Potential impact of process parameters upon the bacterial diversity in the mesophilic anaerobic digestion of beet silage

Metagenomic Analysis of the Long-Term Synergistic Effects of Antibiotics on the Anaerobic Digestion of Cattle Manure

The conversion of cattle manure into biogas in anaerobic digestion (AD) processes has been gaining attention in recent years. However, antibiotic consumption continues to increase worldwide, which is why antimicrobial concentrations can be expected to rise in cattle manure and in digestate. This study examined the long-term synergistic effects of antimicrobials on the anaerobic digestion of cattle manure. The prevalence of antibiotic resistance genes (ARGs) and changes in microbial biodiversity under exposure to the tested drugs was investigated using a metagenomic approach. Methane production was analyzed in lab-scale anaerobic bioreactors. Bacteroidetes, Firmicutes, and Actinobacteria were the most abundant bacteria in the samples. The domain Archaea was represented mainly by methanogenic genera Methanothrix and Methanosarcina and the order Methanomassiliicoccales. Exposure to antibiotics inhibited the growth and development of methanogenic microorganisms in the substrate. Antibiotics also influenced the abundance and prevalence of ARGs in samples. Seventeen types of ARGs were identified and classified. Genes encoding resistance to tetracyclines, macrolide–lincosamide–streptogramin antibiotics, and aminoglycosides, as well as multi-drug resistance genes, were most abundant. Antibiotics affected homoacetogenic bacteria and methanogens, and decreased the production of CH4. However, the antibiotic-induced decrease in CH4 production was minimized in the presence of highly drug-resistant microorganisms in AD bioreactors.

Microbiological insights into anaerobic digestion for biogas, hydrogen or volatile fatty acids (VFAs): a review

In the past decades, considerable attention has been directed toward anaerobic digestion (AD), which is an effective biological process for converting diverse organic wastes into biogas, volatile fatty acids (VFAs), biohydrogen, etc. The microbial bioprocessing takes part during AD is of substantial significance, and one of the crucial approaches for the deep and adequate understanding and manipulating it toward different products is process microbiology. Due to highly complexity of AD microbiome, it is critically important to study the involved microorganisms in AD. In recent years, in addition to traditional methods, novel molecular techniques and meta-omics approaches have been developed which provide accurate details about microbial communities involved AD. Better understanding of process microbiomes could guide us in identifying and controlling various factors in both improving the AD process and diverting metabolic pathway toward production of selective bio-products. This review covers various platforms of AD process that results in different final products from microbiological point of view. The review also highlights distinctive interactions occurring among microbial communities. Furthermore, assessment of these communities existing in the anaerobic digesters is discussed to provide more insights into their structure, dynamics, and metabolic pathways. Moreover, the important factors affecting microbial communities in each platform of AD are highlighted. Finally, the review provides some recent applications of AD for the production of novel bio-products and deals with challenges and future perspectives of AD.

Responses of methane production, microbial community and antibiotic resistance genes to the mixing ratio of gentamicin mycelial residues and wheat straw in anaerobic co-digestion process

Anaerobic co-digestion (AcoD) of gentamicin mycelial residues (GMRs), a kind of nitrogen-rich biowaste, and wheat straw (WS) is an attractive technology for the recycling of GMRs. However, the effects of the co-substrate ratio on methane production, system stability and antimicrobial resistance during co-digestion remain unclear. Thus, this study aimed to fill in the blanks through AcoD of GMRs and WS with different mixing ratios (1:0, 2:1, 1:1, 1:2, 0:1, VS basis) via batch tests. Results showed that AcoD facilitated methane production than mono anaerobic digestion and reduced the accumulation of the toxic substances, such as ammonia nitrogen and humic-like substances. The maximum methane production was obtained at the reactors with the mixing ratio of 1:1 and 1:2 (R-1:1 and R-1:2), which matched with the relative abundance of key enzymes related to methanogenesis predicted by PICRUSt. Microbial community analysis indicated that Methanosaeta was the most dominant methanogen in the AcoD reactors. The highest relative abundance of Methanosaeta (45.1%) was obtained at R-1:1 due to the appropriate AcoD conditions, thus, providing greater possibilities for high stability of AcoD system. Additionally, AcoD of the GMRs and WS under the mixing ratio of 1:1 and 1:2 did not prompt the increase of antibiotic resistance genes (ARGs). Not only that, the likelihood of horizontal gene transfer declined in R-1:1 due to the weaker connection and transport between host and recipient bacteria. Findings of this study suggested that the suitable mixing ratio of GMRs and WS contributes to methane production and system stability, and reduces the dissemination risks of ARGs.

Inhibition of biological acidification and mechanism of crotonaldehyde removal with glucose cometabolism

Biological acidification is an effective method in the treatment or pretreatment of industrial wastewater. Crotonaldehyde is a typical characteristic organic pollutant in petrochemical wastewater, but its effect on biological acidification is unclear. To investigate the inhibitory characteristic of crotonaldehyde on biological acidification and the mechanism of crotonaldehyde removal, variations in volatile fatty acid (VFA) yields, enzyme activities, biodegradation products, and microbial community structures were investigated by batch experiments in the presence of crotonaldehyde. The results showed that crotonaldehyde caused a 50% effect concentration (EC₅₀) on the specific acidogenic activity (SAA) of 204.17 mg/L before 24 h, and then, the inhibitory effect was removed after 48 h as the dosage of crotonaldehyde was less than 1000 mg/L. Accordingly, crotonaldehyde was completely reduced to crotonyl alcohol by nicotinamide adenine dinucleotide (NADH) or oxidized to (E)-crotonic acid by aldehyde dehydrogenase (DHO) after 48 h. Next, 1-buanol and n-butyric acid were further metabolites, while the n-hexanoic acid detected with high-concentration crotonaldehyde might be due to the ORB pathway with 1-buanol as an electron donor. The dominant bacterial communities were Clostridium_sensu_stricto_1, Clostridium_sensu_stricto_11, Clostridium_sensu_stricto_12, which were related to the biodegradation process of crotonaldehyde. The findings of this research could provide a theoretical underpinning for developing the biological technologies to pretreat crotonaldehyde wastewater.

