Microbial community shifts and biogas conversion computation during steady, inhibited and recovered stages of thermophilic methane fermentation on chicken manure with a wide variation of ammonia

Multivariate comparison of taxonomic, chemical and operational data from 80 different full-scale anaerobic digester-related systems

BACKGROUND

The holistic characterization of different microbiomes in anaerobic digestion (AD) systems can contribute to a better understanding of these systems and provide starting points for bioengineering. The present study investigates the microbiome of 80 European full-scale AD systems. Operational, chemical and taxonomic data were thoroughly collected, analysed and correlated to identify the main drivers of AD processes.

RESULTS

The present study describes chemical and operational parameters for a broad spectrum of different AD systems. With this data, Spearman correlation and differential abundance analyses were applied to narrow down the role of the individual microorganisms detected. The authors succeeded in further limiting the number of microorganisms in the core microbiome for a broad range of AD systems. Based on 16S rRNA gene amplicon sequencing, MBA03, Proteiniphilum, a member of the family Dethiobacteraceae, the genus Caldicoprobacter and the methanogen Methanosarcina were the most prevalent and abundant organisms identified in all digesters analysed. High ratios for Methanoculleus are often described for agricultural co-digesters. Therefore, it is remarkable that Methanosarcina was surprisingly high in several digesters reaching ratios up to 47.2%. The various statistical analyses revealed that the microorganisms grouped according to different patterns. A purely taxonomic correlation enabled a distinction between an acetoclastic cluster and a hydrogenotrophic one. However, in the multivariate analysis with chemical parameters, the main clusters corresponded to hydrolytic and acidogenic microorganisms, with SAOB bacteria being particularly important in the second group. Including operational parameters resulted in digester-type specific grouping of microbes. Those with separate acidification stood out among the many reactor types due to their unexpected behaviour. Despite maximizing the organic loading rate in the hydrolytic pretreatments, these stages turned into extremely robust methane production units.

CONCLUSIONS

From 80 different AD systems, one of the most holistic data sets is provided. A very distinct formation of microbial clusters was discovered, depending on whether taxonomic, chemical or operational parameters were combined. The microorganisms in the individual clusters were strongly dependent on the respective reference parameters.

Evaluation of the methanogenic potential of anaerobic digestion of agro-industrial wastes

Waste management technologies have become a way to generate value-added products. Anaerobic digestion (AD) allows biogas generation by treating organic wastes. In this work, the methanogenic potentials of anaerobic digestion of rumen and chicken manure, two typical agro-industrial wastes from the Colombian Caribbean region, were evaluated. On a first stage, the effect of temperature on anaerobic digestion of manure inoculated with liquid rumen was measured. Results revealed that the thermophilic digestion produces more biogas (up to 47% higher than the mesophilic digestion), but the mesophilic digestion has better biogas quality (up to 20% more methane than the thermophilic digestion). On the second experimental stage, it was assessed the effect of temperature regimen and the addition of fat-oil-grease (FOG) on cumulative biogas production, methane percentage, and physicochemical parameters. It was found that the anaerobic digestion of the rumen with FOG in mesophilic conditions had the best performance in terms of quantity and quality of biogas (2520 NL CH₄/kg VS, CH₄ 93%, H₂S 1 mg/L, H₂O 16 mg/L). Finally, rumen and manure had methane concentrations above 40% in all cases studied, after 60 days of anaerobic digestion. It was concluded that rumen and manure are good candidates for biogas generation.

Microbial Behavior and Influencing Factors in the Anaerobic Digestion of Distiller: A Comprehensive Review

Anaerobic digestion technology is regarded as the most ideal technology for the treatment of a distiller in terms of environmental protection, resource utilization, and cost. However, there are some limitations to this process, the most prominent of which is microbial activity. The purpose of this paper is to provide a critical review of the microorganisms involved in the anaerobic digestion process of a distiller, with emphasis on the archaea community. The effects of operating parameters on microbial activity and process, such as pH, temperature, TAN, etc., are discussed. By understanding the activity of microorganisms, the anaerobic treatment technology of a distiller can be more mature. Aiming at the problem that anaerobic treatment of a distiller alone is not effective, the synergistic effect of different substrates is briefly discussed. In addition, the recent literature on the use of microorganisms to purify a distiller was collected in order to better purify the distiller and reduce harm. In the future, more studies are needed to elucidate the interactions between microorganisms and establish the mechanisms of microbial interactions in different environments.

Metagenomic Screening for Lipolytic Genes Reveals an Ecology-Clustered Distribution Pattern

Lipolytic enzymes are one of the most important enzyme types for application in various industrial processes. Despite the continuously increasing demand, only a small portion of the so far encountered lipolytic enzymes exhibit adequate stability and activities for biotechnological applications. To explore novel and/or extremophilic lipolytic enzymes, microbial consortia in two composts at thermophilic stage were analyzed using function-driven and sequence-based metagenomic approaches. Analysis of community composition by amplicon-based 16S rRNA genes and transcripts, and direct metagenome sequencing revealed that the communities of the compost samples were dominated by members of the phyla Actinobacteria, Proteobacteria, Firmicutes, Bacteroidetes, and Chloroflexi. Function-driven screening of the metagenomic libraries constructed from the two samples yielded 115 unique lipolytic enzymes. The family assignment of these enzymes was conducted by analyzing the phylogenetic relationship and generation of a protein sequence similarity network according to an integrated classification system. The sequence-based screening was performed by using a newly developed database, containing a set of profile Hidden Markov models, highly sensitive and specific for detection of lipolytic enzymes. By comparing the lipolytic enzymes identified through both approaches, we demonstrated that the activity-directed complements sequence-based detection, and vice versa. The sequence-based comparative analysis of lipolytic genes regarding diversity, function and taxonomic origin derived from 175 metagenomes indicated significant differences between habitats. Analysis of the prevalent and distinct microbial groups providing the lipolytic genes revealed characteristic patterns and groups driven by ecological factors. The here presented data suggests that the diversity and distribution of lipolytic genes in metagenomes of various habitats are largely constrained by ecological factors.

Transiting from the inhibited steady-state to the steady-state through the ammonium bicarbonate mediation in the anaerobic digestion of low-C/N-ratio food wastes

The current study aimed to determine the effects of NH₄⁺ on anaerobic digestion (AD) metabolism and the feasibility of using NH₄HCO₃ to improve methane production in an AD system when treating a low-C/N-ratio food waste (FW). Increasing the ammonium concentration (500-1000 mg NH₄Cl-N/L) added into the AD system did not limit the methane production but caused the volatile fatty acid (VFA) accumulation, forming an "inhibited steady-state" system. The addition of 200 mg NH₄HCO₃-N/L increased methane yield by 20% by aiding the microbial oxidation of VFAs. The high acetate content (65-85%) and abundance of acetoclastic methanogens (Methanosaeta and Methanosarcina) indicated an efficient acetoclastic methanogenesis process, which was facilitated by NH₄HCO₃. The long-term operation of the AD system demonstrated that NH₄HCO₃, at a concentration of 200 mg N/L, was capable of forming an active buffer system with NH₄⁺ and VFAs, enhancing methane production (221 ± 86 mL/g VS).

