical oxygen demand, confirms the impact of carbon dioxide enrichment on inoculum digestion. Isotope analysis showed an increase in δ2H-CH4 values by approximately 36 mU compared to non-enriched inoculum, implying enhanced hydrogenotrophic methanogenesis. Carbon dioxide enrichment significantly enhances biomethane production and digestion efficiency in anaerobic digestion, offering a sustainable solution for large-scale plant operations.

Enrichment of Methanothrix species via riboflavin-loaded granular activated carbon in anaerobic digestion of high-concentration brewery wastewater amidst continuous inoculation of Methanosarcina barkeri

Effective treatment of high-concentration brewery wastewater through anaerobic digestion (AD) has always been a challenging issue. Enhancing direct interspecies electron transfer (DIET) was demonstrated to increase methane production during AD under high organic loading rate (OLR). Herein, the feasibility of enhancing DIET with the addition of riboflavin-loaded granular activated carbon (RF-GAC) as well as co-addition with Methanosarcina barkeri (Rf-GAC+M.barkeri) was investigated (M.barkeri is well-known to be capable of DIET with electroactive bacteria). During the whole process, the Rf-GAC and the Rf-GAC+M.barkeri group both achieved average COD removal rates above 97 %, which was 14 % higher than that of the control. The average methane production in the Rf-GAC group and the Rf-GAC+M.barkeri group respectively reached 0.334 ± 0.02 L(stp)/g COD and 0.345 ± 0.02 L(stp)/g COD, 1.35 and 1.39 times higher than the 0.247 ± 0.03 L(stp)/g COD reached by the control. The control reactor deteriorated at an OLR of 12 kg COD/(m3·d), whereas the Rf-GAC and the Rf-GAC+M.barkeri group maintained stable as the OLR reached as high as 17.5 kg COD/(m3·d) and the volatile fatty acids concentration was consistently below 10 mM. The RF-GAC performed better than Rf-GAC+M.barkeri in enriching Methanothrix, whose relative abundance was 60.6 % in the former group. Metabolic pathway analysis revealed the addition of RF-GAC upregulated genes related to DIET in Methanothrix species, including hdrA and fpoD. Furthermore, Methanothrix remained the dominant archaea even continuously inoculating pure strains of M.barkeri during the entire operational period. Pure culture experiments proved that GAC inhibited M.barkeri growth. The results of this study can be optimized for practical application of AD treating high-concentration brewery wastewater.

Enhancement of the anaerobic biodegradation efficiency of azo dye by anthraquinone-loaded biochar biofilm: factors affecting biofilm formation and the enhancement mechanism

Carbon-based materials that serve as microbial carriers, and the role of surface-formed biofilms in anaerobic digestion, merit further investigation. This study explored the role and mechanism behind the biodegradation enhancement of biofilms formed onto anthraquinone-loaded biochar (AQS-BC) surfaces through the anaerobic decolorization process of azo dye Reactive Red 2, and optimized the conditions for AQS-BC biofilm formation. The results indicated that the AQS-BC biofilm system exhibited high treatment efficiency and stability in RR2 anaerobic decolorization. RR2 led to the accumulation of volatile fatty acids (VFAs) and inhibition of methane production, while the presence of AQS increased methane production. The effects of sludge concentration, contact time, carbon source concentration, and RR2 concentration on biofilm maturity were also analyzed. Combining biochemical characteristics, electrochemical properties, surface structure, and microbial community analysis, a mechanism for the anaerobic decolorization of RR2 via AQS-BC as a microbial carrier was proposed. This study provides insights into the roles of biofilms in the anaerobic wastewater treatment processes.Graphical

Struvite crystallization eliminates ammonia inhibition in thermal hydrolysis of waste activated sludge: Role of Mg/P ratio

Thermal hydrolysis (TH) is a promising sludge pretreatment technology, but the ammonia it produces can be hazardous to subsequent anaerobic digestion (AD). This study assessed the potential of using struvite crystallization to mitigate ammonia inhibition in the AD process and examined the impact of the Mg/P ratio. The Mg/P ratio of 1.0 effectively reduced the ammonia concentration to 409 ± 22 mg/L, although methane production decreased by 14 %. Reducing the Mg/P ratio to 0.6 resulted in an 11 % increase in methane production. The study revealed that an excess of Mg2+ hindered sludge solubilization and inhibited the AD process by reducing enzyme activities, which led to a microbial community detrimental to methane production. This study provides a new idea to alleviate the ammonia inhibition of sludge AD, which is of great scientific value and practical significance for applying of struvite crystallization to TH.

