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Anaerobic digestion (AD) of sugarcane filter cake (SFC) was investigated by comparing the performance of pre-treatment methods in biochemical methane potential (BMP) tests and semi-continuous experiments. For that, SFC was pre-treated by autoclaving the substrate alone or with sodium hydroxide (NaOH). Experimental data from BMP tests were fitted to a kinetics model and further used for simulating the AD process in a continuous stirred-tank reactor (CSTR). BMP tests showed differences (p < 0.05) in total methane potential (SBMP), which have affected methane yields during simulation in a CSTR. Untreated produced 185 mL CH4 gVS−1, autoclaved pre-treatment 174 mL CH4 gVS−1 and autoclaved with NaOH pre-treatment 222 mL CH4 gVS−1. Interestingly, such higher performance of autoclaved with NaOH pre-treatment was only observed at earlier stages during semi-continuous feeding experiment. At steady-state no significant differences (p > 0.05) in terms of methane yield were observed among the reactors (average of 224 mL CH4 gVS−1). These results demonstrate that the benefits of pre-treatment could only be observed in BMP tests, which is likely explained by a better adaptation of the microbial community to the substrate during long term semi-continuous experiment, making SFC pre-treatment ineffective in a single-stage CSTR and under this feeding regime.

For biogas-producing continuous stirred tank reactors, an increase in dilution rate increases the methane production rate as long as substrate input can be converted fully. However, higher dilution rates necessitate higher specific microbial growth rates, which are assumed to have a strong impact on the apparent microbial biomass yield due to cellular maintenance. To test this, we operated two reactors at 37°C in parallel at dilution rates of 0.18 and 0.07 days-1 (hydraulic retention times of 5.5 and 14 days, doubling times of 3.9 and 9.9 days in steady state) with identical inoculum and a mixture of volatile fatty acids as sole carbon sources. We evaluated the performance of the Anaerobic Digestion Model No. 1 (ADM1), a thermodynamic black box approach (TBA), and dynamic flux balance analysis (dFBA), to describe the experimental observations. All models overestimated the impact of dilution rate on the apparent microbial biomass yield when using default parameter values. Based on our analysis, a maintenance coefficient value below 0.2 kJ per carbon mole of microbial biomass per hour should be used for the TBA, corresponding to 0.12 mmol ATP per gram dry weight per hour for dFBA, which strongly deviates from the value of 9.8 kJ Cmol h-1 that has been suggested to apply to all anaerobic microorganisms at 37°C. We hypothesized that a decrease in dilution rate might select taxa with minimized maintenance expenditure. However, no major differences in the dominating taxa between the reactors were observed based on amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism analysis of mcrA genes. Surprisingly, Methanosaeta dominated over Methanosarcina even at a dilution rate of 0.18 days-1, which contradicts previous model expectations. Furthermore, only 23–49% of the bacterial reads could be assigned to known syntrophic fatty acid oxidizers, indicating that unknown members of this functional group remain to be discovered. In conclusion, m

Ammonia inhibition is an important reason for reactor failures and economic losses in anaerobic digestion. Its impact on acetic acid degradation is well-studied, while its effect on propionic and butyric acid degradation has received little attention and is consequently not considered in the Anaerobic Digestion Model No. 1 (ADM1). To compare ammonia inhibition of the degradation of these three volatile fatty acids (VFAs), we fed a mixture of them as sole carbon source to three continuous stirred tank reactors (CSTRs) and increased ammonium bicarbonate concentrations in the influent from 52 to 277 mM. The use of this synthetic substrate allowed for the determination of degradation efficiencies for the individual acids. While butyric acid degradation was hardly affected by the increase of ammonia concentration, propionic acid degradation turned out to be even more inhibited than acetic acid degradation with degradation efficiencies dropping to 31 and 65% for propionic and acetic acid, respectively. The inhibited reactors acclimatized and approximated pre-disturbance degradation efficiencies toward the end of the experiment, which was accompanied by strong microbial community shifts, as observed by amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism (T-RFLP) of mcrA genes. The acetoclastic methanogen Methanosaeta was completely replaced by Methanosarcina. The propionic acid degrading genus Syntrophobacter was replaced by yet unknown propionic acid degraders. The butyric acid degrading genus Syntrophomonas and hydrogenotrophic Methanomicrobiaceae were hardly affected. We hypothesized that the ammonia sensitivity of the initially dominating taxa Methanosaeta and Syntrophobacter led to a stronger inhibition of the acetic and propionic acid degradation compared to butyric acid degradation and hydrogenotrophic methanogenesis, which were facilitated by the ammonia tolerant taxa Syntrophomonas and Methanomicrobiaceae. We implemented thi

