Methanogenic Fermentation Research Articles

Phytosterols from pressmud residue obtained after methanogenic fermentation

Pressmud, a sugar factory waste, was fermented with methanogenic bacteria in an anaerobic fermenter for 40 days at 31±2°C. The pressmud residue obtained after fermentation was used as a source for the extraction of phytosterols. The anaerobic digestion degraded the organic matter and resulted in enrichment of phytosterols from 0.33% in the pressmud to 3.05% in the residue. Refluxing of 100 g of residue with benzene, petroleum ether, and ethanolic KOH (10∶5∶1) yielded 8 g of soft cake, which on further fractionation with methylcyanide and isopropanol gave three fractions: 1) a crude mixture of phytosterols, 2) resin, and 3) undigested organic matter. The crude mixture of phytosterols after purification on neutral alumina followed by GLC analysis resulted in the separation of 68.7% of β-sitosterol, 18.4% of stigmasterol and 12.9% of campesterol and brassicasterol together. Phytosterols were extracted more easily from fermented than from unfermented samples, because of biodegration of lipophilic compounds by the methanogenic bacteria.

Immobilization of a syntrophic culture of propionate-degrading and methanogenic bacteria present in cellulose-enriched culture

A simple technique for the immobilization of propionate-utilizing bacteria in syntrophic association with methanogens was developed. The immobilization of these bacteria on a polyester support improved the utilization rate of propionate by a factor of 16–20; from 4–5 m M/day to over 80m M/day as compared to mixed cultures. The immobilized culture also had the ability to convert C 1 to C 6 volatile-fatty acids to methane at a rate comparable to propionate. This culture also converted C 7 volatile-fatty acid to methane but at a slower rate. The results suggest that the immobilization of this syntrophic culture retained practically all of the slow-growing groups of anaerobes involved in the conversion of short chain volatile-fatty acids to methane, a rate-limiting step in methanogenic fermentations.

The bacteriology of anaerobic degradation of aromatic compounds.

Revue. Biochemical mechanisms of anaerobic metabolism. Photometabolism. Nitrate-dependent aromatic metabolism. Sulphate-dependent aromatic metabolism. Methanogenic fermentation of aromatic compounds. Anaerobic lignin degradation

Acidogenic and methanogenic fermentation of causticized straw

The effects of pretreatment process variables [straw concentration between 20 and 90 kg volatile solids (VS)/m(3), temperature between 30 and 85 degrees C, and alkaline dosage between 0 and 80 g NaOH/kg VS] on acidogenesis and methanogenesis were investigated. Rates of acidogenesis and methanogenesis were determined using firstorder kinetics, and ultimate acid and methane yields were measured. The acid yield was not affected by pretreatment concentration or temperature, but increased as alkaline dosage increased. The acidogenesis rate was not affected by pretreatment temperature or alkaline dosage, but decreased as the substrate concentration increased. This decrease in the acidogenesis rate was attributed to a decrease in the inoculum: substrate ratio as the substrate concentration increased. The methane yield and methanogenesis rate were not affected by pretreatment substrate concentration or temperature, and both increased with alkaline dosage up to about 40 g NaOH/kg VS, then remained relatively constant above 40 g NaOH/kg VS.

Feasibility of two‐phase anaerobic stabilization of industrial waste with simultaneous production of energy

Abstract Single‐stage high‐rate (or conventional) anaerobic digestion of soft‐drink bottling waste exhibited unbalanced acidogenic and methanogenic fermentations at HRT's below 10 days and loading rates above 2 kg VS m‐3 day‐1. By comparison, the two‐phase digestion process was operated at much higher loading rates and much lower HRT's to afford the same methane yield and COD reduction efficiency as those of the conventional process. The economic advantages of the two‐phase process were that for this waste the digester volume could be reduced by more than 67% and the net energy production increased by more than 73% compared with those of the conventional process.

Kinetics of the methanogenic fermentation of acetate

AbstractThe kinetics of methanogenesis from a stirred batch‐fed calcium acetate enrichment culture have been studied. A detailed kinetic analysis of the culture allowed four distinct phases to be distinguished. Phase 1 was a period of very rapid increase (from low initial values) in the rate of methanogenesis upon addition of acetate, and was not thought to be associated with cell growth. In Phase 2 the rate of methanogenesis increased exponentially with time reflecting exponential growth. Phase 3 was characterised by an approximately constant rate of methane production, and is discussed in relation to the uncoupling of growth and methanogenesis. Phase 4 is a period of rapid decline associated with depletion of acetate. The apparent size of the population of the acetate‐utilising methanogenic bacteria subsequently declined, with a specific decay constant of 0.4 ± 0.1 d−1. The significance of these phases, in particular 2 and 3, for industrial anaerobic digestion is discussed.

