Search

Anaerobic processes are widely used for treating high-strength organic wastewater. Understanding the ecological patterns of the microorganisms involved and the effect of environmental factors on microbial community are important to manage the performance of anaerobic processes. Microbial communities of 12 anaerobic sludge samples acclimated under different environmental conditions were investigated. Genera detected from these anaerobic sludge samples generally presented three distribution patterns: frequently detected with high abundance, frequently detected with low abundance and occasionally detected with permanently low abundance. The type of feed stock was one of the most important process parameters affecting the shape of microbial community (e.g., Syntrophus, Methylomonas and Methylobacillus). Dye wastewater (Bacteroides) and the supplement of conductive materials (genus T78) were also found to shape the microbial community. Some syntrophic bacteria and methanogens were rare in many anaerobic samples. However, correlation analysis suggested that rare genera are potential syntrophic partners and are responsible for syntrophic methanogenesis. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sulfate removal percentages were 99–49% at COD/SO 4 2− ratios from 2 to 0.67. • Acetate was accumulated and propionate was rapidly utilized by SRB. • Propionate was degraded through pyruvate & propanoate metabolism pathway. • Incomplete oxidizing SRB were superior to complete oxidizing SRB. • Pseudomonas and Desulfobulbu s could potentially participate in DIET. Abstract Sulfate influences the organics removal and methanogenic performance during anaerobic wastewater treatment. System performance, microbial community and metabolic pathways in ethanol-fed anaerobic reactors were investigated under different COD/SO 4 2− ratios (2, 1 and 0.67) and control without sulfate addition. The sulfate removal percentages declined (99%, 60% and 49%) with decreasing COD/SO 4 2− ratios, and methanogenesis was completely inhibited. Acetate accumulated to 903–734 mg/L, though propionate was constantly lower than 30 mg/L. Without sulfate, acetate and propionate did not accumulate, despite the extended time for propionate degradation. Incomplete oxidizing sulfate reducing bacteria (Desulfobulbus and Desulfomicrobium) and hydrolysis-acidification genera (Treponema and Bacteroidales) predominated but could not degrade acetate. Desulfobulbus was the key genus for propionate degradation through the pyruvate & propanoate metabolism pathway. Pseudomonas and Desulfobulbu s, possessing genes encoding Type IV pili and cytochrome c6 OmcF, respectively, potentially participated in the direct interspecies electron transfer in sulfate-rich conditions. [ABSTRACT FROM AUTHOR]

Abstract Dye wastewater is one kind of refractory pollutant and it is commonly treated by the integrated anaerobic and aerobic process. A new integrated hydrolysis/acidification and multiple anoxic/aerobic (AO) process was proposed for the removal of color and nitrogen from azo dye wastewater. System performance, the degradation pathway of azo dye and nitrogen metabolic pathway were investigated with quadrupole-time-of-flight and metagenomic analyses. The proposed process removed color and nitrogen efficiently, with the removal percentages of 89.4% and 54.0%, respectively. A colorful intermediate C 16 H 11 N 3 O 7 S 2 during the degradation of azo dye was detected. Controlling a low dissolved oxygen concentration in the multiple AO process could enhance nitrogen removal. The detected bacteria possessing azoreductase for the azo dye degradation included Desulfovibrio aminophilus , Thermoanaerobacter , Lactococcus raffinolactis , Ruminiclostridium and Rhodopirellula. The nitrifying genes of amo and hao were mainly detected in Nitrosomonas , while the denitrifying genes were detected in Thauera, Candidatus Accumulibacte r and Rhodothermus marinus. Highlights • Hydrolysis/acidification and multiple AO process removed color and N effectively. • The color removal efficiency was enhanced under high COD concentrations. • Low DO in the multiple AO reactor induced high nitrogen removal. • A colorful intermediate was detected during RR2 degradation. • Microbial communities were analyzed by high throughput sequencing and metagenomics. [ABSTRACT FROM AUTHOR]