Renewable energy potential of anaerobic mono- and co-digestion of chicken manure, goat manure, potato peels and maize pap in South Africa

The energy sector is an essential part of a country’s economy – it drives innovation and advances in industrialisation. Coal is the primary source of energy in South Africa. Coal contributes 95% of energy production; coal-fired power also contributes to greenhouse gas emissions, and is thus a hazard to human health and the environment. This calls for an energy mix that is renewable, sustainable, and affordable and that is carbon neutral (climate action). We investigated the potential of anaerobic mono-and co-digestion of goat manure, chicken manure, potato peels, maize pap, and cow manure inoculum for mesophilic recovery of renewable energy using the biomethane potential test. The substrates were characterised through proximate and ultimate analyses to determine the composition preferable for mono- and co-digestion. The key considerations in the determination of both the yield and production rate of methane from digestion of biomass are the substrate composition and characterisation. A high percentage of volatile solids favoured optimum biomethane production as highly volatile components provide microbes with balanced nutrients that enhance metabolic processes to produce biomethane. The mono-digestion process produced lower biomethane than did co-digestion. Higher production of biomethane by co-digestion was due to the balance of the micronutrients and macronutrients that favoured microbial metabolism and regulation of pH.

Enhancing biomethane production and pyrene biodegradation by addition of bio-nano FeS or magnetic carbon during sludge anaerobic digestion

Pyrene exerts toxic effects on methanogens during anaerobic digestion of sludge, thus affecting the efficiency of sludge treatment. This study evaluated the facilitated direct interspecific electron transfer (DIET) between bacteria and methanogens when bio-nano FeS or magnetic carbon is added into anaerobic reactors. Results showed that adding 200 mg/L bio-nano FeS or magnetic carbon clearly reduced the accumulation of short-chain fatty acids and avoided acidification during 25 days of anaerobic digestion. The methane productions were 98.38 L/kg total solid (TS) and 73.69 L/kg TS in the bio-nano FeS and magnetic carbon systems, respectively, which accelerated methane production by 58.1% and 33.4%, respectively, compared with the control system (40.26 L/kg TS). The pyrene removal rates reached 77.5% and 72.1% in the bio-nano FeS and magnetic carbon systems, whereas it was only 40.8% in the control system. Analysis of microbial community structure revealed that methanogens (e.g. Methanosarcina and Methanosaeta) and extracellular electron-transfer bacteria (e.g. Pseudomonas, Cloastridia, and Synergistetes) were enriched in the reactors added with bio-nano FeS or magnetic carbon. This result indicates that the addition of bio-nano FeS or magnetic carbon may promote the activity and growth of microorganisms to improve the efficiency of methane production and pyrene degradation by enhancing DIET.

Microbiological Surveillance of Biogas Plants: Targeting Acetogenic Community

Acetogens play a very important role in anaerobic digestion and are essential in ensuring process stability. Despite this, targeted studies of the acetogenic community in biogas processes remain limited. Some efforts have been made to identify and understand this community, but the lack of a reliable molecular analysis strategy makes the detection of acetogenic bacteria tedious. Recent studies suggest that screening of bacterial genetic material for formyltetrahydrofolate synthetase (FTHFS), a key marker enzyme in the Wood-Ljungdahl pathway, can give a strong indication of the presence of putative acetogens in biogas environments. In this study, we applied an acetogen-targeted analyses strategy developed previously by our research group for microbiological surveillance of commercial biogas plants. The surveillance comprised high-throughput sequencing of FTHFS gene amplicons and unsupervised data analysis with the AcetoScan pipeline. The results showed differences in the acetogenic community structure related to feed substrate and operating parameters. They also indicated that our surveillance method can be helpful in the detection of community changes before observed changes in physico-chemical profiles, and that frequent high-throughput surveillance can assist in management towards stable process operation, thus improving the economic viability of biogas plants. To our knowledge, this is the first study to apply a high-throughput microbiological surveillance approach to visualise the potential acetogenic population in commercial biogas digesters.

Novel insights of impacts of solid content on high solid anaerobic digestion of cow manure: Kinetics and microbial community dynamics

High solid anaerobic digestion has become the mainstream technology for sustainable on-farm treatment of solid wastes but has not been optimized with respect to increasing solid content in cow manure (CM). In the present study, CM was batch digested at total solid (TS) of 5%, 10%, 15% and 20% and microbial communities were investigated. The process remained stable up to 15% TS. The biomethane production rate at TS of 10% and 15% was reported to be 352.2 mL g^-1 VS and 318.6 mL g^-1 VS, reaching up to 83% and 75% of TS 5% biomethane, respectively. Kinetics results disclosed that the biodegradable organics could be utilized at increasing solid content with decreasing hydrolysis rate. The abundances of hydrogenotrophic and methylotrophic methanogens increased significantly with increasing solid content. This study is of great importance for understanding and application of high solid anaerobic digestion of cow manure.

Simultaneous nitrogen removal and methane production from Taihu blue algae against ammonia inhibition using integrated bioelectrochemical system (BES)

Simultaneous nitrogen removal and methane production using an integrated bioelectrochemical system (BES) during the anaerobic digestion (AD) process of Taihu blue algae were investigated. Upon an applied voltage of 0.4 V and total solids (TS) ratio of blue algae to anaerobic sludge as 1:1, the highest methanogenesis potential as 69.12 mL/g VS could be obtained, attaining 18.7 times of the TS ratio group of 3:1. Moreover, methane production of the integrated BES group reached 3.18 times of the AD group using conical flask, even with the same TS ratio (1:1) and initial ammonia nitrogen concentration (1000 mg NH₄⁺-N/L). Apart from the bettered electrochemical performance, bio-augmented microbial genus responsible for acetoclastic methanogenesis, power generation, resisting to hostile circumstance, co-existence with hydrogenotrophic methanogens could all be enriched. Therefore, integrated BES with appropriate TS ratio under applied voltage might help offset both the ammonia and electrical stress, thereby to maintain enhanced biomethanation performance.

Microbial diversity dynamics during the self-acidification of dairy slurry

Slurry acidification has been shown to be effective in reducing environmentally damaging gases. However, this involved the use of concentrated acids on farms. Therefore, due to the health and safety concerns, there is an interest in self-acidification of slurry technique. This study was designed to determine the microbial dynamics leading to self-acidification of slurry. A fresh cattle slurry was amended 10% brewing sugar and stored over 30 days. This fermentable carbon source promoted self-acidification of the slurry from pH 7.0 to 4.7 within four days, and was associated with the accumulation of lactic acid and a reduction in methane and relative ammonia emissions. A metagenomics approach through next generation sequencing (NGS) using an Illumina MiSeq platform was used to determine the microbial diversity and dynamics (bacteria and archaea) in the stored amended slurry. 16S ribosomal ribonucleic acid (rRNA) sequence data revealed the presence of the Order of Lactobacillales was associated with the lactic acid production. The operational taxonomic units (OTUs) abundance indicates that the methanogenic community was dominated by hydrogenotrophic methanogens from the member Order of Methanobacteriales, Methanomicrobiales, and Methanosarcinales. The decrease in tolerance by the methanogens in the self-acidified slurry was probably the main reason for the reduced methane emission. These results confirm, at the microbial level, the mechanism of inhibiting methane production via self-acidification during storage period.

