Start-up phase of an anaerobic full-scale farm reactor - Appearance of mesophilic anaerobic conditions and establishment of the methanogenic microbial community

Microbiome assembly and stability during start-up of a full-scale, two-phase anaerobic digester fed cow manure and mixed organic feedstocks

Carbon transformations during anaerobic digestion are mediated by complex microbiomes, but their assembly is poorly understood, especially in full-scale digesters. Gene-centric metagenomics combining functional and taxonomic classification was performed for an on-farm digester during start-up. Cow manure and organic waste pre-treated in a hydrolysis tank were fed to the methane-producing digester and the volatile solids loading rate was slowly increased from 0 to 3.5 kg volatile solids m-3 d-1 over one year. The microbial community in the anaerobic digester exhibited a high ratio of archaea, which were dominated by hydrogenotrophic methanogens. Bacteria in the anaerobic digester had a high abundance of genes for ferredoxin cycling, H2 generation, and more metabolically complex fermentations than in the hydrolysis tank. In total, the results show that a functionally stable microbiome was achieved quickly during start-up and that the microbiome created in the low-pH hydrolysis tank did not persist in the downstream anaerobic digester.

Potential of acetic acid to restore methane production in anaerobic reactors critically intoxicated by ammonia as evidenced by metabolic and microbial monitoring

BACKGROUND

Biogas and biomethane production from the on-farm anaerobic digestion (AD) of animal manure and agri-food wastes could play a key role in transforming Europe's energy system by mitigating its dependence on fossil fuels and tackling the climate crisis. Although ammonia is essential for microbial growth, it inhibits the AD process if present in high concentrations, especially under its free form, thus leading to economic losses. In this study, which includes both metabolic and microbial monitoring, we tested a strategy to restore substrate conversion to methane in AD reactors facing critical free ammonia intoxication.

RESULTS

The AD process of three mesophilic semi-continuous 100L reactors critically intoxicated by free ammonia (> 3.5 g_N L-1; inhibited hydrolysis and heterotrophic acetogenesis; interrupted methanogenesis) was restored by applying a strategy that included reducing pH using acetic acid, washing out total ammonia with water, re-inoculation with active microbial flora and progressively re-introducing sugar beet pulp as a feed substrate. After 5 weeks, two reactors restarted to hydrolyse the pulp and produced CH4 from the methylotrophic methanogenesis pathway. The acetoclastic pathway remained inhibited due to the transient dominance of a strictly methylotrophic methanogen (Candidatus Methanoplasma genus) to the detriment of Methanosarcina. Concomitantly, the third reactor, in which Methanosarcina remained dominant, produced CH4 from the acetoclastic pathway but faced hydrolysis inhibition. After 11 weeks, the hydrolysis, the acetoclastic pathway and possibly the hydrogenotrophic pathway were functional in all reactors. The methylotrophic pathway was no longer favoured. Although syntrophic propionate oxidation remained suboptimal, the final pulp to CH4 conversion ratio (0.41 ± 0.10 LN_CH4 g_VS-1) was analogous to the pulp biochemical methane potential (0.38 ± 0.03 LN_CH4 g_VS-1).

CONCLUSIONS

Despite an extreme free ammonia intoxication, the proposed process recovery strategy allowed CH4 production to be restored in three intoxicated reactors within 8 weeks, a period during which re-inoculation appeared to be crucial to sustain the process. Introducing acetic acid allowed substantial CH4 production during the recovery period. Furthermore, the initial pH reduction promoted ammonium capture in the slurry, which could allow the field application of the effluents produced by full-scale digesters recovering from ammonia intoxication.

Different stages of microbial community during the anaerobic digestion of food waste

Large-scale food waste (FW) disposal has resulted in severe environmental degradation and financial losses around the world. Although FW has a high biomass energy contents and a growing large number of national projects to recover energy from FW by anaerobic digestion (AD) are being developed. AD is a promising solution for FW management and energy generation when compared to typical disposal options including landfill disposal, incineration, and composting. AD of FW can be combined with an existing AD operation or linked to the manufacture of value-added products to reduce costs and increase income. AD is a metabolic process that requires four different types of microbes: hydrolyzers, acidogens, acetogens, and methanogens. Microbes use a variety of strategies to avoid difficult situations in the AD, such as competition for the same substrate between sulfate-reducing bacteria and methane-forming bacteria. An improved comprehension of the microbiology involved in the anaerobic digestion of FW will provide new insight into the circumstances needed to maximize this procedure, including its possibilities for use in co-digestion mechanisms. This paper reviewed the present scientific knowledge of microbial community during the AD and the connection between microbial diversity during the AD of FW.

Insights into the effects of operating parameters on sulfate reduction performance and microbial pathways in the anaerobic sequencing batch reactor

Sulfate-reducing bacteria (SRB)-based anaerobic process has aroused wide concern in the treatment of sulfate-containing wastewater. Chemical oxygen demand-to-sulfate ratio (COD/SO42-) and HRT are two key factors that affect not only the anaerobic treatment performance but also the activity of SRB. In this study, an anaerobic sequencing batch reactor was constructed, and the effects of different operating parameters (COD/SO42-, HRT) on the relationship of sulfate (SO42-) reduction performance, microbial communities, and metabolic pathways were comprehensively investigated. The results indicated that the SO42- removal rates could achieve above 95% under different operating parameters. Bioinformatics analysis revealed that microbial community changed with reactor operation. At the genus level, the enrichment of Propionicclava and Peptoclostridium contributed to the establishment of a homotrophic relationship with Desulfobulbus, the dominant SRB in the reactor, which indicated that they took vital part in maintaining the structural and functional stability of the bacterial community under different operating parameters. In particular, an increasing trend of the relative abundance of functional genes encoding dissimilatory sulfate reduction was detected with the increase of COD/SO42-, which indicated high SO42- reduction potentials. This knowledge will help to reveal the mechanism of the effect of operating parameters on the anaerobic sulfate removal process, thus providing effective guidance for the targeted regulation of anaerobic sequencing batch bioreactors treating SO42--containing wastewater.

Microbial diversity across compartments in an aquaponic system and its connection to the nitrogen cycle

Aquaponics combines hydroponic crop production with recirculating aquaculture. These systems comprise various compartments (fish tank, biofilter, sump, hydroponic table, radial flow settler and anaerobic digester), each with their own specific environmental pressures, which trigger the formation of unique microbial communities. Triplicated aquaponic systems were used to investigate the microbial community composition during three lettuce growing cycles. The sampling of individual compartments allowed community patterns to be generated using amplicon sequencing of bacterial and archaeal 16S rRNA genes. Nitrifying bacteria were identified in the hydroponic compartments, indicating that these compartments may play a larger role than previously thought in the system's nitrogen cycle. In addition to the observed temporal changes in community compositions within the anaerobic compartment, more archaeal reads were obtained from sludge samples than from the aerobic part of the system. Lower bacterial diversity was observed in fresh fish feces, where a highly discrete gut flora composition was seen. Finally, the most pronounced differences in microbial community compositions were observed between the aerobic and anaerobic loops of the system, with unique bacterial compositions in each individual compartment.