Background Demand-driven biogas production could play an important role for future sustainable energy supply. However, feeding a biogas reactor according to energy demand may lead to organic overloading and, thus, to process failures. To minimize this risk, digesters need to be actively steered towards containing more robust microbial communities. This study focuses on acetogenesis and methanogenesis as crucial process steps for avoiding acidification. We fed lab-scale anaerobic digesters with volatile fatty acids under various feeding regimes and disturbances. The resulting microbial communities were analyzed on DNA and RNA level by terminal restriction fragment length polymorphism of the mcrA gene, 16S rRNA gene amplicon sequencing, and a [2-13C]-acetate assay. A modified Anaerobic Digestion Model 1 (ADM1) that distinguishes between the acetoclastic methanogens Methanosaeta and Methanosarcina was developed and fitted using experimental abiotic and biotic process parameters. Results Discontinuous feeding led to more functional resilience than continuous feeding, without loss in process efficiency. This was attributed to a different microbial community composition. Methanosaeta dominated the continuously fed reactors, while its competitor Methanosarcina was washed out. With discontinuous feeding, however, the fluctuating acetic acid concentrations provided niches to grow and co-exist for both organisms as shown by transcription analysis of the mcrA gene. Our model confirmed the higher functional resilience due to the higher abundance of Methanosarcina based on its higher substrate uptake rate and higher resistance to low pH values. Finally, we applied our model to maize silage as a more complex and practically relevant substrate and showed that our model is likely transferable to the complete AD process. Conclusions The composition of the microbial community determined the AD functional resilience against organic overloading in our experiments. In particular, commun

The concept of year-round biogas production to increase the capacity factor of anaerobic digestion (AD) plants in sugarcane biorefineries was investigated for the first time in semi-continuous feeding mode. To simulate the use of sugarcane vinasse during the sugarcane season and sugarcane filter cake (SFC) during the off-season period, a two-stage reactor system based on an acidogenic continuous stirred-tank reactor (1st stage) followed by solid–liquid separation and an upflow anaerobic sludge blanket (UASB) reactor (2nd stage) to convert the COD-rich liquid fraction into biogas was operated. Additionally, to optimize the biogas production from SFC, the effects of its thermo-chemical pre-treatment on AD were investigated in a parallel reactor set-up. The saponification effect provided by autoclaving the substrate with sodium hydroxide improved the hydrolysis/fermentation of SFC in the acidogenic reactor, which in turn resulted in a 28% higher volumetric methane production in the methanogenic reactor (p < 0.05). However, the methane yields observed during operation of the two-stage reactor system were markedly lower than previously found in biochemical methane potential tests using SFC. In this case, the feed-in with low suspended solids required by UASB reactors prevented the utilization of the non-hydrolyzed/fermented solid fraction of SFC (> 60% of the substrate’s methane potential). Nevertheless, the capacity factor of the AD plants in sugarcane biorefineries could be increased from 0.55 up to 0.69 when considering a 200 d a−1 sugarcane season (0.66–0.83 for a longer season of 240 d a−1), representing an increase of 25.7%. The average capacity factor for biogas combined heat and power and upgrading units of around 0.91 (8000 h a−1) would be reached if further developments could improve the solubilization of non-hydrolyzed/fermented solids or alternatively allow their direct use in the methanogenic reactor.

Background Waterweeds (Elodea nuttallii and Elodea canadensis) are invasive neophytes, which have been proliferating at a phenomenal rate during the last decades in German waterways. In case of overgrowth, the strong covering of vegetation can cause problems in hydroelectric power plants and leads to limitations in ship and boat traffic as well as in use for bathing and fishing activities. After vegetation period, dead plants can accumulate and then negatively influence flood protection and water engineering works. For this reason, the aquatic biomass has been periodically removed and disposed without further use. In order to enable the energetic use of this water-containing substrate, the aim of the present study was the optimization of storage methods for an aquatic plant-based feedstock for biogas production. In climatic cold regions, substrate conservation is necessary in order to guarantee a year-round substrate availability. With waterweed (Elodea) taken as an example, the ensiling of aquatic plants was studied. The main focus was to develop practical methods for biomass conservation while producing high biogas yields. Methods Elodea was harvested in the river Parthe in Leipzig-Schönefeld in October 2015. Silage mixtures of Elodea and wheat straw were tested after 180 days of storage for pH, volatile fermentation products, and methane potentials. The effect of different silage moisture contents and straw particle sizes on the substrate quality was studied. Results Results show that waterweeds can be stored by ensiling and can achieve considerable biogas yields. However, with a water content of about 95%, the storability of the material is challenging. Mixed silage of waterweeds and wheat straw were suitable for storage in clamp silos. The pH values were between 4.9 and 6.5, and the volatile fatty acid content as lactic acid ranged from 0.0 to 1.9% total solid. The mixed silages achieved methane potentials between 166 and 228 mL g− 1

The key parameter for the evaluation of substrates to be used in anaerobic digestion plants is the biogas potential. It states the maximum amount of biogas that can be obtained from a given amount of substrate and therefore represents the benchmark for any technical application for biogas production.The biogas yield describes the amount of gas retrieved under technical conditions at a given biogas facility.