Investigation on Recycling Dry Toilet Generated Blackwater by Anaerobic Digestion: From Energy Recovery to Sanitation

Anaerobic digestion (AD) has been widely adapted for blackwater treatment, however, the effect of water-conserving toilet generated blackwater on the AD process is still unknown. In this study, the anaerobic digestion process of dry toilet generated blackwater was investigated by means of a biomethane potential test. It was demonstrated that anaerobic digestion was inhibited and then adapted because of a high total ammonium nitrogen (TAN) level (3673.3 mg/L). The start-up period was 14.04 days and the biomethane potential of dry toilet blackwater was 402.36 mLCH4/gVS (55 days, 38 °C). Inhabitation and adaptation could be described as the increase of free ammonia nitrogen content and acetic acid concentration, followed by an enhancement of the relative abundance of acetic acid-type methanogens (from 33.53–61.52%). The main pathogen in dry toilet blackwater fermentation broth, Pseudomonas aeruginosa, kept multiplying in the first 8 days and then stabilized at a higher level than that of the beginning. This work showed the self-adjustment process and pathogen dynamics of dry toilet blackwater anaerobic digestion and highlights the significance of dry toilet blackwater characteristics when designing and maintaining anaerobic digestion sanitary treatment and reuse systems.

Leachate microbiome profile reveals bacteria, archaea and eukaryote dynamics and methanogenic function during solid waste decomposition

Bacterial, archaeal, and eukaryotic community composition and dynamics in leachate during solid waste decomposition were investigated using Illumina MiSeq sequencing. The functional enzyme-encoding genes of methanogenic pathways were also predicted via PICRUSt. Succession of bacterial, archaeal, and eukaryotic community composition in aerobic phase (AP), anaerobic acid phase (ACP), and methanogenic phase (MP) was observed. The main representatives of microbial phyla, genera, and species significantly (p < 0.05) differed at least two phases. Protist Ciliophora occurred at ACP and was prevalent in MP, suggesting a short food chain establishment in the methanogenesis. Bacterial, archaeal, fungi and eukaryotic community structure were all pH and biochemical oxygen demand (BOD₅) dependent patter. Acetoclastic and hydrogenotrophic methanogenesis pathways with associated functional genes differed during solid waste decomposition and were inhibited in ACP.

Batch-Mode Analysis of Thermophilic Methanogenic Microbial Community Changes in the Overacidification Stage in Beverage Waste Treatment

Biogasification by methane fermentation is an important and effective way to utilize beverage wastes. Beverage wastes are good feedstocks for methane fermentation because of their richness in sugars and proteins, although overacidification and inhibition of methane production caused by high substrate loading often become problematic. This study investigated changes in microbial communities in the overacidification state of the thermophilic methane fermentation process with beverage waste by establishing a simulated batch culture. We assessed 20 mL-scale batch cultures using a simulant beverage waste mixture (SBWM) with different amounts of addition; high cumulative methane production was achieved by adding 5 mL of SBWM (11358 mg-chemical oxygen demand-COD/L of organic loading), and overacidification was observed by adding 10 mL of SBWM (22715 mg-COD/L of organic loading). The results of 16S rRNA amplicon sequence analysis using nanopore sequencer suggested that Coprothermobacter proteolyticus, Defluviitoga tunisiensis, Acetomicrobium mobile, and Thermosediminibacter oceani were predominantly involved in hydrolysis/acidogenesis/acetogenesis processes, whereas Methanothrix soehngenii was the major acetotrophic methane producer. A comparison of microbial population between the methane-producing cultures and overacidification cultures revealed characteristic population changes especially in some minor species under 0.2% of population. We concluded that careful monitoring of population changes of the minor species is a potential indicator for prediction of overacidification.

Evaluation of Anaerobic Co-Digestion to Enhance the Efficiency of Livestock Manure Anaerobic Digestion

In this paper, the anaerobic co-digestion of three different organic wastes, including livestock manure, slaughterhouse waste, and agricultural by-products (ABs), was carried out to enhance the efficiency of mono-digestion of livestock manure. The characteristics of co-digestion were evaluated at different mixing ratios. The experiment was performed using the Batch test and was divided into two parts. The first experimental section (EXP. 1) was designed to evaluate the seasonal characteristics of ABs, which are the different ratios of fruits and vegetables, where the mixing ratio of spring (fruits:vegetables = 3:7) showed the highest biogas yield (0.24 m3/kg volatile solids). The second experiment (EXP. 2) was conducted by using ABs in the ratio that gave the highest biogas yield in EXP. 1 in combinations of three wastes livestock manure, slaughterhouse waste, and ABs. The highest CH4 yield was 0.84 m3/kg volatile solids (VS), which was obtained with a mixing ratio that had even amounts of the three feedstocks. In addition, the results of the second biochemical methane potential test, which assessed the digestive efficiency according to the mixing ratio of the three types of organic waste, showed that the CH4 production rate of the merged digestion was approximately 1.03–1.29 times higher than that of the mono-digestion of livestock manure. The results of our experiment were verified using the modified Gompertz model, the results of which were relatively similar to the experimental results.

Hydrogenotrophic methanogens are the key for a successful bioaugmentation to alleviate ammonia inhibition in thermophilic anaerobic digesters

Bioaugmentation to alleviate ammonia inhibition under thermophilic anaerobic digestion has never been reported, as well as the working mechanism that allows a fast and successful bioaugmentation. Thus two bioaugmentation inocula (an enriched culture, and a mixed culture composed 50/50 by Methanoculleus thermophilus and the enriched culture) on the recovery of ammonia-inhibited thermophilic continuous reactors was assessed. The results showed that bioaugmentation improved methane yield by 11-13% and decreased the volatile fatty acids (VFA) by 45-52% compared to the control reactor (abiotic augmentation). Moreover, the importance of hydrogenotrophic methanogens to a fast and successful bioaugmentation was recognized. Specifically, the instant hydrogen partial pressure reduction by the bioaugmented hydrogenotroph created thermodynamically favourable conditions for the acetate oxidation process and consequently, the catabolism of other VFA. High-throughput sequencing results strengthened this explanation by showing that the bioaugmented M. thermophilus stimulated the growth of syntrophic acetate oxidising bacterium Thermacetogenium phaeum, immediately after bioaugmentation.

