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

Importance of temperature on immuno-metabolic regulation and cancer progression

Cancer immunotherapies emerge as promising strategies for restricting tumour growth. The tumour microenvironment (TME) has a major impact on the anti-tumour immune response and on the efficacy of the immunotherapies. Recent studies have linked changes in the ambient temperature with particular immuno-metabolic reprogramming and anti-cancer immune response in laboratory animals. Here, we describe the energetic balance of the organism during change in temperature, and link this to the immune alterations that could be of relevance for cancer, as well as for other human diseases. We highlight the contribution of the gut microbiota in modifying this interaction. We describe the overall metabolic response and underlying mechanisms of tumourigenesis in mouse models at varying ambient temperatures and shed light on their potential importance in developing therapeutics against cancer.

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.

Molecular insights informing factors affecting low temperature anaerobic applications: Diversity, collated core microbiomes and complexity stability relationships in LCFA-fed systems

Fats, oil and grease, and their hydrolyzed counterparts-long chain fatty acids (LCFA) make up a large fraction of numerous wastewaters and are challenging to degrade anaerobically, more so, in low temperature anaerobic digestion (LtAD) systems. Herein, we perform a comparative analysis of publicly available Illumina 16S rRNA datasets generated from LCFA-degrading anaerobic microbiomes at low temperatures (10 and 20 °C) to comprehend the factors affecting microbial community dynamics. The various factors considered were the inoculum, substrate and operational characteristics, the reactor operation mode and reactor configuration, and the type of nucleic acid sequenced. We found that LCFA-degrading anaerobic microbiomes were differentiated primarily by inoculum characteristics (inoculum source and morphology) in comparison to the other factors tested. Inoculum characteristics prominently shaped the species richness, species evenness and beta-diversity patterns in the microbiomes even after long term operation of continuous reactors up to 150 days, implying the choice of inoculum needs careful consideration. The generalised additive models represented through beta diversity contour plots revealed that psychrophilic bacteria RBG-13-54-9 from family Anaerolineae, and taxa WCHB1-41 and Williamwhitmania were highly abundant in LCFA-fed microbial niches, suggesting their role in anaerobic treatment of LCFAs at low temperatures of 10-20 °C. Overall, we showed that the following bacterial genera: uncultured Propionibacteriaceae, Longilinea, Christensenellaceae R7 group, Lactivibrio, candidatus Caldatribacterium, Aminicenantales, Syntrophus, Syntrophomonas, Smithella, RBG-13-54-9, WCHB1-41, Trichococcus, Proteiniclasticum, SBR1031, Lutibacter and Lentimicrobium have prominent roles in LtAD of LCFA-rich wastewaters at 10-20 °C. This study provides molecular insights of anaerobic LCFA degradation under low temperatures from collated datasets and will aid in improving LtAD systems for treating LCFA-rich wastewaters.

Current Trends in Biological Valorization of Waste-Derived Biomass: The Critical Role of VFAs to Fuel A Biorefinery

The looming climate and energy crises, exacerbated by increased waste generation, are driving research and development of sustainable resource management systems. Research suggests that organic materials, such as food waste, grass, and manure, have potential for biotransformation into a range of products, including: high-value volatile fatty acids (VFAs); various carboxylic acids; bioenergy; and bioplastics. Valorizing these organic residues would additionally reduce the increasing burden on waste management systems. Here, we review the valorization potential of various sustainably sourced feedstocks, particularly food wastes and agricultural and animal residues. Such feedstocks are often micro-organism-rich and well-suited to mixed culture fermentations. Additionally, we touch on the technologies, mainly biological systems including anaerobic digestion, that are being developed for this purpose. In particular, we provide a synthesis of VFA recovery techniques, which remain a significant technological barrier. Furthermore, we highlight a range of challenges and opportunities which will continue to drive research and discovery within the field. Analysis of the literature reveals growing interest in the development of a circular bioeconomy, built upon a biorefinery framework, which utilizes biogenic VFAs for chemical, material, and energy applications.

