Bioelectrochemical Anaerobic Digestion Research Articles

Bioelectrochemical anaerobic digestion mitigates microplastic pollution and promotes methane recovery of wastewater treatment in biofilm system

Bioelectrochemical systems (BES) offer significant potential for treating refractory waste and recovering bioenergy. However, their ability to mitigate microplastic pollution in wastewater remains unexplored. This study showed that BES facilitated the treatment of polyethylene (PE), polyvinyl chloride (PVC), and Mix (PE+PVC) microplastic wastewater and the methane recovery (40.61%, 20.02%, 21.19%, respectively). The lactate dehydrogenase (LDH), adenosine triphosphate (ATP), cytochrome c, and nicotinamide adenine dinucleotide (NADH/NAD+) ratios were elevated with electrical stimulation. Moreover, the applied voltage improved the polysaccharides content of the extracellular polymeric substances (EPS) in the PE-BES but decreased in PVC-BES, while the proteins showed the opposite trend. Metatranscriptomic sequencing showed that the abundance of fermentation bacteria, acetogens, electrogens, and methanogens was greatly enhanced by applying voltage, especially at the anode. Methane metabolism was dominated by the acetoclastic methanogenic pathway, with the applied voltage promoting the enrichment of Methanothrix, resulting in the direct conversion of acetate to acetyl-CoA via acetate-CoA ligase (EC: 6.2.1.1), and increased metabolic activity in the anode. Moreover, applied voltage greatly boosted the function genes expression level related to energy metabolism, tricarboxylic acid (TCA) cycle, electron transport, and transporters on the anode biofilm. Overall, these results demonstrate that BES can mitigate microplastic pollution during wastewater treatment.

Influence of Organic Loading Rate on Methane Production from Brewery Wastewater in Bioelectrochemical Anaerobic Digestion

The effect of bioelectrochemical anaerobic digestion (BEAD) on the methanogenic performance of brewery wastewater at different organic loading rates (OLRs) was investigated and compared to conventional anaerobic digestion. A continuous BEAD reactor was used to treat brewery wastewater at different OLRs of 2, 4, 8, 16, and 20 g COD/L.d. The experimental results showed that the methane production was gradually increased from 0.48 L/L.d at an OLR of 2 g COD/L.d to 5.64 L/L.d at an OLR of 20 g COD/L.d. The methane production of the BEAD system was significantly higher than that of the conventional anaerobic reactor, indicating that BEAD has a better treatment effect for brewery wastewater. The performance of the conventional anaerobic reactor was significantly reduced especially at an OLR of 16 g COD/L.d, while the BEAD system could withstand a higher OLR. Bioelectrochemical systems provide a completely new platform for the anaerobic treatment of brewery wastewater and greatly improve the operation of anaerobic processes.

Influence of applied voltage on bioelectrochemical enhancement of biomethanation for low-rank coal and microbial community distribution

The performance of peat biomethanation was investigated in bioelectrochemical anaerobic digestion at different applied voltages, and compared to conventional anaerobic digestion. The methane yield was stabilized at 16 mL/g peat in the conventional anaerobic digestion. However, in the bioelectrochemical anaerobic digestion, the methane yield was significantly increased to 264 mL/g peat at the applied voltage of 4 V, followed by 1 V, 2 V, 0.5 V and 0 V. The bioelectrochemical system could enrich more electroactive microorganisms on the electrode, as well as in the bulk solution, and further improve the direct interspecies electron transfer for methane production. The 16S rRNA analysis showed a significant increase in the abundance of specific microorganisms in the bulk solution, including Firmicutes phylum and Proteobacteria phylum, in addition to a gradual increase in acetoclastic methanogenesis with an increase in applied voltage. These results provide a solution to turn low-rank coal into a new alternative energy.

