Paul Scherer

Influence of sulphur-containing compounds on the growth of Methanosarcina barkeri in a defined medium

SummaryOptimal growth of Methanosarcina barkeri occurred in a defined medium containing methanol when 2.5–4 mM sodium sulphide was added giving a concentration of 0.04–0.06 mM dissolved sulphide (HS−+S2−. When the sulphide concentration was too low for optimal growth (e.g., 0.1 mM Na2S added) the addition of the redox resin ‘Serdoxit’ acted as a sulphide reservoir and caused a significant stimulation of growth. Furthermore it could be demonstrated that iron sulphide, zinc sulphide or L-methionine could also act as sulphur sources while the addition of sodium sulphate to sulphide-depleted media failed to restore growth. The amino acid L-cysteine (0.85 mM) stimulated growth but could not replace Na2S.Under optimal cysteine-and sulphide concentrations the generation time of this strain was about 7–9 h during growth on methanol, giving a growth yield of about 0.14 g/g methanol consumed. Different M. barkeri strains were also able to grow under these conditions on acetate (30–50 h doubling time) without a significant lag-phase and with complete substrate consumption even though the inoculum was grown on methanol or H2−CO2. When methanol and acetate were present as a mixture in the medium both were used simultaneously.

Anaerobic digestion of renewable biomass: thermophilic temperature governs methanogen population dynamics.

ABSTRACT Beet silage and beet juice were digested continuously as representative energy crops in a thermophilic biogas fermentor for more than 7 years. Fluorescence microscopy of 15 samples covering a period of 650 days revealed that a decrease in temperature from 60°C to 55°C converted a morphologically uniform archaeal population (rods) into a population of methanogens exhibiting different cellular morphologies (rods and coccoid cells). A subsequent temperature increase back to 60°C reestablished the uniform morphology of methanogens observed in the previous 60°C period. In order to verify these observations, representative samples were investigated by amplified rRNA gene restriction analysis (ARDRA) and fluorescence in situ hybridization (FISH). Both methods confirmed the temperature-dependent population shift observed by fluorescence microscopy. Moreover, all samples investigated demonstrated that hydrogenotrophic Methanobacteriales dominated in the fermentor, as 29 of 34 identified operational taxonomic units (OTUs) were assigned to this order. This apparent discrimination of acetoclastic methanogens contradicts common models for anaerobic digestion processes, such as anaerobic digestion model 1 (ADM1), which describes the acetotrophic Euryarchaeota as predominant organisms.

Production of Methane and Hydrogen from Biomass through Conventional and High-Rate Anaerobic Digestion Processes

Anaerobic digestion processes have often been applied for biological stabilization of solid and liquid wastes. These processes generate energy in the form of biogas. Recently, high-rate methane and hydrogen fermentation from renewable biomass has drawn much attention due to current environmental problems, particularly related to global warming. Therefore, laboratory-scale research on this topic has significantly accelerated. The primary aim of this review paper is to summarize the most recent research activities covering production of methane and hydrogen via both conventional single and high-rate two-phase anaerobic digestion processes of natural sources of biomass.

Mesophilic Fermentation of Renewable Biomass: Does Hydraulic Retention Time Regulate Methanogen Diversity?†

ABSTRACT The present long-term study (about 1,100 days) monitored the diversity of methanogens during the mesophilic, anaerobic digestion of beet silage. Six fermentor samples were analyzed by ribosomal RNA gene restriction analysis, fluorescence in situ hybridization, and fluorescence microscopy. Hydrogenotrophic methanogens dominated within the population in all samples analyzed. Multidimensional scaling revealed that a rapid decrease in hydraulic retention time resulted in increased species richness, which in turn led to slightly higher CH4 yields.

Application of a fuzzy logic control system for continuous anaerobic digestion of low buffered, acidic energy crops as mono-substrate

A fuzzy logic control (FLC) system was developed at the Hamburg University of Applied Sciences (HAW Hamburg) for operation of biogas reactors running on energy crops. Three commercially available measuring parameters, namely pH, the methane (CH4) content, and the specific gas production rate (spec. GPR = m3/kg VS/day) were included. The objective was to avoid stabilization of pH with use of buffering supplements, like lime or manure. The developed FLC system can cover most of all applications, such as a careful start‐up process and a gentle recovery strategy after a severe reactor failure, also enabling a process with a high organic loading rate (OLR) and a low hydraulic retention time (HRT), that is, a high throughput anaerobic digestion process with a stable pH and CH4 content. A precondition for a high load process was the concept of interval feeding, for example, with 8 h of interval. The FLC system was proved to be reliable during the long term fermentation studies over 3 years in one‐stage, completely stirred tank reactors (CSTR) with acidic beet silage as mono‐input (pH 3.3–3.4). During fermentation of the fodder beet silage (FBS), a stable HRT of 6.0 days with an OLR of up to 15 kg VS/m3/day and a volumetric GPR of 9 m3/m3/day could be reached. The FLC enabled an automatic recovery of the digester after two induced severe reactor failures. In another attempt to prove the feasibility of the FLC, substrate FBS was changed to sugar beet silage (SBS), which had a substantially lower buffering capacity than that of the FBS. With SBS, the FLC accomplished a stable fermentation at a pH level between 6.5 and 6.6, and a volatile fatty acid level (VFA) below 500 mg/L, but the FLC had to interact and to change the substrate dosage permanently. In a further experiment, the reactor temperature was increased from 41 to 50°C. Concomitantly, the specific GPR, pH and CH4 dropped down. Finally, the FLC automatically enabled a complete recovery in 16 days. Biotechnol. Bioeng. 2009; 102: 736–748.