Abstract Long-term exposure of nitrifiers to high concentrations of free ammonia (FA) and free nitrous acid (FNA) may affect nitrifiers activity and nitrous oxide (N 2 O) emission. Two sequencing batch reactors (SBRs) were operated at influent ammonium nitrogen (NH 4 -N) concentrations of 800 mg/L (SBR H) and 335 mg/L (SBR L), respectively. The NH 4 -N removal rates in SBR H and SBR L were around 2.4 and 1.0 g/L/day with the nitritation efficiencies of 99.3% and 95.7%, respectively. In the simulated SBR cycle, the N 2 O emission factors were 1.61% in SBR H and 2.30% in SBR L. N 2 O emission was affected slightly by FA with the emission factor of 0.22%–0.65%, while N 2 O emission increased with increasing FNA concentrations with the emission factor of 0.22%–0.96%. The dominant ammonia oxidizing bacteria (AOB) were Nitrosomonas spp. in both reactors, and their relative proportions were 38.89% in SBR H and 13.36% in SBR L. Within the AOB genus, a species (i.e. , operational taxonomic unit [OTU] 76) that was phylogenetically identical to Nitrosomonas europaea accounted for 99.07% and 82.04% in SBR H and SBR L , respectively. Additionally, OTU 215, which was related to Nitrosomonas stercoris , accounted for 16.77% of the AOB in SBR L. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Effect of dosing ferroferric oxide (Fe 3 O 4 ) on the anaerobic treatment of azo dye Reactive Red 2 (RR2) was investigated in two anaerobic sequencing batch reactors (ASBRs). System performance, dye degradation pathways, and microbial activities and structure were examined. The addition of Fe 3 O 4 significantly improved treatment efficiency, with the removal efficiency of RR2 increased by 116%, the maximum methane (CH 4 ) yield potential and the peak CH 4 production rate improved by 7.7% and 22.3%, and the lag phase shortened by 39.6%, respectively. The activity of the electron transport system was significantly enhanced by dosing Fe 3 O 4 , with the maximum value increased by 77% and conductivity of the anaerobic sludge increased by 178%. According to the proposed pathway for the degradation of RR2, the degradation products from complete cleavage of the N N bond in RR2 were obtained at the presence of Fe 3 O 4 , while were absent without Fe 3 O 4 . At high initial dye concentrations, the dosage of Fe 3 O 4 alleviated the inhibition to microbes by RR2, and high degradation rate and removal efficiency were maintained. The microbial community structure changed during the long-term acclimation with the dosage of Fe 3 O 4 . Paludibacter , Trichococcus and Methanosarcina were predominant and their relative abundances increased with the addition of Fe 3 O 4 . [ABSTRACT FROM AUTHOR]

Direct interspecies electron transfer (DIET) is a new mechanism responsible for syntrophic methane production. Supplementation of conductive material in syntrophic communities can facilitate electron transfer and enhance methane production. Ferroferric oxide (Fe 3 O 4 ) was dosed in an anaerobic sequencing batch reactor (ASBR) fed with tryptone-based synthetic wastewater to examine its effect on the anaerobic treatment process. Long-term dosage of Fe 3 O 4 not only enhanced the maximum methane production rate by 78.3% in a reaction cycle but also improved methane production when hydrogen/carbon dioxide or acetate was used as the substrate. The conductivity of anaerobic sludge, activity of the electron transport chain, and extracellular electron transfer ability were enhanced with the addition of Fe 3 O 4 , inducing enhanced system performance for methane production. Proteiniclasticum and Prolixibacter were the enriched acidogens responsible for hydrolysis and acidification. With the addition of Fe 3 O 4 , Methanosarcina was the dominant methanogen, and metagenomic analysis further revealed the genes involved in the hydrogenotrophic pathway of methanogenesis. Methanosarcina might be involved in DIET, and Fe 3 O 4 was responsible for its stimulation. [ABSTRACT FROM AUTHOR]

