Archaea and Bacteria Acclimate to High Total Ammonia in a Methanogenic Reactor Treating Swine Waste

Possibility of using tannins to control greenhouse gas production during digestate storage

The presented paper deals with the testing of a possibility to reduce emissions of undesirable greenhouse gases (CH₄, CO_2; NO_x) and their mixture (biogas) during the storage of digestate using applications of secondary plant metabolites (tannins). The experiment was conducted in laboratory conditions in which the digestate was placed in fermentation chambers. Prior to the fermentation process, preparations were applied to the digestate, which contained tannins: Tanenol Antibotrytis (TA), Tanenol Clar (TC) and Tanenol Rouge (TR) in three concentrations (0.5, 1.0 and 2.0% w/w). The application of these preparations demonstrably affected the production of biogas and the contents of CH₄, CO₂ and N therein. The application of TR preparation in the concentration of 1.0% and 2.0% significantly reduced the production of biogas as compared with all variants. The preparation further inhibited the process of CH₄ development. In contrast, the other preparations with the content of different kinds of TA and TC increased the production of biogas (on average by 15%), CH₄ (on average by 7%) and CO₂ (on average by 12%) as compared with the control variant and TR variant. These two variants reduced the concentration of N in biogas on average by 38%. Thus, the tested Tanenol tannin preparations can be used in different concentrations either to control emissions of greenhouse gases during the storage of digestate or, in case of increased production of CO₂ for its reuse in order to increase methane yields in the process of anaerobic fermentation.

Dynamics of microbial community in response to co-feedstock composition in anaerobic digestion

To enable the utilization of seasonal biomasses in e.g., farm-scale biogas plants, the process should be flexible and ensure stable gas production. However, information about microbial community dynamics in long-term co-digestion with versatile co-feedstocks is lacking. This study investigated the effects of co-feedstock changes on the performance and evolution of microbial consortia during 428-day anaerobic digestion of cow slurry. Co-feedstocks consisted of hydrocarbon-, protein- and lipid-rich materials. A high throughput 16S ribosomal RNA gene sequencing was used to analyze the taxonomic profile of microbial communities. Due to the low loading rate, the changes were subtle in bacteria, but a shift on archaeal genera in response to different and changing feedstock compositions was observed. Despite drastic changes in co-feedstock composition, stable and flexible anaerobic digestion with relatively constant core microbiome can be achieved with cautious operation of the process.

A multifaceted screening of applied voltages for electro-assisted anaerobic digestion of blackwater: Significance of temperature, hydrolysis/acidogenesis, electrode corrosion, and energy efficiencies

A microbial electrolysis cell-assisted anaerobic digester (MEC-AD) was operated with vacuum toilet blackwater at different applied voltages (0-1.6 V) at room temperature (R₂₀). A parallel MEC-AD was operated at 35 °C (R₃₅) to provide a kinetics index at mesophilic temperature. Both reactors failed at 1.6 V due to the alkaline pH created by anodic corrosion. In R₂₀, the best performance was observed at 1.2 V, with methane yield, COD removal, hydrolysis and acidogenesis efficiency increased by 59.9%, 27.0%, 52.0%, and 44.9%, respectively, compared to those of 0 V. Enrichment of hydrolytic and syntrophic bacteria (e.g., Clostridium, Bacteroidales, Sedimentibacter, Syntrophomonas) and increased abundance of genes encoding complex organics (e.g., proteins, carbohydrates, lipids) metabolism in R₂₀ at 1.2 V corresponded to the enhanced hydrolysis/acidogenesis processes. R₂₀ at 1.2 V generated 1.16 times more net energy than R₃₅ at the optimum voltage for methane yield (0.8 V), indicating ambient temperature operation of MEC-AD systems would be a more sustainable strategy.

