The biomethanation of cow manure in a continuous anaerobic digester can be boosted via a bioaugmentation culture containing Bathyarchaeota

A bioaugmentation approach was used to enhance the performance of anaerobic digestion (AD) using cow manure (CM) as the substrate in a continuous system. To obtain the desirable microbial culture for bioaugmentation, a biochemical methane potential test (BMP) was used to evaluate three commonly used inocula namely (1) municipal solid waste (MSW), (2) wastewater treatment plant (WWTP), and (3) cow manure digester (CMMD) for their hydrolytic capacity. The highest lignocellulose removal (56% for cellulose and 50% for hemicellulose) and the most profusion of cellulolytic bacteria were obtained when CM was inoculated with CMMD. CMMD was thus used as the seed inoculum in a continuously operated reactor (R_a) with the fiber fraction of CM as the substrate to further enrich cellulolytic microbes. After 100 days (HRT: 30 days), the Bacteria fraction mainly contained Ruminofilibacter, norank_o_SBR1031, Treponema, Acetivibrio. Surprisingly, the Archaea fraction contained 97% 'cellulolytic archaea' norank_c_Bathyarchaeia (Phylum Bathyarchaeota). This enriched consortium was used in the bioaugmentation experiment. A positive effect of bioaugmentation was verified, with a substantial daily methane yield (DMY) enhancement (24.3%) obtained in the bioaugmented reactor (R_b) (179 mL CH₄/gVS/d) than that of the control reactor (R_c) (144 mL CH₄/gVS/d) (P < 0.05). Meanwhile, the effluent of R_b enjoyed an improved cellulose reduction (14.7%) than that of R_c, whereas the amount of hemicellulose remained similar in both reactors' effluent. When bioaugmentation stopped, its influence on the hydrolysis and methanogenesis sustained, reflected by an improved DMY (160 mL CH₄/gVS/d) and lower cellulose content (53 mg/g TS) in R_b than those in R_c (DMY 144 mL/CH₄/gVS/d and cellulose content 63 mg/g TS, respectively). The increased DMY of the continuous reactor seeded with a specifically enriched consortium able to degrade the fiber fraction in CM shows the feasibility of applying bioaugmentation in AD of CM.

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.

Long-term investigation of microbial community composition and transcription patterns in a biogas plant undergoing ammonia crisis

Ammonia caused disturbance of biogas production is one of the most frequent incidents in regular operation of biogas reactors. This study provides a detailed insight into the microbial community of a mesophilic, full-scale biogas reactor (477 kWh h-1 ) fed with maize silage, dried poultry manure and cow manure undergoing initial process disturbance by increased ammonia concentration. Over a time period of 587 days, the microbial community of the reactor was regularly monitored on a monthly basis by high-throughput amplicon sequencing of the archaeal and bacterial 16S rRNA genes. During this sampling period, the total ammonia concentrations varied between 2.7 and 5.8 g l-1 [NH4 + -N]. To gain further inside into the active metabolic pathways, for selected time points metatranscriptomic shotgun analysis was performed allowing the quantification of marker genes for methanogenesis, hydrolysis and syntrophic interactions. The results obtained demonstrated a microbial community typical for a mesophilic biogas plant. However in response to the observed changing process conditions (e.g. increasing NH4 + levels, changing feedstock composition), the microbial community reacted highly flexible by changing and adapting the community composition. The Methanosarcina-dominated archaeal community was shifted to a Methanomicrobiales-dominated archaeal community in the presence of increased ammonia conditions. A similar trend as in the phylogenetic composition was observed in the transcription activity of genes coding for enzymes involved in acetoclastic methanogenesis and syntrophic acetate oxidations (Codh/Acs and Fthfs). In accordance, Clostridia simultaneously increased under elevated ammonia concentrations in abundance and were identified as the primary syntrophic interaction partner with the now Methanomicrobiales-dominated archaeal community. In conclusion, overall stable process performance was maintained during increased ammonia concentration in the studied reactor based on the microbial communities' ability to flexibly respond by reorganizing the community composition while remaining functionally stable.