Conductive materials can facilitate syntrophic methane (CH) production by improving direct interspecies electron transfer. The effect of a conductive material, ferroferric oxide (FeO), on the anaerobic treatment of tryptone-based high-strength wastewater was investigated in two anaerobic sequencing batch reactors (ASBRs). One was the control reactor without amendment of FeO, and the other was the FeO-amended reactor. In an ASBR reaction cycle, the dosage of FeO increased the CH production rate by 12.2%, shortened the methanogenic lag phase by 32.3%, and improved the COD removal rate by 8.1%. During anaerobic treatment, the dosage of FeO not only enhanced the CH production from acetate but also facilitated the hydrolysis/acidification process fed by tryptone. Maximum electron transport activities were increased by 40.4, 137.3, and 64.6% in the processes of the ASBR reaction cycle, the CH production from acetate, and the hydrolysis/acidification of tryptone, respectively. Among all tested quorum sensing signal substances, N-octanoyl- l-homoserine lactone was dominant in both ASBRs, with the highest concentration in the biomass and the lowest concentration in the water phase. In addition, the concentration of signal substance was high in the ASBR cycle and low in the CH production from acetate and the hydrolysis/acidification of tryptone. Proteiniclasticum and vadinCA02 were dominant acidogens, and their relative abundances increased during the long-term operation with FeO dosing. Methanosarcina was the predominant methanogen, contributing to interspecies electron transfer. [ABSTRACT FROM AUTHOR]

Conductive materials can enhance direct interspecies electron transfer (DIET) during the anaerobic treatment of wastewater and provide ecological advantages for syntrophic methane (CH 4 ) production. The effects of ferroferric oxide (Fe 3 O 4 ) on the system performance and microbial communities were examined during the anaerobic treatment of synthetic wastewater with mixed organic carbon. The addition of Fe 3 O 4 did not enhance the relative abundance of methanogens, but increased the maximum CH 4 production rate by 15.4% and shortened the lag phase by 13.9%. Methanosarcina was the predominant methanogen contributing to DIET. Proteiniclasticum and Kosmotoga were dominant upon the addition of Fe 3 O 4 and were responsible for protein degradation. More extracellular proteins were produced and a filamentous morphology was observed upon the addition of Fe 3 O 4 . Short-term Fe 3 O 4 addition also improved the performance of the anaerobic treatment in the control reactor, and the Fe 3 O 4 rather than the microbial morphology was the more important factor enhancing DIET. [ABSTRACT FROM AUTHOR]

[Display omitted] • Contents of essential amino acids in microbial aggregates were determined. • The concentration of amino acids markedly varied in different samples. • Glutamic acid, lysine, and alanine was the top 3 most abundant amino acids. • Several syntrophic bacteria and methanogens cannot produce all amino acids. • Amino acids cross-feeding might exist between syntrophs and methanogens. Anaerobic digestion is a prevalent bioenergy production process relying on a complex network of symbiotic interactions, where the nutrient based cross-feeding is an essential microbial mechanism. Here, the cross-feeding function was assessed by analyzing extracellular polymeric substances-associated amino acids in microbial aggregates collected from 14 lab-scale anaerobic digesters, as well as deciphering their genetically biosynthetic potential by syntrophic bacteria and methanogens. The total concentration of essential amino acids ranged from 1.2 mg/g VSS to 174.0 mg/g VSS. The percentages of glutamic acid (8.5 ∼ 37.6%), lysine (2.7 ∼ 22.6%), alanine (5.6 ∼ 13.2%), and valine (3.0 ∼ 10.4%) to the total amount of detected amino acids were the highest in most samples. Through metagenomics analysis, several investigated syntrophs (i.e., Smithella , Syntrophobacter , Syntrophomonas , and Mesotoga) and methanogens (i.e., Methanothrix and Methanosarcina) were auxotrophies, but the genetic ability of syntrophs and methanogens to synthesize some essential amino acids could be complementary, implying potential cross-feeding partnership. [ABSTRACT FROM AUTHOR]