Mesophilic and Thermophilic Anaerobic Digestion of Wheat Straw in a CSTR System with 'Synthetic Manure': Impact of Nickel and Tungsten on Methane Yields, Cell Count, and Microbiome

Lignocellulosic residues, such as straw, are currently considered as candidates for biogas production. Therefore, straw fermentations were performed to quantitatively estimate methane yields and cell counts, as well as to qualitatively determine the microbiome. Six fully automated, continuously stirred biogas reactors were used: three mesophilic (41 °C) and three thermophilic (58 °C). They were fed every 8 h with milled wheat straw suspension in a defined, buffered salt solution, called 'synthetic manure'. Total reflection X-ray fluorescence spectrometry analyses showed nickel and tungsten deficiency in the straw suspension. Supplementation of nickel and subsequently tungsten, or with an increasing combined dosage of both elements, resulted in a final concentration of approximately 0.1 mg/L active, dissolved tungsten ions, which caused an increase of the specific methane production, up to 63% under mesophilic and 31% under thermophilic conditions. That is the same optimal range for pure cultures of methanogens or bacteria found in literature. A simultaneous decrease of volatile fatty acids occurred. The Ni/W effect occurred with all three organic loading rates, being 4.5, 7.5, and 9.0 g volatile solids per litre and day, with a concomitant hydraulic retention time of 18, 10, or 8 days, respectively. A maximum specific methane production of 0.254 m³ CH₄, under standard temperature and pressure per kg volatile solids (almost 90% degradation), was obtained. After the final supplementation of tungsten, the cell counts of methanogens increased by 300%, while the total microbial cell counts increased by only 3-62%. The mesophilic methanogenic microflora was shifted from the acetotrophic Methanosaeta to the hydrogenotrophic Methanoculleus (85%) by tungsten, whereas the H₂-CO₂-converter, Methanothermobacter, always dominated in the thermophilic fermenters.

Ex-situ biogas upgrading in thermophilic up-flow reactors: The effect of different gas diffusers and gas retention times

Four different types of ceramic gas distributors (Al₂O₃ of 1.2 μm and SiC of 0.5, 7 and 14 μm) were evaluated to increase biomethane formation during ex-situ biogas upgrading process. Each type of gas diffuser was tested independently at three different gas retention times of 10, 5 and 2.5 h, at thermophilic conditions. CH₄ production rate increased by increasing input gas flow rate for all type of distributors, whereas CH₄ concentration declined. Reactors equipped with SiC gas distributors effectively improved biomethane content fulfilling natural gas standards. Microbial analysis showed high abundance of hydrogenotrophic methanogens and proliferated syntrophic bacteria, i.e. syntrophic acetate oxidizers and homoacetogens, confirming the effect of H₂ to alternate anaerobic digestion microbiome and enhance hydrogenotrophic methanogenesis. A detailed anaerobic bioconversion model was adapted to simulate the operation of the R₁-R₄ reactors. The model was shown to be effective for the simulation of biogas upgrading process in up-flow reactors.

Energy Availability Determines Strategy of Microbial Amino Acid Synthesis in Volatile Fatty Acid-Fed Anaerobic Methanogenic Chemostats

In natural communities, microbes exchange a variety of metabolites (public goods) with each other, which drives the evolution of auxotroph and shapes interdependent patterns at community-level. However, factors that determine the strategy of public goods synthesis for a given community member still remains to be elucidated. In anaerobic methanogenic communities, energy availability of different community members is largely varied. We hypothesized that this uneven energy availability contributed to the heterogeneity of public goods synthesis ability among the members in these communities. We tested this hypothesis by analyzing the synthetic strategy of amino acids of the bacterial and archaeal members involved in four previously enriched anaerobic methanogenic communities residing in thermophilic chemostats. Our analyses indicate that most of the members in the communities did not possess ability to synthesize all the essential amino acids, suggesting they exchanged these essential public goods to establish interdependent patterns for survival. Importantly, we found that the amino acid synthesis ability of a functional group was largely determined by how much energy it could obtain from its metabolism in the given environmental condition. Moreover, members within a functional group also possessed different amino acid synthesis abilities, which are related to their features of energy metabolism. Our study reveals that energy availability is a key driver of microbial evolution in presence of metabolic specialization at community level and suggests the feasibility of managing anaerobic methanogenic communities for better performance through controlling the metabolic interactions involved.

Nitrogen removal in vermifiltration: Mechanisms, influencing factors, and future research needs

To meet global health and sanitation goals, there is a continued need for sustainable wastewater treatment alternatives that require minimal energy and investment. Vermifiltration, a technology gaining relevance in Africa and Asia, may be an alternative to traditional wastewater treatment systems due to its cost-effectiveness, ease of application and maintenance, and sustainability. However, nitrogen removal in vermifiltration is not well understood since most of the prior research focuses on organics removal. Thus, a state of the art review is necessary to separately focus on the mechanisms associated with nitrogen removal in vermifiltration, along with the factors affecting nitrogen removal. For the first time, this review attempts to present the types of vermifilter based on their flow pattern. The review further discusses the current status of the application of vermifiltration, along with the benefits and limitations associated with the adoption of this technology. It also explores possible strategies that could be adopted to maximize the nitrogen removal potential of vermifilters as optimizing nitrogen removal is critical for improving the performance of vermifiltration based treatment systems.

Soil-Derived Inocula Enhance Methane Production and Counteract Common Process Failures During Anaerobic Digestion

Although soil-borne methanogens are known to be highly diverse and adapted to extreme environments, their application as potential (anaerobic) inocula to improve anaerobic digestion has not been investigated until now. The present study aimed at evaluating if soil-derived communities can be beneficial for biogas (methane, CH₄) production and endure unfavorable conditions commonly associated with digestion failure. Nine study sites were chosen and tested for suitability as inoculation sources to improve biogas production via in situ measurements (CH₄ fluxes, physical and chemical soil properties, and abundance of methanogens) and during a series of anaerobic digestions with (a) combinations of both sterile or unsterile soil and diluted fermenter sludge, and (b) pH-, acetate-, propionate-, and ammonium-induced disturbance. Amplicon sequencing was performed to assess key microbial communities pivotal for successful biogas production. Four out of nine tested soil inocula exerted sufficient methanogenic activity and repeatedly allowed satisfactory CH₄/biogas production even under deteriorated conditions. Remarkably, the significantly highest CH₄ production was observed using unsterile soil combined with sterile sludge, which coincided with both a higher relative abundance of methanogens and predicted genes involved in CH₄ metabolism in these variants. Different bacterial and archaeal community patterns depending on the soil/sludge combinations and disturbance variations were established and these patterns significantly impacted CH₄ production. Methanosarcina spp. seemed to play a key role in CH₄ formation and prevailed even under stressed conditions. Overall, the results provided evidence that soil-borne methanogens can be effective in enhancing digestion performance and stability and, thus, harbor vast potential for further exploitation.