Bioaugmentation with a propionate-degrading methanogenic culture to improve methane production from chicken manure

Volatile fatty acid (VFA) accumulation caused by high ammonia concentrations is often encountered during the anaerobic digestion (AD) of ammonia-rich substrates. In this study, propionate-degrading methanogenic cultures were introduced to augment the semi-continuous AD of chicken manure under high ammonia levels. Introduction of a methanogenic culture enhanced the methane yield in the bioaugmented digester by 17-26% when the organic loading rate (OLR) was 2-4 g L^-1d^-1 compared to that in the control. When the OLR was further increased from 4.0 L^-1d^-1 to 5.0 g L^-1d^-1, and bioaugmentation ceased, methane yield improved by 15-18% under a high total ammonia nitrogen level of 5.0-8.4 g NH₄⁺-N/L. Moreover, bioaugmentation reconstructed the methanogenic community in the digester, promoting the dominance of hydrogenotrophic Methanobacterium and slightly increasing the abundance of aceticlastic Methanothrix and the syntrophic propionate-oxidizing bacteria Syntrophobacter, which were the key contributors to the improved AD under high ammonia concentrations.

Microbial adaptation and response to high ammonia concentrations and precipitates during anaerobic digestion under psychrophilic and mesophilic conditions

This study explored microbial adaptation to high ammonia concentrations (<1000 mg/L to 4000 mg/L) during anaerobic digestion (AD) under psychrophilic and mesophilic conditions, the latter of which yielded precipitates facilitating investigation of microbial response. The experimental setup was performed at bench-scale using microbial consortia from four different operating anaerobic digesters treating different organic wastes (WW-wastewater sludge, MN-manure, FW- food waste and CO-co-digestion (FW & MN)). Adaptation experiments were conducted with semi-continuous flow mode to resemble large-scale operation. Metagenome and 16S RNA analysis were performed for the first time in a psychrophilic reactor during an ammonia acclimation process. These analyses were also performed in mesophilic reactor exposed to precipitates and high ammonia levels. Diversity reduced when adaptation occurred successfully from 1.1 to 4 g/L of total ammonia nitrogen (TAN) under psychrophilic conditions, while the microbial community became more diverse under mesophilic conditions with ammonia inhibition. We report for the first time Methanocorposculum as a robust hydrogenotrophic methanogen at high ammoniacal concentrations under psychrophilic conditions. Additionally, Methanosarcina was present in low and high ammoniacal concentrations in mesophilic conditions, but there was a shift in species dominance. Methanosarcina barkeri stands out as a more resilient methanogen compared to Methanosarcina mazei, which initially dominated at <1.1 g/L TAN. We also explored the effects of sudden precipitates on methanogenic communities and methane production when they occurred under mesophilic conditions in two reactors. Methane production declined by more than 50% when precipitates occurred and was accompanied by pH reduction and VFA accumulation. Diversity data corroborated that methanogens were severely reduced. These two reactors were not able to recover with 50 days of added operation, demonstrating potential for long-term negative impacts of precipitate formation on AD performance stemming from negative impact to methanogenic communities.

Sustained effect of zero-valent iron nanoparticles under semi-continuous anaerobic digestion of sewage sludge: Evolution of nanoparticles and microbial community dynamics

The effects of adding zero-valent iron nanoparticles (nZVI) on the physicochemical, biological and biochemical responses of a semi-continuous anaerobic digestion of sewage sludge have been assessed. Two sets of consecutive experiments of 103 and 116 days, respectively, were carried out in triplicate. nZVI were magnetically retained in the reactors, and the effect of punctual doses (from 0.27 to 4.33 g L^-1) over time was studied. Among the different parameters monitored, only methane content in the biogas was significantly higher when nZVI was added. However, this effect was progressively lost after the addition, and in 5-7 days, the methane content returned to initial values. The increase in the oxidation state of nanoparticles seems to be related to the loss of effect over time. Higher dose (4.33 g L^-1) sustained positive effects for a longer time along with higher methane content, but this fact seems to be related to microbiome acclimation. Changes in microbial community structure could also play a role in the mechanisms involved in methane enhancement. In this sense, the microbial consortium analysis reported a shift in the balance among acetogenic eubacterial communities, and a marked increase in the relative abundance of members assigned to Methanothrix genus, recognized as acetoclastic species showing high affinity for acetate, which explain the rise in methane content in the biogas. This research demonstrates that biogas methane enrichment in semicontinuous anaerobic digesters can be achieved by using nZVI nanoparticles, thus increasing energy production or reducing costs of a later biogas upgrading process.