Anaerobic digestion of sugarcane straw co-digested with sugarcane filter cake was investigated with a special focus on macronutrients supplementation for an optimized conversion process. Experimental data from batch tests and a semi-continuous experiment operated in different supplementation phases were used for modeling the conversion kinetics based on continuous stirred-tank reactors. The semi-continuous experiment showed an overall decrease in the performance along the inoculum washout from the reactors. By supplementing nitrogen alone or in combination to phosphorus and sulfur the specific methane production significantly increased (P < 0.05) by 17% and 44%, respectively. Although the two-pool one-step model has fitted well to the batch experimental data (R2 > 0.99), the use of the depicted kinetics did not provide a good estimation for process simulation of the semi-continuous process (in any supplementation phase), possibly due to the different feeding modes and inoculum source, activity and adaptation.

Die Erzeugung von Biogas aus Rückständen, Nebenprodukten und Abfällen einerseits sowie nachwachsenden Rohstoffen andererseits ist eine Option zur Biomassekonversion, die in den letzten Jahren erheblich an Marktbedeutung gewonnen hat. Biogas bzw. das daraus gewinnbare Biomethan zeichnet sich durch eine vergleichsweise einfache Erzeugung und durch eine hohe Flexibilität in Bezug auf mögliche Nutzungsoptionen im Energiesystem aus; d. h. ein Einsatz im Wärme-, Strom- und Kraftstoffmarkt ist möglich.Im Folgenden werden zunächst die biochemischen Grundlagen der anaeroben Vergärung zur Erzeugung von Biogas beschrieben. Vor dem Hintergrund der daraus resultierenden Anforderungen und Randbedingungen für eine verfahrenstechnische Umsetzung werden anschließend die einzelnen Teilprozesstechniken sowie deren Kombinationsmöglichkeiten anhand von ausgewählten Anwendungsbeispielen dargestellt. Mit dem Ziel einer möglichst effizienten Nutzung der eingesetzten Biomasse werden abschließend neben den Verwendungsoptionen für Biogas bzw. Biomethan auch die stofflichen und/oder energetischen Nutzungskonzepte der weiteren Gärprodukte erläutert.

Different methods for optimization the anaerobic digestion (AD) of sugarcane filter cake (FC) with a special focus on volatile fatty acids (VFA) production were studied. Sodium hydroxide (NaOH) pretreatment at different concentrations was investigated in batch experiments and the cumulative methane yields fitted to a dual-pool two-step model to provide an initial assessment on AD. The effects of nitrogen supplementation in form of urea and NaOH pretreatment for improved VFA production were evaluated in a semi-continuously operated reactor as well. The results indicated that higher NaOH concentrations during pretreatment accelerated the AD process and increased methane production in batch experiments. Nitrogen supplementation resulted in a VFA loss due to methane formation by buffering the pH value at nearly neutral conditions (∼6.7). However, the alkaline pretreatment with 6 g NaOH/100 g FCFM improved both the COD solubilization and the VFA yield by 37%, mainly consisted by n-butyric and acetic acids.

Purpose: Effective therapies for KRAS-mutant colorectal cancer (CRC) are a critical unmet clinical need. Previously, we described genetically engineered mouse models (GEMM) for sporadic Kras-mutant and non-mutant CRC suitable for preclinical evaluation of experimental therapeutics. To accelerate drug discovery and validation, we sought to derive low-passage cell lines from GEMM Kras-mutant and wild-type tumors for in vitro screening and transplantation into the native colonic environment of immunocompetent mice for in vivo validation. Experimental Design: Cell lines were derived from Kras-mutant and non-mutant GEMM tumors under defined media conditions. Growth kinetics, phosphoproteomes, transcriptomes, drug sensitivity, and metabolism were examined. Cell lines were implanted in mice and monitored for in vivo tumor analysis. Results: Kras-mutant cell lines displayed increased proliferation, mitogen-activated protein kinase signaling, and phosphoinositide-3 kinase signaling. Microarray analysis identified significant overlap with human CRC-related gene signatures, including KRAS-mutant and metastatic CRC. Further analyses revealed enrichment for numerous disease-relevant biologic pathways, including glucose metabolism. Functional assessment in vitro and in vivo validated this finding and highlighted the dependence of Kras-mutant CRC on oncogenic signaling and on aerobic glycolysis. Conclusions: We have successfully characterized a novel GEMM-derived orthotopic transplant model of human KRAS-mutant CRC. This approach combines in vitro screening capability using low-passage cell lines that recapitulate human CRC and potential for rapid in vivo validation using cell line-derived tumors that develop in the colonic microenvironment of immunocompetent animals. Taken together, this platform is a clear advancement in preclinical CRC models for comprehensive drug discovery and validation efforts.