Immediate Effects of Ammonia Shock on Transcription and Composition of a Biogas Reactor Microbiome

The biotechnological process of biogas production from organic material is carried out by a diverse microbial community under anaerobic conditions. However, the complex and sensitive microbial network present in anaerobic degradation of organic material can be disturbed by increased ammonia concentration introduced into the system by protein-rich substrates and imbalanced feeding. Here, we report on a simulated increase of ammonia concentration in a fed batch lab-scale biogas reactor experiment. Two treatment conditions were used simulating total ammonia nitrogen concentrations of 4.9 and 8.0 g/L with four replicate reactors. Each reactor was monitored concerning methane generation and microbial composition using 16S rRNA gene amplicon sequencing, while the transcriptional activity of the overall process was investigated by metatranscriptomic analysis. This allowed investigating the response of the microbial community in terms of species composition and transcriptional activity to a rapid upshift to high ammonia conditions. Clostridia and Methanomicrobiales dominated the microbial community throughout the entire experiment under both experimental conditions, while Methanosarcinales were only present in minor abundance. Transcription analysis demonstrated clostridial dominance with respect to genes encoding for enzymes of the hydrolysis step (cellulase, EC 3.2.1.4) as well as dominance of key genes for enzymes of the methanogenic pathway (methyl-CoM reductase, EC 2.8.4.1; heterodisulfide reductase, EC 1.8.98.1). Upon ammonia shock, the selected marker genes showed significant changes in transcriptional activity. Cellulose hydrolysis as well as methanogenesis were significantly reduced at high ammonia concentrations as indicated by reduced transcription levels of the corresponding genes. Based on these experiments we concluded that, apart from the methanogenic archaea, hydrolytic cellulose-degrading microorganisms are negatively affected by high ammonia concentrations. Further, Acholeplasma and Erysipelotrichia showed lower abundance under increased ammonia concentrations and thus might serve as indicator species for an earlier detection in order to counteract against ammonia crises.

Revealing the correlation of biomethane generation, DOM fluorescence, and microbial community in the mesophilic co-digestion of chicken manure and sheep manure at different mixture ratio

Batch co-digestion tests of chicken manure (CM) and sheep manure (SM) at different ratio (R_s/c) were conducted under mesophilic condition (35 °C). Batch kinetic analysis of bioCH₄ production, excitation-emission matrix (EEM) fluorescence of dissolved organic matter (DOM), and microbial community were investigated. The well-fitted modified Gompertz model (R², 0.98-0.99) resulted that the co-digestion markedly improved the methane production rate and shortened the lag phase time. The highest bioCH₄ yield of 219.67 mL/gVS_add and maximum production rate of 0.378 mL/gVS_add/h were obtained at an optimum R_s/c of 0.4. Additionally, a significant variation of DOM was detected at the R_s/c of 0.4 with a consistent degradation of soluble microbial byproduct-like and protein-like organics. The positive synergy effects of co-digestion conspicuously enhanced the bioCH₄ production efficiency. FI₃₇₀ and NADH were significantly correlated to R_s/c (p < 0.05). Moreover, the correlations among process indicator, EEM-peaks and different environmental parameters were evaluated by Pearson correlation analysis. The high diversity of acetoclastic methanogens and hydrogenotrophic methanogens in the co-digestion improved the stability of process. Graphical Abstract.

A Review of the Role of Critical Parameters in the Design and Operation of Biogas Production Plants

Many operating parameters, individually or together, may influence the performance of anaerobic digestion towards biogas or digestate yield and quality maximization. The most preferred method of optimizing an anaerobic digestion plant often relies on how carefully the crucial parameters, such as pH, temperature, organic loading rate, hydraulic retention time, and pressure, are chosen. There is a large amount of literature available on optimization of anaerobic digestion; however, given the continued development and implementation of innovative technologies, together with the introduction of increasingly complex systems, it is necessary to update present knowledge on process parameters and their role on operational ranges and flexibilities in real-life anaerobic digestion system. Accordingly, the present review discusses the importance of the selection of operational parameters in existing technologies and their impact on biogas yield. Notably, the four broad areas of feedstock utilization (substrate, inoculum, codigestion and pretreatment), process condition (pH, temperature, pressure, and reactor design), reactor control (HRT and OLR) and inhibition (Ammonia and VFAs) are covered in this review. In addition, particular emphasis is placed on the most recent innovations that have been or may be implemented in current or future biogas plants.

Optimizing biomethane production of mesophilic chicken manure and sheep manure digestion: Mono-digestion and co-digestion kinetic investigation, autofluorescence analysis and microbial community assessment

Optimization of mesophilic methane production from Chicken manure (CM) and Sheep manure (SM) at total solid (TS) of 8% and 1.6% were obtained by sequence tests in mono-digestion. However, the positive synergy of co-digestion with an optimum CM/SM of 2.5 (310 mLCH₄/gVS_added) resulted in a high hydrolytic capacity and methane production. The modified Gompertz model (R² > 0.98) and modified Aiba model (R² > 0.88) illustrated co-digestion significantly improved the methane generation rate with strong ammonia tolerance. Dissolved Organic Matter (DOM) variation in response to the metabolic rate of microbial community illustrated that the SMP-like and protein-like components half-split by EEM-PARAFAC were significantly negative corresponded to bio-methane production. Moreover, the canonical correlation analysis (CCA) resulted a significant difference between the substrate and DOM composition. Potential functional metabolic illustrated statistically significance difference between mono and co-digestion, however, Methanosaeta and Syntrophobacter predominated the syntrophic methanogenesis. The constructed complex metabolic cooperation caused the co-digestion stable and high efficiency.

Recent Updates on the Use of Agro-Food Waste for Biogas Production

The production of biogas from anaerobic digestion (AD) of residual agro-food biomasses represents an opportunity for alternative production of energy from renewable sources, according to the European Union legislation on renewable energy. This review provides an overview of the various aspects involved in this process with a focus on the best process conditions to be used for AD-based biogas production from residual agro-food biomasses. After a schematic description of the AD phases, the biogas plants with advanced technologies were described, pointing out the strengths and the weaknesses of the different digester technologies and indicating the main parameters and operating conditions to be monitored. Subsequently, a brief analysis of the factors affecting methane yield from manure AD was conducted and the AD of fruit and vegetables waste was examined. Particular attention was given to studies on co-digestion and pre-treatments as strategies to improve biogas yield. Finally, the selection of specific microorganisms and the genetic manipulation of anaerobic bacteria to speed up the AD process was illustrated. The open challenges concern the achievement of the highest renewable energy yields reusing agro-food waste with the lowest environmental impact and an increment of competitiveness of the agricultural sector in the perspective of a circular economy.

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.