Fermentation characteristics of bedded pack barn dairy cattle manure on methane yield, carbon, and nitrogen content in solid-state anaerobic digestion

This study aimed to estimate the fermentation characteristics of bedded pack barn dairy cattle manure (BDCM) in terms of methane yield, fibrous material, and nitrogen content in batch solid-state anaerobic digestion (SSAD). SSAD was performed in triplicate using a 1,400 ml polypropylene bottle at a constant temperature of 39 °C until less than 1% methane was produced. The cumulative methane content of BDCM was 142.5 N mL/g volatile solids (VSs). The methane content rapidly increased for 18 days, reaching 63.4 ± 4.6% until the end of the experiment. The ultimate biodegradability and total VS removal of BDCM were 23.1 and 19.0%, respectively. The slopes of the non-fibrous and hemicellulose carbon fractions, and acid detergent insoluble carbon by digestion time were -0.174 (p < 0.001), -0.141 (p = 0.003), and -0.051 (p < 0.001), respectively. The non-fibrous and hemicellulose nitrogen fraction contents quadratically decreased during SSAD (p = 0.001 and p = 0.008). No significant decrease was observed in the acid detergent insoluble nitrogen content (p = 0.840). The results of the present study provide basic data on the digestion characteristics of BDCM and could help determine fermentation conditions in the anaerobic digestion of BDCM.

Overview on agricultural potentials of biogas slurry (BGS): applications, challenges, and solutions

The residual slurry obtained from the anaerobic digestion (AD) of biogas feed substrates such as livestock dung is known as BGS. BGS is a rich source of nutrients and bioactive compounds having an important role in establishing diverse microbial communities, accelerating nutrient use efficiency, and promoting overall soil and plant health management. However, challenges such as lower C/N transformation rates, ammonia volatilization, high pH, and bulkiness limit their extensive applications. Here we review the strategies of BGS valorization through microbial and organomineral amendments. Such cohesive approaches can serve dual purposes viz. green organic inputs for sustainable agriculture practices and value addition of biomass waste. The literature survey has been conducted to identify the knowledge gaps and critically analyze the latest technological interventions to upgrade the BGS for potential applications in agriculture fields. The major points are as follows: (1) Bio/nanotechnology-inspired approaches could serve as a constructive platform for integrating BGS with other organic materials to exploit microbial diversity dynamics through multi-substrate interactions. (2) Advancements in next-generation sequencing (NGS) pave an ideal pathway to study the complex microflora and translate the potential information into bioprospecting of BGS to ameliorate existing bio-fertilizer formulations. (3) Nanoparticles (NPs) have the potential to establish a link between syntrophic bacteria and methanogens through direct interspecies electron transfer and thereby contribute towards improved efficiency of AD. (4) Developments in techniques of nutrient recovery from the BGS facilities' negative GHGs emissions and energy-efficient models for nitrogen removal. (5) Possibilities of formulating low-cost substrates for mass-multiplication of beneficial microbes, bioprospecting of such microbes to produce bioactive compounds of anti-phytopathogenic activities, and developing BGS-inspired biofertilizer formulations integrating NPs, microbial inoculants, and deoiled seed cakes have been examined.

Application of bioelectrochemical systems to regulate and accelerate the anaerobic digestion processes

Anaerobic digestion (AD) serves as a potential bioconversion process to treat various organic wastes/wastewaters, including sewage sludge, and generate renewable green energy. Despite its efficiency, AD has several limitations that need to be overcome to achieve maximum energy recovery from organic materials while regulating inhibitory substances. Hence, bioelectrochemical systems (BESs) have been widely investigated to treat inhibitory compounds including ammonia in AD processes and improve the AD operational efficiency, stability, and economic viability with various integrations. The BES operations as a pretreatment process, inside AD or after the AD process aids in the upgradation of biogas (CO₂ to methane) and residual volatile fatty acids (VFAs) to valuable chemicals and fuels (alcohols) and even directly to electricity generation. This review presents a comprehensive summary of BES technologies and operations for overcoming the limitations of AD in lab-scale applications and suggests upscaling and future opportunities for BES-AD systems.

Microbial Community Successional Changes in a Full-Scale Mesophilic Anaerobic Digester from the Start-Up to the Steady-State Conditions

Anaerobic digestion is a widely used technology for sewage sludge stabilization and biogas production. Although the structure and composition of the microbial communities responsible for the process in full-scale anaerobic digesters have been investigated, little is known about the microbial successional dynamics during the start-up phase and the response to variations occurring in such systems under real operating conditions. In this study, bacterial and archaeal population dynamics of a full-scale mesophilic digester treating activated sludge were investigated for the first time from the start-up, performed without adding external inoculum, to steady-state operation. High-throughput 16S rRNA gene sequencing was used to describe the microbiome evolution. The large majority of the reads were affiliated to fermentative bacteria. Bacteroidetes increased over time, reaching 22% of the total sequences. Furthermore, Methanosaeta represented the most abundant methanogenic component. The specific quantitative data generated by real-time PCR indicated an enrichment of bacteria and methanogens once the steady state was reached. The analysis allowed evaluation of the microbial components more susceptible to the shift from aerobic to anaerobic conditions and estimation of the microbial components growing or declining in the system. Additionally, activated sludge was investigated to evaluate the microbial core selected by the WWTP operative conditions.

Using a high-throughput sequencing technology to evaluate the various forage source epiphytic microbiota and their effect on fermentation quality and microbial diversity of Napier grass

Napier grass (Pennisetum purpureum) is well-known due to its high biomass production. The epiphytic microbiota was prepared from Napier, alfalfa, and red clover grass and served as an inoculum. The chopped sterilized Napier grass was inoculated with reconstituted epiphytic microbiota, and treatments were designed as: distilled water (N0); Napier grass epiphytic microbiota (NP); alfalfa epiphytic microbiota (AL); and red clover epiphytic microbiota (RC). The results reveal that the reconstituted epiphytic microbiota bacteria efficiently adapted in Napier grass silage, improved fermentation, and produced lactic acid. The alfalfa-grass inoculum rapidly dropped pH and enhanced the lactic acid (LA) and the ratio of lactic acid-to-acetic acid (LA/AA) during the entire ensiling process. However, red clover attains high lactic acid, while Napier grass produces high acetic acid-type fermentation at terminal silage. After day 60 of ensiling, Lactobacillus proportion was higher in AL (85.45%), and RC (59.44%), inocula as compared with NP (36.41%), inoculum. The NP inoculum terminal silage was diverse than AL and RC inocula and dominated by Enterobacter (16.32%) and Enterobacteriaceae (10.16%) and also significantly (p < 0.05) higher in acetic acid. The present study concluded that AL and RC epiphytic microbiota successfully develop and more efficient than Napier grass microbiota. It is suggested that abundant microbiota isolate from alfala and red clover and develop more economical and efficient inocula for quality fermentation of Napier grass silage in practice.