Molecular Microbial Community Analysis as an Analysis Tool for Optimal Biogas Production

The microbial diversity in anaerobic digestion (AD) is important because it affects process robustness. High-throughput sequencing offers high-resolution data regarding the microbial diversity and robustness of biological systems including AD; however, to understand the dynamics of microbial processes, knowing the microbial diversity is not adequate alone. Advanced meta-omic techniques have been established to determine the activity and interactions among organisms in biological processes like AD. Results of these methods can be used to identify biomarkers for AD states. This can aid a better understanding of system dynamics and be applied to producing comprehensive models for AD. The paper provides valuable knowledge regarding the possibility of integration of molecular methods in AD. Although meta-genomic methods are not suitable for on-line use due to long operating time and high costs, they provide extensive insight into the microbial phylogeny in AD. Meta-proteomics can also be explored in the demonstration projects for failure prediction. However, for these methods to be fully realised in AD, a biomarker database needs to be developed.

Metagenomic insights into aniline effects on microbial community and biological sulfate reduction pathways during anaerobic treatment of high-sulfate wastewater

For comprehensive insights into the change of sulfate reduction pathway responding to the toxic stress and the shift of microbial community and performance of sulfate reduction, we built a laboratory-scale expanded granular sludge bed reactor (EGSB) treating high-sulfate wastewater with elevated aniline concentrations from 0 to 480 mg/L. High-throughput sequencing and metagenomic approaches were applied to decipher the molecular mechanisms of sulfate reduction under aniline stress through taxonomic and functional profiles. The increasing aniline in the anaerobic system induced the accumulation of volatile fatty acids (VFA), further turned the bioreactor into acidification, which was the principal reason for the deterioration of system performance and finally resulted in the accumulation of toxic free sulfide. Moreover, aniline triggered the change of bacterial community and genes relating to sulfate reduction pathways. The increase of aniline from 0 to 320 mg/L enriched total sulfate-reducing bacteria (SRB), and the most abundant genus was Desulfomicrobium, accounting for 66.85-91.25% of total SRB. The assimilatory sulfate reduction pathway was obviously inhibited when aniline was over 160 mg/L, while genes associated with dissimilatory sulfate reduction pathways all exhibited an upward tendency with the increasing aniline content. The enrichment of aniline-resistant SRB (e.g. Desulfomicrobium) carrying genes associated with the dissimilatory sulfate reduction pathway also confirmed the underlying mechanism that sulfate reduction turned into dissimilation under high aniline condition. Taken together, these results comprehensively provided solid evidence for the effects of aniline on the biological sulfate reduction processes treating high-sulfate wastewater and the underlying molecular mechanisms which may highlight the important roles of SRB and related sulfate reduction genes during treatment.

Population dynamics of microbial species under high and low ammonia nitrogen in the alternate layer bioreactor landfill (ALBL) approach

Anaerobic landfill process is still believed to be a complex ecosystem due to the lack of knowledge on the functional activities of microbial species. This research sought to introduce a novel landfill bioreactor, named here as the alternate layer bioreactor landfill (ALBL) of fresh MSW (FW) and stabilized waste (CT) to avoid inhibitory conditions for the microbial species in anaerobic landfill. The stabilized waste layer in the bottom of landfill cell significantly changed microbial ecology of fresh MSW which in turn reduced the concentrations of NH₄-N (29-31%) and VFAs (33-38%) in the ALBL approach, compared to fresh MSW disposal in sanitary landfill. The reduction of NH₄-N favored early onset of methanogenesis within 6 weeks and methane (CH₄) content of landfill gas increased from 11% to 40-50% (v/v), owing to the coexistence of Methanosarcinales (36-50%) and Methanomicrobiales (26-28%) archaea. The acetoclastic methanogenesis was achieved by reducing NH₄-N toxicity in the ALBL.

Effect of tannic acid combined with fluoride and lignosulfonic acid on anaerobic digestion in the agricultural waste management chain

Livestock waste is stored and used as soil fertilizer or directly as substrate for biogas production. Methane emissions from manure storages and ammonia inhibition of anaerobic digesters fed with manure, are well-known problems related to manure management. This study examines the effect of adding tannic acid with fluoride (TA-NaF) and lignosulfonic acid (LS) on methanogenic activity in batch reactors with ammonia inhibited maize silage digestate and in batch reactors with manure. Lignosulfonic acid counteracted urea induced ammonia inhibition of methanogenesis, whereas TA-NaF inhibited methanogenesis itself. Stable carbon isotope ratio analysis and methanogen community analysis suggested that TA-NaF affected acetoclastic methanogens the most. The combined findings suggest that TA-NaF could be used to reduce methane emissions from stored manure. Conversely, LS could be used as supplement in anaerobic digesters prone to urea induced ammonia inhibition.