16s rRNA gene sequencing and radioisotopic analysis reveal the composition of ammonia acclimatized methanogenic consortia

Different mesophilic and thermophilic methanogenic consortia were acclimatised and enriched to extreme total ammonia (9.0 and 5.0 g NH₄⁺-N L^-1, respectively) and free ammonia (1.0 and 1.4 g NH₃-N L^-1, respectively) levels in this study. [2-¹⁴C] acetate radioisotopic analyses showed the dominance of aceticlastic methanogenesis in all enriched consortia. According to 16S rRNA gene sequencing result, in mesophilic consortia, methylotrophic Methanomassiliicoccus luminyensis was predominant, followed by aceticlastic Methanosarcina soligelidi. A possible scenario explaining the dominance of M. luminyensis includes the use of methylamine produced by Tissierella spp. and biomass build-up by metabolizing acetate. Nevertheless, further studies are needed to pinpoint the exact metabolic pathway of M. luminyensis. In thermophilic consortia, aceticlastic Methanosarcina thermophila was the sole dominant methanogen. Overall, results derived from this study demonstrated the efficient biomethanation ability of these ammonia-tolerant methanogenic consortia, indicating a potential application of these consortia to solve ammonia toxicity problems in future full-scale reactors.

Hyperthermophilic composting significantly decreases N2O emissions by regulating N2O-related functional genes

This study reported for the first time that hyperthermophilic composting (HTC) could mitigate 90% of the cumulative amount of N₂O emissions compared to traditional composting (TC) in a full-scale experiment. The concentrations of NO₂^--N and NO₃^--N in HTC were significantly lower than those in TC, which may be the main reason for the reduced N₂O emissions. Furthermore, this study found that the decrease in N₂O emissions in HTC compared to TC was mainly due to the inhibition of the abundance of the bacterial amoA and norB genes, which could decrease the nitrification rate and control N₂O formation, respectively. Partial least squares path modeling revealed that a high temperature was the key factor in lowering N₂O emissions in HTC, while physicochemical properties were the dominant factor in enhancing N₂O emissions in TC. These results suggested that HTC is a promising technique for reducing N₂O emissions in manure composting.

Nutrient recovery technologies integrated with energy recovery by waste biomass anaerobic digestion

Anaerobic digestion widely considered as a promising waste biomass disposal treatment approach, is attracting increasing interest in all corners of the globe. However, due to the specific features of different types of waste biomass, the bioenergy conversion efficiency of this process is not ideal. Another problematic aspect of anaerobic digestion is that the nutrient rich effluent sometimes needs to be treated before discharge. This review presents the recent achievements of waste biomass digestion from the perspective of energy recovery and nutrient recovery. In this work, the anaerobic treatment characteristics of common types of waste biomass are summarized and compared. With a focus of nutrient recovery and post treatment issues, the challenges and technical hurdles encountered in the anaerobic digestion of waste biomass are critically reviewed. Finally, an integrated system of anaerobic digestion, anaerobic ammonia oxidation (anammox) and phosphorus recovery is proposed for efficient energy and nutrient recovery from waste biomass.

Terminal restriction fragment length polymorphism is an "old school" reliable technique for swift microbial community screening in anaerobic digestion

The microbial community in anaerobic digestion has been analysed through microbial fingerprinting techniques, such as terminal restriction fragment length polymorphism (TRFLP), for decades. In the last decade, high-throughput 16S rRNA gene amplicon sequencing has replaced these techniques, but the time-consuming and complex nature of high-throughput techniques is a potential bottleneck for full-scale anaerobic digestion application, when monitoring community dynamics. Here, the bacterial and archaeal TRFLP profiles were compared with 16S rRNA gene amplicon profiles (Illumina platform) of 25 full-scale anaerobic digestion plants. The α-diversity analysis revealed a higher richness based on Illumina data, compared with the TRFLP data. This coincided with a clear difference in community organisation, Pareto distribution, and co-occurrence network statistics, i.e., betweenness centrality and normalised degree. The β-diversity analysis showed a similar clustering profile for the Illumina, bacterial TRFLP and archaeal TRFLP data, based on different distance measures and independent of phylogenetic identification, with pH and temperature as the two key operational parameters determining microbial community composition. The combined knowledge of temporal dynamics and projected clustering in the β-diversity profile, based on the TRFLP data, distinctly showed that TRFLP is a reliable technique for swift microbial community dynamics screening in full-scale anaerobic digestion plants.

Biochemical Conversion and Microbial Community in Response to Ternary pH Buffer System during Anaerobic Digestion of Swine Manure

The ternary pH buffer system with ammonia-carbonates-volatile fatty acids (VFAs) is essential to anaerobes for bioenergy recovery via anaerobic digestion (AD). However, ammonia and VFAs are recognized as potential inhibitors that depress methanogenesis. In this study, biochemical conversion and the microbial community in batch AD at total solid (TS) from 4% to 14% were investigated to reveal their response to the ternary pH buffer system. The rapid ammonia release, probably promoted by Anaerosphaera and Eubacterium inferred from the concurrent peak of their relative abundance, triggered total ammonia (TAN) inhibition with the accumulation of VFAs in the start-up stage of high solid AD (HSAD, TS ≥ 8%). Along with evolution of the microbial community to resist high TAN and VFAs, methanogenesis recovered with improved degradation of VFAs and reduction of COD. When exposed to 3500 mg·N·L−1 TAN at 8% TS, aceticlastic Methanosarcina became dominant first and then together with hydrogenotrophic Methanoculleus, achieved the optimal biochemical conversion. While in HSAD at 11–14% TS, the main pathway of methanogenesis appeared to have shifted from the aceticlastic pathway to the hydrogenotrophic pathway, as inferred by changes in the relative abundance of methanogens, and this could have been induced by the increasing concentration of high free ammonia (FAN, ≥588 mg·N·L−1). Although the anaerobes had acclimatized to high TAN, the propionate-oxidizing bacteria and acetate-oxidizing bacteria might have again been inhibited by high FAN, frustrating the H2 supply for FAN-tolerant Methanoculleus and causing an 8.2–11.3% depression of COD reduction (mainly propionate residual).

Marker microbiome clusters are determined by operational parameters and specific key taxa combinations in anaerobic digestion

In this study, microbiomes of 36 full-scale anaerobic digesters originated from 22 different biogas plants were compared by terminal restriction fragment length polymorphism (TRFLP) analysis. Regarding the differences in microbial community composition, a weighting of the environmental parameters could be derived from higher to lower importance as follows: (i) temperature, (ii) TAN and NH₃ concentrations and conductivity, and (iii) the chemical composition of the supplied feedstocks. Biotic interactions between specific bacterial and archaeal community arrangements were revealed, whereby members of the phyla Bacteroidetes and Cloacimonetes combined with the archaeal genus Methanothrix dominated the conversion of homogeneous feedstocks, such as waste water sludge or industrial waste. As most of the detected TRFs were only found in a certain number of anaerobic digestion plants, each plant develops its unique microbiome. The putative rare species, the specialists, are potentially hidden drivers of microbiome functioning as they provide necessary traits under, e.g., process-inconvenient conditions.

