Addition Of Conductive Materials Research Articles

Mechanisms of horizontal gene transfer and viral contribution to the fate of intracellular and extracellular antibiotic resistance genes in anaerobic digestion supplemented with conductive materials under ammonia stress

The addition of conductive materials (CMs) is an effective strategy for mitigating ammonia inhibition during anaerobic digestion (AD). However, the introduction of CMs can result in increased antibiotic resistance genes (ARGs) pollution, potentially facilitated by enhanced horizontal gene transfer (HGT). The complex dynamics of intracellular and extracellular ARGs (iARGs/eARGs) and the mechanisms underlying their transfer, mediated by CMs, in ammonia-stressed AD systems remain unclear. In this study, we investigated the effects of three commonly used CMs—nano magnetite (Mag), nano zero-valent iron (nZVI), and granular activated carbon (GAC)—on the fate of iARGs and eARGs during the AD of waste activated sludge under ammonia stress. The results revealed an unexpected enrichment of iARGs by 1.5 %–10.9 % and a reduction of eARGs by 14.1 %–25.2 % in CM-supplemented AD. This discrepancy in the dynamics of iARGs and eARGs may be attributed to changes in microbial hosts and the horizontal transfer of ARGs. Notably, CMs activated prophages within antibiotic-resistant bacteria (ARB) and their symbiotic partners involved in vitamin B12 provision, leading to the lysis of ARB and the subsequent release of eARGs for transformation. Additionally, the abundance of potentially mobile ARGs, which co-occurred with mobile genetic elements, increased by 56.6 %–134.5 % with CM addition, highlighting an enhanced potential for the HGT of ARGs. Specifically, Mag appeared to promote both transformation and conjugation processes, while nZVI only promoted conjugation. Moreover, none of the three CMs had any discernible impact on transduction. GAC proved superior to both nano Mag and nZVI in controlling the enrichment of iARGs, reducing eARGs, and limiting HGTs simultaneously. Overall, these findings provide novel insights into the role of viruses and the mechanisms of ARG spread in CM-assisted AD, offering valuable information for developing strategies to mitigate ARG pollution in practical applications.

Evaluating Biogas Production of Polylactic acid with the addition of Conductive Materials

Objectives:The demand for polylactic acid (PLA) is increasing as an alternative to conventional petroleum-based plastics due to its eco-friendly characteristics. PLA can be processed through anaerobic digestion (AD) along with other organic wastes to promote efficient and controlled biodegradation. This study aimed to evaluate the feasibility of biogas production through AD of PLA and to enhance efficiency through the addition of conductive materials.Methods:Two sets of biochemical methane potential (BMP) tests were conducted. The first BMP test involved substrate/inoculum ratios (SIRs) of 0.6, 0.8, 1.0, 1.2, 1.4, and 1.6 (g COD PLA/g COD seed sludge). Conductive materials powdered activated carbon (PAC), carbon nanotube (CNT), and Magnetite were individually added to reactors at a concentration of 3 g/L in the second test.Results and Discussion:The study revealed an increasing trend in methane production and methane yield with higher levels of PLA input. However, a decline in methane yield was observed when PLA was injected at levels surpassing 35g COD/L. This phenomenon can be attributed to a prolonged Lag phase, indicating a longer adaptation period for microorganisms, consequently resulting in a reduction of the conversion rate from 1g COD substrate to methane. The introduction of conductive material led to elevated cumulative methane production and methane yield in comparison to the control group. Notably, Magnetite exhibited the highest increase rate among the tested materials. Additionally, the addition of PAC demonstrated favorable results in terms of methane production rate at 99.4mL/L/Day and a Lag phase of 5.7 days. Conclusion:Experiments were conducted to evaluate the effects of PLA biogas production and the injection of PAC, CNT, and Magnetite at various substrate/inoculum ratios. When PLA was used as a substrate for anaerobic digestion, its feasibility was confirmed. However, it exhibited lower efficiency compared to other substrates. Therefore, the addition of a conductive material was found to increase the biogas production efficiency.

