Growth kinetics of thermophilic Methanosarcina spp. isolated from full-scale biogas plants treating animal manures

This study determines the growth kinetics of thermophilic strains of Methanosarcina spp. from full-scale thermophilic biogas plants. The complete set of kinetic parameters, including maximum specific growth rate μ(max), half saturation constant K(S), acetate threshold concentration and cell growth yield Y(X/S), were determined for six Methanosarcina strains newly isolated from full-scale reactors and the type strain Methanosarcina thermophila TM-1(T). The kinetic experiments were performed in media supplemented with acetate and activated carbon at the optimum growth temperatures of the individual strains, 50-55 degrees C. The μ(max) values of the isolates were in the range of 0.044-0.064 h(-1), the K(S) ranged from 6.5 to 24.7 mM acetate and the threshold for acetate utilization from 0.11 to 0.40 mM. The cell growth yields of the strains were between 0.78 and 2.97 g dry weight cells mol(-1) acetate. The six isolates exhibited significantly higher μ(max) and had higher affinity to acetate than the type strain M. thermophila TM-1(T). Generally, the affinities of thermophilic Methanosarcina strains tested in this study cover a similar range to those reported in the literature for mesophilic Methanosarcina spp. with acetate as substrate. The strains isolated from plants treating mixtures of animal manures and industrial organic wastes had higher affinity for acetate and lower thresholds than strains isolated from reactors operating solely on manures.     

Monitoring of accelerated naphthalene-biodegradation in a bioaugmented soil slurry

The effect of microbial inoculation on the mineralization of naphthalene in a bioslurry treatment was evaluated in soil slurry microcosms. Inoculation by Pseudomonas putida G7 carrying the naphthalene dioxygenase (nahA) gene resulted in rapid mineralization of naphthalene, whereas indigenous microorganisms in the PAH-contaminated soil required a 28 h adaptation period before significant mineralization occurred. The number of nahA-like gene copies increased in both the inoculated and non-inoculated soil as mineralization proceeded, indicating selection towards naphthalene dioxygenase producing bacteria in the microbial community. In addition, 16S rRNA analysis by denaturing gradient gel electrophoresis (DGGE) analysis showed that significant selection occurred in the microbial community as a result of biodegradation. However, the indigenous soil bacteria were not able to compete with the P. putida G7 inoculum adapted to naphthalene biodegradation, even though the soil microbial community slightly suppressed naphthalene mineralization by P. putida G7.     

Anaerobic waste digestion in Germany – Status and recent developments

Anaerobic treatment processes are especially suited for the utilization of wet organic wastes from agriculture and industry as well as for the organic part of source-separated household wastes. The anaerobic degradation is a very cost-effective method for treating biogenic wastes because the formed biogas can be used for heat and electricity production and the digester residues can be recycled to agriculture as a secondary fertilizer. The anaerobic technology will be used today also for the common treatment of wastes together with renewable energy crops in order to reduce the CO₂-emissions according the Kyoto protocol. Various process types are applied in Germany which differ in material, reaction conditions and in the form of the used reactor systems. The widespread introduction of anaerobic digestion in Germany has shown that biogenic organic wastes are a valuable source for energy and nutrients. Anaerobic waste treatment is done today in approx. 850 biogas plants on small farm scale as well as on large industrial scale with the best beneficial and economic outcome. Due to some new environmental protection acts which promote the recycling of wastes and their utilization for renewable energy formation it can be expected that several hundreds new biogas plants will be built per year in Germany. For using the synergetic effects of a combined fermentation of wastes and energy crops new process types must be developed in order to optimize the substrate combinations and the process conditions for maximum biodegradation.     

Selected microbial consortium of raw and digested pig slurry and its susceptibility to enterocins

A consortium of bacterial genera from raw and digested pig slurry (pig farm at Figa, Slovakia; input and output samples) was counted from February to October 2000. The total counts of enterococci and staphylococci were well-balanced in input samples, with visible reduction of cells in May (3.22 and/or 4.21 log c.f.u./ml). Among organisms important from a sanitary perspective only a slight reduction after standard slurry treatment was found between input and output samples (2.0 log cycles), with no effect in April and May. However, their counts were high (8.1–9.01 log c.f.u./ml). Yersinia sp. were detected in rather high counts (6.47; 6.39 log c.f.u./ml). But these species, as well as pseudomonads and Aeromonas sp. were very effectively reduced by standard slurry treatment. Enterocins (CCM4231, V24 and EC24) produced by our own isolates of enterococci were used to determine the susceptibility of selected microbial strains from slurry to those enterocins. For quantifying the inhibitory activity of enterocins, the titre (expressed in activity-arbitrary units [AU/ml]), corresponding to the reciprocal of the highest dilution showing a distinct inhibition zone of the indicator, was determined. Under the conditions used, enterocins used were active against the selected microbial consortium by activity from 100 up to 800 AU/ml. Moreover, enterocin V24 reduced the growth of Enterobacter cloacae ECL751 as well as Pseudomonas sp. minimally with differences of 1. 54 and 2.2 log cycles.     