Long-term high-solids anaerobic digestion of food waste: Effects of ammonia on process performance and microbial community

A long-term high solids anaerobic digestion of food waste was conducted to identify microbial mechanisms of ammonia inhibition during digestion and to clarify correlations between ammonia accumulation, microbial community dynamics (diversity, composition, and interactions), and process stability. Results show that the effects of ammonia on process performance and microbial community were indirectly caused by volatile fatty acid accumulation. Excess free ammonia blocked acetate metabolism, leading to process instability. Accumulated acetate caused feedback inhibition at the acetogenesis stage, which resulted in considerable accumulation of propionate, valerate, and other long-chain fatty acids. This high concentration of volatile fatty acids reduced the abundance of syntrophic acetogenic bacteria and allowed hydrolytic fermentative bacteria to dominate. The normally interactive and orderly metabolic network was broken, which further exacerbated the process instability. These results improve the understanding of microbial mechanisms which contribute to process instability and provide guidance for the microbial management of anaerobic digesters.

Inhibition of anaerobic digestion processes: Applications of molecular tools

Inhibition of anaerobic digestion (AD) due to perturbation caused by substrate composition and/or operating conditions can significantly reduce performance. Such perturbations could be limited by elucidating microbial community response to inhibitors and devising strategies to increase community resilience. To this end, advanced molecular methods are increasingly being applied to study the AD microbiome, a diverse community of microbial populations with complex interactions. This literature review of AD inhibition studies indicates that inhibitory concentrations are highly variable, likely stemming from differences in community structure or activity profile and previous exposure to inhibitors. More recent molecular methods such as 'omics' tools, substrate mapping, and real-time sequencing are helping to unravel the complexity of AD inhibition by elucidating physiological and ecological significance of key microbial populations. The AD community must strive towards developing predictive abilities to avoid system failure (e.g., real-time tracking of an indicator species) to improve resilience of AD systems.

Impact of a high ammonia-ammonium-pH system on methane-producing archaea and sulfate-reducing bacteria in mesophilic anaerobic digestion

A novel strategy for acclimation to ammonia stress was implemented by stimulating a high ammonia-ammonium-pH environment in a high-solid anaerobic digestion (AD) system in this study. Three semi-continuously stirred anaerobic reactors performed well over the whole study period under mesophilic conditions, especially in experimental group (R-2) when accommodated from acclimation period which the maximum total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN) increased to 4921 and 2996mg/L, respectively. Moreover, when it accommodated the high ammonia-ammonium-pH system, the daily biogas production and methane content were similar to those in R-1 (the blank control to R-2), but the hydrogen sulfide (H₂S) content lower than the blank control. Moreover, mechanistic studies showed that high ammonia stress enhanced the activity of coenzyme F₄₂₀. The results of real-time fluorescent quantitative polymerase chain reaction (PCR) showed that ammonia stress decreased the abundance of sulfate-reducing bacteria and increased the abundance of methane-producing archaea.

Anaerobic digestion of spent mushroom substrate under thermophilic conditions: performance and microbial community analysis

Spent mushroom substrate (SMS) is the residue of edible mushroom production occurring in huge amounts. The SMS residue can be digested for biogas production in the mesophilic anaerobic digestion. In the present study, performance of batch thermophilic anaerobic digestion (TAD) of SMS was investigated as well as the interconnected microbial population structure changes. The analyzed batch TAD process lasted for 12 days with the cumulative methane yields of 177.69 mL/g volatile solid (VS). Hydrolytic activities of soluble sugar, crude protein, and crude fat in SMS were conducted mainly in the initial phase, accompanied by the excessive accumulation of volatile fatty acids and low methane yield. Biogas production increased dramatically from days 4 to 6. The degradation rates of cellulose and hemicellulose were 47.53 and 55.08%, respectively. The high-throughput sequencing of 16S rRNA gene amplicons revealed that Proteobacteria (56.7%-62.8%) was the dominant phylum in different fermentative stages, which was highly specific compared with other anaerobic processes of lignocellulosic materials reported in the literature. Crenarchaeota was abundant in the archaea. The most dominant genera of archaea were retrieved as Methanothermobacter and Methanobacterium, but the latter decreased sharply with time. This study shows that TAD is a feasible method to handle the waste SMS.

Methods of ammonia removal in anaerobic digestion: a review

The anaerobic digestion of substrates with high ammonia content has always been a bottleneck in the methanisation process of biomasses. Since microbial communities in anaerobic digesters are sensitive to free ammonia at certain conditions, the digestion of nitrogen-rich substrates such as livestock wastes may result in inhibition/toxicity eventually leading to process failures, unless appropriate engineering precautions are taken. There are many different options reported in literature to remove ammonia from anaerobic digesters to achieve a safe and stable process so that along with high methane yields, a good quality of effluents can also be obtained. Conventional techniques to remove ammonia include physical/chemical methods, immobilization and adaptation of microorganisms, while novel methods include ultrasonication, microwave, hollow fiber membranes and microbial fuel cell applications. This paper discusses conventional and novel methods of ammonia removal from anaerobic digesters using nitrogen-rich substrates, with particular focus on recent literature available about this topic.

Anaerobic co-digestion of chicken manure and microalgae Chlorella sp.: Methane potential, microbial diversity and synergistic impact evaluation

Anaerobic digestion (AD) is a promising alternative for livestock manure management. This paper presents the experimental results obtained through a batch experiment by using chicken manure (CM) and microalgae Chlorella sp. as co-substrates. The effect of co-digestion was evaluated by varying CM to Chlorella sp. ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10: 0 based on the volatile solids (VS)). The major objective of this study is to evaluate the feasibility and synergistic impact of co-digestion of CM and Chlorella sp. Enhanced 14.20% and 76.86% methane production than CM and Chlorella sp. mono-digestion respectively was achieved in co-digestion at the ratio 8:2. In addition, the co-digestion at the ratio 8:2 showed significantly higher methane yield than the weighted average of the individual substrates' specific methane yield (WSMY), indicating strong synergy effect. The Illumina Miseq sequencing analysis showed that the AD process suppressed the acetoclastic methanogenesis Methanosaeta content; but partly enhanced hydrogenotrophic methanogenesis Methanosarcina, Methanospirillum and Methanobacterium, which was responsible for the methane production. The pre-treated microalgae was then introduced at the optimal ratio 8:2 to estimate the effect of pre-treatment of microalgae on AD process. However, the pre-treatment exhibited no positive effect.

Microbial community redundancy in anaerobic digestion drives process recovery after salinity exposure

Anaerobic digestion of high-salinity wastewaters often results in process inhibition due to the susceptibility of the methanogenic archaea. The ability of the microbial community to deal with increased salinity levels is of high importance to ensure process perseverance or recovery after failure. The exact strategy of the microbial community to ensure process endurance is, however, often unknown. In this study, we investigated how the microbial community is able to recover process performance following a disturbance through the application of high-salinity molasses wastewater. After a stable start-up, methane production quickly decreased from 625 ± 17 to 232 ± 35 mL CH₄ L^-1 d^-1 with a simultaneous accumulation in volatile fatty acids up to 20.5 ± 1.4 g COD L^-1, indicating severe process disturbance. A shift in feedstock from molasses wastewater to waste activated sludge resulted in complete process recovery. However, the bacterial and archaeal communities did not return to their original composition as before the disturbance, despite similar process conditions. Microbial community diversity was recovered to similar levels as before disturbance, which indicates that the metabolic potential of the community was maintained. A mild increase in ammonia concentration after process recovery did not influence methane production, indicating a well-balanced microbial community. Hence, given the change in community composition following recovery after salinity disturbance, it can be assumed that microbial community redundancy was the major strategy to ensure the continuation of methane production, without loss of functionality or metabolic flexibility.