Removal of nickel(II) from wastewater using a zeolite-packed anaerobic bioreactor: Bacterial diversity and community structure shifts

In recent years, overexploited industrialization and urbanization activities have led to significant amounts of heavy metals released into the environment. Metal ion contamination of water, especially with toxic metals such as nickel(II) [Ni(II)], which is extensively applied in the electroplating industry, has been a serious problem. The aim of the present study was to evaluate the Ni(II) removal from real industrial wastewater using a 2 L, lab-scale, up-flow, anaerobic, zeolite-packed bioreactor inoculated with a heterotrophic consortium as the bioadsorbent. High-throughput sequencing of 16S rRNA genes revealed significant shifts in their bacterial diversity and structural composition along the bioreactor treatment location, where the bacterial genus was dominated by Kosmotogae followed by Firmicutes as Ruminococcus and Clostridium. However, Fervidobacterium and the Geobacter genus were absent at the end of the bioreactor treatment, suggesting that they play a key role in the beginning of Ni(II) removal anaerobic treatment. The physico-chemical results revealed that the Ni(II) removal rate was 99% for 250-500 ppm metal tested, with an efficient alkalinity rate and high production of biogas, which confirmed that anaerobic digestion of microorganisms was successfully performed through the process. Finally, this anaerobic bioreactor configuration offers an accessible and ecofriendly high-rate metal removal strategy from mining and electroplating effluents.

Microbial community and molecular ecological network in the EGSB reactor treating antibiotic wastewater: Response to environmental factors

In this study, one lab-scale EGSB reactor (1.47 L volume) was designed to treat the antibiotic wastewater under different environmental factors, including the addition of cephalexin (CFX), Temperature (T) and Hydraulic Retention Time (HRT). The microbial community structure in EGSB reactor was analyzed with high-throughput sequencing technology to investigate their response to environmental factors changes, and then the random-matrix-theory (RMT)-based network analysis was used to investigate the microbial community's molecular ecological network in EGSB systems treating antibiotics wastewater. Moreover, the explanatory value of each environmental factor on the change of microbial community structure was obtained through the result of redundancy analysis (RDA). The results showed that the addition of cephalexin (CFX), decline of T and decline of HRT (8 h) would decrease the removal efficiency of COD decreasing. And the removal efficiency of CFX would not be affected by decline of T and HRT, except the producing and degrading process of CFX by-products was changed obviously. The result of RDA analysis suggested the environmental factors mainly affected bacterial and fungal microbial community structure but not archaeal ones. The result of high-throughput sequencing showed the relative abundance (RA) of Firmicutes had been obviously affected by T and HRT, which might be main reason leading to the decrease of COD removal efficiency. In addition, molecular ecological network analysis showed the growth of Bacteroidetes occupied the niche of functional microorganism and led to the unstable operation of EGSB when T declined. What's more, the molecular ecological network analysis revealed that Exophiala which belonged to fungi Ascomycota phylum was the hub genus to degrade complex refractory organic pollutants, and Aceticlastic methanogens Methanosaeta was the core functional archaea genus.

Microbial diversity and fermentation profile of red clover silage inoculated with reconstituted indigenous and exogenous epiphytic microbiota

The study investigated the effects of transplantation and reconstitution of indigenous and exogenous epiphytic microbiota on the fermentation quality and microbial community of red clover silage. Sterile red clover was inoculated with distilled water (RC0), extracted epiphytic microbiota of red clover (RC), maize (MZ), and sorghum (SG). RC inoculation rapidly decreased pH at the onset of ensiling. The LA concentration and ratio of LA/AA were higher in RC silage during entire ensiling while MZ silage during late phase of ensiling. Pediococcus was dominant in RC early silage, while Lactobacillus was abundant in MZ final silage. The SG terminal silage had higher pH (>4.50) and dominated by Sphingomonas, Enterobacter, and Novosphingobium. RC and MZ microbiota were beneficial in enhancing fermentation quality and microbial community in red clover silage. Transplantation and reconstitution of epiphytic microbiota can be a successful method to assess the effective and eco-friendly additive for the targeted crop.

Survey of microbes in industrial-scale second-generation bioethanol production for better process knowledge and operation

The microbes present in bioethanol production processes have been previously studied in laboratory-scale experiments, but there is a lack of information on full-scale industrial processes. In this study, the microbial communities of three industrial bioethanol production processes were characterized using several methods. The samples originated from second-generation bioethanol plants that produce fuel ethanol from biowaste, food industry side streams, or sawdust. Amplicon sequencing targeting bacteria, archaea, and fungi was used to explore the microbes present in biofuel production and anaerobic digestion of wastewater and sludge. Biofilm-forming lactic acid bacteria and wild yeasts were identified in fermentation samples of a full-scale plant that uses biowaste as feedstock. During the 20-month monitoring period, the anaerobic digester adapted to the bioethanol process waste with a shift in methanogen profile indicating acclimatization to high concentrations of ammonia. Amplicon sequencing does not specifically target living microbes. The same is true for indirect parameters, such as low pH, metabolites, or genes of lactic acid bacteria. Since rapid identification of living microbes would be indispensable for process management, a commercial method was tested that detects them by measuring the rRNA of selected microbial groups. Small-scale testing indicated that the method gives results comparable with plate counts and microscopic counting, especially for bacterial quantification. The applicability of the method was verified in an industrial bioethanol plant, inspecting the clean-in-place process quality and detecting viability during yeast separation. The results supported it as a fast and promising tool for monitoring microbes throughout industrial bioethanol processes.