Effect of substrates and voltages on the performance of bio-electrochemical anaerobic digestion

This research study investigates the effect of feedstock chemical composition and voltage supply on methane production from bio-electrochemical anaerobic digestion (BEAD). The experimental work was conducted on batch biomethane potential (BMP) bottles equipped with electrodes and connected to external power. Three substrates with distinct elemental compositions, waste activated sludge (WAS), and cow manure (CM), organic fraction of municipal solid waste (OFMSW), were tested under different voltages (0.7–1.5V). The BMP tests showed that OFMSW had the highest methane yield in the AD control reactors, followed by WAS and CM, which concurred with the estimated theoretical yields. Supplying voltage enhanced the performance of all BEAD reactors, but with different levels of improvement; methane yield, organics removal, and net energy efficiency increased by 7–46%, 16–54%, and 5–37%, respectively, compared to the equivalent controls. The strong relationship between the voltage and substrates with methane production was confirmed statistically through analysis of variance and t-test. Moreover, a regression model was established between the feedstock elemental fractions, power supply, and methane yield, with an adjusted correlation coefficient of 0.9 and a maximum prediction error of 5.4%. The overall findings of this research provide valuable operation and performance insights on the potential bio-electrochemical upgrades to AD systems.

Contribution analysis of different electron transfer pathways to methane production in anaerobic digestion coupled with bioelectrochemical system

The contribution analysis of different electron transfer pathways to CH4 production was investigated in bioelectrochemical anaerobic digestion (BEAD). It demonstrates that the indirect interspecies electron transfer (IIET) pathway and the direct interspecies electron transfer (DIET) pathways contributed to 41.7 % and 58.3 % of the CH4 production in the BEAD reactor, respectively. The DIET pathway was further divided into DIET via electrode (eDIET) and biological DIET (bDIET) in the bulk solution, and contributed 11.1 % and 47.2 % of CH4 production, respectively. This indicates that the dominant electron transfer pathway for CH4 production is from the bulk solution, rather than on the polarized electrode. The electroactive microorganisms were well enriched in the bulk solution by the electric field generated between anode and cathode. The enriched electroactive microorganisms significantly improved the CH4 production in the bulk solution through the bDIET pathway.

Insights into the impact of polyethylene microplastics on methane recovery from wastewater via bioelectrochemical anaerobic digestion

Bioelectrochemical anaerobic digestion (BEAD) is a promising next-generation technology for simultaneous wastewater treatment and bioenergy recovery. While knowledge on the inhibitory effect of emerging pollutants, such as microplastics, on the conventional wastewater anaerobic digestion processes is increasing, the impact of microplastics on the BEAD process remains unknown. This study shows that methane production decreased by 30.71% when adding 10 mg/L polyethylene microplastics (PE-MP) to the BEAD systems. The morphology of anaerobic granular sludge, which was the biocatalysts in the BEAD, changed with microbes shedding and granule crack when PE-MP existed. Additionally, the presence of PE-MP shifted the microbial communities, leading to a lower diversity but higher richness and tight clustering. Moreover, fewer fermentative bacteria, acetogens, and hydrogenotrophic methanogens (BEAD enhanced) grew under PE-MP stress, suggesting that PE-MP had an inhibitory effect on the methanogenic pathways. Furthermore, the abundance of genes relevant to extracellular electron transfer (omcB and mtrC) and methanogens (hupL and mcrA) decreased. The electron transfer efficiency reduced with extracellular cytochrome c down and a lower electron transfer system activity. Finally, phylogenetic investigation of communities by reconstruction of unobserved states analysis predicted the decrease of key methanogenic enzymes, including EC 1.1.1.1 (Alcohol dehydrogenase), EC 1.2.99.5 (Formylmethanofuran dehydrogenase), and EC 2.8.4.1 (Coenzyme-B sulfoethylthiotransferase). Altogether, these results provide insight into the inhibition mechanism of microplastics in wastewater methane recovery and further optimisation of the BEAD process.