Impact of Nanoparticle Addition and Ozone Pre-Treatment on Mesophilic Methanogenesis in Temperature-Phased Anaerobic Digestion

Biodegradable organic waste offers significant opportunities for resource recovery within the frame of the circular economy. In this work, the effects of carbon-encapsulated iron nanoparticles and ozone pre-treatments in the mesophilic methanogenic stage of a temperature-phased an-aerobic digestion have been studied using biochemical methanogenic potential (BMP) tests and modeling simulation. To do that, digestates from a pre-treated thermophilic acidogenic reactor that co-digested sludge and wine vinasse were used. The addition of nanoparticles favored the removal of particulate matter, which increased by 9% and 6% in terms of total solids and volatile solids, respectively. When combined with ozone pre-treatment, these increases were 27% and 24%, respectively, demonstrating enhanced AD efficiency. The dose of iron nanoparticles encapsulated in carbon did not result in a statistically significant increase in methane production when sludge and vinasse were used as feedstock. The combination of nanoparticles with the ozone pre-treatment significantly improved the methanogenic phase of the second stage, increasing the methane production yield by 22% and reducing the lag phase from 10 days to 3 days, according to the modified Gompertz model.

Biofilm mass transfer and thermodynamic constraints shape biofilm in trickle bed reactor syngas biomethanation

Syngas (H2, CO2, CO) produced thermochemically from lignocellulosic biomass is an underexploited source for resource recovery and valorisation through its biological conversion for the production of a wide range of chemicals and fuels. Syngas biomethanation is one such promising bioconversion pathway, displaying interesting features such as high conversion efficiency and product selectivity, as methane is the sole product of the process. The biological conversion of syngas to high purity biomethane is still typically associated with a number of challenges related to the syngas composition, CO toxicity, and gas–liquid mass transfer limitations. In this work, the syngas biomethanation process carried out in trickle bed reactors was investigated at its boundary conditions to explore the limits of the process, focusing on syngas composition and mass-transfer conditions potentially limiting process performance. The process was found to be robust when exposed to CO excess, but highly sensitive to H2 excess, which caused severe inhibition even under small amounts of excess H2. This implies that biomethane purity comparable to natural gas can be achieved by addition of renewable H2, but this requires precise control to avoid process failure. Modulating the liquid recirculation rate and gas residence time allowed for a maximum methane productivity of 9.8 ± 0.5 mmol CH4 h−1 Lreactor−1 with full conversion of H2 and CO at a gas residence time of 1 h. Nevertheless, increasing the gas–liquid mass transfer with increasing liquid recirculation rate did not lead to increased methane productivity, which suggested additional rate-limiting bottlenecks in the process. Careful investigation of other factors potentially limiting the process led to the conclusion that diffusive transport of syngas components in the biofilm was the main bottleneck of the process. This diffusive limitation leads to a scenario of severe substrate scarcity in the biofilm phase that conditions the thermodynamic feasibility of the different biochemical reactions involved in syngas biomethanation. In turn, these thermodynamic constraints were found to drive the stratification of microbial groups and sequential consumption of syngas components along the height of the reactor.

Biochars from waste as an additive material in anaerobic co-digestion: Characterization and application in batch and semi-continuous systems

The conversion of organic waste into energy through anaerobic digestion (AD) is a profitable and environmentally friendly strategy. Enhancing the process is crucial for optimizing and maximizing biogas and methane production. To achieve this, various strategies can be employed, such as anaerobic co-digestion (co-AD) and the use of biochar. Biochar aids in process stability, provides buffering capacity, mitigates inhibitory toxins, immobilizes microorganisms, facilitates microbial colonization, and accelerates electron transfer between microorganisms. This study aimed to produce biochar from different wastes and pyrolysis temperatures and to investigate its use as an additive material in the co-AD of fruit and vegetable waste (FVW) and laying chicken manure (LCM) in batch and semi-continuous systems. Thermogravimetric analysis (TGA) and differential scanning calorimetry were performed to determine the pyrolysis temperature for biochar production, defining temperatures of 450 and 550 °C. A biochemical methane potential (BMP) test was conducted in 120 mL reactors (working volume) with the addition of 10 g/L of biochar from FVW, LCM, and wood pruning waste (WPW). WPW450 biochar showed the highest fixed carbon content, rough surface, and deep porous structure, factors that contributed to a 28 % increase in methane production compared to the control. Semi-continuous tests were conducted in 50 L reactors (working volume) using a reduced dosage (1 g/L) of WPW450 biochar, providing process stability and better biogas quality, resulting in a 31 % increase in methane production. The reduction in biochar dosage did not negatively impact the semi-continuous system, which showed a 74 % higher methane yield compared to the batch system. The results of this study highlight the importance of biochar addition to increase methane production in the co-AD of FVW and LCM at different scales, as well as the study of different biomasses and temperatures for biochar production.