Novel start-up process for the efficient degradation of high COD wastewater with up-flow anaerobic sludge blanket technology and a modified internal circulation reactor

To avoid wastage of water resources and operating cost increases caused by the traditional start-up process of large amounts of dilution influent chemical oxygen demand (COD), a novel start-up process (NSP) was developed and verified with water hyacinth juice (WHJ) on an up-flow anaerobic sludge blanket (UASB) and modified internal circulation (MIC) reactor. Results show that UASB and MIC reactors were started successfully and that the MIC reactor exhibited a superior performance. The NSP time of the MIC reactor (46 days) was less than that of the UASB reactor (52 days), although the start-up organic loading rate (OLR) of the MIC reactor was higher than that of the UASB reactor. Interestingly, high-throughput sequencing analysis indicated that the reactor configuration significantly impacted the microbial diversity, however, the UASB and MIC reactors had similar predominant methanogens: Methanosaeta and Methanosarcina. Therefore, acetoclastic methanogenesis is the primary pathway of methane formation during WHJ treatment.

A model predictive optimal control system for the practical automatic start-up of anaerobic digesters

The optimal automatic start-up of anaerobic digesters has remained an elusive problem over the years to be solved at the lowest possible costs, including that of process monitoring. In this work, a non-linear model predictive control (NMPC) system was developed, under two proposed configurations, for the optimal start-up of anaerobic digesters treating soluble non-recalcitrant substrates. The minimum set of low cost practical control variables (CVs) selected for process start-up include (i) the effluent quality as acetate COD, (ii) the level of aceticlastic methanogenic biomass in the reactor, and (iii) the methane production rate (only for one of the NMPC configurations). The manipulated variables (MVs) consist of the volumetric inflow rates of the organic substrate, dilution water, and of a possible concentrated alkali addition. To be able to apply the above selected CVs (technically and economically feasible to measure/estimate), a simplified tailored AD model was specifically designed as the prediction model, integral part of the NMPC system. The NMPC system developed was evaluated for a case scenario consisting of the automatic start-up of a high rate AD reactor treating a readily biodegradable carbohydrate based substrate. The AD plant was virtually represented by the complex Anaerobic Digestion Model No. 1. Compared to other manual start-up strategies, the two configurations of the NMPC developed appeared to reach the target methane production rate faster (39 and 18 days for the NMPC versus 70-75 days for the manual strategies) together with an overall superior CV set-point tracking error performance. Interestingly, the two configurations of the NMPC developed appear to propose two very different, almost opposite, start-up feeding strategies to both eventually start-up the reactor successfully with no process destabilizations throughout. A number of practical scenarios were also considered to evaluate the NMPC configurations for robustness and any possible improvements. These tests indicate that the NMPC objective function formulation is a key factor of the success and robustness exhibited during start-up.

Effects of moisture and carbon/nitrogen ratio on gaseous emissions and maturity during direct composting of cornstalks used for filtration of anaerobically digested manure centrate

This study investigated the maturity and gaseous emission during direct composting of cornstalks used as organic media for filtration of anaerobically digested manure centrate. Effects of moisture and carbon/nitrogen (C/N) ratio on composting performance were evaluated. Results show that cornstalks could effectively retain suspended solids and organic matter in digested manure centrate to lower their C/N ratio and attain microbial inoculation. Filtered cornstalks became more compostable when their moisture decreased from 76% to 60% or C/N ratio increased from 12 to 24. Nevertheless, such adjustment aggravated the emission of greenhouse and odours gases during composting. Regardless of composting conditions, the phylum Firmicutes was the most dominant with reduced abundance during composting. Similar reduction also occurred to several abundant phyla, including Atribacteria, Synergistetes and Euryarchaeota. By contrast, the phylum Bacteroidetes, Chloroflexi, Proteobacteria and Actinobacteria enriched as composting progressed. In addition, compost maturity was insignificantly affected by matrix moisture and C/N ratio.

Phosphorus Input Alters the Assembly of Rice (Oryza sativa L.) Root-Associated Communities

Rice root-associated microbial community play an important role in plant nutrient acquisition, biomass production, and stress tolerance. Herein, root-associated community assembly was investigated under different phosphate input levels in phosphorus (P)-deficient paddy soil. Rice was grown in a long-term P-depleted paddy soil with 0 (P0), 50 (PL), or 200 (PH) mg P₂O₅ kg^-1 application. DNA from root endophytes was isolated after 46 days, and PCR amplicons from archaea, bacteria, and fungi were sequenced by an Illumina Miseq PE300 platform, respectively. P application had no significant effect on rice root endophytic archaea, which were dominated by ammonia-oxidizing Candidatus Nitrososphaera. By contrast, rice root endophytic community structure of the bacteria and fungi was affected by soil P. Low P input increased endophytic bacterial diversity, whereas high P input increased rhizosphere fungi diversity. Bacillus and Pleosporales, associated with phosphate solubilization and P uptake, dominated in P0 and PH treatments, and Pseudomonas were more abundant in the PL treatment than in the P0 and PH treatments. Co-occurrence network analysis revealed a close interaction between endophytic bacteria and fungi. Soil P application affected both the rice root endosphere and soil rhizosphere microbial community and interaction between rice root endophytic bacteria, and fungi, especially species related to P cycling.

Microbiota adaptation after an alkaline pH perturbation in a full-scale UASB anaerobic reactor treating dairy wastewater

The aim of this study was to understand how the microbial community adapted to changes, including a pH perturbation, occurring during the start-up and operation processes in a full-scale methanogenic UASB reactor designed to treat dairy wastewater. The reactor performance, prokaryotic community, and lipid degradation capacity were monitored over a 9-month period. The methanogenic community was studied by mcrA/mrtA gene copy-number quantification and methanogenic activity tests. A diverse prokaryotic community characterized the seeding sludge as assessed by sequencing the V4 region of the 16S rRNA gene. As the feeding began, the bacterial community was dominated by Firmicutes, Synergistetes, and Proteobacteria phyla. After an accidental pH increase that affected the microbial community structure, a sharp increase in the relative abundance of Clostridia and a decrease in the mcrA/mrtA gene copy number and methanogenic activity were observed. After a recovery period, the microbial population regained diversity and methanogenic activity. Alkaline shocks are likely to happen in dairy wastewater treatment because of the caustic soda usage. In this work, the plasticity of the prokaryotic community was key to surviving changes to the external environment and supporting biogas production in the reactor.