Promoting direct interspecies electron transfer for methane production in bioelectrochemical anaerobic digestion: Impact of electrode surface area and switching circuit

The bioelectrochemical enhancement of direct interspecies electron transfer (DIET) for methane production was investigated in a UASB reactor under different electrode surface areas. The specific methane production rate is stabilized at 316.7 mL/g COD in the bioelectrochemical UASB (BUASB) reactor with an electrode surface area of 10 m2/m3, which is significantly higher than the 216.8 mL/g COD of the UASB reactor. The electroactive bacteria, involved in the DIET for methane production, is signifianctly increased in the BUASB reactor. When the electrode surface area is expanded to (20 and 30) m2/m3, the specific methane production rates in the BUASB reactor are further increased to (358.4 and 361.0) mL/g COD, respectively (p-value > 0.05). The theoretical methane production from the electrode surface is approximate 3.1% of the total methane production in all BUASB reactors, and the bioelectrochemical methane production is mainly attributed to the biological DIET pathway (54%) in the bulk solution. The BUASB reactor at the electrode surface area of 20 m2/m3 showes better performance according to the methane production, process stability, and enrichment of electroactive microorganisms. The bioelectrochemical system provides a new platform that can dramatically improve the performance of UASB process for treating brewery wastewater.

Electrifying anaerobic granular sludge for enhanced waste anaerobic digestion and biogas production

Bioelectrochemical anaerobic digestion (BEAD) is an attractive way to enhance biogas production in the anaerobic digestion process. Exploring cost-effective biocatalysts with remarkable catalytic ability is a pivotal issue for the industrial application of BEAD systems. In this study, intact anaerobic granular sludge (AGS) was employed as a biocatalyst in an attempt to achieve high-efficiency CH4 production via interactions between exoelectrogens and methanogens. The biogas production in the BEAD system was optimized by controlling the applied voltage (0, 0.6, 0.8, and 1 V) and acetate load (1000, 5000, and 10000 mg/L). The CH4 production rate increased with applied voltage and acetate loading, while the overall energy efficiency was the highest at an applied voltage of 0.8 V and an acetate load of 5000 mg/L. The BEAD system with AGS as the biocatalyst was also efficient for the degradation of highly concentrated organic waste, with an average methane production rate of 86.23 ± 7.12 L/m2/d and CH4 content as high as 88.87%. Microbial communities including organic-degrading bacteria and exoelectrogens (e.g., Syntrophomonas, Geobacter) and hydrogenotrophic methanogenic archaea (r.g., Methanobacterium) were enriched at the anode and the cathode, respectively. The AGS-based BEAD system represents a promising industrial application in biogas production.

Performance of bioelectrode based on different carbon materials in bioelectrochemical anaerobic digestion for methanation of maize straw

The performance of the bioelectrochemical anaerobic digestion (BEAD) reactor was investigated with different carbon material-modified electrodes for the methanation of maize straw. The carbon material-modified electrodes used titanium (Ti) mesh modified with carbon nanotube (CNT), carbon black (CB), and activated carbon (AC). The maximum cumulative methane production obtained in the Ti–CNT reactor was (616.4 ± 9.3) mL/g VS, while the maximum methane production rate in the Ti–AC reactor was (61.9 ± 1.0) mL/g VS.d.The electroactive bacteria were well enriched by the different electrodes, and the enriched electroactive bacteria further facilitate the direct interspecies electron transfer (DIET) for methane production. Additionally, we found the phylum Firmicutes showed a linear relationship to methanogenic performance, as well as the Genus Proteiniborus. The Ti–CNT electrode shows better performance by the electrochemical analysis. These findings provide critical knowledge for the large-scale use of the BEAD process and the treatment of maize straw.