During anaerobic digestion, methanogenic activities and pathways can be affected by intermediates. Here, the effects of intermediates acetate, propionate, and ethanol on methanogenesis were investigated. Four anaerobic sequencing batch reactors were acclimated with propionate (ASBR_P), ethanol/propionate (ASBR_EP), acetate/propionate (ASBR_AP), and ethanol/acetate/propionate (ASBR_EAP). Ethanol was the easiest one to be biodegraded, thereby enhancing the maximum methane production rate and shortening the lag phase, while the longest acclimation time and lowest methane production rate were observed in ASBR_P. Different microbial communities and syntrophic patterns existed in four reactors. Desulfovibrio and Geobacter were the dominant ethanol-oxidizing bacteria in ASBR_EP and ASBR_EAP, respectively. Both Desulfovibrio and Geobacter possessed the potential of extracellular electron transfer, which might be the advantage of ethanol dosage for enhancing methanogenesis through direct interspecies electron transfer. Methanosarcina was enriched in ASBR_P and ASBR_AP, while Methanosaeta in ASBR_EP and ASBR_EAP. Genes responsible for acetoclastic methanogenesis were significantly enriched in ASBR_EAP, possibly resulting in the highest methanogenic activity from acetate. Results from this study will advance the optimization of practical anaerobic systems, which can be achieved by regulating the intermediates with different fermenting pathways. • Organics affected methanogenic activity and microbial community significantly. • Ethanol could enhance the CH 4 production rate and reduce the lag phase efficiently. • Types of VFAs affected the enriched ethanol oxidizing Desulfovibrio and Geobacter. • Ethanol might affect VFA degradation by influencing the acclimated microorganisms. • The contribution of ethanol to methanogenesis should be evaluated comprehensively. [ABSTRACT FROM AUTHOR]

• Stable operation of anammox was achieved with the intermittent addition of VFAs. • Reproduction of denitrifiers was suppressed by intermittent dosing organic carbon. • Anammox bacteria showed low activities with VFAs but without inorganic carbon. • Ca. Kuenenia interacted with Thauera in both nitrogen and carbon metabolisms. • Amino acids and vitamins cross-feeding existed between Ca. Kuenenia and Thauera. Organic carbon can affect nitrogen removal in the anaerobic ammonia oxidation (anammox) process. Two continuous up-flow anaerobic sludge blanket (UASB) reactors were operated under autotrophic (UASB N , without organic carbon) and mixotrophic (UASB CN , with the intermittent addition of acetate and propionate) conditions. Stable operation of anammox systems was achieved, with the nitrogen removal rate and percentage of 2.12 g/(L·d) and 86.4% in UASB N , and 2.09 g/(L·d) and 85.0% in UASB CN , respectively. The network of Candidatus Kuenenia , Thauera , and Nitrosomanas contributed to both nitrogen and carbon metabolisms, and the intermittent addition of acetate and propionate strengthened Ca. Kuenenia 's ability to utilize several types of carbon sources. Anammox bacteria showed activity in the presence of organic carbon and without inorganic carbon, confirming the mixotrophic characteristic of Ca. Kuenenia. Cross-feeding of amino acids and vitamins existed among functional microorganisms, with extracellular polymeric substances acting as the media for microbial interactions. [ABSTRACT FROM AUTHOR]

• Methanogenic inhibition mitigation by conductive materials was reviewed. • pH could be maintained by enhancing organic degradation with conductive materials. • Conductive materials ensured energy supply of methanogens for anti-ammonia inhibition. • Methanogens competition in sulfate-rich conditions was enhanced by conductive materials. • Extracellular polymeric substances were promoted for nano-cytotoxicity resistance. Methanogenesis can be promoted by the addition of conductive materials. Although stimulating effects of conductive materials on methane (CH 4) 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 CH 4 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. [ABSTRACT FROM AUTHOR]

• This study clarified the co-occurrence network of syntrophs and methanogens. • Diverse quorum sensing genes were detected in all anaerobic sludge samples. • Two quorum sensing signals are suggested to impact the regulation of type IV pili. • Environmental factors significantly affected the syntrophic patterns. Interspecies electron transfer plays an important role in syntrophic methanogenesis. Direct interspecies electron transfer (DIET) between syntrophic oxidizers and methanogens via conductive pili has been only confirmed in some specific co-cultures. This study examined potential syntrophic cooperation via type IV pili and quorum sensing between widespread syntrophic bacteria and methanogens through a metagenomic analysis of 12 anaerobic sludge samples. We found that Methanosaeta and Methanosarcina , which are reported to have DIET ability, were dominant in most methanogenic samples. Putative conductive pili genes were found in some typical syntrophic bacteria, which has rarely been reported previously. The existence of diverse quorum-sensing genes suggested that various quorum-sensing systems might participate in the communication of anaerobic microorganisms. Specifically, the diffusible signal factor and 3′-5′ cyclic diguanosine monophosphate related genes were mainly assigned to syntrophic bacteria. These results suggest that the combined regulation of these signals might be responsible for the biosynthesis of type IV pili and affect syntrophic interaction during methanogenesis. These novel results provide fresh evidence to support the widespread existence of DIET in anaerobic methanogenic systems; therefore, regulating the quorum-sensing system may promote syntrophic interaction. [ABSTRACT FROM AUTHOR]