Modeling the dynamic volatile fatty acids profiles with pH and hydraulic retention time in an anaerobic baffled reactor during the startup period

To predict the dynamic profiles in volatile fatty acids (VFAs) with pH and hydraulic retention time (HRT) during the startup of a 4-compartment ABR, a mathematical model was constructed by introducing pH and thermodynamic inhibition functions into the biochemical processes derived from the ADM1. The calibration of inhibition parameter for propionate uptake effectively improved the prediction accuracy of VFAs. The developed model could simulate the VFAs profiles very well no matter the observable change of pH or/and HRT. The simulation results indicated that both H₂-producing acetogenesis and methanogenesis in the ABR would be inhibited with a pH less than 4.61, and the propionate oxidation could be thermodynamically restricted even with a neutral pH. A decreased HRT would enhanced the acidogenesis and H₂-producing acetogenesis in the first 3 compartments, but no observable increase in effluent VFAs could be found due to the synchronously enhanced methanogenesis in the last compartment.

Ammonium inhibition through the decoupling of acidification process and methanogenesis in anaerobic digester revealed by high throughput sequencing

OBJECTIVE

To reveal the shifts of microbial communities along ammonium gradients, and the relationship between microbial community composition and the anaerobic digestion performance using a high throughput sequencing technique.

RESULTS

Methane production declined with increasing ammonium concentration, and was inhibited above 4 g l^-1. The volatile fatty acids, especially acetate, accumulated with elevated ammonium. Prokaryotic populations showed different responses to the ammonium concentration: Clostridium, Tepidimicrobium, Sporanaerobacter, Peptostreptococcus, Sarcina and Peptoniphilus showed good tolerance to ammonium ions. However, Syntrophomonas with poor tolerance to ammonium may be inhibited during anaerobic digestion. During methanogenesis, Methanosarcina was the dominant methanogen.

CONCLUSION

Excessive ammonium inhibited methane production probably by decoupling the linkage between acidification process and methanogenesis, and finally resulted in different performance in anaerobic digestion.

Overcoming organic and nitrogen overload in thermophilic anaerobic digestion of pig slurry by coupling a microbial electrolysis cell

The combination of the anaerobic digestion (AD) process with a microbial electrolysis cell (MEC) coupled to an ammonia stripping unit as a post-treatment was assessed both in series operation, to improve the quality of the effluent, and in loop configuration recirculating the effluent, to increase the AD robustness. The MEC allowed maintaining the chemical oxygen demand removal of the whole system of 46±5% despite the AD destabilization after doubling the organic and nitrogen loads, while recovering 40±3% of ammonia. The AD-MEC system, in loop configuration, helped to recover the AD (55% increase in methane productivity) and attained a more stable and robust operation. The microbial population assessment revealed an enhancement of AD methanogenic archaea numbers and a shift in eubacterial population. The AD-MEC combined system is a promising strategy for stabilizing AD against organic and nitrogen overloads, while improving the quality of the effluent and recovering nutrients for their reutilization.

Influence of Hydraulic Retention Time and Reactor Configuration During Fermentation of Diluted Chicken Manure

In this study, single-stage and two-phase semi-continuous thermophilic anaerobic reactors fed with diluted (3 % total solids (TS) and 1.8 % volatile solids (VS)) chicken manure at three different hydraulic retention times (HRTs) were compared interms of biogas production rate, methane content of the produced biogas, and VS and TS removal. Along the study, HRTs of 16, 12, and 8 days were implemented to the single-stage and the two-phase systems. It was observed that the single-stage anaerobic system was superior to the two-phase anaerobic system according to their biogas production rates (517 vs. 356, 551 vs. 359, 459 vs. 386 (mL/g VS_feed)) at all HRTs. On the other hand, methane content of the biogas produced was higher in the two-phase system compared to the single-stage system.

Modeling the performance of an anaerobic baffled reactor with the variation of hydraulic retention time

Anaerobic baffled reactors (ABRs) have been widely used in engineering but very few models have been developed to simulate its performance. Based on the integration of biomass retention and liquid-gas mass transfer of biogas into the biochemical process derived in the International Water Association (IWA) Anaerobic Digestion Model No.1 (ADM1), a mathematical model was developed to predict volatile fatty acids (VFAs), chemical oxygen demand (CODCr) and biogas in a 4-compartment ABR operated with variable hydraulic retention time (HRT). The model was calibrated and validated with the experimental data obtained from the reactor when the HRT decreased from 2.0 to 1.0d by stages. It was found that the predicted VFAs, CODCr and biogas agreed well with the experimental data. Consequently, the developed model was a reliable tool to enhance the understanding among the mechanisms of the anaerobic digestion in ABRs, as well as to reactor's designing and operation.

Integrated approach to sustain biogas production in anaerobic digestion of chicken manure under recycled utilization of liquid digestate: Dynamics of ammonium accumulation and mitigation control

The dynamics of ammonium accumulation and mitigation control in anaerobic digestion of chicken manure under the recycled utilization of liquid digested slurry were investigated by using an integrated approach in two laboratory-scale semi-continuously stirred tank reactors. In the reactor with direct recycled utilization of the anaerobic digested liquid slurry, total volatilized fatty acids (in CH3COOH) and NH4(+)-N increased from 1600mg/L to 8000mg/L and from 2600mg/L to 5000mg/L, respectively. The daily volumetric biogas production decreased from 1.4±0.1L/(L·d) to 0.8±0.1L/(L·d) with a reduction efficiency of 43±4%. Air stripping was integrated for ammonium mitigation of recycled liquid digested slurry and was shown to effectively reduce the ammonium to 3000mg/L. Correspondingly, the biogas production was recovered back to 1.4±0.1L/(L·d). This indicated the potential of the integration of air stripping for ammonium mitigation in an anaerobic digestion process with liquid digested slurry recirculation.

The microbial community structure in industrial biogas plants influences the degradation rate of straw and cellulose in batch tests

BACKGROUND

Materials rich in lignocellulose, such as straw, are abundant, cheap and highly interesting for biogas production. However, the complex structure of lignocellulose is difficult for microbial cellulolytic enzymes to access, limiting degradation. The rate of degradation depends on the activity of members of the microbial community, but the knowledge of this community in the biogas process is rather limited. This study, therefore, investigated the degradation rate of cellulose and straw in batch cultivation test initiated with inoculums from four co-digestion biogas plants (CD) and six wastewater treatment plants (WWTP). The results were correlated to the bacterial community by 454-pyrosequencing targeting 16S rRNA gene and by T-RFLP analysis targeting genes of glycoside hydrolase families 5 (cel5) and 48 (cel48), combined with construction of clone libraries.