Application of Various Machine Learning Models for Process Stability of Bio-Electrochemical Anaerobic Digestion

The application of a machine learning (ML) model to bio-electrochemical anaerobic digestion (BEAD) is a future-oriented approach for improving process stability by predicting performances that have nonlinear relationships with various operational parameters. Five ML models, which included tree-, regression-, and neural network-based algorithms, were applied to predict the methane yield in BEAD reactor. The results showed that various 1-step ahead ML models, which utilized prior data of BEAD performances, could enhance prediction accuracy. In addition, 1-step ahead with retraining algorithm could improve prediction accuracy by 37.3% compared with the conventional multi-step ahead algorithm. The improvement was particularly noteworthy in tree- and regression-based ML models. Moreover, 1-step ahead with retraining algorithm showed high potential of achieving efficient prediction using pH as a single input data, which is plausibly an easier monitoring parameter compared with the other parameters required in bioprocess models.

Performance of Bioelectrode Based on Different Carbon Materials in Bioelectrochemical Anaerobic Digestion for the Methanation of Maize Straw

Performance of Bioelectrode Based on Different Carbon Materials in Bioelectrochemical Anaerobic Digestion for the Methanation of Maize Straw

Performance of Bioelectrode Based on Different Carbon Materials in Bioelectrochemical Anaerobic Digestion for Methanation of Maize Straw

Performance of Bioelectrode Based on Different Carbon Materials in Bioelectrochemical Anaerobic Digestion for Methanation of Maize Straw

Bioelectrochemical Enhancement of Methanogenic Metabolism in Anaerobic Digestion of Food Waste Under Salt Stress Conditions

Bioelectrochemical anaerobic digestion, a promising concept, has been proven to improve anaerobic digestion (AD) performance in methane production. However, it has been challenged by the unstable performances attributed to high-salt stress in food waste (FW). In this study, an Fe anode-assisted bioelectrochemical anaerobic digester (R1) was proposed to facilitate FW treatment. Batch experiments were conducted under different salt stresses to understand the impact of Fe-carbon microbial electrolysis cells on the performance of AD of FW. The results indicated that R1 achieved the highest specific methane yield of 0.15 L/g VS·day–1 as compared with the controls after being exposed to 20 g/L Na+. As demonstrated from metagenomic and metaproteomics analysis, the gene abundance and enzyme activity of salt-tolerant microbial communities were improved with the presence of an Fe anode in AD, which might be achieved by participating in the biosynthesis of key kinases or altering the metabolic pathways of cells. Methanothrix, a dominant species of salt-tolerant methanogenic archaea, could rely on CO2 reduction by using iron electrodes as an electron contact to facilitate methane metabolism. The enzyme of sodium transport ATPase 5 capability in excreting Na+ from the cell and regulating the cell penetration was enriched in R1, thereby significantly improving the salt tolerance under high salinities.

Design Configurations and Operating Parameters of Bio-electrochemically Enhanced Anaerobic Digestion

Bio-electrochemical anaerobic digestion (AD) is one of the most recent advancement in anaerobic treatment processes. Microbial electrolysis cells (MECs) are used for bio-electrochemical treatment, where the supplied external power is used to enhance the performance of AD. Multiple studies have investigated the viability of MECs under various operating parameters and for different organic wastes. The present paper aims at reviewing the latest literature regarding bio-electrochemical enhanced AD through MECs. It was concluded that MEC reactors significantly enhance AD performance under different supplied voltages, temperatures, electrodes configuration, as well as other operating parameters. Based on the compiled literature, further comprehensive life cycle assessment of MECs is recommended prior to any full-scale implementation.

Effects of voltage supply on the methane production rates and pathways in an anaerobic digestion reactor using different electron donors

The effects of voltage on the methane production rate (k) of various types of anaerobic sludge biomasses are quantitatively demonstrated. Voltage is supplied to the anaerobic digestion (AD) sludges independently and quickly improves the methane production rates and specific methanogenic activities (SMAs), regardless of bio-electrochemical activation of the sludge. This supports previous findings that bio-electrochemical AD (BEAD) shows higher stabilization and methane production rates than those of AD. However, in reactors fed with H2/CO2, SMA and k are not significantly increased by the voltage supply, indicating that direct electron transfer for hydrogenotrophic methanogenesis is not a major methane formation pathway. The voltage supply contributed to indirect electron transfer for H2 production. Therefore, indirect electron transfer via H2 is a significant factor in hydrogenotrophic methanogenesis. These findings indicate changes in the general pathways of AD achieved using a voltage supply and provide a better understanding of previous BEAD studies.