Enhanced anaerobic digestion of food waste by the addition of cobalt iron oxide

In this study, the impact of cobalt iron oxide(CoFe2O4) on the anaerobic digestion (AD) of food waste (FW) was investigated including the variations in pH, VFAs, ORP, Fe2+/Fe3+ concentrations, SCOD, dehydrogenase activity, methane production and microbial community structure. The results showed that CoFe2O4 had a positive effect on the anaerobic digestion of food waste. CoFe2O4 could promote the release of SCOD, increase the dehydrogenase concentration and reduce ORP resulting in an increase of methane production. At a CoFe2O4 concentration of 200 mg/L, the cumulative methane production reached to 414.75 mL/(gVS) which was increased by 79.1% compared to the control group(231.59 mL/(gVS)). Meanwhile, the variation of microbial community showed that CoFe2O4 could increase the relative abundance of Methanobacterium and the methane production pathway in the AD was shifted from acetoclastic to hydrogenotrophic.

Impact of thermal hydrolysis on VFA-based carbon source production from fermentation of sludge and digestate for denitrification: experimentation and upscaling implications

Stricter nutrient discharge limits at wastewater treatment plants (WWTPs) are increasing the demand for external carbon sources for denitrification, especially at cold temperatures. Production of carbon sources at WWTP by fermentation of sewage sludge often results in low yields of soluble carbon and volatile fatty acids (VFA) and high biogas losses, limiting its feasibility for full-scale application. This study investigated the overall impact of thermal hydrolysis pre-treatment (THP) on the production of VFA for denitrification through the fermentation of municipal sludge and digestate. Fermentation products and yields, denitrification efficiency and potential impacts on methane yield in the downstream process after carbon source separation were evaluated. Fermentation of THP substrates resulted in 37–70 % higher soluble chemical oxygen demand (sCOD) concentrations than fermentation of untreated substrates but did not significantly affect VFA yield after fermentation. Nevertheless, THP had a positive impact on the denitrification rates and on the methane yields of the residual solid fraction in all experiments. Among the different carbon sources tested, the one produced from the fermentation of THP-digestate showed an overall better potential as a carbon source than other substrates (e.g. sludge). It obtained a relatively high carbon solubilisation degree (39 %) and higher concentrations of sCOD (19 g sCOD/L) and VFA (9.8 g VFACOD/L), which resulted in a higher denitrification rate (8.77 mg NOx-N/g VSS∙h). After the separation of the carbon source, the solid phase from this sample produced a methane yield of 101 mL CH4/g VS. Furthermore, fermentation of a 50:50 mixture of THP-substrate and raw sludge produced also resulted in a high VFA yield (283 g VFACOD/kg VSin) and denitrification rate of 8.74 mg NOx-N/g VSS∙h, indicating a potential for reduced treatment volumes. Calculations based on a full-scale WWTP (Käppala, Stockholm) demonstrated that the carbon sources produced could replace fossil-based methanol and meet the nitrogen effluent limit (6 mg/L) despite their ammonium content. Fermentation of 50–63 % of the available sludge at Käppala WWTP in 2028 could produce enough carbon source to replace methanol, with only an 8–20 % reduction in methane production, depending on the production process. Additionally, digestate production would be sufficient to generate 81 % of the required carbon source while also increasing methane production by 5 % if a portion of the solid residues were recirculated to the digester.