Investigation into the microbial communities and associated crude oil-contamination along a Gulf War impacted groundwater system in Kuwait

During the First Gulf War (1991) a large number of oil wells were destroyed and oil fires subsequently extinguished with seawater. As a result Kuwait's sparse fresh groundwater resources were severely contaminated with crude oil. Since then limited research has focused on the microbial community ecology of the groundwater and their impact on the associated contamination. Here, the microbial community ecology (bacterial, archaeal and eukaryotic) and how it relates to the characteristics of the hydrocarbon contaminants were examined for the first time since the 1991 event. This study was conducted using 15 wells along the main groundwater flow direction and detected several potential hydrocarbon degrading microorganisms such as Hyphomicrobiaceae, Porphyromonadaceae and Eurotiomycetes. The beta diversity of the microbial communities correlated significantly with total petroleum hydrocarbon (TPH) concentrations and salinity. The TPH consisted mainly of polar compounds present as an unresolved complex mixture (UCM) of a highly recalcitrant nature. Based on the proportions of TPH to dissolved organic carbon (DOC), the results indicate that some minor biodegradation has occurred within highly contaminated aquifer zones. However, overall the results from this study suggest that the observed variations in TPH concentrations among the sampled wells are mainly induced by mixing/dilution with pristine groundwater rather than by biodegradation of the contaminants. The findings make an important contribution to better understand the fate of the groundwater pollution in Kuwait, with important implications for the design of future remediation efforts.

Electroactive microorganisms enriched from activated sludge remove nitrogen in bioelectrochemical reactor

The bioelectrochemical anaerobic nitrogen removal was demonstrated in an anaerobic batch reactor equipped with a pair of polarized bioelectrodes. The bioelectrochemical reactor was operated in sequential batch mode after inoculating activated sludge and polarizing the electrode to 0.6 V. The medium contains ammonium, nitrite, alkalinity and trace minerals, but no organic carbon source. By the repetitive sequential operation, simultaneous removals of ammonium, nitrite and alkalinity were improved, and the electrochemical activity of the bulk sludge was confirmed from the redox peaks of the cyclic voltammogram. This indicates that ammonia oxidizing exoelectrogens (AOE) and denitritating electrotrophs (DNE) were enriched more in the bulk solution. Biogas production that mainly consisted of nitrogen was observed from the bioelectrochemical reactor, and the minor components in the biogas were methane and carbon dioxide. This demonstrates that AOE use nitrite as an electron acceptor to oxidize ammonia. The requirements of nitrite and alkalinity for the removal of ammonia nitrogen are around 0.72 mg NO₂-N/mg NH₄-N and 1.73 mg as CaCO₃/mg NH₄-N, respectively, and nitrate was not produced as a by-product. The bacterial groups involved in the bioelectrochemical nitrogen removal are electroactive autotrophs and can be enriched from activated sludge by polarized electrode. This bioelectrochemical ammonia oxidation is a novel approach recommended for treatment of nitrogen-rich wastewater.

The microbial community responsible for dechlorination and benzene ring opening during anaerobic degradation of 2,4,6‑trichlorophenol