Principles, Advances, and Perspectives of Anaerobic Digestion of Lipids

Several problems associated with the presence of lipids in wastewater treatment plants are usually overcome by removing them ahead of the biological treatment. However, because of their high energy content, waste lipids are interesting yet challenging pollutants in anaerobic wastewater treatment and codigestion processes. The maximal amount of waste lipids that can be sustainably accommodated, and effectively converted to methane in anaerobic reactors, is limited by several problems including adsorption, sludge flotation, washout, and inhibition. These difficulties can be circumvented by appropriate feeding, mixing, and solids separation strategies, provided by suitable reactor technology and operation. In recent years, membrane bioreactors and flotation-based bioreactors have been developed to treat lipid-rich wastewater. In parallel, the increasing knowledge on the diversity of complex microbial communities in anaerobic sludge, and on interspecies microbial interactions, contributed to extend the knowledge and to understand more precisely the limits and constraints influencing the anaerobic biodegradation of lipids in anaerobic reactors. This critical review discusses the most important principles underpinning the degradation process and recent key discoveries and outlines the current knowledge coupling fundamental and applied aspects. A critical assessment of knowledge gaps in the field is also presented by integrating sectorial perspectives of academic researchers and of prominent developers of anaerobic technology.

Unveiling the characterization and development of prokaryotic community during the start-up and long-term operation of a pilot-scale anaerobic membrane bioreactor for the treatment of real municipal wastewater

The anaerobic membrane bioreactor (AnMBR) is a promising sustainable process and technology for the treatment of municipal wastewater from the perspective of carbon neutrality. In this study, a large pilot-scale AnMBR was constructed and the microbial community development of the anaerobic digested sludge in the AnMBR was determined during the treatment of municipal wastewater. The AnMBR system was conducted for 217 days during a long-term operation with the feed of real municipal wastewater. The characterization and dynamics of the microorganisms revealed that a stable prokaryotic community was gradually achieved. In the community of methane-producing archaea (or methanogens), the acetotrophic methanogen Methanosaeta was significantly enriched at an ambient temperature of 25 °C with an overwhelming relative abundance in the entire community. The abundance of Methanosaeta was even higher than the most abundant bacterial phyla Chloroflexi, Firmicutes, Proteobacteria and Bacteroidetes. This phenomenon is quite different from that found in other typical anaerobic systems. The massive enrichment of methanogens is the key to maintaining stable methane production in the treatment of municipal wastewater by the AnMBR. The interspecies cooperation of major functional bacterial groups including protein/carbohydrate/cellulose-degrading (genera Anaerovorax, Aminomonas, Levilinea, Flexilinea and Ruminococcus etc.), sulfate-reducing (Desulfovibrio and Desulfomicrobium etc.) and syntrophic (Syntrophorhabdus and Syntrophus etc.) bacteria with acetotrophic and hydrogenotrophic archaea enhances the stability of reactor operation and help to acclimate the entire prokaryotic community to the characteristics of real municipal wastewater.

Effects of temperature and HRT on biogas production in moving and fixed bed of a novel upflow anaerobic hybrid (UAHB) reactor

The upflow anaerobic hybrid (UAHB) reactor combines the advantages of a upflow anaerobic sludge blanket (UASB-type) reactor and an anaerobic filter in a single compartment. A novel configuration of the UAHB reactor, composed of two three-phase separators (3PHS), was proposed to evaluate the biogas production in the moving and fixed bed in the treatment of synthetic sewage at a temperature range of 14-21 °C and hydraulic retention time (HRT) of 12, 10 and 8 h. The bench-scale reactor was operated in three different phases with organic loading rate (VOLR) of 0.6 (0.3-0.7), 0.7 ± 0.2, and 1.1 ± 0.1 kg COD m^-3 d^-1, respectively, for 225 days. The average removal efficiency of chemical oxygen demand (COD_t) was 78 (42-89)%, and the total biogas yield was 3090 (1704-4782) mL d^-1, with 66% of the lower 3PHS (moving bed) and 34% of the upper 3PHS (fixed bed). However, no significant difference was observed between the biogas yield on the 3PHS (p-value = 0.5048), thus confirming the influence of temperature in the biogas production. The average percentage of methane was 76 (60-82)% for both beds, and the filter media increased the production by 21%. Thus, it can be concluded that the fixed bed suppressed the instability of the moving bed regarding the biogas production and contributed to the final quality of the effluent.