Anaerobic digestion of spectinomycin mycelial residues pretreated by thermal hydrolysis: removal of spectinomycin and enhancement of biogas production

Anaerobic digestion (AD) is an effective technology to dispose antibiotic mycelial residues, but biogas production is influenced by hydrolysis rates and antibiotic residue. Herein, the effects of thermal hydrolysis pretreatment for AD of spectinomycin mycelial residues (SMRs) were investigated. The results showed that the removal ratio of spectinomycin was increased while the temperature of pretreatment was escalating. Meanwhile, thermal hydrolysis facilitated the dissolution of organic matters. However, non-biodegradable substances measured by fluorescence excitation-emission matrix accumulated and thus had an adverse influence on biogas production. Based on batch assays, the optimal pretreatment temperature for SMRs was 120 °C. The removal of spectinomycin was benefit for biogas production (increasing by 7.6%), and the overall biogas production increased by 27.6% compared with 289.90 mL gVS^-1 of untreated SMRs. The microbial community analysis revealed that spectinomycin (265 mg L^-1) might influence bacteria in the early stage of AD (first 5 days), while redundancy analysis showed that spectinomycin had a non-significant influence on community succession over the 32 days of fermentation.

Increasing the methane production rate of hydrogenotrophic methanogens using biochar as a biocarrier

The existence of CO₂ in biogas will affect its practicality, so the methanation of CO₂ is of great significance. Carrier materials play a key role in bioconversion of CO₂ to methane during biogas upgrading. Herein, different materials were used to evaluate the bioconversion process of CO₂ to methane, which consisted of black ceramsite (BC) and biochars prepared from corn straw and digestate. The results showed that after adding the carrier materials, the methane production rate increased by more than 20%, and the corn straw biochar (CSB) group even increased by more than 70%. This may be attributed to the large specific surface area and more functional groups in corn straw biochar which was suitable for the immobilization of hydrogenotrophic methanogens (HMs). Therefore, corn straw biochar is a good carrier material for the accelerated bioconversion of CO₂ to methane.

A state-of-the-art review on the application of nanomaterials for enhancing biogas production

Anaerobic digestion (AD) of organic wastes is among the most promising approaches used for the simultaneous treatment of various waste streams, environment conservation, and renewable bioenergy generation (biomethane). Among the latest innovations investigated to enhance the overall performance of this process both qualitatively and quantitatively, the application of some nanoparticles (NPs) has attracted a great deal of attention. Typically, the NPs of potential benefit to the AD process could be divided into three groups: (i) zero-valent iron (ZVI) NPs, (ii) metallic and metal oxides NPs, and (iii) carbon-based NPs. The present review focuses on the latest findings reported on the application of these NPs in AD process and presents their various mechanisms of action leading to higher or lower biogas production rates. Among the NPs studies, ZVI NPs could be regarded as the most promising nanomaterials for enhancing biogas production through stabilizing the AD process as well as by stimulating the growth of beneficial microorganisms to the AD process and the enzymes involved. Future research should focus on various attributes of NPs when used as additives in biogas production, including facilitating mixing and pumping operations, enriching the population and diversity of beneficial microorganisms for AD, improving biogas release, and inducing the production and activity of AD-related enzymes. The higher volume of methane-enriched biogas would be translated into higher returns on investment and could therefore, result in further growth of the biogas production industry. Nevertheless, efforts should be devoted to decreasing the price of NPs so that the enhanced biogas and methane production (by over 90%, compared to control) would be more economically justified, facilitating the large-scale application of these compounds. In addition to economic considerations, environmental issues are also regarded as major constraints which should be addressed prior to widespread implementation of NP-augmented AD processes. More specifically, the fate of NPs augmented in AD process should be scrutinized to ensure maximal beneficial impacts while adverse environmental/health consequences are minimized.

Differences of methanogenesis between mesophilic and thermophilic in situ biogas-upgrading systems by hydrogen addition

To investigate the differences in microbial community structure between mesophilic and thermophilic in situ biogas-upgrading systems by H2 addition, two reactors (35 °C and 55 °C) were run for four stages according to different H2 addition rates (H2/CO2 of 0:1, 1:1, and 4:1) and mixing mode (intermittent and continuous). 16S rRNA gene-sequencing technology was applied to analyze microbial community structure. The results showed that the temperature is a crucial factor in impacting succession of microbial community structure and the H2 utilization pathway. For mesophilic digestion, most of added H2 was consumed indirectly by the combination of homoacetogens and strict aceticlastic methanogens. In the thermophilic system, most of added H2 may be used for microbial cell growth, and part of H2 was utilized directly by strict hydrogenotrophic methanogens and facultative aceticlastic methanogens. Continuous stirring was harmful to the stabilization of mesophilic system, but not to the thermophilic one.

Efficient removal of atrazine by iron-modified biochar loaded Acinetobacter lwoffii DNS32

In order to efficiently remove commonly used herbicide atrazine in farmland, an iron-modified biochar (FeMBC) was fabricated via chemical co-precipitation of Fe³⁺ onto corn stalks biochar. The composites of FeMBC and Acinetobacter lwoffii DNS32 (bFeMBC) effectively accelerated the degradation rate of atrazine (100 mg L^-1) in inorganic salt culture solution. TEM，XRD，XPS and FTIR were used to study the basic properties of the Materials. FeMBC promoted the formation of bacterial biofilm, -NH functional group on the surface of bacterial extracellular polymers (EPS) and FeMBC could interact with the aromatic ring of atrazine through Hbonding, which were conducive for microbial capture of atrazine. Meanwhile, the pores (2-10 μm) of FeMBC facilitated the passage of the DNS32 strain and the atrazine molecule, which contributed to the efficient capture and degradation of atrazine by DNS32 strain. BFeMBC amendment helped to maintain the bacterial diversity in the atrazine contaminated soil. The increase of rare bacteria (relative abundance of 0.01%-0.05%) richness plays a certain role in stabilizing nutrient cycling, thereby promoting microbial nutrient utilization activities and has the function of pollutant degradation. This may contribute to the digestion of atrazine and its intermediate metabolites，reducing the stress of microbial in atrazine contaminated soil. bFeMBC amendment may be a promising in situ remediation technique for soil atrazine contamination.

Candidatus Syntrophosphaera thermopropionivorans: a novel player in syntrophic propionate oxidation during anaerobic digestion

Propionate is an important intermediate in the anaerobic mineralization of organic matter. In methanogenic environments, its degradation relies on syntrophic associations between syntrophic propionate-oxidizing bacteria (SPOB) and Archaea. However, only 10 isolated species have been identified as SPOB so far. We report syntrophic propionate oxidation in thermophilic enrichments of Candidatus Syntrophosphaera thermopropionivorans, a novel representative of the candidate phylum Cloacimonetes. In enrichment culture, methane was produced from propionate, while Ca. S. thermopropionivorans contributed 63% to total bacterial cells. The draft genome of Ca. S. thermopropionivorans encodes genes for propionate oxidation via methymalonyl-CoA. Phylogenetically, Ca. S. thermopropionivorans affiliates with the uncultured Cloacimonadaceae W5 and is more distantly related (86.4% 16S rRNA gene identity) to Ca. Cloacimonas acidaminovorans. Although Ca. S. thermopropionivorans was enriched from a thermophilic biogas reactor, Ca. Syntrophosphaera was in particular associated with mesophilic anaerobic digestion systems. 16S rRNA gene amplicon sequencng and a novel genus-specific quantitative PCR assay consistently identified Ca. Syntrophosphaera/Cloacimonadaceae W5 in 9 of 12 tested full-scale biogas reactors thereby outnumbering other SPOB such as Pelotomaculum, Smithella and Syntrophobacter. Taken together the ubiquity and abundance of Ca. Syntrophosphaera, those SPOB might be key players for syntrophic propionate metabolism that have been overlooked before.