Effects of biochar, granular activated carbon, and magnetite on the electron transfer of microbials during the anaerobic digestion process: Insights into nitrogen heterocyclic compounds degradation

Anaerobic digestion (AD) of the hydrothermal liquefaction aqueous phase is often inhibited by high levels of nitrogen heterocyclics, which hinder its valorization. Despite the potential benefits of conductive materials in promoting the degradation of toxic compounds through the establishment of direct interspecies electron transfer (DIET), there is still a gap in the understanding of their role and related mechanisms in nitrogen heterocyclic degradation. In this study, the AD process was improved by the addition of conductive materials. Subsequently, the cumulative methane production increased by 7.2% (with biochar), 15.4% (with granular activated carbon), and 24.3% (with magnetite). Besides, The addition of conductive materials significantly improved the complexity and stability of the microbial communities, especially the DIET potential microorganisms—Methanosaetaceae and Syntrophobacteraceae, Anaerolineaceae, Clostridiaceae, Geobacteraceae, Desulfovibrionaceae. Thermodynamic analysis and pyridine degradation pathways further supported enhanced pyridine degradation via the addition of conductive materials.

Combined effects of various conductive materials and substrates on enhancing methane production performance

The addition of conductive materials (CMs) to anaerobic digestion (AD) has recently been receiving considerable attention as it could improve the rate of methane production through the direct interspecies electron transfer (DIET) mechanism. Although several DIETs via CMs have been studied, research directly comparing the effects of different CM additions under the same experimental conditions remains limited and no studies till date that consider the combined effects of substrate together with CM additions. In this study used three different CMs; granular activated carbon (GAC), multi-walled carbon nanotubes (MWCNT), and polyaniline (PANI) to evaluate their effect on methane production in two sets of studies, one using sodium propionate and the other using ethanol as substrates. The results showed that when sodium propionate was used, there were no changes observed in the methane production rate, despite the addition of CM. Contrastingly, when ethanol was used, methane production was enhanced, where GAC, MWCNT, and PANI were 2.3, 1.9. and 1.2 times faster than the control, respectively. Furthermore, microbial analysis indicated that when ethanol substrate was used, there was an increase in Geobacteraceae, which contributes to the DIET. The order of Geobacteraceae abundance (GAC > MWCNT > PANI > Control) corresponded with a higher rate of methane production, implicating that abundance of Geobacteraceae could directly improve the AD performance. These results show that the combined effect of substrate and CM is very important for DIET to improve AD performance, and that ethanol as substrate with GAC as CM are the most effective combination.

High-Sensitivity Composite Dual-Network Hydrogel Strain Sensor and Its Application in Intelligent Recognition and Motion Monitoring

Flexible electronic sensors are attracting more and more attention because of their outstanding flexibility and foldability. Based on this background, a composite hydrogel with excellent flexibility, good stability, and high sensitivity is prepared in this work. This high-performance hydrogel is composed of polyacrylamide, sodium alginate, MXene, and PEDOT:PSS through dynamic supramolecular cross-linking. The electrical conductivity is significantly enhanced by the addition of the conductive polymer PEDOT:PSS and MXene. Hydrogel conductivity increased by 150% with the addition of conductive materials at the same tensile strain. It exhibits high sensitivity (GF = 1.99) and excellent linearity over a wide operating range of 1000% of strain, which ensures the detection performance of the hydrogel sensor under large strain conditions. In addition, it has excellent repeatability (600 cycles) and fast response/recovery times (0.624 s/0.912 s). Due to this excellent performance, it was made into a smart sensor to explore its application in smart electronic skin. The hydrogel sensor and data acquisition module were integrated for real-time monitoring of pressure. We combine it with deep learning algorithms to provide a new solution for human motion recognition, such as joint flexion, facial expression change, health monitoring, and handwriting recognition.