Temporal variation of eukaryotic community structures in UASB reactor treating domestic sewage as revealed by 18S rRNA gene sequencing

Eukaryotes are important components of ecosystems in wastewater treatment processes. However, little is known about eukaryotic community in anaerobic wastewater treatment systems. In this study, eukaryotic communities in an up flow anaerobic sludge blanket (UASB) reactor treating domestic sewage during two years of operation were investigated using V4 and V9 regions of 18S rRNA gene for amplicon sequencing. In addition, activated sludge and influent sewage samples were also analyzed and used as the references for aerobic eukaryotic community to characterize anaerobic eukaryotes. The amplicon sequence V4 and V9 libraries detected different taxonomic groups, especially from the UASB samples, suggesting that commonly used V4 and V9 primer pairs could produce a bias for eukaryotic communities analysis. Eukaryotic community structures in the UASB reactor were influenced by the immigration of eukaryotes via influent sewage but were clearly different from the influent sewage and activated sludge. Multivariate statistics indicated that protist genera Cyclidium, Platyophrya and Subulatomonas correlated with chemical oxygen demand and suspended solid concentration, and could be used as bioindicators of treatment performance. Uncultured eukaryotes groups were dominant in the UASB reactor, and their physiological roles need to be examined to understand their contributions to anaerobic processes in future studies.

Carbohydrate Hydrolytic Potential and Redundancy of an Anaerobic Digestion Microbiome Exposed to Acidosis, as Uncovered by Metagenomics

The enzymatic hydrolysis of lignocellulosic biomass is mainly driven by the action of carbohydrate-active enzymes. By characterizing the gene profiles at the different stages of the anaerobic digestion experiment, we showed that the microbiome retains its hydrolytic functional redundancy even during severe acidosis, despite significant changes in taxonomic composition. By analyzing reconstructed bacterial genomes, we demonstrate that Bacteroidetes hydrolytic gene diversity likely favors the abundance of this phylum in some anaerobic digestion systems. Further, we observe genetic redundancy within the Bacteroidetes group, which accounts for the preserved hydrolytic potential during acidosis. This work also uncovers new polysaccharide utilization loci involved in the deconstruction of various biomasses and proposes the model of acetylated glucomannan degradation by Bacteroidetes. Acetylated glucomannan-enriched biomass is a common substrate for many industries, including pulp and paper production. Using naturally evolved cocktails of enzymes for biomass pretreatment could be an interesting alternative to the commonly used chemical pretreatments.

Increased hydrolysis of easily digestible biomass may lead to acidosis of anaerobic reactors and decreased methane production. Previously, it was shown that the structure of microbial communities changed during acidosis; however, once the conditions are back to optimal, biogas (initially CO₂) production quickly restarts. This suggests the retention of the community functional redundancy during the process failure. In this study, with the use of metagenomics and downstream bioinformatics analyses, we characterize the carbohydrate hydrolytic potential of the microbial community, with a special focus on acidosis. To that purpose, carbohydrate-active enzymes were identified, and to further link the community hydrolytic potential with key microbes, bacterial genomes were reconstructed. In addition, we characterized biochemically the specificity and activity of selected enzymes, thus verifying the accuracy of the in silico predictions. The results confirm the retention of the community hydrolytic potential during acidosis and indicate Bacteroidetes to be largely involved in biomass degradation. Bacteroidetes showed higher diversity and genomic content of carbohydrate hydrolytic enzymes that might favor the dominance of this phylum over other bacteria in some anaerobic reactors. The combination of bioinformatic analyses and activity tests enabled us to propose a model of acetylated glucomannan degradation by Bacteroidetes.

IMPORTANCE The enzymatic hydrolysis of lignocellulosic biomass is mainly driven by the action of carbohydrate-active enzymes. By characterizing the gene profiles at the different stages of the anaerobic digestion experiment, we showed that the microbiome retains its hydrolytic functional redundancy even during severe acidosis, despite significant changes in taxonomic composition. By analyzing reconstructed bacterial genomes, we demonstrate that Bacteroidetes hydrolytic gene diversity likely favors the abundance of this phylum in some anaerobic digestion systems. Further, we observe genetic redundancy within the Bacteroidetes group, which accounts for the preserved hydrolytic potential during acidosis. This work also uncovers new polysaccharide utilization loci involved in the deconstruction of various biomasses and proposes the model of acetylated glucomannan degradation by Bacteroidetes. Acetylated glucomannan-enriched biomass is a common substrate for many industries, including pulp and paper production. Using naturally evolved cocktails of enzymes for biomass pretreatment could be an interesting alternative to the commonly used chemical pretreatments.

Microbial Profile of the Leachate from Mexico City’s Bordo Poniente Composting Plant: An Inoculum to Digest Organic Waste

In recent years, municipal solid waste (MSW) management has become a complex problem worldwide. Similarly, Mexico City is facing such a situation for the management and treatment of organic fraction of municipal solid waste (OFMSW). Therefore, in this work, we investigated whether leachate from the composting plant, Bordo Poniente, located in Mexico City can be used as an inoculum for the treatment of OFMSW using thermophilic anaerobic digestion (AD) with a hydraulic retention time of 30 days. We analyzed the physicochemical properties of the leachate and performed a biochemical methane potential test. Archaeal and bacterial diversity was also identified using high throughput DNA sequencing of 16S rDNA libraries. Methane yield was 0.29 m3 CH4/kg VSadded in the positive control and 0.16 m3 CH4/kg VSadded in the treatment group. The phylum, Bacteroidetes, and genus, Methanosarcina, prevailed in the leachate. However, in thermophilic conditions, the microbial communities changed, and the phylum, Firmicutes, genera, Methanoculleus, and candidate genus, vadinCA11, were dominant in the treatment group. We concluded that the leachate contains a suitable initial charge of many active bacteria and methanogenic archaea which contribute to the AD process, hence it can be used as an inoculum for the treatment of OFMSW.

Acetate promotes microbial reductive debromination of tetrabromobisphenol A during the startup phase of anaerobic wastewater sludge bioreactors

The detection of increasing concentrations of tetrabromobisphenol A (TBBPA) in wastewater treatment plants is raising concerns as TBBPA has been identified as a potentially toxic flame retardant. The objectives of this study were to evaluate the effect of acetate biostimulation on TBBPA microbial reductive debromination, and the response of anaerobic sludge associated microbial communities repeatedly exposed to TBBPA. Results indicate that the bulk of the microbial community did not experience significant shifts as a result of TBBPA exposure, and that only a small fraction of the community responded to the presence of TBBPA. Taxa most likely responsible for TBBPA transformation affiliated to Clostridiales and the wastewater sludge group Blvii28. The biostimulating effect of acetate was only observed during reactor startup, when acetogenesis was likely not yet occurring. However, when acetate likely started to be microbially generated in the reactor, acetate addition resulted in a slight but significant inhibiting effect on TBBPA transformation. A significant increase of hydrogenotrophic methanogens in the TBBPA-spiked reactor overtime implies that TBBPA degraders were not in direct competition with methanogens for H₂. These results strongly suggest that TBBPA degrading taxa might have been primarily using acetate as an electron donor for the reductive debromination of TBBPA.