Direct interspecies electron transfer (DIET) via electrically conductive pili (e-pili) and c-type cytochrome between acetogens and methanogens has been proposed as an essential pathway for methane production. Supplements of conductive materials have been extensively found to promote methane production in microbial anaerobic treatment systems. This review comprehensively presents recent findings of DIET and the addition of conductive materials for methanogenesis and summarizes important results through aspects of electron flux, organic degradation, and microbial interaction. Conductive materials improve DIET and methanogenesis by acting as either substitute of e-pili or electron conduit between e-pili and electron acceptors. Other effects of conductive materials such as the change of redox potential may also be important factors for the stimulation. The type and organic loading rate of substrates affect the occurrence of DIET and stimulating effects of conductive materials. Geobacter , which can participate in DIET, were less enriched in anaerobic systems cultivated with non-ethanol substrates, suggesting the existence of other syntrophs with the capability of DIET. The coupling of communication systems such as quorum sensing may be a good strategy to achieve the formation of biofilm or granule enriched with syntrophic partners capable of DIET. • Conductive materials facilitate DIET with different mechanisms. • Organic substrates affect stimulating effects of conductive materials on DIET. • DIET syntrophs are expanding with the application of bioinformatic techniques. • Coupling quorum sensing systems may be good to enrich DIET syntrophs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The r-/K-selection theory was applied to anaerobic digestion with sulfate reduction. • The rapid-filling mode enabled reactors to exhibit a fast reaction rate. • The operational mode altered the ethanol metabolic pathway. • The effect of operational mode on bioreactors depended on types of organic carbon. • R-strategists Desulfomicrobium and K-strategists Geobacter were enriched. Anaerobic digestion (AD) is promising for treating high-strength wastewater. However, the effect of operational parameters on microbial communities of AD with sulfate is not yet fully understood. To explore this, four reactors were operated under rapid- and slow-filling modes with different organic carbons. Reactors in the rapid-filling mode generally exhibited a fast kinetic property. For example, the degradation of ethanol was 4.6 times faster in ASBR ER than in ASBR ES , and the degradation of acetate was 11.2 times faster in ASBR AR than in ASBR AS. Nevertheless, reactors in the slow-filling mode could mitigate propionate accumulation when using ethanol as organic carbon. Taxonomic and functional analysis further supported that rapid- and slow-filling modes were suitable for the growth of r-strategists (e.g., Desulfomicrobium) and K-strategists (e.g., Geobacter), respectively. Overall, this study provides valuable insights into microbial interactions of AD processes with sulfate through the application of the r/K selection theory. [ABSTRACT FROM AUTHOR]

The detection of acyl homoserine lactones (AHLs) in activated sludge is essential for clarifying their function in wastewater treatment processes. An LC–MS/MS method was developed for the detection of AHLs in both the aqueous and solid phases of activated sludge. In addition, the effects of proteases and extracellular polymeric substances (EPS) on the detection of AHLs were evaluated by adding protease inhibitors and extracting EPS, respectively. Recoveries of each AHL were improved by adding 50 μL of protease inhibitor, and recoveries were also improved from 0 to 56.9% to 24.2%–105.8% by EPS extraction. Applying the developed method to determine the type and concentration of AHLs showed that C 4 -HSL, C 6 -HSL, C 8 -HSL and 3-oxo-C 8 -HSL were widely detected in a suspended activated sludge system. The dominant AHL was C 8 -HSL, with a highest concentration of 304.3 ng/L. C 4 -HSL was mainly distributed in the aqueous phase, whereas C 6 -HSL, C 8 -HSL and 3-oxo-C 8 -HSL were preferentially distributed in the sludge phase. [ABSTRACT FROM AUTHOR]