Effect of influent pH on hydrolytic acidification performance and bacterial community structure in EGSB for pretreating crotonaldehyde manufacture wastewater after ozonation

The objective of this work was to evaluate the effect of influent pH on the hydrolytic acidification (HA) performance and microbial community structure in an expanded granular sludge bed (EGSB) pretreating crotonaldehyde manufacture wastewater (CMW) after ozonation. The results showed that higher chemical oxygen demand (COD) removal rate (40.1%) and acidification degree (27.6%) were obtained at pH 8.0 than those at pH 6.0 and pH 4.0. The concentration of extractable extracellular polymeric substance (EPS) in the sludge gradually decreased with the pH decreasing from 8.0 to 4.0. A similar change was also observed for the concentration of total volatile fatty acids (TVFA) in the effluent. The optimal detoxification efficiency by the HA process was obtained at pH 8.0, with higher removal efficiency (all higher than 90%) of the main toxic pollutants (crotonaldehyde, 5-formyl-6-methyl-4,5-dihydropyran, etc.) and higher anaerobic biodegradation rate (44.5%) in biochemical methane potential (BMP) assay. Among the predominant genera, the Acinetobacter and Pseudomonas were possibly related to biodegradation of pollutants, since their higher relative abundance also coincided with the better performance of the HA process at pH 8.0.

[Description of bacterial microbiota in biosolids generated in the San Fernando wastewater treatment plant. Itagüí, Colombia]

OBJECTIVE

To describe bacterial microbiota in the biosolids generated in one of the largest wastewater treatment plants of Colombia.

MATERIALS AND METHODS

Using NGS technology, 16S rRNA Gene Amplicon libraries were amplified and sequenced. The Roche 454 FLX Titanium platform was used, while the V1-V3 and V6-V9 hypervariable regions were amplified and analyzed independently. Amplicon processing and bacterial classification were performed using the AmpliconNoise pipeline and the RDP Classifier tool.

RESULTS

The analysis showed that the most dominant Phyla in the biosolids were Chlo-roflexi, Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. The most dominant genera were Pseudomonas, Dysgonomonas and Proteiniphilum; however, the dominant group according in the V1-V3 variable region was Anaerolineaceae, which does not conform to the species described for this family. Pathogenic bacteria such as Salmonella and E. coli/Shigella were not detected in the studied biosolid sample.

CONCLUSIONS

In the biosolids samples analyzed, environmental bacteria involved in organic matter stabilization processes during secondary biological treatments and anaerobic digestion were predominant. One of the dominant species in this sludge is a novel species of the Anaerolineaceae group. At the time of the study, it was found that the anaerobic digester system was able to maintain pathogenic bacteria at very low concentrations.

The Effects of Different Oxytetracycline and Copper Treatments on the Performance of Anaerobic Digesters and the Dynamics of Bacterial Communities

Oxytetracycline and copper are the common residues in animal manures. Meanwhile, anaerobic digestion is considered as a clean biotechnology for the disposal of animal manures. In this paper, the performance of anaerobic digesters and the dynamics of bacterial communities under the different treatments of oxytetracycline and copper were discussed. The parameters of methane production and pH values were studied to reflect the performance of anaerobic digester. Results showed that the changes of methane production and pH values were not obvious compared with the control. This means that the treatments of oxytetracycline and copper almost have no effects on the performance of anaerobic digesters. This phenomenon might be due to the chelation reaction between oxytetracycline and copper. This chelation reaction might reduce the toxicity of oxytetracycline. The study on the dynamics of bacterial communities was based on the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method. Results indicated that the bacterial communities had significant differences under the different treatments of oxytetracycline and copper. Uncultured Bacteroidetes bacterium (CU922272.1) and uncultured Bacteroidetes bacterium (AB780945.1) showed adaptability to the different treatments of oxytetracycline and copper and were the dominant bacterial communities.

The active microbial community more accurately reflects the anaerobic digestion process: 16S rRNA (gene) sequencing as a predictive tool

BACKGROUND

Amplicon sequencing methods targeting the 16S rRNA gene have been used extensively to investigate microbial community composition and dynamics in anaerobic digestion. These methods successfully characterize amplicons but do not distinguish micro-organisms that are actually responsible for the process. In this research, the archaeal and bacterial community of 48 full-scale anaerobic digestion plants were evaluated on DNA (total community) and RNA (active community) level via 16S rRNA (gene) amplicon sequencing.

RESULTS

A significantly higher diversity on DNA compared with the RNA level was observed for archaea, but not for bacteria. Beta diversity analysis showed a significant difference in community composition between the DNA and RNA of both bacteria and archaea. This related with 25.5 and 42.3% of total OTUs for bacteria and archaea, respectively, that showed a significant difference in their DNA and RNA profiles. Similar operational parameters affected the bacterial and archaeal community, yet the differentiating effect between DNA and RNA was much stronger for archaea. Co-occurrence networks and functional prediction profiling confirmed the clear differentiation between DNA and RNA profiles.

CONCLUSIONS

In conclusion, a clear difference in active (RNA) and total (DNA) community profiles was observed, implying the need for a combined approach to estimate community stability in anaerobic digestion.