Carbon, iron, and polymer-based conductive materials for improving methane production in anaerobic wastewater treatment systems: A review on their direct interspecific electron transfer mechanism

Organic compounds in wastewater have a high potential to be converted to (bio)methane (CH4) via anaerobic processes for energy recovery. Facilitating direct interspecies electron transfer (DIET) between microorganisms with the addition of conductive materials, as opposed to the conventional anaerobic biological process, has been viewed as an efficient strategy for boosting the efficiency of CH4 production. In recent years, extensive research has been conducted on the performance, mechanisms, and technical uses of conductive materials, such as carbon, iron and polymer-based materials in anaerobic wastewater treatment systems. In this review, the properties of conductive materials have been comprehensively reviewed and summarized, along with their application strategies to enhance CH4 production. In addition, the paper focuses on the methane production mechanism in anaerobic bioreactors, in the presence of carbon, iron, and polymer-based materials. The DIET theory employed for methane synthesis and the involvement of various organic wastes including ethanol, butyrate, propionate, and complex organic compounds are also elaborated upon. The prospective future research directions were also identified and stated in this review.

Enhancing anaerobic digestion of food waste with granular activated carbon immobilized with riboflavin

Previous studies have shown that anaerobic digestion of food waste can be enhanced by addition of conductive materials that stimulate direct interspecies electron transfer (DIET) between bacteria and methanogens. However, at extremely high organic loading rates (OLRs), volatile fatty acids (VFAs) still tend to accumulate even in the presence of conductive materials because of an imbalance between the formation of fermentation products and the rate of methanogenesis. In this study, granular activated carbon (GAC) immobilized with riboflavin (GAC-riboflavin) was added to an anaerobic digester treating food waste. The GAC-riboflavin reactor operated stably at OLRs as high as 11.5 kgCOD/ (m3·d) and kept VFA concentrations below 69.4 mM, COD removal efficiencies, methane production rates, and biogas methane concentrations were much higher in the GAC-riboflavin reactor than the GAC- and non-amended reactors. Transcripts associated with genes that code for proteins involved in DIET based metabolism were somewhat more highly expressed by Methanothrix in the GAC-riboflavin reactor. However, it is unlikely that riboflavin acted as an electron shuttle to stimulate DIET. Rather, it seemed to provide nutrients that enhanced the growth of microorganisms involved in the anaerobic digestion process, including those that are capable of DIET.

Carbon cloth amendment for boosting high-solids anaerobic digestion with percolate recirculation: Spatial patterns of microbial communities

The addition of conductive materials in anaerobic digestion (AD) is a promising method for boosting biomethane recovery from organic waste. However, conductive additives have rarely been investigated for the high-solids anaerobic digestion (HSAD). Here, the impact of adding carbon cloth in the solid phase of an HSAD system with percolate recirculation was investigated. Furthermore, spatial patterns of microbial communities in suspended biomass, percolate, and carbon cloth attached biofilm were assessed. Carbon cloth increased biomethane yield from source-separated organics (SSO) by 20% more than the unamended control by shortening the lag phase (by 15%) and marginally improving the methanogenesis rate constant (by ∼8%) under a batch operation for 50 days. Microbial community analysis demonstrated higher relative abundances of the archaeal population in the carbon cloth amended reactor than in unamended control (12%–21% vs. 5%–15%). Compared to percolate and suspension, carbon cloth attached microbial community showed higher enrichment of known electroactive Pseudomonas species along with Methanosarcina and Methanobacterium species, indicating the possibility of DIET-based syntrophy among these species.