Sugar beet silage as highly flexible feedstock for on demand biogas production

On demand biogas production is a great option to complement solar and wind power for the energy revolution. Alternatives like feedstock management are important in order to avoid expensive and complex adjustments for gas storage systems. The use of sugar beet silage (S) is a good option because it mainly contains carbohydrates that are easily degradable. Anaerobic digestion was performed for 63 days in four completely stirred tank reactors (CSTR) with different ratios of maize silage (M) and S. M given every hour was used as a base load for the fermentation and S was given two times a day every 12h. Biogas and methane production rates were measured every 5min in order to achieve data with high resolution. Also, pH value, VFA/TIC values and volatile fatty acids were measured during the experiment. The process remained stable in CSTR1 (M:S1:0), CSTR2 (M:S6:1) and CSTR3 (M:S3:1). Instabilities occurred in CSTR4 (M:S1:3) after an operation time of 33 days. Nevertheless, methane yields more than doubled for CSTR3 within 5min after the input of S. Use of sugar beet as a feedstock for biogas production is a further application for this agricultural commodity.

Characteristics of on-demand biogas production by using sugar beet silage

On-demand electricity generation can be achieved by just-in-time biogas production instantly utilized in co-generation units. For this goal, easily degradable substrates like sugar beet silage have a high potential. Potential for on-demand biogas production from co-digestion of sugar beet silage (SS) with grass silage (GS) was evaluated in two experiments at organic loading rates (OLRs) of 1.5 kgVS m^-3 day^-1 and 2.5 kgVS m^-3 day^-1, respectively. Each experiment was fed with intermittent feeding system at 8 hrs interval at the same feedstock ratios (volatile solids based) of GS:SS-1:0, 3:1 and 1:3, respectively. Modelling by Gaussian equation was performed in order to understand the effects of SS on biogas production. Addition of sugar beet silage led to maximum biogas production within a short time, but it differed significantly depending on feedstock ratios and OLRs, respectively. At OLR 1.5 kgVS m^-3 day^-1, during mono fermentation of grass silage maximum biogas production rate of 0.27 l_N hr^-1 was reached at 2.74 hrs. Production rate did not change at feedstock ratio of GS:SS-3:1 but increased to 0.64 l_N hr^-1 at GS:SS-1:3 within a shorter time span (1.58 hrs). On the contrary, at OLR of 2.5 kgVS m^-3 day^-1 time span between feedstock input and maximum biogas production did not differ significantly (p > 0.05) among the reactors. Biogas production rates were 0.60 l_N hr^-1 within 2.27 hrs and 0.82 l_N hr^-1 within 2.30 hrs at GS:SS-3:1 and GS:SS-1:3, respectively. Surprisingly, there was no time lag between maximum biogas and methane production rates, irrespectively of OLR. This implies that once the whole microbial community is adapted to intermittent substrate input, the metabolic products are instantly utilized through the all steps of anaerobic substrate degradation. Applying this finding opens new perspectives for on-demand biogas energy production.

Co-Digestion of Sugar Beet Silage Increases Biogas Yield from Fibrous Substrates

This study tested the hypothesis that the easily degradable carbohydrates of the sugar beet silage (S) will improve the anaerobic digestion of grass silage (G) more profoundly compared to co-digestion of sugar beet silage with maize silage (M). M : S and G : S mixtures were tested in two continuous laboratory-scale AD experiments at volatile solid ratios of 1 : 0, 6 : 1, 3 : 1, and 1 : 3 at organic loading rates of 1.5 kgVS m⁻³ day⁻¹. While the sugar beet effects in mixtures with maize silage were negligible, co-digestion with grass silage showed a beneficial performance. There, the specific methane production rate was 0.27 l_N kg⁻¹VS h⁻¹at G : S ratio of 6 : 1 compared to G : S 1 : 0 with 0.14 l_N kg⁻¹VS h⁻¹. In comparison to G : S 1 : 0, about 44% and 62% higher biogas yields were obtained at G : S 6 : 1 and 3 : 1, respectively. Also, the highest methane concentration was found in G : S at ratio of 1 : 3. Synergistic increase of methane yield was found in co-digestion in both experiments, but higher effect was realized in G : S, independently of the amount of sugar beet silage. The findings of this study emphasize the improvement of AD of grass silage by even low addition of sugar beet silage.