Performance and Microbial Community Dynamics in Anaerobic Digestion of Waste Activated Sludge: Impact of Immigration

Waste activated sludge (WAS) is a byproduct of municipal wastewater treatment. WAS contains a large proportion of inactive microbes, so when it is used as a substrate for anaerobic digestion (AD), their presence can interfere with monitoring of active microbial populations. To investigate how influent cells affect the active and inactive microbial communities during digestion of WAS, we operated model mesophilic bioreactors with conventional conditions. Under six different hydraulic retention times (HRTs; 25, 23, 20, 17, 14, and 11.5 d), the chemical oxygen demand (COD) removal and CH4 production of the AD were within a typical range for mesophilic sludge digesters. In the main bacteria were proteobacteria, bacteroidetes, and firmicutes in both the WAS and the bioreactors, while in main archaeal methanogen group was Methanosarcinales in the WAS and methanomicrobiales in the bioreactors. Of the 106 genera identified, the estimated net growth rates were negative in 72 and positive in 34. The genera with negative growth included many aerobic taxa. The genera with positive growth rates included methanogens and syntrophs. In some taxa, the net growth rate could be positive or negative, depending on HRT, so their abundance was also affected by HRT. This study gives insights into the microbial dynamics of a conventional sludge anaerobic digester by distinguishing potentially active (growing) and inactive (non-growing, dormant) microbes and by correlating population dynamics with process parameters.

Comparative analysis of deep sequenced methanogenic communities: identification of microorganisms responsible for methane production

BACKGROUND

Although interactions between microorganisms involved in biogas production are largely uncharted, it is commonly accepted that methanogenic Archaea are essential for the process. Methanogens thrive in various environments, but the most extensively studied communities come from biogas plants. In this study, we employed a metagenomic analysis of deeply sequenced methanogenic communities, which allowed for comparison of taxonomic and functional diversity as well as identification of microorganisms directly involved in various stages of methanogenesis pathways.

RESULTS

A comprehensive metagenomic approach was used to compare seven environmental communities, originating from an agricultural biogas plant, cattle-associated samples, a lowland bog, sewage sludge from a wastewater treatment plant and sediments from an ancient gold mine. In addition to the native consortia, two laboratory communities cultivated on maize silage as the sole substrate were also analyzed. Results showed that all anaerobic communities harbored genes of all known methanogenesis pathways, but their abundance varied greatly between environments and that genes were encoded by different methanogens. Identification of microorganisms directly involved in different stages of methane production revealed that hydrogenotrophic methanogens, such as Methanoculleus, Methanobacterium, Methanobrevibacter, Methanocorpusculum or Methanoregula, predominated in most native communities, whereas acetoclastic Methanosaeta seemed to be the key methanogen in the wastewater treatment plant. Furthermore, in many environments, the methylotrophic pathway carried out by representatives of Methanomassiliicoccales, such as Candidatus Methanomethylophilus and Candidatus Methanoplasma, seemed to play an important role in methane production. In contrast, in stable laboratory reactors substrate versatile Methanosarcina predominated.

CONCLUSIONS

The metagenomic approach presented in this study allowed for deep exploration and comparison of nine environments in which methane production occurs. Different abundance of methanogenesis-related functions was observed and the functions were analyzed in the phylogenetic context in order to identify microbes directly involved in methane production. In addition, a comparison of two metagenomic analytical tools, MG-RAST and MetAnnotate, revealed that combination of both allows for a precise characterization of methanogenic communities.

Full-scale agricultural biogas plant metal content and process parameters in relation to bacterial and archaeal microbial communities over 2.5 year span

A start-up of 4 MW agricultural biogas plant in Vučja vas, Slovenia, was monitored from 2011 to 2014. The start-up was carried out in 3 weeks with the intake of biomass from three operating full-scale 1-2 MW donor agricultural biogas plants. The samples were taken from donor digesters and from two serial digesters during the start-up over the course of 2.5 years. Bacterial and Archaeal microbial communities progressively diverged from the composition of donor digesters during the start-up phase. The rate of change of Bacterial community decreased exponentially over the first 2.5 years as dynamics within the first 70 days was comparable to that of the next 1.5 years, whereas approximately constant rate was observed for Archaea. Despite rearrangements, the microbial communities remained functionally stable and produced biogas throughout the whole 2.5 years of observation. All systems parameters measured were ordered according to their Kernel density (Gaussian function) ranging from the most dispersed (substrate categories used as cosubstrates, quantities of each cosubstrate, substate dry and volatile matter, process parameters) towards progressively least dispersed (trace metal and ion profiles, aromatic-polyphenolic compounds, biogas plant functional output (energy)). No deficiency was detected in trace metal content as the distribution of metals and elements fluctuated within the suggested limits for biogas over 2.5 year observation. In contrast to the recorded process variables, Bacterial and Archaeal microbial communities exhibited directed changes oriented in time. Variation partitioning showed that a large fraction of variability in the Bacterial and Archaeal microbial communities (55% and 61%, respectively) remained unexplained despite numerous measured variables (n = 44) and stable biogas production. Our results show that the observed reorganization of microbial communities was not directly associated with impact on the full-scale biogas reactor performance. Novel parameters need to be determined to elucidate the variables directly associated with the reorganization of microbial communities and those relevant for sustained function such as the more in-depth interaction between TSOC, trace metal profiles, aromatic-polyphenolic compounds and ionic strength (e.g. electrical conductivity).

High-Throughput Sequencing Analysis of the Actinobacterial Spatial Diversity in Moonmilk Deposits

Moonmilk are cave carbonate deposits that host a rich microbiome, including antibiotic-producing Actinobacteria, making these speleothems appealing for bioprospecting. Here, we investigated the taxonomic profile of the actinobacterial community of three moonmilk deposits of the cave "Grotte des Collemboles" via high-throughput sequencing of 16S rRNA amplicons. Actinobacteria was the most common phylum after Proteobacteria, ranging from 9% to 23% of the total bacterial population. Next to actinobacterial operational taxonomic units (OTUs) attributed to uncultured organisms at the genus level (~44%), we identified 47 actinobacterial genera with Rhodoccocus (4 OTUs, 17%) and Pseudonocardia (9 OTUs, ~16%) as the most abundant in terms of the absolute number of sequences. Streptomycetes presented the highest diversity (19 OTUs, 3%), with most of the OTUs unlinked to the culturable Streptomyces strains that were previously isolated from the same deposits. Furthermore, 43% of the OTUs were shared between the three studied collection points, while 34% were exclusive to one deposit, indicating that distinct speleothems host their own population, despite their nearby localization. This important spatial diversity suggests that prospecting within different moonmilk deposits should result in the isolation of unique and novel Actinobacteria. These speleothems also host a wide range of non-streptomycetes antibiotic-producing genera, and should therefore be subjected to methodologies for isolating rare Actinobacteria.