Response of methanogenic granules enhanced by magnetite to ammonia stress

Excessive ammonia has an inhibitory effect on anaerobic granular sludge (AnGS) when treating industrial wastewater with high concentration of ammonia and organic matters. The addition of conductive materials has been widely reported to improve the AnGS activity, which has the potential to alleviate the ammonia inhibition. In this study, the addition of magnetite was carried out to enhance the activity of AnGS in UASB reactor, then the response of AnGS to different ammonia levels was investigated. Results showed that magnetite facilitated the enrichment of Methanosaeta and Clostridium sensu stricto 1. Under the ammonia stress (up to 5 g TAN/L), it was interesting that Methanosaeta was better retained (abundance of 45.8%), and the abundance of ammonia-resistant Clostridium sensu stricto 1 increased to 34.3% in presence of magnetite. RT-qPCR analysis revealed that Methanosaeta could maintain metabolically active for counteracting the ammonia inhibition along with the higher transcription of genes encoding for CO2-dependent pathway. The electron transport activity and ATP content of AnGS were 1.25–2.12 and 1.23–2.56 folds higher than those in the control group, respectively. In addition, the AnGS could maintain the stability of structure because Methanosaeta was the skeleton of AnGS. As a result, the analysis of enzyme activity showed that the overall methanogenic metabolism was more active, thus ensured the effective operation of UASB reactor. This study provided the scientific understanding about the role of magnetite to alleviate the ammonia inhibition, and had important implications for stable treatment and recycling of industrial wastewater.

Conductive Scaffolds for Bone Tissue Engineering: Current State and Future Outlook.

Bone tissue engineering strategies attempt to regenerate bone tissue lost due to injury or disease. Three-dimensional (3D) scaffolds maintain structural integrity and provide support, while improving tissue regeneration through amplified cellular responses between implanted materials and native tissues. Through this, scaffolds that show great osteoinductive abilities as well as desirable mechanical properties have been studied. Recently, scaffolding for engineered bone-like tissues have evolved with the use of conductive materials for increased scaffold bioactivity. These materials make use of several characteristics that have been shown to be useful in tissue engineering applications and combine them in the hope of improved cellular responses through stimulation (i.e., mechanical or electrical). With the addition of conductive materials, these bioactive synthetic bone substitutes could result in improved regeneration outcomes by reducing current factors limiting the effectiveness of existing scaffolding materials. This review seeks to overview the challenges associated with the current state of bone tissue engineering, the need to produce new grafting substitutes, and the promising future that conductive materials present towards alleviating the issues associated with bone repair and regeneration.

A new insight on improved biomethanation using graphene oxide from fermented Assam lemon waste

The present study comprises valorization of Assam lemon waste through anaerobic digestion. The uniqueness of the study lies in its process of substituting cow dung with a mixed anaerobic culture (MAC) and in evaluating the effect of graphene oxide (GO) on the fermentation process. A sequential improvement of biomethane yield was observed to be 93.86 ± 0.31, 216.54 ± 1.63, 219.64 ± 0.14 and 231.55 ± 0.27 ml/g VSfed in presence of single variable such as substrate concentration, time, GO and inoculum volume, respectively. Further optimization was carried out adopting central composite design (CCD) based response surface methodology (RSM). The maximum biomethane yield of 243.23 ± 1.99 ml/g VSfed was achieved when the solid loading was kept at 25 g TS/L, 0.06% (w/v) concentration of GO, incubated for 30 days at 37 °C which has resulted into 19.04% enhanced methane yield. Kinetic analysis exhibited lowest deviation with experimental cumulative methane yield, lowest value of λ (4.37 days) and RMSE (5.85) in modified Gompertz model. Digested biomass characterization revealed 18.46% reduction in crystallinity along with a major change in FTIR peaks. Materials and energy flow of the underlying process show 70.88% efficiency of the process with 4.96 kJ/g net energy gain. The report on AD of generated Assam lemon waste to biomethane with the intervention of GO is rare. Thus the result obtained from the current study will encourage the scientific community to improve the biomethane yield by the addition of conductive materials.