This study describes the dechlorination ability of acclimated biomass, the high-throughput sequencing of the 16S ribosomal RNA (rRNA) gene of such microorganisms, and the analysis of their community structure in relation to special functions. Two types of acclimated biomass (AB-1 and AB-2) were obtained via different acclimated treatment processes and were used to degrade 2,4,6‑trichlorophenol. The degradation pathway and characteristics of trichlorophenol degradation were different between the two groups. AB-1 degraded trichlorophenol only to 4-chlorophenol. AB-2 completely dechlorinated trichlorophenol and opened the benzene ring. The 16S rRNA high-throughput sequencing method was employed to examine the microbial diversity. It was found that the microbial richness and diversity of AB-1 were higher than those of AB-2. Firmicutes and Bacteroidetes were 2.7-fold and 4.3-fold more abundant, respectively, in AB-1 than in AB-2. Dechlorination bacteria in AB-1 mainly included Desulfobulbus, Desulfovibrio, Dechloromonas, and Geobacter. The above-mentioned bacteria were less abundant in AB-2, but the abundance of Desulfomicrobium was twofold higher in AB-2 than in AB-1. The two types of acclimated biomass contained different hydrogen (H₂)-producing bacteria. AB-2 showed higher abundance and diversity of hydrogen-producing bacteria. There was no Ignavibacteriae in AB-1, whereas its abundance in AB-2 was 8.4%. In this biomass, Ignavibacteriae was responsible for opening of the benzene ring. This study indicates that the abundance and diversity of microorganisms are not necessarily beneficial to the formation of a functional dechlorinating community. The H₂-producing bacteria (which showed greater abundance and diversity) and Ignavibacterium were assumed to be core functional populations that gave AB-2 stronger dechlorination and phenol-degradation abilities. Control of lower oxidation reduction potential (E_h) and higher temperatures by means of fresh aerobic activated sludge as the starting microbial group, caused rapid complete dechlorination of 2,4,6‑trichlorophenol and benzene ring opening.

The auto fluorescence characteristics, specific activity, and microbial community structure in batch tests of mono-chicken manure digestion

Batch tests inoculated with granular and suspended sludge of mono chicken manure (CM) digestion were conducted. Kinetic analysis showed a maximum bio-CH₄ generation (6 mL/gVS/d) at an optimal TS of 10-12%. At a TS of 25%, serious inhibition was found for granular sludge and even greater inhibition for the suspended sludge caused by free ammonia. The auto fluorescence of Excitation-mission matrix with parallel factor analysis (PARAFAC) showed that the dissolved organic matter (DOM) varied between the form C1, C2, C3 and C4. The split component of the SMP-like C2 and protein-like C4 significantly related to the bio-methane production in time series. The canonical correlation analysis (CCA) indicated that ammonia, pH, and TS influenced the PARAFAC component significantly. The aceticlastic methanogens of the genus Methanosaeta and acetogens of the genus Syntrophobacter predominated in the CM sludge. The methanogens and acetogens formed a metabolic cooperation, making the process a stable methane produced activity.

Effect of pH and temperature on microbial community structure and carboxylic acid yield during the acidogenic digestion of duckweed

BACKGROUND

Duckweeds (Lemnaceae) are efficient aquatic plants for wastewater treatment due to their high nutrient-uptake capabilities and resilience to severe environmental conditions. Combined with their rapid growth rates, high starch, and low lignin contents, duckweeds have also gained popularity as a biofuel feedstock for thermochemical conversion and alcohol fermentation. However, studies on the acidogenic anaerobic digestion of duckweed into carboxylic acids, another group of chemicals which are precursors of higher-value chemicals and biofuels, are lacking. In this study, a series of laboratory batch experiments were performed to determine the favorable operating conditions (i.e., temperature and pH) to maximize carboxylic acid production from wastewater-derived duckweed during acidogenic digestion. Batch reactors with 25 g/l solid loading were operated anaerobically for 21 days under mesophilic (35 °C) or thermophilic (55 °C) conditions at an acidic (5.3) or basic (9.2) pH. At the conclusion of the experiment, the dominant microbial communities under various operating conditions were assessed using high-throughput sequencing.

RESULTS

The highest duckweed-carboxylic acid conversion of 388 ± 28 mg acetic acid equivalent per gram volatile solids was observed under mesophilic and basic conditions, with an average production rate of 0.59 g/l/day. This result is comparable to those reported for acidogenic digestion of other organics such as food waste. The superior performance observed under these conditions was attributed to both chemical treatment and microbial bioconversion. Hydrogen recovery was only observed under acidic thermophilic conditions, as 23.5 ± 0.5 ml/g of duckweed volatile solids added. More than temperature, pH controlled the overall structure of the microbial communities. For instance, differentially abundant enrichments of Veillonellaceae acidaminococcus were observed in acidic samples, whereas enrichments of Clostridiaceae alkaliphilus were found in the basic samples. Acidic mesophilic conditions were found to enrich acetoclastic methanogenic populations over processing times longer than 10 days.

