Stability and reproducibility of low-temperature anaerobic biological wastewater treatment

Ecogenomics Reveals Microbial Metabolic Networks in a Psychrophilic Methanogenic Bioreactor Treating Soy Sauce Production Wastewater

An ecogenomic analysis of the methanogenic microbial community in a laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor treating soy sauce-processing wastewater revealed a synergistic metabolic network. Granular sludge samples were collected from the UASB reactor operated under psychrophilic (20°C) conditions with a COD removal rate >75%. A 16S rRNA gene amplicon sequencing-based microbial community analysis classified the major microbial taxa as Methanothrix, Methanobacterium, Pelotomaculaceae, Syntrophomonadaceae, Solidesulfovibrio, and members of the phyla Synergistota and Bacteroidota. Draft genomes of dominant microbial populations were recovered by metagenomic shotgun sequencing. Metagenomic- and metatranscriptomic-assisted metabolic reconstructions indicated that Synergistota- and Bacteroidota-related organisms play major roles in the degradation of amino acids. A metagenomic bin of the uncultured Bacteroidales 4484-276 clade encodes genes for proteins that may function in the catabolism of phenylalanine and tyrosine under microaerobic conditions. Syntrophomonadaceae and Pelotomaculaceae oxidize fatty acid byproducts presumably derived from the degradation of amino acids in syntrophic association with aceticlastic and hydrogenotrophic methanogen populations. Solidesulfovibrio organisms are responsible for the reduction of sulfite and may support the activity of hydrogenotrophic methanogens and other microbial populations by providing hydrogen and ammonia using nitrogen fixation-related proteins. Overall, functionally diverse anaerobic organisms unite to form a metabolic network that performs the complete degradation of amino acids in the psychrophilic methanogenic microbiota.

Cold adaptation and replicable microbial community development during long-term low-temperature anaerobic digestion treatment of synthetic sewage

The development and activity of a cold-adapting microbial community was monitored during low-temperature anaerobic digestion (LtAD) treatment of wastewater. Two replicate hybrid anaerobic sludge bed-fixed-film reactors treated a synthetic sewage wastewater at 12°C, at organic loading rates of 0.25-1.0 kg chemical oxygen demand (COD) m-3 d-1, over 889 days. The inoculum was obtained from a full-scale anaerobic digestion reactor, which was operated at 37°C. Both LtAD reactors readily degraded the influent with COD removal efficiencies regularly exceeding 78% for both the total and soluble COD fractions. The biomass from both reactors was sampled temporally and tested for activity against hydrolytic and methanogenic substrates at 12°C and 37°C. Data indicated that significantly enhanced low-temperature hydrolytic and methanogenic activity developed in both systems. For example, the hydrolysis rate constant (k) at 12°C had increased 20-30-fold by comparison to the inoculum by day 500. Substrate affinity also increased for hydrolytic substrates at low temperature. Next generation sequencing demonstrated that a shift in a community structure occurred over the trial, involving a 1-log-fold change in 25 SEQS (OTU-free approach) from the inoculum. Microbial community structure changes and process performance were replicable in the LtAD reactors.

Use of PCR-DGGE Based Molecular Methods to Analyse Microbial Community Diversity and Stability during the Thermophilic Stages of an ATAD Wastewater Sludge Treatment Process as an Aid to Performance Monitoring

PCR and PCR-DGGE techniques have been evaluated to monitor biodiversity indexes within an ATAD (autothermal thermophilic aerobic digestion) system treating domestic sludge for land spread, by examining microbial dynamics in response to elevated temperatures during treatment. The ATAD process utilises a thermophilic population to generate heat and operates at elevated pH due to degradation of sludge solids, thus allowing pasteurisation and stabilisation of the sludge. Genera-specific PCR revealed that Archaea, Eukarya and Fungi decline when the temperature reaches 59°C, while the bacterial lineage constitutes the dominant group at this stage. The bacterial community at the thermophilic stage, its similarity index to the feed material, and the species richness present were evaluated by PCR-DGGE. Parameters such as choice of molecular target (16S rDNA or rpoB genes), and electrophoresis condition, were optimised to maximise the resolution of the method for ATAD. Dynamic analysis of microbial communities was best observed utilising PCR-DGGE analysis of the V6-V8 region of 16S rDNA, while rpoB gene profiles were less informative. Unique thermophilic communities were shown to quickly adapt to process changes, and shown to be quite stable during the process. Such techniques may be used as a monitoring technique for process health and efficiency.