RESULTS

UniFrac principal coordinate analysis of 16S rRNA gene amplicons revealed a clustering of WWTPs, while the CDs were more separated from each other. Bacteroidetes and Firmicutes dominated the community with a comparably higher abundance of the latter in the processes operating at high ammonia levels. Sequences obtained from the cel5 and cel 48 clone libraries were also mainly related to the phyla Firmicutes and Bacteroidetes and here ammonia was a parameter with a strong impact on the cel5 community. The results from the batch cultivation showed similar degradation pattern for eight of the biogas plants, while two characterised by high ammonia level and low bacterial diversity, showed a clear lower degradation rate. Interestingly, two T-RFs from the cel5 community were positively correlated to high degradation rates of both straw and cellulose. One of the respective partial cel5 sequences shared 100 % identity to Clostridium cellulolyticum.

CONCLUSION

The degradation rate of cellulose and straw varied in the batch tests dependent on the origin of the inoculum and was negatively correlated with the ammonia level. The cellulose-degrading community, targeted by analysis of the glycoside hydrolase families 5 (cel5) and 48 (cel48), showed a dominance of bacteria belonging the Firmicutes and Bacteriodetes, and a positive correlation was found between the cellulose degradation rate of wheat straw with the level of C. cellulolyticum.

Microbial population dynamics in response to increasing loadings of pre-hydrolyzed pig manure in an expanded granular sludge bed

In recent years, pig manure (PM) has been regarded as a valuable substrate for energy and resource recovery via bioprocesses such as anaerobic digestion (AD), however, the efficiency of digesting raw PM is limited by the presence of refractory compounds. In this study, we applied a series of pretreatment on raw PM, consisting of subsequent thermochemical pretreatment, enzymatic hydrolysis, tyndallization and filtration. The liquid PM hydrolysates were fed to an expanded granular sludge bed (EGSB) for the production of biogas. The general performance and population dynamics of the EGSB reactor were assessed during an extended operational period of 339 days. An efficient and stable digestion process was achieved under high organic loading rates (OLRs) up to 21 kg-COD/(m(3)·d), agreeing with a sludge loading rate of 0.75 kg-COD/(kg-VSS·d), 1600 mg-NH4(+)-N/L and 17 mg/L of free ammonia nitrogen. The tyndallization decreased the total amount of active cells from 1 × 10(8) to 1 × 10(2) CFU/ml. Hence, bio-augmentation with pigs' intestinal microbiota was absent and the community dynamics were mainly credited to the composition of the substrate (i.e. PM hydrolysates) and the environmental conditions inside the reactor. The results showed the influence of both the seed community and the imposed loading rates on the evolutionary trajectory of the EGSB microbial community. Four bacterial genera (Clostridium, Cytophaga, Bacillus and Bacteroides) and two methanogenic genera (Methanosaeta and Methanobacterium) dominated the communities. An obvious shift from aceticlastic Methanosaeta to hydrogenotrophic Methanobacterium appeared when the OLR was increased to over 10 kg-COD/(m(3)·d).

Effect of the Organic Loading Rate Increase and the Presence of Zeolite on Microbial Community Composition and Process Stability During Anaerobic Digestion of Chicken Wastes

This study investigates the effect of the organic loading rate (OLR) increase from 1.0 to 3.5 g VS L(-1) day(-1) at constant hydraulic retention time (HRT) of 35 days on anaerobic reactors' performance and microbial diversity during mesophilic anaerobic digestion of ammonium-rich chicken wastes in the absence/presence of zeolite. The effects of anaerobic process parameters on microbial community structure and dynamics were evaluated using a 16S ribosomal RNA gene-based pyrosequencing approach. Maximum 12 % of the total ammonia nitrogen (TAN) was efficiently removed by zeolite in the fixed zeolite reactor (day 87). In addition, volatile fatty acids (VFA) in the fixed zeolite reactor accumulated in lower concentrations at high OLR of 3.2-3.5 g VS L(-1) day(-1). Microbial communities in the fixed zeolite reactor and reactor without zeolite were dominated by various members of Bacteroidales and Methanobacterium sp. at moderate TAN and VFA levels. The increase of the OLR accompanied by TAN and VFA accumulation and increase in pH led to the predominance of representatives of the family Erysipelotrichaceae and genera Clostridium and Methanosarcina. Methanosarcina sp. reached relative abundances of 94 and 57 % in the fixed zeolite reactor and reactor without zeolite at the end of the experimental period, respectively. In addition, the diminution of Synergistaceae and Crenarchaeota and increase in the abundance of Acholeplasmataceae in parallel with the increase of TAN, VFA, and pH values were observed.

Evaluation of functional microbial community's difference in full-scale and lab-scale anaerobic digesters feeding with different organic solid waste: Effects of substrate and operation factors

Samples taken from the full-scale and lab-scale anaerobic digesters feeding with different organic solid waste were investigated with assessment of the substrate effects. To understand the substrate effects on the microbial community diversity, heterogeneity, and functional structure, twelve samples were analyzed by constructing 16S rRNA gene clone libraries and statistical analysis. Microbial diversity varied according to substrate types and operating parameters. With acetoclastic methanogen of genus Methanosaeta predominated in full scale and Methanosarcina predominated in the lab-scale digesters, a significant difference archaeal communities were found. Principal component analysis clearly indicates that both bacterial and archaeal communities create independent clusters according to substrate types. However, the relationship between acetogenic bacteria and the acetoclastic methanogens had a similar variation tends in most of full-scale and lab-scale reactors. Canonical correlation analysis and variance partitioning analysis implied that bacterial and archaeal community variations were significantly affected by substrate and the operation conditions.

Impact of the substrate loading regime and phosphoric acid supplementation on performance of biogas reactors and microbial community dynamics during anaerobic digestion of chicken wastes

This study evaluates the effects of increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) as well as phosphoric acid addition on mesophilic reactors' performance and biogas production from chicken wastes. Furthermore, microbial community composition in reactors was characterized by a 16S rRNA gene-based pyrosequencing analysis. Each step of increasing OLR impacted on the activity of microorganisms what caused a temporary decrease in biogas production. The addition of phosphoric acid resulted in the increased biogas production with values between 361 and 447 mL g(VS)(-1) from day 61 to day 74 compared to control reactor (309-350 mL g(VS)(-1)). With reactors' operation, Bacteroidetes phylotypes were noticeably replaced with Firmicutes representatives, and significant increase of Clostridium sp. was identified. Within Euryarchaeota, Methanosarcina sp. dominated in all analyzed samples, in which high ammonium levels were detected (3.4-4.9 NH4(+)-N g L(-1)). These results can help in better understanding the anaerobic digestion process of simultaneously ammonium/phosphate-rich substrates.