First proof of concept for full-scale, direct, low-temperature anaerobic treatment of municipal wastewater

Municipal wastewater constitutes the largest fraction of wastewater, and yet treatment processes are largely removal-based. High-rate anaerobic digestion (AD) has revolutionised the sustainability of industrial wastewater treatment and could additionally provide an alternative for municipal wastewater. While AD of dilute municipal wastewater is common in tropical regions, the low temperatures of temperate climates has resulted in slow uptake. Here, we demonstrate for the first time, direct, high-rate, low-temperature AD of low-strength municipal wastewater at full-scale. An 88 m³ hybrid reactor was installed at the municipal wastewater treatment plant in Builth Wells, UK and operated for 290 days. Ambient temperatures ranged from 2 to 18 °C, but remained below 15 °C for > 100 days. Influent BOD fluctuated between 2 and 200 mg L^-1. However, BOD removal often reached > 85%. 16S rRNA amplicon sequencing of DNA from the biomass revealed a highly adaptable core microbiome. These findings could provide the basis for the next-generation of municipal 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.

Dual-chamber differs from single-chamber microbial electrosynthesis in biogas production performance under low temperature (15℃)

In this study, single-chamber and dual-chamber Microbial electrosynthesis (MES) with carbon fiber brushes as electrodes were operated at 15°C to compare and analyze the difference in methanogenic performance. Metatranscriptomic analysis showed that the relative abundance of electroactive microorganisms Syntrophomonas, Pseudomonas and Bacteroides in each group exceeded 90%, while the abundance of Geobacter was less than 4%. Acetoclastic methanogens Methahnosarcina was more enriched in dual-chamber MES (61.74%~70.42%), and Methanothrix showed higher abundance in single-chamber MES (33.44%~51.71%). Methahnosarcina and Methanothrix could interact with electroactive microorganisms to improve the electron transfer efficiency through direct interspecies electron transfer (DIET). Analysis of the methane metabolic pathways of low-temperature MES found acetoclastic pathway was domination, and single-chamber MES achieved acetate to acetyl-CoA through acetate-CoA ligase (EC: 6.2.1.1), whereas dual-chamber MES was by acetate kinase (EC: 2.7.2.1) and phosphate acetyltransferase (EC: 2.3.1.8). These results are beneficial to further research on the treatment of low-temperature wastewater.

Effects of micro-aeration on microbial niches and antimicrobial resistances in blackwater anaerobic digesters

Anaerobic digestion (AD) of source-diverted blackwater (toilet flush) at ambient room temperature presents challenges for fast hydrolysis of particulate matters. This study investigated the effect of different micro-aeration dosages for blackwater AD. Sequencing batch reactors were operated at ambient room temperature (22 ± 1°C) with micro-aeration (0, 5, 10, 50, and 150 mg O₂ g^-1 COD_feed per cycle) and gradually reduced hydraulic retention times from 5 d to 2 d. The methanogenesis efficiencies were greater at low oxygen dosages (i.e., 0, 5, 10) while the volatile fatty acids (VFAs) accumulated more at high oxygen dosages (i.e., 50, 150). Microbial communities were significantly different under different oxygen dosages (p<0.05), with segregation of microbial ecological niches in low and high oxygen dosage communities. The low-oxygen-dosage niche (0, 5, and 10 mg g^-1 COD_feed) was inhabited by fermenting and syntrophic bacteria (e.g., Cytophaga, Syntrophomonas) and methanogens (e.g., Methanobacterium, Methanolinea, Methanosaeta). The high-oxygen-dosage niche (50 and 150 mg g^-1 COD_feed) had significantly (p<0.05) more facultative anaerobic bacteria (Ignavibacteriales and Cloacamonales), and aerobic bacteria (Rhodocyclales). Moreover, blackwater can be a source of antimicrobial resistance genes (ARGs), which are affected by different oxygen dosages. The ARG variation correlated with the microbial community composition (p<0.05). Low-oxygen-dosage communities contained a higher prevalence of mobile gene elements (intI1 and korB) and tetM, ermB, sul1, sul2, and blaCTX-M than the high-oxygen-dosage communities, indicating that oxygen dosage influenced the prevalence of populations carrying ARGs. These findings suggest that application of micro-aeration to AD can be used to control ARG profiles.