A functional approach to uncover the low-temperature adaptation strategies of the archaeon Methanosarcina barkeri

Low-temperature anaerobic digestion (LTAD) technology is underpinned by a diverse microbial community. The methanogenic archaea represent a key functional group in these consortia, undertaking CO2 reduction as well as acetate and methylated C1 metabolism with subsequent biogas (40 to 60% CH4 and 30 to 50% CO2) formation. However, the cold adaptation strategies, which allow methanogens to function efficiently in LTAD, remain unclear. Here, a pure-culture proteomic approach was employed to study the functional characteristics of Methanosarcina barkeri (optimum growth temperature, 37°C), which has been detected in LTAD bioreactors. Two experimental approaches were undertaken. The first approach aimed to characterize a low-temperature shock response (LTSR) of M. barkeri DSMZ 800(T) grown at 37°C with a temperature drop to 15°C, while the second experimental approach aimed to examine the low-temperature adaptation strategies (LTAS) of the same strain when it was grown at 15°C. The latter experiment employed cell viability and growth measurements (optical density at 600 nm [OD600]), which directly compared M. barkeri cells grown at 15°C with those grown at 37°C. During the LTSR experiment, a total of 127 proteins were detected in 37°C and 15°C samples, with 20 proteins differentially expressed with respect to temperature, while in the LTAS experiment 39% of proteins identified were differentially expressed between phases of growth. Functional categories included methanogenesis, cellular information processing, and chaperones. By applying a polyphasic approach (proteomics and growth studies), insights into the low-temperature adaptation capacity of this mesophilically characterized methanogen were obtained which suggest that the metabolically diverse Methanosarcinaceae could be functionally relevant for LTAD systems.

Treatment of low-strength wastewater in an anaerobic down-flow hanging sponge (AnDHS) reactor at low temperature

The process performance of a novel anaerobic down-flow hanging sponge (AnDHS) reactor for the treatment of low strength wastewater was investigated. A lab-scale experiment was conducted in which 300-400 mgCOD L(-1) of artificial wastewater was fed in over 600 days. The reactor exhibited sufficient performance: 70-90% of total COD removal, and 60-90% of methane recovery were maintained at 20°C, with a hydraulic retention time (HRT) of 2 h. It was possible to maintain COD removal by extending the HRT to 4 h at 15°C and 10 h at 10°C. With regard to the wastewater feed, one-pass mode (without effluent recirculation) gave better performance in COD removal as compared with recirculation mode. The results of batch feeding experiments using single substrates (such as acetate, propionate or sucrose) indicated that acetate degradation was more strongly affected by decreasing operational temperature. In addition, the AnDHS reactor system had no significant problems related to sludge retention such as massive loss of sludge throughout the experiment. Microbial structure analysis of the retained sludge with respect to the domain Archaeal 16S rRNA gene showed the proliferation of relatives of both the acetate-utilizing genus Methanosaeta and the hydrogen-utilizing genus Methanolinea.

Balance of neutral and deterministic components in the dynamics of activated sludge floc assembly

Understanding the processes that generate patterns of community structure is a central focus of ecological research. With that aim, we manipulated the structure of bacterial activated sludge to test the influence of the species richness and composition of bacterial communities on the dynamics of activated sludge floc assembly in lab-scale bioreactors. Bacterial community structure was analyzed using denaturing gradient gel electrophoresis of RT-PCR amplified 16S rRNA. Fingerprinting of four parallel reactors, started with the same source communities added in different proportions, converged to patterns that were more similar than expected by chance, suggesting a deterministic selection in floc development. Evidence for neutral dynamics was suggested by the dependence of the rate of replacement of species (bacterial taxa-time relationships) on the number of available species in the source community. Further indication of stochastic dynamics was obtained by the application of the Sloan neutral model for prokaryotes. The fitting of the observed data to the model predictions revealed that the importance of the stochastic component increased with the size of the reservoir of species richness from which the community is drawn. Taken together, the results illustrate how both neutral and deterministic dynamics operate simultaneously in the assembly of the bacterial floc and show that the balance of the two depends on the richness of the source community.