Revealing the anaerobic acclimation of microbial community in a membrane bioreactor for coking wastewater treatment by Illumina Miseq sequencing

The dynamic change of microbial community during sludge acclimation from aerobic to anaerobic in a MBR for coking wastewater treatment was revealed by Illumina Miseq sequencing in this study. The diversity of both Bacteria and Archaea showed an increase-decrease trajectory during acclimation, and exhibited the highest at the domestication interim. Ignavibacteria changed from a tiny minority (less than 1%) to the dominant bacterial group (54.0%) along with acclimation. The relative abundance of Betaproteobacteria kept relatively steady, as in this class some species increased coupled with some other species decreased during acclimation. The dominant Archaea shifted from Halobacteria in initial aerobic sludge to Methanobacteria in the acclimated anaerobic sludge. The dominant bacterial and archaeal groups in different acclimation stages were indigenous microorganisms in the initial sludge, though some of them were very rare. This study supported that the species in "rare biosphere" might eventually become dominant in response to environmental change.

A year of monitoring 20 mesophilic full-scale bioreactors reveals the existence of stable but different core microbiomes in bio-waste and wastewater anaerobic digestion systems

BACKGROUND

Anaerobic digestion (AD) is a microbe-driven process of biomass decomposition to CH₄ and CO₂. In addition to renewable and cost-effective energy production, AD has emerged in the European Union as an environmentally friendly model of bio-waste valorisation and nutrient recycling. Nevertheless, due to the high diversity of uncharacterised microbes, a typical AD microbiome is still considered as "dark matter".

RESULTS

Using the high-throughput sequencing of small rRNA gene, and a monthly monitoring of the physicochemical parameters for 20 different mesophilic full-scale bioreactors over 1 year, we generated a detailed view of AD microbial ecology towards a better understanding of factors that influence and shape these communities. By studying the broadly distributed OTUs present in over 80% of analysed samples, we identified putatively important core bacteria and archaea to the AD process that accounted for over 70% of the whole microbial community relative abundances. AD reactors localised at the wastewater treatment plants were shown to operate with distinct core microbiomes than the agricultural and bio-waste treating biogas units. We also showed that both the core microbiomes were composed of low (with average community abundance ≤ 1%) and highly abundant microbial populations; the vast majority of which remains yet uncharacterised, e.g. abundant candidate Cloacimonetes. Using non-metric multidimensional scaling, we observed microorganisms grouping into clusters that well reflected the origin of the samples, e.g. wastewater versus agricultural and bio-waste treating biogas units. The calculated diversity patterns differed markedly between the different community clusters, mainly due to the presence of highly diverse and dynamic transient species. Core microbial communities appeared relatively stable over the monitoring period.

CONCLUSIONS

In this study, we characterised microbial communities in different AD systems that were monitored over a 1-year period. Evidences were shown to support the concept of a core community driving the AD process, whereas the vast majority of dominant microorganisms remain yet to be characterised.

Microbiome dynamics and adaptation of expression signatures during methane production failure and process recovery

This study aimed to uncover microbial dynamics and transcriptional adaptations during mesophilic AD of maize silage and slurry. While one digester performed under optimal conditions, the investigations also evaluated the microbiome during a temperature drop mediated process failure accompanied by acidification and how it contributed to a process recovery. Composition and pathway activities were analyzed by whole genome shotgun (WGS) and metatranscriptome sequencing, respectively. A biodiversity of 112 species was observed with noticeable shifts over process time. Although four distinct groups of microbes could be identified with a correlating versatility according to substrate and to process disturbance, also tremendous effects on gene expression were monitored especially of the archaeal methane metabolism. Particularly, the expression of acetogenotrophic methanogenesis related genes was identified to be relevant for process regeneration.

Biochar and activated carbon act as promising amendments for promoting the microbial debromination of tetrabromobisphenol A

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential environmental health impacts as it has been shown to cause various deleterious effects in humans. The fact that the highest concentrations of TBBPA have been reported in wastewater sludge is concerning as effluent discharge and biosolids land application are likely a route by which TBBPA can be further disbursed to the environment. Our objectives in this study were to evaluate the effect of biochar (BC) and activated carbon (AC) in promoting the biodegradation of TBBPA, and characterize the response of anaerobic sludge microbial communities following amendments. Both carbonaceous amendments were found to promote the reductive debromination of TBBPA. Nearly complete transformation of TBBPA to BPA was observed in the amended reactors ∼20 days earlier than in the control reactors. In particular, the transformation of diBBPA to monoBBPA, which appears to be the rate-limiting step, was accelerated in the presence of either amendment. Overall, microbial taxa responding to the amendments, i.e., 'sensitive responders', represented a small proportion of the community (i.e., 7.2%), and responded positively. However, although both amendments had a similar effect on TBBPA degradation, the taxonomic profile of the sensitive responders differed greatly from one amendment to the other. BC had a taxonomically broader and slightly more pronounced effect than AC. This work suggests that BC and AC show great potential to promote the biodegradation of TBBPA in anaerobic sludge, and their integration into wastewater treatment processes may be helpful for removing TBBPA and possibly other emerging hydrophobic contaminants.

Adaptation of Methanogenic Inocula to Anaerobic Digestion of Maize Silage

A well-balanced microbial consortium is crucial for efficient biogas production. In turn, one of a major factor that influence on the structure of anaerobic digestion (AD) consortium is a source of microorganisms which are used as an inoculum. This study evaluated the influence of inoculum sources (with various origin) on adaptation of a biogas community and the efficiency of the biomethanization of maize silage. As initial inocula for AD of maize silage the samples from: (i) an agricultural biogas plant (ABP) which utilizes maize silage as a main substrate, (ii) cattle slurry (CS), which contain elevated levels of lignocelluloses materials, and (iii) raw sewage sludge (RSS) with low content of plant origin materials were used. The adaptation of methanogenic consortia was monitored during a series of passages, and the functionality of the adapted consortia was verified through start-up operation of AD in two-stage reactors. During the first stages of the adaptation phase, methanogenic consortia occurred very slowly, and only after several passages did the microbial community adapts to allow production of biogas with high methane content. The ABP consortium revealed highest biogas production in the adaptation and in the start-up process. The biodiversity dynamics monitored during adaptation and start-up process showed that community profile changed in a similar direction in three studied consortia. Native communities were very distinct to each other, while at the end of the Phase II of the start-up process microbial diversity profile was similar in all consortia. All adopted bacterial communities were dominated by representatives of Porphyromonadaceae, Rikenellaceae, Ruminococcaceae, and Synergistaceae. A shift from low acetate-preferring acetoclastic Methanosaetaceae (ABP and RSS) and/or hydrogenotrophic Archaea, e.g., Methanomicrobiaceae (CS) prevailing in the inoculum samples to larger populations of high acetate-preferring acetoclastic Methanosarcinaceae was observed by the end of the experiment. As a result, three independent, functional communities that syntrophically produced methane from acetate (primarily) and H₂/CO₂, methanol and methylamines were adapted. This study provides new insights into the specific process by which different inocula sampled from typical methanogenic environments that are commonly used to initiate industrial installations gradually adapted to allow biogas production from maize silage.