The microcosm of a biogas fermenter: Comparison of moderate hyperthermophilic (60°C) with thermophilic (55°C) conditions

An automated biogas fermenter running continuously for about two years using fodder and sugar beet silage as mono‐substrate without manure addition was analyzed simultaneously by amplified ribosomal DNA restriction analysis and microscopy. In this long‐term fermentation study, an oscillating population of prokaryotes was observed. The presence of most bacteria expected to be involved in hydrolysis of biomass via the anaerobic food chain was confirmed. In any case the methanogen population appeared more stable as it exhibited a lesser degree of variability. The more fluctuating population structure of the bacteria might be due to the fact that most of them were carbohydrate fermenting species which were therefore somewhat interchangeable. Hydrogenotrophic methanogens using H2+CO2 as substrate (Methanobacteriales and Methanomicrobiales) clearly dominated. Therefore, the methanogenesis of energy crops is apparently initiated by gasification to H2+CO2 followed by the biogasification to CH4+CO2. Acetotrophic methanogens (Methanosarcinales) represented a minority with a proportion of 10% or less of the methanogenic population (only at 55°C). The acetotrophic Methanosaeta seemed to be completely absent at temperatures of 55 or 60°C. Pure culture studies established previously that Methanobacteria tolerate at least a sixfold higher ammonium concentration (6000 mg/L) than Methanosaeta and a twofold higher ammonium concentration than Methansarcina. This indicates that running industrial scale fermenters at thermophilic instead of the common mesophilic conditions might be an effective way to exclude the more stress susceptible (e.g. high concentration of ammonium, H2S and acetate) acetotrophic methanogens and therefore improve the reliability of such plants.

Impact of bioaugmentation by compost on the performance and ecology of an anaerobic digester fed with energy crops

The influence of compost as inoculum during continuous anaerobic digestion of fodder beet silage was studied over 330 days. Two simultaneously driven mesophilic fermentors (Inoc-1/Inoc-2) were inoculated with manure and sewage sludge. Only the digester Inoc-2 was inoculated additionally with compost. After 160 days fermentor Inoc-2 reached a hydraulic retention time (HRT) around 15 days whereas Inoc-1 remained at a HRT of 40d. After changing the substrate feed from one to three times a day both digesters stabilised at a shorter HRT; Inoc-2 at 10 days and Inoc-1 around 20 days. An additional inoculation of fermentor Inoc-1 by compost shortened the HRT to 10 days and revealed a minor increased gas production of about 6%. Fluorescence in situ hybridization indicated that probably an archaeal population shift was responsible for the observed stimulations. An addition of compost induced a methanogenic community change towards hydrogenotrophic methanogens.

Vanadium and molybdenum requirement for the fixation of molecular nitrogen by two Methanosarcina strains

AbstractNitrogen fixation of the Methanosarcina barkeri strains “Fusaro” (DSM 804) and “227” (DSM 1538) was found to be dependent on the presence of vanadium or molybdenum whereby molybdenum (added as Na2-molybdate) was preferred to vanadium (added as VCl3). Strain “227” showed less pronounced effects on diazotrophic growth with respect to vanadium and molybdenum. Rhenium (ReCl3) or tungsten (Na2-tungstate) could not replace vanadium or molybdenum. The optimum concentrations were found to be 2μM for vanadium and 5μM for molybdenum (strain “Fusaro”). This Mo optimum of methanogenesis was 10-fold higher with N2 than with NH4Cl as nitrogen source. A vanadium requirement with NH4Cl could not be detected. No interferences were observed if molybdenum and vanadium were added simultaneously under diazotrophic conditions. Growth yields were smallest for strain “227” grown diazotrophically (

Isolation and characterization of the Co-methyl and Co-aquo derivative of 5-hydroxybenzimidazolylcobamide (factor III) from Methanosarcina barkeri grown on methanol

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