Thermophilic Alkaline Fermentation Followed by Mesophilic Anaerobic Digestion for Efficient Hydrogen and Methane Production from Waste-Activated Sludge: Dynamics of Bacterial Pathogens as Revealed by the Combination of Metagenomic and Quantitative PCR Analyses

Thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM) for hydrogen and methane production from waste-activated sludge (WAS) was investigated. The TM process was also compared to a process with mesophilic alkaline fermentation followed by a mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The results showed that both hydrogen yield (74.5 ml H₂/g volatile solids [VS]) and methane yield (150.7 ml CH₄/g VS) in the TM process were higher than those (6.7 ml H₂/g VS and 127.8 ml CH₄/g VS, respectively) in the MM process. The lowest methane yield (101.2 ml CH₄/g VS) was obtained with the M process. Taxonomic results obtained from metagenomic analysis showed that different microbial community compositions were established in the hydrogen reactors of the TM and MM processes, which also significantly changed the microbial community compositions in the following methane reactors compared to that with the M process. The dynamics of bacterial pathogens were also evaluated. For the TM process, the reduced diversity and total abundance of bacterial pathogens in WAS were observed in the hydrogen reactor and were further reduced in the methane reactor, as revealed by metagenomic analysis. The results also showed not all bacterial pathogens were reduced in the reactors. For example, Collinsella aerofaciens was enriched in the hydrogen reactor, which was also confirmed by quantitative PCR (qPCR) analysis. The study further showed that qPCR was more sensitive for detecting bacterial pathogens than metagenomic analysis. Although there were some differences in the relative abundances of bacterial pathogens calculated by metagenomic and qPCR approaches, both approaches demonstrated that the TM process was more efficient for the removal of bacterial pathogens than the MM and M processes.IMPORTANCE This study developed an efficient process for bioenergy (H₂ and CH₄) production from WAS and elucidates the dynamics of bacterial pathogens in the process, which is important for the utilization and safe application of WAS. The study also made an attempt to combine metagenomic and qPCR analyses to reveal the dynamics of bacterial pathogens in anaerobic processes, which could overcome the limitations of each method and provide new insights regarding bacterial pathogens in environmental samples.

Microbial community structures and functions of wastewater treatment systems in plateau and cold regions

Wastewater treatment plants (WWTPs) in plateau regions have unique microbial community structures. In this study, Illumina high-throughput sequencing technology was applied to investigate microbial communities of plateau WWTPs. The research showed that microbial diversities and richness were negatively associated with the altitude and positively to the water temperature to a certain extent. The dominant phyla of plateau and control WWTPs were similar, which mainly included Proteobacteria, Bacteroidetes, Chloroflexi and Firmicutes. In plateau WWTPs, the LEfSe analysis found 4 biomarkers which can catabolize aromatic compounds, indicating the microorganisms that can degrade refractory organics might survive better in plateau WWTPs. The analysis of functional genera and enzymes showed that there was no significant difference in abundances of organic degrading bacteria, but the nitrogen removal bacteria were less abundant and phosphorus removal bacteria were more abundant in plateau WWTPs.

Sugar beet silage as highly flexible feedstock for on demand biogas production

On demand biogas production is a great option to complement solar and wind power for the energy revolution. Alternatives like feedstock management are important in order to avoid expensive and complex adjustments for gas storage systems. The use of sugar beet silage (S) is a good option because it mainly contains carbohydrates that are easily degradable. Anaerobic digestion was performed for 63 days in four completely stirred tank reactors (CSTR) with different ratios of maize silage (M) and S. M given every hour was used as a base load for the fermentation and S was given two times a day every 12h. Biogas and methane production rates were measured every 5min in order to achieve data with high resolution. Also, pH value, VFA/TIC values and volatile fatty acids were measured during the experiment. The process remained stable in CSTR1 (M:S1:0), CSTR2 (M:S6:1) and CSTR3 (M:S3:1). Instabilities occurred in CSTR4 (M:S1:3) after an operation time of 33 days. Nevertheless, methane yields more than doubled for CSTR3 within 5min after the input of S. Use of sugar beet as a feedstock for biogas production is a further application for this agricultural commodity.

Impact of zero-valent iron nanoparticles on the activity of anaerobic granular sludge: From macroscopic to microcosmic investigation

The study aimed at evaluating the influence of nano zero-valent iron (nZVI) on the activity of anaerobic granular sludge (AGS) from both macroscopic and microcosmic aspects using different methodologies. The tolerance response of AGS to nZVI was firstly investigated using short-term and long-term experiments, and also compared with anaerobic flocs. The Fe fate and distribution, the change of contents/structure of extracellular polymeric substances (EPS), and the variation of microbial community in the AGS after exposure to nZVI were further explored. Contrary to the anaerobic floc, insignificant inhibition of nZVI at dosage lower than 30 mmoL/L on the activity of AGS was observed. Additionally, the extra hydrogen gas released from the oxidation of nZVI was presumably suggested to stimulate the hydrogenotrophic methanogenesis process, resulting in 30% methane production enhancement when exposure to 30 mmoL/L nZVI. The microscopic analysis indicated that nZVI particles were mainly adsorbed on the surface of AGS in the form of iron oxides aggregation without entering into the interior of the granule, protecting most cells from contact damage. Moreover, surrounded EPS located outer surface of anaerobic granule could react with nZVI to accelerate the corrosion of nZVI and slow down H₂ release from nZVI dissolution, thus further weakening the toxicity of nZVI to anaerobic microorganisms. The decrease in bacteria involved in glucose degradation and aceticlastic methanogens as well as the increase of hydrogenotrophic methanogens indicated a H₂ mediated shift toward the hydrogenotrophic pathway enhancing the CH₄ production.

Influence of organic load rate (OLR) on the hydrolytic acidification of 2-butenal manufacture wastewater and analysis of bacterial community structure

The influence of organic loading rate (OLR) on the performance of hydrolytic acidification process for treating 2-butenal manufacture wastewater was comprehensively studied, while its impact on microbial community was thoroughly investigated. The results demonstrated that over 21.0% of the average COD removal rate was observed in the range of OLR from 0.52 to 3.98g COD/L·d, whereas it reduced to 15.3% with increasing OLR to 6.09g COD/L·d. The acidification degree dramatically decreased from 17.1% to 4.7% when OLR increased from 3.98 to 6.09g COD/L·d. In addition, the removal rates of three kinds of typical matters were less than 65% at the OLR 6.09g COD/L·d. Illumina MiSeq sequencing revealed that Proteobacteria, Chloroflexi, Firmicutes, and Bacteroidetes were dominant phyla at different OLRs. Finally, multivariate analysis suggested that the genera Longilinea and T78 had a positive correlation with the degradation of three kinds of typical matters and COD removal rates.

Effects of alkali types on waste activated sludge (WAS) fermentation and microbial communities

The effects of two alkali agents, NaOH and Ca(OH)₂, on enhancing waste activated sludge (WAS) fermentation and short chain fatty acids (SCFAs) accumulation were studied in semi-continuous stirred tank reactors (semi-CSTR) at different sludge retention time (SRT) (2-10 d). The optimum SRT for SCFAs accumulation of NaOH and Ca(OH)₂ adding system was 8 d and 10 d, respectively. Results showed that the average organics yields including soluble chemical oxygen demand (SCOD), protein, and carbohydrate in the NaOH system were as almost twice as that in the Ca(OH)₂ system. For Ca(OH)₂ system, sludge hydrolysis and protein acidification efficiencies were negatively affected by Ca²⁺ precipitation, which was revealed by the decrease of Ca²⁺ concentration, the rise of zeta potential and better sludge dewaterability in Ca(OH)₂ system. In addition, Firmicutes, Proteobacteria and Actinobacteria were the main microbial functional groups in both types of alkali systems. NaOH system obtained higher microbial quantities which led to better acidification. For application, however, Ca(OH)₂ was more economically feasible owning to its lower price and better dewaterability of residual sludge.