A method for growing stationary plant suspension cell cultures

Summary Stationary culture of plant cell suspensions has been achieved. Slurries, produced when small amounts of agar (0.1–0.4%) were added to culture media, were used to suspend plant cells. Growth proceeded more slowly than in standard shake culture, but cells remained viable for months of culture. This method of growing plant cells in stationary culture should be useful for general applications including long-term cell culture, shipment of cultures, and physiological, molecular biological, and pathological studies. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable. Editor’s Statement This procedure for growing stationary suspension cultures in an agar slurry should be useful for shipping suspensions and for long-term maintenance of little used or back-up cultures.     

Inactivation of virus during anaerobic digestion of manure in laboratory scale biogas reactors

Reduction of porcine parvovirus, bovine enterovirus and faecal enterococci were measured in biogas reactors continuously run on manure and manure supplemented with household waste at 35°C and 55°C and in batch test run at 70°C. The aim of the experiments was to study the sanitation effect of anaerobic digestion and to evaluate the use of faecal enterococci as an indicator of sanitation. Parallel studies on the reduction of virus and faecal enterococci were done in physiological saline solution. Heat ínactivation was found to be an important factor in thermophilic biogas plants and the overall dominant factor at 70°C. However, other environmental factors with a substantial virucidal and bactericidal effect were involved in inactivation. The death rates for faecal enterococci were generally higher than for porcine parvovirus and lower than for bovine enterovirus. For faecal enterococci, a logarithmic reduction of 4 (corresponding to the recommended minimum guaranteed retention time) was obtained after 300 hours at 35°C and after 1–2 hours at 55°C. In continuously-fed reactors, a high reduction rate was initially seen for the virus tested, followed by a reduction in the rate. For porcine parvovirus, a minimum guaranteed retention time of 11–12 hours is necessary at 55°C in the initial phase (0–4 hours) and 54 hours hereafter (4–48 h). Correspondingly, for bovine enterovirus a MGRT of 23 hours was necessary at 35°C and < 0.5 hours at 55°C. The data indicate that faecal enterococci measurements give a good indication of inactivation of enterovirus and other more heat sensitive virus, especially under thermophilic conditions. Parvovirus is very suitable for comparative investigations on inactivation in the temperature range of 50–80°C, due to the extreme thermal resistance of this virus. However, in stipulating sanitation demands for biogas reactors it seems more reasonable to use less resistant virus, such as a reovirus or picornavirus, which better represents the pathogenic animal virus.Abbreviations BEV bovine enterovirus - CFU colony forming unit - FE faecal enterococci - HRT hydraulic retention time - MGRT minimum guaranteed retention time - ND not detected - PPV porcine parvovirus - TCID₅₀ tissue cell infective dose 50 % - VFA volatile fatty acids - VS volatile solids     

Energy cover crops for biogas production increase soil organic carbon stocks: A modeling approach

Energy cover crops for biogas production through anaerobic digestion (AD) are inserted between two primary crops. They replace either bare soil or nonharvested cover crops, and their management is usually intensified to produce more biomass. They allow the production of renewable energy as well as digestate, used as an organic fertilizer, without directly competing with food production. Because of the increased biomass production and export and of the return of a digested biomass to the soil, the impact of energy cover crops on soil organic carbon (SOC) is questioned. The objective of this paper was to study the difference in SOC stocks induced by the introduction of energy cover crops for AD coupled with the application of the resulting amount of digestate. We used the AD model Sys-Metha combined with the soil C model AMG to simulate SOC stocks for 13 case studies in France, with scenarios comparing different intercrop management practices, with or without cover crops, harvested or not. Our results indicated that the higher biomass production of energy cover crops (from 6.7 to 11.1 t DM ha⁻¹) in comparison with nonharvested cover crops (2 t DM ha⁻¹) or bare soil led to higher humified C input (belowground input and digestate), despite the high C fraction exported in AD. This resulted in an increase in SOC stocks in comparison with nonharvested cover crops or bare soil (from 0.01 to 0.12 t C ha⁻¹ year⁻¹ over 30 years). The uncertainties in the model parameters did not modify these results. However, in the case of equal biomass production between energy cover crops and nonharvested cover crops, SOC stocks would be lower with energy cover crops.     

Use of lignite slurry as inoculating medium for vesicular arbuscular mycorrhiza in chinese potato (Coleus parviflorus)

Tubers of Coleus parviflorus were inoculated with spores of the vesicular arbuscular mycorrhizal fungus Glomus microcarpum. The spores had been suspended in a lignite slurry and stored in a refrigerator for 1–6 months periods. Inoculation took place by soaking the tubers in the slurry for 3 h followed by drying in the shade, subsequent planting of such tubers gave rise to nearly 100% infection even after 6 months of storage.