Enhancement of sludge electro-dewatering by anthracite powder modification

Electro-dewatering of sludge has received considerable attention due to its low energy consumption for sludge deep-dewatering. However, prior studies have shown the resistance of dried sludge near anode significantly hinders electro-dewatering. The dewatering performance may be improved by reducing the resistance with the addition of conductive material into sludge. We conditioned municipal sludge by anthracite powder, an inexpensive product, to increase solid conductivity, followed by electro-dewatering. After running for 20 min under a constant voltage of 30 V, when the anthracite powder mass was 10%–22% of raw sludge dry solids mass (DS), the final dry solids content of the mud cake after dehydration was 6.2%–12.9% higher than that from dehydration of unconditioned sludge. The average filtrate flow rate ranged from 0.0243 to 0.0285 g s−1. The lowest unit energy consumption, 0.19 kW h·kgwater−1, which was 14% lower than that of control, was reached when 18% DS of anthracite was added. Our theoretical analysis indicates that properly increasing solid conductivity of sludge can reduce the adverse effect caused by the high electrical resistance of sludge near anode. The experimental results, along with the theoretical analysis, show that using anthracite powder for sludge modification is an economical approach to improve sludge dewatering rate and reduce energy consumption.

Enhancing anaerobic digestion process with addition of conductive materials

Anaerobic digestion is widely used for the treatment of wastewater for its low costs and bioenergy production, but the performances of anaerobic digestion often need improving in practical applications. The addition of conductive materials could lead to direct interspecies electron transfer (DIET) among the anaerobic microorganisms, and consequently enhance the efficiencies of anaerobic digestion. In this paper, the effects of DIET via conductive materials on chemical organic demand (COD) removal, volatile fatty acid (VFA) consumption and methane production were reviewed. The reports on the increase of conductive microorganisms due to the addition of conductive materials were discussed. Results regarding activities of microorganisms and morphology and properties of sludge were described and commented, and future research needs were also proposed which included better understanding of the roles of DIET in each step of anaerobic digestion, mechanisms of metabolism of pollutants in DIET-established systems and inhibition of excessive dosage of conductive materials.

Enhancement of Anaerobic Digestion of Waste-Activated Sludge by Conductive Materials under High Volatile Fatty Acids-to-Alkalinity Ratios

Anaerobic digestion (AD) represents a suitable option for the management of the waste-activated sludge (WAS) produced in municipal wastewater treatment plants. Nevertheless, due to its complex characteristics, WAS is often barely degradable under conventional anaerobic processes. The use of conductive materials during AD provides a promising route for enhancing WAS digestion, through the effects of direct inter-species electron transfer (DIET). The present paper aims to evaluate the effects of the addition of four different materials—granular activated carbon (GAC), granular iron, and aluminium and steel scrap powders—in semi-continuous lab-scale reactors under very high volatile fatty acids-to-alkalinity ratios. In particular, the use of metallic aluminium in WAS digestion was investigated for the first time and compared to the other materials. The AD of WAS without the addition of conductive materials was impossible, while the use of steel powder and zero-valent iron is shown not to improve the digestion process in a satisfactory way. On the contrary, both GAC and Al allow for effective WAS degradation. At stable conditions, methane yields of about 230 NmLCH4/gVS and 212 NmLCH4/gVS are recorded for GAC- and Al-amended reactors, respectively. These two materials are the most promising in sustaining WAS AD through DIET also in case of unbalanced volatile fatty acids-to-alkalinity ratios.

Temporary addition of carbon fibers facilitates methanogenic degradation of ethanol during anaerobic treatment