Experimental study on the desorption behavior of high-volatile bituminous coals following CO2 and CH4 injection at various compositional ratios

CO2-ECBM (Enhanced Coalbed Methane recovery) offers the dual benefits of increasing methane production and reducing carbon emissions through sequestration. Previous studies have primarily focused on the competitive adsorption effects of different gas compositions during the CO2-ECBM. However, the dynamic changes in desorption volume, desorption strain, and gas composition for different compositional ratios of CO2/CH4 after injecting CO2 remain unclear. Therefore, high-volatile bituminous coals from the southern margin of the Junggar Basin are chosen for desorption experiments with five different compositional ratios of CO2/CH4. Desorption volume, desorption strain, and gas composition of the coal samples are monitored during the desorption process. Finally, the mechanism influencing the dynamic changes in gas composition during desorption is analyzed. The results indicate that as CO2 concentration increases, both desorption volume and desorption strain correspondingly increase. At the same desorption volume, a higher CO2 concentration results in greater desorption strain. For different compositional ratios of CO2/CH4, CH4 concentration gradually decreases while CO2 concentration gradually increases over desorption time. The concentration of the desorption gas is influenced by the initial CO2 concentration and the pore structure. Specifically, higher initial CO2 concentrations, better pore opening, and more developed mesopores and macropores lead to greater changes in composition concentrations during desorption. Different concentrations of CO2 all promote CH4 production, with higher CO2 concentrations enhancing CH4 production efficiency more significantly, especially for samples that are more difficult to produce. The research findings can provide guidance for the efficient production of CBM after CO2 injection.

An algal regulation-based molasses vinasse anaerobic digestion strategy for enhancing organic matter removal and methane production

Microalgae are suitable type of anaerobic co-digestion (AcoD) substrate that can effectively alleviate microbial inhibition caused by substrate characteristics (molasses vinasse, MV). Therefore, our investigated the synergistic effects, organic matter removal, and potential microbiological impacts in the AcoD of MV and Desmodesmus opoliensis strain GXU-A4. We conducted batch AcoD using simple dehydrated GXU-A4 (Fresh D. opoliensis, FDO) and lipid-extracted GXU-A4 (Pretreated D. opoliensis, PDO). The highest methane potential of PDO biomass was 124.9 ± 0.8 mL g−1 VS, while AcoD with MV increased methane production by 11 % and promoted acetic acid production. FDO biomass reduced nitrogen-containing organic matter and humic-like production. Microbial community and functional prediction analyses revealed that AcoD altered the distribution of hydrolytic acidogenic bacteria, such as Bacteroidetes and Cloacimonadota (W5). Our study provide a new insight into the control strategy of AcoD for methane production, removal of organic matter, and microbial mechanisms in algae biomass.

Effects of polypropylene microplastics on digestion performance, microbial community, and antibiotic resistance during microbial anaerobic digestion

As an emerging pollutant, microplastics (MPs) have attracted increasing attention worldwide. The effects of polypropylene (PP) MPs on digestion performance, behaviors of dominant microbial communities, antibiotic resistance genes (ARGs) and mobile genetic elements in microbial anaerobic digesters were investigated. The results showed that the addition of PP-MPs to digesters led to an increase in methane production of 10.8% when 300 particles/g TSS of PP-MPs was introduced compared with that in digester not treated with PP-MPs. This increase was attributed to the enrichment of acetogens such as Syntrophobacter (42.0%), Syntrophorhabdus (27.0%), and Syntrophomonas (10.6%), and methanogens including Methanobacterium and Methanosaeta. tetX was highly enriched due to PP-MP exposure, whereas parC exhibited the greatest increase (35.5% – 222.7%). Horizontal gene transfer via ISCR1 and intI1 genes might play an important role in the spread of ARGs. Overall, these findings provide comprehensive insight into the ecological dynamics of PP-MPs during microbial anaerobic digestion.

Enhancing proton-coupled electron transfer drives efficient methanogenesis in anaerobic digestion

The enhancement of electron or proton transfer between syntrophic microbes has been widely recognised as a means for improving methane generation. However, the uncoupled supplementation of electrons and protons in multiphase anaerobic environment hinders the balanced uptake of electrons and protons in the cytoplasm of methanogens, limiting methanogenesis efficiency. Herein, the cooperative effect of a proton-conductive material (PM) and an electron-conductive material (EM) in enhancing proton-coupled electron transfer (PCET) and driving efficient methanogenesis in anaerobic digestion was investigated. The cooperation of the PM and EM significantly increased methane production and the maximum methane generation rate by 78.9 % and 103.5 %, respectively, indicating enhanced methanogenesis efficiency. Analysis of the physicochemical properties, biochemical components, and microbial dynamics revealed that the cooperation of the PM and EM improved the metabolism of syntrophic microbes, which was critically dependent on electron and proton transfer. This enhancement was primarily due to the improvement in PCET, as mainly supported by hydrogen/deuterium kinetic isotope effect measurements, multi-omics integration analyses and reaction thermodynamics and kinetics analyses. Our findings suggest that the PCET enhancement stimulated efficient membrane-bound enzymatic reactions related to electron-driven proton translocation and facilitated electron and proton supply for CO2 reduction to realise highly efficient methane generation. These findings are expected to provide a new insight into effective electron and proton coupling transfer for methanogenic metabolism in multiphase anaerobic environments.