Carbon-based electrode fabrication and performance of bioelectrochemical anaerobic digestion for sewage sludge

Carbon-based electrode fabrication and performance of bioelectrochemical anaerobic digestion for sewage sludge

Effect of a side-stream voltage supplied by sludge recirculation to an anaerobic digestion reactor

This study showed that side stream voltage supplied by sludge recirculation from an auxiliary bio-electrochemical anaerobic digestion (ABEAD) reactor appears to have a similar effect as main stream voltage supply to an anaerobic digestion (AD) reactor. The increased sludge recirculation rate enhanced the operation stability at a high OLR. H2-producing bacterial community was improved in bio-electrochemical anaerobic digestion (BEAD) and ABEAD reactors and was increased with increase in sludge recirculation rate. Despite the dominance of hydrogenotrophic methanogens in all reactors, high operational performances of BEAD and ABEAD reactors supports the results of H2-producing bacteria increase in those reactors. The ABEAD reactors having 1/7 of the capacity of the main AD reactor showed possibility of integration of BEAD technology into new and existing facilities economically. The findings of this study would provide useful information for approaching the commercialization of BEAD and suggest direction of further research for practical applications.

Changes of Bacterial Communities in an Anaerobic Digestion and a Bio-Electrochemical Anaerobic Digestion Reactors According to Organic Load

Bacterial communities change in bulk solution of anaerobic digestion (AD) and bio-electrochemical anaerobic digestion reactors (BEAD) were monitored at each organic loading rate (OLR) to investigate the effect of voltage supply on bacterial species change in bulk solution. Chemical oxygen demand (COD) degradation and methane production from AD and BEAD reactors were also analyzed by gradually increasing food waste OLR. The BEAD reactor maintained stable COD removal and methane production at 6.0 kg/m3·d. The maximum OLR of AD reactor for optimal operation was 4.0 kg/m3·d. pH and alkalinity decline and volatile fatty acid (VFA) accumulation, which are the problem in high load anaerobic digestion of readily decomposable food wastes, were again the major factors destroying the optimal operation condition of the AD reactor at 6.0 kg/m3·d. Contrarily, the electrochemically activated dense communities of exoelectrogenic bacteria and VFA-oxidizing bacteria prevented VFAs from accumulating inside the BEAD reactor. This maintained stable pH and alkalinity conditions, ultimately contributing to stable methane production.

Enhanced methane production from acetate intermediate by bioelectrochemical anaerobic digestion at optimal applied voltages

Bioelectrochemical anaerobic digestion of acetate, the main intermediate product in anaerobic digestion of methane, was evaluated at different applied voltages (0.5, 1.0 and 1.5 V) in comparison to the control (without electrodes). At 1.0 V, the maximum methane yield (0.351 L CH4·g−1 COD) and soluble chemical oxygen demand removal (83.6% SCOD) were observed with an acetate concentration of 2 g L−1. These values were 2.1 and 1.5 times higher than in the control reactor (0.167 L CH4·g−1 COD and 54% SCOD), respectively. At the applied voltages of 0.5 and 1.5 V, lower efficiency of methane production was observed due to insufficient potential drive and high-voltage inhibition, respectively, although the methane yields were still higher than that of the control. The maximum current generation of 19.5 mA was obtained at 1.0 V condition, suggesting that a high electron transport rate was closely related to higher methane production. The lower Tafel slopes and polarization resistances indicated better bioelectrochemical anaerobic digestion performance with enhanced redox reactions and low electron transfer resistances.

미생물 전기화학적 혐기성소화에서 메탄의 발생량, 함량, 수율에 대한 연구

미생물 전기화학적 혐기성소화에서 메탄의 발생량, 함량, 수율에 대한 연구