High reproducibility of ammonia-oxidizing bacterial communities in parallel sequential batch reactors

AIMS

To investigate whether the ammonia-oxidizing bacterial (AOB) communities of replicate nitrifying bioreactors (i) co-evolve or diverge over time and (ii) are stable or dynamic during periods of complete nitrification.

METHODS AND RESULTS

Three sequential batch reactors (SBR) were inoculated with sludge from a municipal wastewater treatment plant, fed with ammonium-enriched tap water and operated in parallel for 134 days. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) demonstrated co-evolvement of the AOB communities over time. During start-up, temporary decreases in nitrification were noticed, and the AOB community rate of change values (Delta(t(week))) were medium to high (12-22%). During the adjacent period of complete nitrification, low AOB community dynamics were observed (Delta(t(week)) < 5%). Further pragmatic processing of the DGGE profiles revealed a high range-weighted richness and a medium functional organization of the AOB communities.

CONCLUSIONS

After a start-up period, high functional stability and low dynamics of the AOB communities were observed. Deterministic rather than stochastic driving forces led to AOB community co-evolvement in the replicate SBR.

SIGNIFICANCE AND IMPACT OF THE STUDY

Replicates in identical set-ups are reproducible, and pragmatic processing of DGGE patterns is a straightforward tool to score and compare the functionality of the bacterial communities.

A novel ecological role of the Firmicutes identified in thermophilic microbial fuel cells

Significant effort is currently focused on microbial fuel cells (MFCs) as a source of renewable energy. Most studies concentrate on operation at mesophilic temperatures. However, anaerobic digestion studies have reported on the superiority of thermophilic operation and demonstrated a net energy gain in terms of methane yield. As such, our studies focused on MFC operation and microbiology at 55 degrees C. Over a 100-day operation, these MFCs were stable and achieved a power density of 37 mW m(-2) with a coulombic efficiency of 89%. To infer activity and taxonomic identity of dominant members of the electricity-producing community, we performed phylogenetic microarray and clone library analysis with small subunit ribosomal RNA (16S rRNA) and ribosomal RNA gene (16S rDNA). The results illustrated the dominance (80% of clone library sequences) of the Firmicutes in electricity production. Similarly, rRNA sequences from Firmicutes accounted for 50% of those taxa that increased in relative abundance from current-producing MFCs, implying their functional role in current production. We complemented these analyses by isolating the first organisms from a thermophilic MFC. One of the isolates, a Firmicutes Thermincola sp. strain JR, not only produced more current than known organisms (0.42 mA) in an H-cell system but also represented the first demonstration of direct anode reduction by a member of this phylum. Our research illustrates the importance of using a variety of molecular and culture-based methods to reliably characterize bacterial communities. Consequently, we revealed a previously unidentified functional role for Gram-positive bacteria in MFC current generation.

Temporal microbial diversity changes in solvent-degrading anaerobic granular sludge from low-temperature (15°C) wastewater treatment bioreactors

Anaerobic sludge granules were obtained from laboratory-scale anaerobic bioreactors used to treat pharmaceutical-like (methanol-, acetone- and propanol-contaminated) wastewater under low-temperature conditions (15 degrees C). The microbial diversity and diversity changes of the sludge samples were ascertained by applying 16S rRNA gene cloning and terminal restriction fragment length polymorphism (TRFLP) analyses, respectively, and using sludge samples from the inoculum, throughout and at the conclusion of the bioreactor trial. Data from genetic fingerprinting correlated well with those from physiological activity assays of the reactor biomass. Specifically, for example, TRFLP profiles indicated the dominance of hydrogenotrophic methanogens within the archaeal community, thus supporting the findings of specific methanogenic activity measurements. TRFLP data supported the hypothesis that the deviation between the replicated reactors, in terms of treatment efficiency, was associated with succession within the microbial communities present, and indicated that community development was linked to both operating temperature and wastewater composition. Fluorescence in situ hybridization (FISH) was also applied, to quantitatively assess the abundance of selected microbial groups, and revealed the underestimation of the abundance Methanosarcina by gene cloning analysis and demonstrated the spatial arrangement of these organisms within the architecture of the low-temperature solvent-degrading anaerobic biofilms.