Combined Stochastic and Deterministic Processes Drive Community Assembly of Anaerobic Microbiomes During Granule Flotation

Advances in null-model approaches have resulted in a deeper understanding of community assembly mechanisms for a variety of complex microbiomes. One under-explored application is assembly of communities from the built-environment, especially during process disturbances. Anaerobic digestion for biological wastewater treatment is often underpinned by retaining millions of active granular biofilm aggregates. Flotation of granules is a major problem, resulting in process failure. Anaerobic aggregates were sampled from three identical bioreactors treating dairy wastewater. Microbiome structure was analysed using qPCR and 16S rRNA gene amplicon sequencing from DNA and cDNA. A comprehensive null-model approach quantified assembly mechanisms of floating and settled communities. Significant differences in diversity were observed between floating and settled granules, in particular, we highlight the changing abundances of Methanosaeta and Lactococcus. Both stochastic and deterministic processes were important for community assembly. Homogeneous selection was the primary mechanism for all categories, but dispersal processes also contributed. The lottery model was used to identify clade-level competition driving community assembly. Lottery “winners” were identified with different winners between floating and settled groups. Some groups changed their winner status when flotation occurred. Spirochaetaceae, for example, was only a winner in settled biomass (cDNA-level) and lost its winner status during flotation. Alternatively, Arcobacter butzerli gained winner status during flotation. This analysis provides a deeper understanding of changes that occur during process instabilities and identified groups which may be washed out—an important consideration for process control.

Key syntrophic partnerships identified in a granular activated carbon amended UASB treating municipal sewage under low temperature conditions

Two laboratory-scale up-flow anaerobic sludge blankets (UASB) reactors, one with and one without granular activated carbon (GAC), were operated for municipal sewage treatment at low temperatures (16.5 ± 2.0 °C). During the 120-day operation, the GAC-amended reactor significantly enhanced COD removal (from 62% to 75%, P < 0.05) and methane production (from 87 to 218 mg CH₄-COD/reactor/d) than the non-GAC reactor. Bacterial communities were significantly different between the two reactors (P < 0.05). Geobacter, a key indicator for direct interspecies electron transfer (DIET), had the highest differential score (LEfSe analysis), showing significantly higher abundances in the GAC-amended reactor (3.7-8.8%) than the non-GAC reactor (0.9-4.0%). GAC also enriched syntrophic bacteria, Syntrophomonas, Syntrophus and sulfate reducing bacteria. Methanobacterium dominated the archaeal community in the GAC-amended reactor sludge (35.7%) and GAC-biofilm (75.3%), and was less abundant in the non-GAC reactor (9.9%). It indicates that GAC enriched microbial syntrophic partners with potential electro-activities in the anaerobic digestion process.

Reactor configuration influences microbial community structure during high-rate, low-temperature anaerobic treatment of dairy wastewater

Low temperature anaerobic digestion remains in its infancy, despite increasing interest for the treatment of complex wastewaters. In this study, the feasibility of low-temperature anaerobic treatment of dairy wastewater was assessed during a 443-day laboratory-scale bioreactor trial. The bioreactors were operated in triplicate at organic loading rates of 7.5-9 kgCODm^-3d^-1 throughout five operational phases. The structure of the microbial community was analysed using quantitative real-time PCR and amplicon sequencing of 16S rRNA genes from DNA and rRNA. The results indicated that low-temperature treatment of dairy wastewater is feasible at 15 °C, but that reactor configuration remains extremely important. The upflow anaerobic sludge bed (UASB) configuration out-performed the expanded granular sludge bed (EGSB)-based configurations. Decreased temperatures resulted in significant reductions in microbiome diversity. Methanosaeta was identified as a dominant genus throughout the trial, while Lactococcus was identified as an important bacterial genus at low-temperatures. However, the relative abundance of Lactococcus was significantly influenced by reactor configuration.