Syntrophic methanogenesis can be improved by the addition of conductive materials. In this study, conductive carbon fibers (CFs) were applied to efficiently enrich syntrophic microorganisms with potential direct interspecies electron transfer (DIET) ability and promote methanogenic activity. With ethanol as the substrate, CFs shortened the acclimation time remarkably. The maximum methane production rate and the ethanol degradation rate of suspended biomass were increased by 40% and 68%, respectively, even when CFs were subsequently removed. However, with acetate and propionate as the mixed substrate, CFs decreased the methanogenic activity. In the reactor fed with ethanol, CFs increased the relative abundance of Geobacter, Desulfovibrio, and methanogens by 57%, 39%, and 63%, respectively. Methanosaeta possessed most methane production genes and might involve in DIET. Furthermore, CFs increased the relative abundance of ethanol-degradation genes assigned to Geobacter, Desulfovibrio and Pelobacter, suggesting the promoted ethanol-degradation. The triggered electron transport system activity and acetoclastic methanogenesis also explained the accelerated effects on ethanol-degradation by long-term acclimation with CFs. Notably, the dominance of Geobacter and Methanosaeta combined with the increased electron transfer constant in the CFs-amended ethanol reactor indicated the potential role of DIET after the removal of CFs, which deserved further clarification.

Inhibition mitigation of methanogenesis processes by conductive materials: A critical review

Methanogenesis can be promoted by the addition of conductive materials. Although stimulating effects of conductive materials on methane (CH4) production has been extensively reported, the crucial roles on recovering methanogenic activities under inhibitory conditions have not been systematically discussed. This critical review presents the current findings on the effects of conductive materials in methanogenic systems under volatile fatty acids (VFAs), ammonia, sulfate, and nano-cytotoxicity stressed conditions. Conductive materials induce fast VFAs degradation, avoiding VFAs accumulation during anaerobic digestion. Under high ammonia concentrations, conductive materials may ensure sufficient energy conservation for methanogens to maintain intracellular pH and proton balance. When encountering the competition of sulfate-reducing bacteria, conductive materials can benefit electron competitive capability of methanogens, recovering CH4 production activity. Conductive nanomaterials stimulate the excretion of extracellular polymeric substances, which can prevent cells from nano-cytotoxicity. Future perspectives about unraveling mitigation mechanisms induced by conductive materials in methanogenesis processes are further discussed.

Effect of Adding Granular Activated Carbon (GAC)/Manganese Dioxide (MnO2) for the Anaerobic Digestion of Waste Activated Sludge

The addition of conductive materials or metal oxide nanoparticles to an anaerobic system is an attractive strategy to enhance anaerobic digestion. The effect of granular activated carbon (GAC) and/or manganese dioxide (MnO2) on waste activated sludge (WAS) anaerobic digestion was investigated by batch experiments. The experiments were provided in control, GAC, MnO2, and GAC/MnO2 groups, which were named R0, R1, R2, and R3, respectively. The sludge characteristics, microbial activity, and microbial community structure were systematically investigated. Results showed that CH4 yield rate was evidently increased by 68.18% and 51.35% in R1 and R3, respectively, whereas the cumulative CH4 production decreased by 21.25% in R2, compared with R0. Moreover, the fermentation process could be promoted with the addition of GAC and/or MnO2. The phosphate precipitation generated by Mn2+ and phosphate released from WAS blocked the anaerobic metabolic channel and then decreased the production of CH4 in R2. The increase in CH4 yield rate in R3 was mainly attributed to the conductivity and adsorption of GAC and the catalysis of MnO2. Additionally, the microbial activity could be promoted with the addition of GAC, MnO2, and GAC/MnO2 in anaerobic digestion. Microbial community structure analysis showed that the abundance of the Methanobacterium and Methanosaeta increased with the addition of GAC and MnO2, which could enhance the interspecies electron transfer between fermenting bacteria and methanogens and boost fermentation and CH4 production.

Role of GAC-MnO2 catalyst for triggering the extracellular electron transfer and boosting CH4 production in syntrophic methanogenesis