Metagenomic insight into the microbial networks and metabolic mechanism in anaerobic digesters for food waste by incorporating activated carbon

Powdered activated carbon (AC) is commonly used as an effective additive to enhance anaerobic digestion (AD), but little is known about how the metabolic pathways resulting from adding AC change the microbial association network and enhance food waste treatment. In this work, the use of AC in an anaerobic digestion system for food waste was explored. Using bioinformatics analysis, taxonomic trees and the KEGG pathway analysis, changes in microbial network and biometabolic pathways were tracked. The overall effect of these changes were used to explain and validate improved digestion performance. The results showed that AC accelerated the decomposition of edible oil in food waste, enhancing the conversion of food waste to methane with the optimized dosage of 12 g AC per reactor. Specifically, when AC was added, the proponoate metabolic pathway that converts propanoic acid to acetic acid became more prominent, as measured by 16S rRNA in the microbial community. The other two metabolic pathways, Lipid Metabolism and Methane Metabolism, were also enhanced. Bioinformatics analysis revealed that AC promoted the proliferation of syntrophic microorganisms such as Methanosaeta and Geobacter, forming a highly intensive syntrophic microbial network.

Anaerobic digestion of nitrogen rich poultry manure: Impact of thermophilic biogas process on metal release and microbial resistances

Poultry manure is a nitrogen rich fertilizer, which is usually recycled and spread on agricultural fields. Due to its high nutrient content, chicken manure is considered to be one of the most valuable animal wastes as organic fertilizer. However, when chicken litter is applied in its native form, concerns are raised as such fertilizers also include high amounts of antibiotic resistant pathogenic Bacteria and heavy metals. We studied the impact of an anaerobic thermophilic digestion process on poultry manure. Particularly, microbial antibiotic resistance profiles, mobile genetic elements promoting the resistance dissemination in the environment as well as the presence of heavy metals were focused in this study. The initiated heat treatment fostered a community shift from pathogenic to less pathogenic bacterial groups. Phenotypic and molecular studies demonstrated a clear reduction of multiple resistant pathogens and self-transmissible plasmids in the heat treated manure. That treatment also induced a higher release of metals and macroelements. Especially, Zn and Cu exceeded toxic thresholds. Although the concentrations of a few metals reached toxic levels after the anaerobic thermophilic treatment, the quality of poultry manure as organic fertilizer may raise significantly due to the elimination of antibiotic resistance genes (ARG) and self-transmissible plasmids.

The full-scale anaerobic digestion microbiome is represented by specific marker populations

Anaerobic digestion is a well-established microbial-based technology for the treatment of organic waste streams and subsequent biogas recovery. A robust and versatile microbial community to ensure overall stability of the process is essential. Four full-scale anaerobic digestion plants were followed for one year to link operational characteristics with microbial community composition and structure. Similarities between digesters, community dynamics and co-occurrence between bacteria and archaea within each digester were analysed. Free ammonia concentration (>200 mg N L^-1) and conductivity (>30 mS cm^-1) hindered acetoclastic methanogenesis by Methanosaetaceae. Thus, methanogenesis was pushed to the hydrogenotrophic pathway carried out by Methanobacteriales and Methanomicrobiales. Firmicutes dominated the overall bacterial community in each of the digesters (>50%), however, principal coordinate analysis of Bray-Curtis indices showed that each of the four digesters hosted a unique microbial community. The uniqueness of this community was related to two phylotypes belonging to the Syntrophomonas genus (Phy32 and Phy34) and to one unclassified bacterium (Phy2), which could both be considered marker populations in the community. A clear differentiation in co-occurrence of methanogens with several bacteria was observed between the different digesters. Our results demonstrated that full-scale anaerobic digestion plants show constant dynamics and co-occurrence patterns in function of time, but are unique in terms of composition, related to the presence of marker populations.

Identification of syntrophic acetate-oxidizing bacteria in anaerobic digesters by combined protein-based stable isotope probing and metagenomics

Inhibition of anaerobic digestion through accumulation of volatile fatty acids occasionally occurs as the result of unbalanced growth between acidogenic bacteria and methanogens. A fast recovery is a prerequisite for establishing an economical production of biogas. However, very little is known about the microorganisms facilitating this recovery. In this study, we investigated the organisms involved by a novel approach of mapping protein-stable isotope probing (protein-SIP) onto a binned metagenome. Under simulation of acetate accumulation conditions, formations of (13)C-labeled CO2 and CH4 were detected immediately following incubation with [U-(13)C]acetate, indicating high turnover rate of acetate. The identified (13)C-labeled peptides were mapped onto a binned metagenome for improved identification of the organisms involved. The results revealed that Methanosarcina and Methanoculleus were actively involved in acetate turnover, as were five subspecies of Clostridia. The acetate-consuming organisms affiliating with Clostridia all contained the FTFHS gene for formyltetrahydrofolate synthetase, a key enzyme for reductive acetogenesis, indicating that these organisms are possible syntrophic acetate-oxidizing (SAO) bacteria that can facilitate acetate consumption via SAO, coupled with hydrogenotrophic methanogenesis (SAO-HM). This study represents the first study applying protein-SIP for analysis of complex biogas samples, a promising method for identifying key microorganisms utilizing specific pathways.

Deeper insight into the structure of the anaerobic digestion microbial community; the biogas microbiome database is expanded with 157 new genomes

This research aimed to better characterize the biogas microbiome by means of high throughput metagenomic sequencing and to elucidate the core microbial consortium existing in biogas reactors independently from the operational conditions. Assembly of shotgun reads followed by an established binning strategy resulted in the highest, up to now, extraction of microbial genomes involved in biogas producing systems. From the 236 extracted genome bins, it was remarkably found that the vast majority of them could only be characterized at high taxonomic levels. This result confirms that the biogas microbiome is comprised by a consortium of unknown species. A comparative analysis between the genome bins of the current study and those extracted from a previous metagenomic assembly demonstrated a similar phylogenetic distribution of the main taxa. Finally, this analysis led to the identification of a subset of common microbes that could be considered as the core essential group in biogas production.