In this study, the effects of four types of organic compounds (tryptone, acetate/propionate, glucose and ethanol) on methanogenesis, electron transfer processes and microbial community structure were examined. When tryptone and acetate/propionate were used, the dominant methanogenic pathway was aceticlastic methanogenesis and Methanosarcina was the most abundant methanogen. When glucose or ethanol were provided as the external carbon source, the aceticlastic and hydrogenotrophic pathways were utilised simultaneously, and Methanosarcina and Methanobacterium were enriched. However, the reactor fed with glucose was prone to acidification because volatile fatty acids accumulated in the medium, which inhibited methane synthesis. Geobacter was dominant in the reactor fed with ethanol and 45% of genes encoding pili synthesis were attributable to Geobacter , indicating that direct interspecies electron transfer may be a possible mechanism during syntrophic methanogenesis. [ABSTRACT FROM AUTHOR]

Mechanistic understanding of acetoclastic methanogenesis is pivotal for optimizing anaerobic digestion for efficient methane production. In this study, two different operational modes, continuous flow reactor (CFR) and sequencing batch reactor (SBR), accompanied with solids retention times (SRT) of 10 days (SBR 10d and CFR 10d) and 25 days (SBR 25d and CFR 25d) were implemented to elucidate their impacts on microbial communities and energy metabolism of methanogens in acetate-fed systems. Microbial community analysis revealed that the relative abundance of Methanosarcina (16.0%–46.0%) surpassed Methanothrix (3.7%–22.9%) in each reactor. SBRs had the potential to enrich both Methanothrix and Methanosarcina. Compared to SBRs, CFRs had lower total relative abundance of methanogens. Methanosarcina exhibited a superior enrichment in reactors with 10-day SRT, while Methanothrix preferred to be acclimated in reactors with 25-day SRT. The operational mode and SRT were also observed to affect the distribution of acetate-utilizing bacteria, including Pseudomonas , Desulfocurvus , Mesotoga , and Thauera. Regarding enzymes involved in energy metabolism, Ech and Vho/Vht demonstrated higher relative abundances at 10-day SRT compared to 25-day SRT, whereas Fpo and MtrA-H showed higher relative abundances in SBRs than those in CFRs. The relative abundance of genes encoding ATPase harbored by Methanothrix was higher than Methanosarcina at 25-day SRT. Additionally, the relative abundance of V/A-type ATPase (typically for methanogens) was observed higher in SBRs compared to CFRs, while the F-type ATPase (typically for bacteria) exhibited higher relative abundance in CFRs than that in SBRs. [Display omitted] • Reduction in SMR shortened the lag phase in acetoclastic methanogenesis. • SBRs with 25-day SRT tend to enrich both Methanosarcina and Methanothrix. • SRT of 10 days benefited the enrichment of Methanosarcina , particularly in SBR. • The V/A-type and F-type ATPase were mainly affected by operational modes. [ABSTRACT FROM AUTHOR]

Some microorganisms with the nitrification function can carry out nitrogen conversion under oxygen-limited conditions. In this study, a continuous-flow biofilm reactor was operated to investigate the removal of ammonium nitrogen (NH4-N) under microaerobic or anoxic conditions. After more than 100 days of long-term operation, the NH4-N removal rate and removal percentage reached 2.92 mg/(L·h) and 72.3%, respectively. In the batch experiments, NH4-N removal was achieved regardless of the presence or absence of nitrite. The main microorganisms relating to nitrogen metabolism in the system were Nitrospira, Nitrosomonas, Candidatus Kuenenia, and denitrifying bacteria. The metagenomics analysis indicated that these functional microorganisms constituted the main nitrogen metabolic network in the system, and microorganisms such as Rhodanobacter, Nitrosomonas, Defluvii, and Cyanobacteria had the possible capacity for oxygen production. Without organic carbon in the synthetic wastewater, heterotrophs including denitrifying bacteria might utilize organic carbon such as extracellular polymeric substances produced by autotrophs. The removal of NH4-N under oxygen-limited conditions might be achieved through interactions among nitrifying bacteria, anammox bacteria, and heterotrophs, which deserves further investigation. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Carbon fibers could enrich ethanol-oxidizing Geobacter and Desulfovibrio. • Methanogenesis from ethanol was improved even when carbon fibers were removed. • Acetoclastic methanogenesis was triggered by carbon fibers in ethanol reactors. • The promotion of carbon fibers was strongly affected by organic substrates. [ABSTRACT FROM AUTHOR]