The addition of conductive materials or metal oxide nanoparticles (NPs) to anaerobic systems is an attractive strategy to enhance the anaerobic digestion and the production of CH4. This study proposed a strategy to boost the CH4 production by adding granular activated carbon (GAC)-MnO2 nanocomposites into an anaerobic methanogenic system. The associated mechanisms and the microbial community structure during anaerobic digestion were investigated systematically. Compared with a control with GAC only, after adding GAC-MnO2 composite the chemical oxygen demand (COD) removal efficiency and CH4 yield were increased by 77% and 36%, respectively. The addition of GAC-MnO2 stimulated the secretion of extracellular polymeric substance (EPS), while the secretion of humic substances was inhibited. The spatial distribution of EPS in the anaerobic sludge affects the extracellular electron transfer efficiency as well. Manganese ions concentrated in the EPS layer facilitated the electron flow and, thus, accelerated the extracellular electron transfer. The enhancement of anaerobic methanogenesis can be mainly attributed to the reduction/oxidation cycle of Mn4+/Mn2+. Electron transfer system activity and Cytochrome C content reached up to 341 and 38 nmol/L, respectively, under optimal conditions. 16S rRNA gene sequencing analysis indicated that Spirochaetaceae, Cloacibacterium, and Treponema were the dominant bacteria. The abundance of the methanogenic archaea Methanobacterium and Methanosaeta were increased with the addition of GAC-MnO2.

Enhanced biomethane recovery from fat, oil, and grease through co-digestion with food waste and addition of conductive materials

In this study, the effect of conductive additives on co-digestion of fat, oil, and grease (FOG) and food waste (FW) was evaluated. Initially, biochemical methane potential (BMP) test was conducted for optimization of mixing ratio of FW and FOG. The optimal methane production (800 L (kg VS)−1) was obtained from co-digestion of 70% FW + 30% FOG (w/w), which was 1.2 times and 12 times of that obtained from mono-digestion of FW and FOG, respectively. This optimal mixing ratio was used for subsequent fed-batch studies with the addition of two conductive additives, granular activated carbon (GAC) and magnetite. The addition of GAC significantly shortened the lag phase (from 7 to 3 d), reduced accumulation of various volatile fatty acids (VFAs), and enhanced methane production rate (50–80% increase) compared to the control and magnetite-amended bioreactor. Fourier transformation infrared (FTIR) analysis suggested that the degradation of lipids, protein and carbohydrates was the highest in GAC amended reactor, followed by magnetite and control reactors. GAC addition also enriched more abundant and diverse bacteria and methanogens than control. Magnetite addition also showed similar trends but to a lesser degree. The substantial enrichment of syntrophic LCFA β-oxidizing bacteria (e.g. Syntrophomonas) and methanogenic archaea in the GAC-amended bioreactor likely attributed to the superior methanogenesis kinetics in GAC amended bioreactor. Our findings suggest that the addition of GAC could provide a sustainable strategy to enrich kinetically efficient syntrophic microbiome to favor methanogenesis kinetics in co-digestion of FW and FOG.

Novel Geobacter species and diverse methanogens contribute to enhanced methane production in media-added methanogenic reactors

To determine whether the addition of conductive materials could enhance methane production by direct interspecies electron transfer (DIET), we operated three anaerobic reactors amended with non-conductive (ceramic) or conductive materials (anthracite and granular activated carbon (GAC)). Throughout eight months of operation, ethanol was consistently detected as the major fermentation product. The specific yield in the anthracite and GAC-added reactors increased by 31.5% and 43.3%, respectively, compared to the ceramic-added reactor. 16S rRNA gene sequencing results indicated Geobacter was dominant (up to 55% of total sequences), whereas acids-degrading syntrophic bacteria were low in abundance (<2%). Using metagenomic analysis, the draft genome of the dominant Geobacter population (bin GAC1) was reconstructed and observed to possess genetic abilities of ethanol oxidation, hydrogen production, and extracellular electron transfer, and represented a phylogenetically novel Geobacter species. While Methanosaeta was the dominant methanogen, reactors containing conductive materials harbored more diverse and abundant archaeal populations, as revealed by FISH, qPCR, and metagenomics. Our findings suggested that a novel Geobacter population could oxidize ethanol and employed both hydrogen transfer and DIET depending on the accessibility of conductive materials. Thermodynamic advantages of DIET over hydrogen production could lead to enhanced methane production in reactors with conductive materials.