High salinity in molasses wastewaters shifts anaerobic digestion to carboxylate production

Biorefinery wastewaters are often treated by means of anaerobic digestion to produce biogas. Alternatively, these wastewaters can be fermented, leading to the formation of carboxylates. Here, we investigated how lab-scale upflow anaerobic sludge blanket reactors could be shifted to fermentation by changing organic loading rate, hydraulic retention time, pH, and salinity. A strong increase in volatile fatty acid concentration up to 40 g COD L(-1) was achieved through increasing salinity above 30 mS cm(-1), as well as a decrease in methane production by more than 90%, which could not be obtained by adjusting the other parameters, thus, indicating a clear shift from methane to carboxylate production. Microbial community analysis revealed a shift in bacterial community to lower evenness and richness values, following the increased salinity and VFA concentration during the fermentation process. A selective enrichment of the hydrogenotrophic Methanomicrobiales took place upon the shift to fermentation, despite a severe decrease in methane production. Particle size distribution revealed a strong degranulation of the sludge in the reactor, related to the high salinity, which resulted in a wash-out of the biomass. This research shows that salinity is a key parameter enabling a shift from methane to carboxylate production in a stable fermentation process.

Linkages of Firmicutes and Bacteroidetes populations to methanogenic process performance

To identify potential linkages between specific bacterial populations and process performance in anaerobic digestion, the dynamics of bacterial community structure was monitored with high-throughput sequencing in triplicate anaerobic digesters treating animal waste. Firmicutes and Bacteroidetes were found as the two most abundant populations, however, with contrasting population dynamics in response to organic overloading. Firmicutes dominated the bacterial community during stable process performance at low organic loading rate, representing over 50 % of the bacterial abundance. In contrast, the onset of organic overloading raised the relative abundance of Bacteroidetes from 20 ± 2.6 to 44 ± 3.1 %. In addition to the significant negative correlation between the relative abundance of Firmicutes and Bacteroidetes, populations of Firmicutes and Bacteroidetes were found to be linked to process parameters including organic loading rate, volatile fatty acids concentration, and methane production. Therefore, the population abundance ratio of Firmicutes to Bacteroidetes (F/B ratio) was suggested as a potential indicator for process performance. The interactions between Firmicutes and Bacteroidetes populations could be exploited to develop strategies for the prevention of performance perturbation in anaerobic digestion processes.

Genomic characterization of Defluviitoga tunisiensis L3, a key hydrolytic bacterium in a thermophilic biogas plant and its abundance as determined by metagenome fragment recruitment

The genome sequence of Defluviitoga tunisiensis L3 originating from a thermophilic biogas-production plant was established and recently published as Genome Announcement by our group. The circular chromosome of D. tunisiensis L3 has a size of 2,053,097bp and a mean GC content of 31.38%. To analyze the D. tunisiensis L3 genome sequence in more detail, a phylogenetic analysis of completely sequenced Thermotogae strains based on shared core genes was performed. It appeared that Petrotoga mobilis DSM 10674(T), originally isolated from a North Sea oil-production well, is the closest relative of D. tunisiensis L3. Comparative genome analyses of P. mobilis DSM 10674(T) and D. tunisiensis L3 showed moderate similarities regarding occurrence of orthologous genes. Both genomes share a common set of 1351 core genes. Reconstruction of metabolic pathways important for the biogas production process revealed that the D. tunisiensis L3 genome encodes a large set of genes predicted to facilitate utilization of a variety of complex polysaccharides including cellulose, chitin and xylan. Ethanol, acetate, hydrogen (H2) and carbon dioxide (CO2) were found as possible end-products of the fermentation process. The latter three metabolites are considered to represent substrates for methanogenic Archaea, the key organisms in the final step of the anaerobic digestion process. To determine the degree of relatedness between D. tunisiensis L3 and dominant biogas community members within the thermophilic biogas-production plant, metagenome sequences obtained from the corresponding microbial community were mapped onto the L3 genome sequence. This fragment recruitment revealed that the D. tunisiensis L3 genome is almost completely covered with metagenome sequences featuring high matching accuracy. This result indicates that strains highly related or even identical to the reference strain D. tunisiensis L3 play a dominant role within the community of the thermophilic biogas-production plant.

Evaluation of wild herbivore faeces from South Africa as a potential source of hydrolytically active microorganisms

This study assessed faecal matter from three indigenous South African herbivores-zebra, giraffe and impala-as a potential source for hydrolytically active aerobic and facultatively anaerobic bacteria. Herbivore droppings were collected freshly in a local nature reserve in Pietermaritzburg, South Africa. Soil samples adjacent to faecal collection sites and faeces from a domestic herbivore, the Nguni cow, were included as controls. Hydrolase and dehydrogenase activity in faecal matter and soil samples were measured by the fluorescein diacetate and the triphenyltetrazolium chloride assay. Viable counts and counts for amylase, cellulase, esterase and protease producers were established using plate count agar and solid media containing cellulose, skim milk, starch and Tween 80. Zebra droppings produced the highest hydrolase and dehydrogenase activity. Faecal matter of the three indigenous herbivores generally produced higher hydrolytic activity than Nguni cow faeces and soil controls, thereby confirming that these materials are potential targets for hydrolytic enzyme mining.

Metagenomic analysis and functional characterization of the biogas microbiome using high throughput shotgun sequencing and a novel binning strategy

BACKGROUND

Biogas production is an economically attractive technology that has gained momentum worldwide over the past years. Biogas is produced by a biologically mediated process, widely known as "anaerobic digestion." This process is performed by a specialized and complex microbial community, in which different members have distinct roles in the establishment of a collective organization. Deciphering the complex microbial community engaged in this process is interesting both for unraveling the network of bacterial interactions and for applicability potential to the derived knowledge.

RESULTS

In this study, we dissect the bioma involved in anaerobic digestion by means of high throughput Illumina sequencing (~51 gigabases of sequence data), disclosing nearly one million genes and extracting 106 microbial genomes by a novel strategy combining two binning processes. Microbial phylogeny and putative taxonomy performed using >400 proteins revealed that the biogas community is a trove of new species. A new approach based on functional properties as per network representation was developed to assign roles to the microbial species. The organization of the anaerobic digestion microbiome is resembled by a funnel concept, in which the microbial consortium presents a progressive functional specialization while reaching the final step of the process (i.e., methanogenesis). Key microbial genomes encoding enzymes involved in specific metabolic pathways, such as carbohydrates utilization, fatty acids degradation, amino acids fermentation, and syntrophic acetate oxidation, were identified. Additionally, the analysis identified a new uncultured archaeon that was putatively related to Methanomassiliicoccales but surprisingly having a methylotrophic methanogenic pathway.

CONCLUSION

This study is a pioneer research on the phylogenetic and functional characterization of the microbial community populating biogas reactors. By applying for the first time high-throughput sequencing and a novel binning strategy, the identified genes were anchored to single genomes providing a clear understanding of their metabolic pathways and highlighting their involvement in anaerobic digestion. The overall research established a reference catalog of biogas microbial genomes that will greatly simplify future genomic studies.