Optimization of the anaerobic digestion process and the metabolic pathway of methanogenesis of Jerusalem artichoke straw with the mixed addition of iron filings and biochar

This study explored the feasibility of the mixed addition of iron filings and biochar in the anaerobic digestion of Jerusalem artichoke straw (JAS), using iron filings and biochar as mixed additives for mid-temperature batch anaerobic digestion experiments, and applied response surface methodology to investigate the interactive effects of different ratios of iron filings and biochar (FE/BC), solid content, and initial pH on the cumulative methane production from JAS. The results showed that the optimal conditions for methane production were an FE/BC of 2.45:7.55, an initial pH of 7.59, and a solid content of 8.80 %. Under these conditions, the cumulative methane production was 278.11 mL g−1 volatile solid (VS) contents, which was very close to the predicted value (286.42 mL g−1 VS), with a relative error of less than 5 %, indicating the effectiveness of the model. The optimized conditions with mixed addition (HB) exhibited good synergistic promotion, increasing cumulative methane production by 48.69 % compared to the control without additives and by 22.29 % and 29.57 % compared to the single addition of iron filings and biochar, respectively. Moreover, the HB treatment under optimized conditions achieved good economic benefits. Metagenomic analysis showed that the relative abundances of bacterial taxa including Fermentimonas, DMER64, Bacteroidetes_VadinHA17, unclassified Synergistaceae, Clostridium, Ruminiclostridium, and unclassified Anaerolineaceae were higher in HB samples, and Methanothrix was also enriched. Methane metabolism pathway analysis indicated that the anaerobic digestion of JAS with the mixed addition of iron filings and biochar enhanced the acetoclastic methane production pathway, thereby increasing methane production.

Intensification of ex-situ biomethanation in a bubble column bioreactor by addition of colonized biochips

Biological methanation is a promising sustainable energy technology. To intensify ex-situ biomethanation, a 3-L bubble column reactor was operated continuously under thermophilic conditions, with and without colonized biochips. Studies in batch reactors showed biofilm formation on biochips, with an archaea:bacteria ratio of 5.7 compared to 3.2 in planktonic phase with Methanothermobacter being the dominant archaea. Using colonized biochips in the bubble column increased methane production rate (MPR) nearly threefold, achieving a steady MPR of 15.7 ± 0.5 NLCH4/Lr.d at 84.4 ± 0.9 % methane content. Gas retention time (GRT) was 0.3 h, with 97.4 % and 96.5 % conversion of H2 and CO2, respectively. Volatile fatty acid (VFA) production was under 40 mg/L per day, indicating dominant hydrogenotrophic methanogenic (HM) pathway. The results suggest biofilm formation significantly enhances MPR in ex-situ methanation reactors, advancing towards industrial application.

Enhancing methane production from corn straw via illumination-assisted Fe3O4/g-C3N4 nanocomposite in anaerobic digestion

This study proposes a novel anaerobic digestion (AD) strategy combining recyclable photoactivated nanomaterials with illumination to enhance electronic transfer for anaerobic microorganisms. Results showed that 7000 Lux illumination increased methane production yield and rate. Incorporating Fe3O4 into graphite carbon nitride (g-C3N4) created a recyclable Fe3O4/g-C3N4 (FG) nanocomposite with improved light absorption, conductivity, redox properties, and methane promotion. The highest methane yield from corn straw was achieved with 7000 Lux and 1.5 g/L FG nanocomposite, 22.6% higher than the dark control. The AD system exhibited increased adenosine triphosphate content, improved redox performance, reduced electron transfer resistance, and higher photocurrent intensity. These improvements bolstered the microorganisms and key genes involved in hydrolysis and acidification, which in turn optimized the acetoclastic pathway. Furthermore, this strategy promoted microorganisms associated with direct interspecies electron transfer, fostering a favorable environment for methanogenic activities, paving the way for future anaerobic reactor developments.