Optimization of a metatranscriptomic approach to study the lignocellulolytic potential of the higher termite gut microbiome

Background

Thanks to specific adaptations developed over millions of years, the efficiency of lignin, cellulose and hemicellulose decomposition of higher termite symbiotic system exceeds that of many other lignocellulose utilizing environments. Especially, the examination of its symbiotic microbes should reveal interesting carbohydrate-active enzymes, which are of primary interest for the industry. Previous metatranscriptomic reports (high-throughput mRNA sequencing) highlight the high representation and overexpression of cellulose and hemicelluloses degrading genes in the termite hindgut digestomes, indicating the potential of this technology in search for new enzymes. Nevertheless, several factors associated with the material sampling and library preparation steps make the metatranscriptomic studies of termite gut prokaryotic symbionts challenging.

Methods

In this study, we first examined the influence of the sampling strategy, including the whole termite gut and luminal fluid, on the diversity and the metatranscriptomic profiles of the higher termite gut symbiotic bacteria. Secondly, we evaluated different commercially available kits combined in two library preparative pipelines for the best bacterial mRNA enrichment strategy.

Results

We showed that the sampling strategy did not significantly impact the generated results, both in terms of the representation of the microbes and their transcriptomic profiles. Nevertheless collecting luminal fluid reduces the co-amplification of unwanted RNA species of host origin. Furthermore, for the four studied higher termite species, the library preparative pipeline employing Ribo-Zero Gold rRNA Removal Kit “Epidemiology” in combination with Poly(A) Purist MAG kit resulted in a more efficient rRNA and poly-A-mRNAdepletion (up to 98.44% rRNA removed) than the pipeline utilizing MICROBExpress and MICROBEnrich kits. High correlation of both Ribo-Zero and MICROBExpresse depleted gene expression profiles with total non-depleted RNA-seq data has been shown for all studied samples, indicating no systematic skewing of the studied pipelines.

Conclusions

We have extensively evaluated the impact of the sampling strategy and library preparation steps on the metatranscriptomic profiles of the higher termite gut symbiotic bacteria. The presented methodological approach has great potential to enhance metatranscriptomic studies of the higher termite intestinal flora and to unravel novel carbohydrate-active enzymes.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4076-9) contains supplementary material, which is available to authorized users.

Microbial population dynamics in urban organic waste anaerobic co-digestion with mixed sludge during a change in feedstock composition and different hydraulic retention times

Microbial communities play an essential role in the biochemical pathways of anaerobic digestion processes. The correlations between microorganisms' relative abundance and anaerobic digestion process parameters were investigated, by considering the effect of different feedstock compositions and hydraulic retention times (HRTs). Shifts in microbial diversity and changes in microbial community richness were observed by changing feedstock composition from mono-digestion of mixed sludge to co-digestion of food waste, grass clippings and garden waste with mixed sludge at HRT of 30, 20, 15 and 10 days. Syntrophic acetate oxidation along with hydrogenotrophic methanogenesis, mediated by Methanothermobacter, was found to be the most prevalent methane formation pathway, with the only exception of 10 days' HRT, in which Methanosarcina was the most dominant archaea. Significantly, the degradation of complex organic polymers was found to be the most active process, performed by members of S1 (Thermotogales), Thermonema and Lactobacillus in a reactor fed with a high share of food waste. Conversely, Thermacetogenium, Anaerobaculum, Ruminococcaceae, Porphyromonadaceae and the lignocellulosic-degrading Clostridium were the significantly more abundant bacteria in the reactor fed with an increased share of lignocellulosic biomass in the form of grass clippings and garden waste. Finally, microbes belonging to Coprothermobacter, Syntrophomonas and Clostridium were correlated significantly with the specific methane yield obtained in both reactors.

Functional bacterial and archaeal diversity revealed by 16S rRNA gene pyrosequencing during potato starch processing wastewater treatment in an UASB

Microbial community structure of sludge sampled from an UASB treating potato starch processing wastewater (PSPW) was investigated. Operational taxonomic units revealed at 97% sequence identity tolerance was 2922, 2869 and 3919 for bottom, middle and top sections of the reactor, respectively. Overall abundant phylum observed within the UASB was low-G+C-Gram-positive bacteria affiliated to Firmicutes (26.01%) followed by Chloroflexi (16.70%), Proteobacteria (12.71%), Cloacimonetes (10.72%), Bacteroidetes (7.87%), Synergistetes (9.02%) and Euryarchaeota (8.82%). Whiles Firmicutes had dominated the bottom and top section by 34.01% and 28.64%, respectively, middle section was predominantly Euryarchaeota (24.32%) with major dominance in methanogens affiliated to genus Methanosaeta. The results demonstrated substantial stratification of the microbial community structure along the reactor height with various functional bacterial groups which subsequently allowed degradation of organics in PSPW in sequential mode. The findings herein would provide guidance for optimizing the anaerobic process and operation of the UASB.

Microbial community structure in a full-scale anaerobic treatment plant during start-up and first year of operation revealed by high-throughput 16S rRNA gene amplicon sequencing

High-throughput amplicon sequencing of six biomass samples from a full-scale anaerobic reactor at a Norwegian wood and pulp factory using Biothane Biobed Expanded Granular Sludge Bed (EGSB) technology during start-up and first year of operation was performed. A total of 106,166 16S rRNA gene sequences (V3-V5 region) were obtained. The number of operational taxonomic units (OTUs) ranged from 595 to 2472, and a total of 38 different phyla and 143 families were observed. The predominant phyla were Bacteroidetes, Chloroflexi, Firmicutes, Proteobacteria, and Spirochaetes. A more diverse microbial community was observed in the inoculum biomass coming from an Upflow Anaerobic Sludge Blanket (USAB) reactor, reflecting an adaptation of the inoculum diversity to the specific conditions of the new reactor. In addition, no taxa classified as obligate pathogens were identified and potentially opportunistic pathogens were absent or observed in low abundances. No Legionella bacteria were identified by traditional culture-based and molecular methods.