Comparing the inhibitory thresholds of dairy manure co-digesters after prolonged acclimation periods: Part 2--correlations between microbiomes and environment

Here, we studied the microbiome succession and time-scale variability of four mesophilic anaerobic reactors in a co-digestion study with the objective to find links between changing environmental conditions and the microbiome composition. The changing environmental conditions were ensured by gradual increases in loading rates and mixing ratios of three co-substrates with a constant manure-feeding scheme during an operating period longer than 900 days. Each co-substrate (i.e., alkaline hydrolysate, food waste, and glycerol) was co-digested separately. High throughput 16S rRNA gene sequencing was used to examine the microbiome succession. The alkaline hydrolysate reactor microbiome shifted and adapted to high concentrations of free ammonia, total volatile fatty acids, and potassium to maintain its function. The addition of food waste and glycerol as co-substrates also led to microbiome changes, but to a lesser extent, especially in the case of the glycerol reactor microbiome. The divergence of the food waste reactor microbiome was primarily linked to increasing free ammonia levels in the reactor; though, these levels remained below previously reported inhibitory levels for acclimated biomass. The glycerol reactor microbiome succession included an increase in Syntrophomonadaceae family members, which have previously been linked to long-chain fatty acid degradation. The glycerol reactor exhibited rapid failure and limited adaptation at the end of the study.

Biogas Upgrading via Hydrogenotrophic Methanogenesis in Two-Stage Continuous Stirred Tank Reactors at Mesophilic and Thermophilic Conditions

This study proposes an innovative setup composed by two stage reactors to achieve biogas upgrading coupling the CO2 in the biogas with external H2 and subsequent conversion into CH4 by hydrogenotrophic methanogenesis. In this configuration, the biogas produced in the first reactor was transferred to the second one, where H2 was injected. This configuration was tested at both mesophilic and thermophilic conditions. After H2 addition, the produced biogas was upgraded to average CH4 content of 89% in the mesophilic reactor and 85% in the thermophilic. At thermophilic conditions, a higher efficiency of CH4 production and CO2 conversion was recorded. The consequent increase of pH did not inhibit the process indicating adaptation of microorganisms to higher pH levels. The effects of H2 on the microbial community were studied using high-throughput Illumina random sequences and full-length 16S rRNA genes extracted from the total sequences. The relative abundance of archaeal community markedly increased upon H2 addition with Methanoculleus as dominant genus. The increase of hydrogenotrophic methanogens and syntrophic Desulfovibrio and the decrease of aceticlastic methanogens indicate a H2-mediated shift toward the hydrogenotrophic pathway enhancing biogas upgrading. Moreover, Thermoanaerobacteraceae were likely involved in syntrophic acetate oxidation with hydrogenotrophic methanogens in absence of aceticlastic methanogenesis.

Microbial community dynamics in replicate anaerobic digesters exposed sequentially to increasing organic loading rate, acidosis, and process recovery

BACKGROUND

Volatile fatty acid intoxication (acidosis), a common process failure recorded in anaerobic reactors, leads to drastic losses in methane production. Unfortunately, little is known about the microbial mechanisms underlining acidosis and the potential to recover the process. In this study, triplicate mesophilic anaerobic reactors of 100 L were exposed to acidosis resulting from an excessive feeding with sugar beet pulp and were compared to a steady-state reactor.

RESULTS

Stable operational conditions at the beginning of the experiment initially led to similar microbial populations in the four reactors, as revealed by 16S rRNA gene T-RFLP and high-throughput amplicon sequencing. Bacteroidetes and Firmicutes were the two dominant phyla, and although they were represented by a high number of operational taxonomic units, only a few were dominant. Once the environment became deterministic (selective pressure from an increased substrate feeding), microbial populations started to diverge between the overfed reactors. Interestingly, most of bacteria and archaea showed redundant functional adaptation to the changing environmental conditions. However, the dominant Bacteroidales were resistant to high volatile fatty acids content and low pH. The severe acidosis did not eradicate archaea and a clear shift in archaeal populations from acetotrophic to hydrogenotrophic methanogenesis occurred in the overfed reactors. After 11 days of severe acidosis (pH 5.2 ± 0.4), the process was quickly recovered (restoration of the biogas production with methane content above 50 %) in the overfed reactors, by adjusting the pH to around 7 using NaOH and NaHCO3.

CONCLUSIONS

In this study we show that once the replicate reactors are confronted with sub-optimal conditions, their microbial populations start to evolve differentially. Furthermore the alterations of commonly used microbial parameters to monitor the process, such as richness, evenness and diversity indices were unsuccessful to predict the process failure. At the same time, we tentatively propose the replacement of the dominant Methanosaeta sp. in this case by Methanoculleus sp., to be a potential warning indicator of acidosis.

Analysis of trichloroethylene removal and bacterial community function based on pH-adjusted in an upflow anaerobic sludge blanket reactor

The study reported the upflow anaerobic sludge blanket (UASB) reactor performance in treating wastewater containing trichloroethylene (TCE) and characterized variations of bacteria composition and structure by changing the pH from 6.0 to 8.0. A slightly acidic environment (pH < 7.0) had a greater impact on the TCE removal. Illumina pyrosequencing was applied to investigate the bacterial community changes in response to pH shifts. The results demonstrated that pH greatly influenced the dominance and presence of specific populations. The potential TCE degradation pathway in the UASB reactor was proposed. Importantly, the genus Dehalobacter which was capable of reductively dechlorinating TCE was detected, and it was not found at pH of 6.0, which presumably is the reason why the removal efficiency of TCE was the lowest (80.73 %). Through Pearson correlation analyses, the relative abundance of Dehalobacter positively correlated with TCE removal efficiency (R = 0.912). However, the relative abundance of Lactococcus negatively correlated with TCE removal efficiency according to the results from Pearson correlation analyses and redundancy analysis (RDA).

Influence of ferric oxyhydroxide addition on biomethanation of waste activated sludge in a continuous reactor

This study investigated the potential of enhancing the activity of iron-reducing bacteria (IRBs) to increase the biomethanation rate of waste activate sludge (WAS). The effects of biostimulation by ferric oxyhydroxide (Phase 2) and bioaugmentation with an enriched IRB consortium (Phase 3) were examined in a continuous anaerobic reactor treating WAS. Compared to the control operation (Phase 1), significant rises in methane yield (10.8-59.4%) and production rate (24.5-52.9%) were demonstrated by the biostimulation and bioaugmentation treatments. Visible structural changes were observed in bacterial community with the phases while not in archaeal community. Acinetobacter- and Spirochaetales-related populations were likely the major players driving anaerobic iron respiration and thus leading to enhanced biomethanation performance, in Phases 2 and 3, respectively. Our results suggest an interesting new potential for enhancing biomethanation of WAS.