• Redox materials changed energy supplying mode in syntrophic methanogenesis. • A low system redox potential could facilitate the DIET methanogenic pathway. • Promoted methanogenesis was related with the increased available energy. • Energy competition existed between hydrogenotrophic and DIET methanogenesis. The aim of this study was to investigate the syntrophic methanogenesis from the perspective of energy transfer and competition. Effects of redox materials and redox potential on direct interspecies electron transfer (DIET) were examined through thermodynamic analysis based on the energy distribution principle. Types of redox materials could affect the efficiency of DIET via changing the total energy supply of the syntrophic methanogenesis. Decreasing system redox potential could facilitate DIET through increasing the total available energy. The competition between hydrogenotrophic methanogens and DIET methanogens might be the reason for the low proportion of the DIET pathway in the syntrophic methanogenesis. A facilitation mechanism of DIET was proposed based on the energy distribution. Providing sufficient electrons, inhibiting hydrogenotrophic methanogens and adding more competitive redox couples to avoid hydrogen generation might be beneficial for the facilitation of DIET. [ABSTRACT FROM AUTHOR]

Microbial source tracking (MST) technology represents an innovative approach employed to trace fecal contamination in environmental water systems. The performance of primers may be affected by amplification techniques, target primer categories, and regional differences. To investigate the influence of these factors on primer recognition performance, a meta-analysis was conducted on the application of MST in water environments using three databases: Web of Science, Scopus, and PubMed (n = 2291). After data screening, 46 studies were included in the final analysis. The investigation encompassed Polymerase Chain Reaction (PCR)/quantitative PCR (qPCR) methodologies, dye-based (SYBR)/probe-based (TaqMan) techniques, and geographical differences of a human host-specific (HF183) primer and other 21 additional primers. The results indicated that the primers analyzed were capable of differentiating host specificity to a certain degree. Nonetheless, by comparing sensitivity and specificity outcomes, it was observed that virus-based primers exhibited superior specificity and recognition capacity, as well as a stronger correlation with human pathogenicity in water environments compared to bacteria-based primers. This finding highlights an important direction for future advancements. Moreover, within the same category, qPCR did not demonstrate significant benefits over conventional PCR amplification methods. In comparing dye-based and probe-based techniques, it was revealed that the probe-based method's advantage lay primarily in specificity, which may be associated with the increased propensity of dye-based methods to produce false positives. Furthermore, the heterogeneity of the HF183 primer was not detected in China, Canada, and Singapore respectively, indicating a low likelihood of regional differences. The variation among the 21 other primers may be attributable to regional differences, sample sources, detection techniques, or alternative factors. Finally, we identified that economic factors, climatic conditions, and geographical distribution significantly influence primer performance. [Display omitted] • Meta-analysis for primers and impact factors to their recognition performance. • Viruses-based primers showed a better specificity and recognition ability. • Regional differences of HF183 was not observed in China, Canada, and Singapore. • The influence factors from sample to environment of 21 primers had been listed. • Meta-analysis of economy, climate, and geographic zone on the primers. [ABSTRACT FROM AUTHOR]

• VFAs degradation and methanogenesis were promoted by dosing Fe 3 O 4. • Sulfate inhibited methanogenesis by disrupting the syntrophic interaction. • Ferroferric oxide rebuilt efficient syntrophic interaction in sulfate environment. • Abundance of genes related to syntrophic methanogenesis increased by dosing Fe 3 O 4. Methanogenesis can be inhibited by volatile fatty acids (VFAs) accumulation and sulfate during anaerobic wastewater treatment. In this study, effects of ferroferric oxide (Fe 3 O 4) on VFAs degradation and methanogenesis in sulfate-containing environment were investigated. Methanogenesis in reactors with or without sulfate were both favored through the addition of Fe 3 O 4. In reactors without sulfate, the dosage of Fe 3 O 4 increased the maximum methane production rate by 21.7% accompanied with faster acetate and propionate degradation. Metagenomic analysis showed that Fe 3 O 4 mainly promoted electron exchange between Mesotoga , Syntrophobacter , Smithella and Methanosaeta without altering the syntrophic patterns. However, in the sulfate-containing reactor with low methanogenic efficiency, syntrophic ethanol users and Methanosaeta were replaced by sulfate-reducing bacteria and Methanosarcina , respectively. The supplement of Fe 3 O 4 re-enriched the syntrophic partners inhibited by sulfate and rebuilt a new syntrophic interaction with high efficiency similar to that in sulfate-free environment, leading to better methanogenic performance in sulfate-containing environment. [ABSTRACT FROM AUTHOR]