CONCLUSIONS

Operating conditions have a significant effect on the yield and composition of the end products resulting from acidogenic digestion of duckweed. Wastewater-derived duckweed is a technically feasible alternative feedstock for the production of advanced biofuel precursors; however, techno-economic analysis is needed to determine integrated full-scale system feasibility and economic viability.

Coupling Bioflocculation of Dehalococcoides mccartyi to High-Rate Reductive Dehalogenation of Chlorinated Ethenes

Continuous bioreactors operated at low hydraulic retention times have rarely been explored for reductive dehalogenation of chlorinated ethenes. The inability to consistently develop such bioreactors affects the way growth approaches for Dehalococcoides mccartyi bioaugmentation cultures are envisioned. It also affects interpretation of results from in situ continuous treatment processes. We report bioreactor performance and dehalogenation kinetics of a D. mccartyi-containing consortium in an upflow bioreactor. When fed synthetic groundwater at 11-3.6 h HRT, the upflow bioreactor removed >99.7% of the influent trichloroethene (1.5-2.8 mM) and produced ethene as the main product. A trichloroethene removal rate of 98.51 ± 0.05 me^- equiv L^-1 d^-1 was achieved at 3.6 h HRT. D. mccartyi cell densities were 10¹³ and 10¹² 16S rRNA gene copies L^-1 in the bioflocs and planktonic culture, respectively. When challenged with a feed of natural groundwater containing various competing electron acceptors and 0.3-0.4 mM trichloroethene, trichloroethene removal was sustained at >99.6%. Electron micrographs revealed that D. mccartyi were abundant within the bioflocs, not only in multispecies structures, but also as self-aggregated microcolonies. This study provides fundamental evidence toward the feasibility of upflow bioreactors containing D. mccartyi as high-density culture production tools or as a high-rate, real-time remediation biotechnology.

The effects of CO2 and H2 on CO metabolism by pure and mixed microbial cultures

BACKGROUND

Syngas fermentation, the bioconversion of CO, CO₂, and H₂ to biofuels and chemicals, has undergone considerable optimization for industrial applications. Even more, full-scale plants for ethanol production from syngas fermentation by pure cultures are being built worldwide. The composition of syngas depends on the feedstock gasified and the gasification conditions. However, it remains unclear how different syngas mixtures affect the metabolism of carboxidotrophs, including the ethanol/acetate ratios. In addition, the potential application of mixed cultures in syngas fermentation and their advantages over pure cultures have not been deeply explored. In this work, the effects of CO₂ and H₂ on the CO metabolism by pure and mixed cultures were studied and compared. For this, a CO-enriched mixed culture and two isolated carboxidotrophs were grown with different combinations of syngas components (CO, CO:H₂, CO:CO₂, or CO:CO₂:H₂).

RESULTS

The CO metabolism of the mixed culture was somehow affected by the addition of CO₂ and/or H₂, but the pure cultures were more sensitive to changes in gas composition than the mixed culture. CO₂ inhibited CO oxidation by the Pleomorphomonas-like isolate and decreased the ethanol/acetate ratio by the Acetobacterium-like isolate. H₂ did not inhibit ethanol or H₂ production by the Acetobacterium and Pleomorphomonas isolates, respectively, but decreased their CO consumption rates. As part of the mixed culture, these isolates, together with other microorganisms, consumed H₂ and CO₂ (along with CO) for all conditions tested and at similar CO consumption rates (2.6 ± 0.6 mmol CO L^-1 day^-1), while maintaining overall function (acetate production). Providing a continuous supply of CO by membrane diffusion caused the mixed culture to switch from acetate to ethanol production, presumably due to the increased supply of electron donor. In parallel with this change in metabolic function, the structure of the microbial community became dominated by Geosporobacter phylotypes, instead of Acetobacterium and Pleomorphomonas phylotypes.

CONCLUSIONS

These results provide evidence for the potential of mixed-culture syngas fermentation, since the CO-enriched mixed culture showed high functional redundancy, was resilient to changes in syngas composition, and was capable of producing acetate or ethanol as main products of CO metabolism.