Growth and Break-Up of Methanogenic Granules Suggests Mechanisms for Biofilm and Community Development

Methanogenic sludge granules are densely packed, small, spherical biofilms found in anaerobic digesters used to treat industrial wastewaters, where they underpin efficient organic waste conversion and biogas production. Each granule theoretically houses representative microorganisms from all of the trophic groups implicated in the successive and interdependent reactions of the anaerobic digestion (AD) process. Information on exactly how methanogenic granules develop, and their eventual fate will be important for precision management of environmental biotechnologies. Granules from a full-scale bioreactor were size-separated into small (0.6-1 mm), medium (1-1.4 mm), and large (1.4-1.8 mm) size fractions. Twelve laboratory-scale bioreactors were operated using either small, medium, or large granules, or unfractionated sludge. After >50 days of operation, the granule size distribution in each of the small, medium, and large bioreactor sets had diversified beyond-to both bigger and smaller than-the size fraction used for inoculation. Interestingly, extra-small (XS; <0.6 mm) granules were observed, and retained in all of the bioreactors, suggesting the continuous nature of granulation, and/or the breakage of larger granules into XS bits. Moreover, evidence suggested that even granules with small diameters could break. "New" granules from each emerging size were analyzed by studying community structure based on high-throughput 16S rRNA gene sequencing. Methanobacterium, Aminobacterium, Propionibacteriaceae, and Desulfovibrio represented the majority of the community in new granules. H2-using, and not acetoclastic, methanogens appeared more important, and were associated with abundant syntrophic bacteria. Multivariate integration (MINT) analyses identified distinct discriminant taxa responsible for shaping the microbial communities in different-sized granules.

Microbial Community Redundancy and Resilience Underpins High-Rate Anaerobic Treatment of Dairy-Processing Wastewater at Ambient Temperatures

High-rate anaerobic digestion (AD) is a reliable, efficient process to treat wastewaters and is often operated at temperatures exceeding 30°C, involving energy consumption of biogas in temperate regions, where wastewaters are often discharged at variable temperatures generally below 20°C. High-rate ambient temperature AD, without temperature control, is an economically attractive alternative that has been proven to be feasible at laboratory-scale. In this study, an ambient temperature pilot scale anaerobic reactor (2 m³) was employed to treat real dairy wastewater in situ at a milk processing plant, at organic loading rates of 1.3 ± 0.6 to 10.6 ± 3.7 kg COD/m³/day and hydraulic retention times (HRT) ranging from 36 to 6 h. Consistent high levels of COD removal efficiencies, ranging from 50 to 70% for total COD removal and 70 to 84% for soluble COD removal, were achieved during the trial. Within the reactor biomass, stable active archaeal populations were observed, consisting mainly of Methanothrix (previously Methanosaeta) species, which represented up to 47% of the relative abundant active species in the reactor. The decrease in HRT, combined with increases in the loading rate had a clear effect on shaping the structure and composition of the bacterial fraction of the microbial community, however, without affecting reactor performance. On the other hand, perturbances in influent pH had a strong impact, especially when pH went higher than 8.5, inducing shifts in the microbial community composition and, in some cases, affecting negatively the performance of the reactor in terms of COD removal and biogas methane content. For example, the main pH shock led to a drop in the methane content to 15%, COD removals decreased to 0%, while the archaeal population decreased to ~11% both at DNA and cDNA levels. Functional redundancy in the microbial community underpinned stable reactor performance and rapid reactor recovery after perturbations.

RNA-based spatial community analysis revealed intra-reactor variation and expanded collection of direct interspecies electron transfer microorganisms in anaerobic digestion

Granular activated carbon (GAC) has been shown to mediate direct interspecies electron transfer (DIET) in anaerobic digestion. Adding GAC to up-flow anaerobic sludge bed reactor increased the total biomass slightly from 20.0 to 26.6 gVSS/reactor, and maximum organic removal capacity remarkably from 285 to 1660 mgCOD/L/d. Since GAC occupied 7% of reactor volume (denser than suspended sludge, settled to the reactor bottom), we used a spatial sampling strategy (sludge bed top/mid/bottom layers, and tightly attached GAC-biofilm) and DNA- and RNA-based community analyses. RNA-based analysis demonstrated significant community differences between the non-GAC and GAC-amended reactors (p < 0.05) based on ANOSIM statistical analysis. In comparison, DNA-based analysis showed little community difference between these reactors (p > 0.05). RNA-based analysis revealed active enrichments in GAC-biofilm, including bacteria Geobacter, Syntrophus, Desulfovibrio and Blvii28, and archaea Methanosaeta and Methanospirillum. These are potential electro-active syntrophic microorganisms related with DIET, which expand the previously defined list of DIET microorganisms.