In view of problems arising from the grid-connected wind turbine with the frequency converter, we propose a conceptual design of grid-connected wind turbine based on speed regulating differential mechanism (SRDM). The SRDM regulates its output speed and torque self-adaptively referring to wind rotor and makes the synchronous generator (SG) keep a constant speed to output electricity in steady frequency without the normal frequency converter and it has excellent low voltage ride through (LVRT). This paper offers the kinematics and dynamics analysis of the designed wind turbine and builds the SIMULINK model based on FAST (fatigue, aerodynamics, structures and turbulence) software. The simulation of speed, torque and power of wind rotor under average wind speed of 12 m/s and turbulence intensity of 20% can verify the feasibility of the designed wind turbine. [ABSTRACT FROM AUTHOR]

Direct interspecies electron transfer (DIET) is a new electron-transfer strategy for enhanced propionate degradation. Ethanol can enrich the DIET species of Geobacter and conductive ferroferric oxide (Fe 3 O 4) can promote DIET. Therefore, coupled effects of ethanol and Fe 3 O 4 on propionate degradation were investigated. The maximum CH 4 production rate was increased by 81.4% by adding Fe 3 O 4 when simultaneously fed with ethanol and propionate, while the improvement could not be observed without ethanol. The sludge conductivity and the electron transfer system activity by adding Fe 3 O 4 were increased by 2.66 and 2.73 times, respectively. Besides, the relative abundance of functional microbes such as Geobacter , Syntrophobacter , Smithella , and Methanosaeta , and their functional genes were increased by the supplement of Fe 3 O 4. The improvement of propionate degradation by adding Fe 3 O 4 was largely attributed to the co-existence of ethanol degradation. The DIET between Geobacter and Methanosaeta might provide more energies or rapidly consume the oxidation products to promote the propionate degradation. Unlabelled Image • CH 4 production was enhanced by dosing Fe 3 O 4 with organics of ethanol and propionate. • Fe 3 O 4 increased the sludge conductivity and electron transfer system activity. • Fe 3 O 4 promoted the relative abundance of functional microbes and their genes. • DIET might promote the degradation of propionate by providing more energies. [ABSTRACT FROM AUTHOR]

• Acetate enriched incomplete and complete SRBs while ethanol enriched incomplete SRB. • Complete SRB had higher competitiveness for acetate than methanogens. • Incomplete SRB could cooperate with methanogen to produce methane. • Methanogens and methanogenic pathways changed with the dosage of Fe 3 O 4. Effects of ferroferric oxide (Fe 3 O 4) and organic carbon on co-metabolism of sulfate and organic carbon were investigated. With Fe 3 O 4 , the degradation of acetate and sulfate was inhibited when fed with acetate, while the degradation of acetate and propionate produced from ethanol was promoted when fed with ethanol. The dominant sulfate reducing bacteria (SRB) of acetate-fed reactors were Desulfobacteraceae (complete oxidizing SRB, CO-SRB) and Desulfurmonas (incomplete oxidizing SRB, IO-SRB). IO-SRBs of Desulfobulbus and Desulfomicrobium were dominant in ethanol-fed reactors. CO-SRB had higher competitiveness than methanogens to utilize acetate, while IO-SRBs might cooperate with methanogens to produce methane when dosed with ethanol and Fe 3 O 4. The dosage of Fe 3 O 4 changed the dominant methanogen from Methanosarcina to Methanosaeta with acetate as the organic carbon, while increased the relative abundance of Methanosaeta with ethanol as the organic carbon. [ABSTRACT FROM AUTHOR]