Methanogenic Degradation of Sodium Benzoate in Profundal Sediments from a Small Eutrophic Lake

Enrichments were established to examine the potential of Blelham Tarn profundal sediment to metabolize benzoate to CH4 and CO2. Longadaptation times were required before benzoate-dependent CH4 production occurred, though both increased inoculum size and prior methanogenic adaption to aliphatic fatty acids reduced the adaptation time. Benzoate was metabolized according to the stoichiometry: 4C6H5COOH + 18H2O 15CH4 + 13CO2. The optimum temperature for CH4 production from benzoate in the enrichments was 37°C irrespective of the enrichment temperature. Methanogenic benzoate degradation was associated with a particulatefloc in the enrichments and Methanobacterium soehngenii was tentatively identified as an important constituent of this floc by scanning electron microscopy. Anaerobic benzoate fermentation was observed after 4 h in undiluted sediment by the use of [14C]benzoate, and the temperature optimum for 14C-labelled gas formation was 28°C. The 14CH4: 14CO2 ratio indicated that methanogenic fermentation of benzoate was occurring in situ. CO2 became the main gaseous product from [14C]benzoate when sulphate was added to sediment, and 20 mm-molybdate reversed this effect. Methanogenesis was slightly inhibited by addition of 20 mm-molybdate. Methanogenic benzoate fermentation in sediments was found to be inhibited by H2.

Support materials for stationary fixed film reactors for high-rate methanogenic fermentations

Needle punched polyester material and red drain tile clay were most effective in developing an active biomass film. Maximum methane production rates (0.045–0.055 m3/m2/day, or 4.5–5.5 m3/m3/day for a reactor with 100 m2 film support area per m3) were achieved in 40–50 days.

Methanogenic fermentation of the naturally occurring aromatic amino acids by a microbial consortium.

Methanogenic fermentation of the naturally occurring aromatic amino acids by a microbial consortium.

The methanogenic fermentation of plant phenolics [proceedings

The methanogenic fermentation of plant phenolics [proceedings

Effect of iron on conversion of acetic acid to methane during methanogenic fermentations.

Addition of iron (as a solution of reagent grade FeCl2, up to 20 mmol/1) to a methanogenic culture utilizing acetic acid markedly increased conversion of acetic acid to methane. The optimum soluble iron concentration was between 0.2 and 2 mM, with higher concentrations becoming slightly less stimulating. Most of the iron added precipitated within days after addition (mostly as ferrous carbonate or phosphate). Conversion of acetic acid to methane in liquid from municipal sewage digesters and from laboratory food processing waste digesters was also increased markedly by addition of iron. Results indicate that optimization of the conversion of acetic acid to methane in methanogenic fermentations requires soluble iron levels many times higher than those often required for maximum growth and activity in microbial cultures.

Biochemistry of the bacterial catabolism of aromatic compounds in anaerobic environments.

Methods of aerobic degradation of aromatic compounds in the biosphere are well understood, but it is only relatively recently that it has been shown how some bacteria can also degrade these substrates in the absence of molecular oxygen. This occurs by photometabolism (Athiorhodaceae), nitrate respiration (Pseudomonas and Moraxella sp.) and methanogenic fermentation (a consortium) in which the benzene nucleus is first reduced and then cleaved by hydrolysis to yield aliphatic acids for cell growth. These methods may be used by microbial communities to catabolise man-made pollutants.

Methanogenic fermentation of benzoate in an enrichment culture

Enrichment cultures inoculated with black mud fermented benzoate according to the stoichiometric equation: 4 C6H5CO2H+18 H2O → 15 CH4+13 CO2.Trans-2-hydroxycyclohexanecarboxylate, 2-oxo-cyclohexanecarboxylate, pimelate, caproate, butyrate, acetate, and molecular hydrogen were shown to be regular components of the culture fluid occurring in low concentrations. Inhibition of methanogenesis by chloroform, 4-chlorobutyrate, or 2-bromooctanoate resulted in a cessation of the benzoate breakdown after all intermediates had accumulated. It is proposed that benzoate is fermented via a direct reductive pathway to butyrate, acetate, H2, and CO2, whereafter butyrate is converted to acetate and H2, and the latter substrates are fermented to CH4 and CO2 by methane producers.

Intermediate energy technology in China

Intermediate energy technology — construction and operation of small projects using mass labour participation and local materials, minimizing capital investment and combining modern and traditional approaches — has become an important part of China's energetics. Construction of small energy projects originated during the aborted Great Leap, but a rational - and apparently successful - expansion dates only since 1969. Small mines now produce almost one-third of the country's raw coal, and small hydro-stations generate one-third of China's hydroelectricity. Methanogenic fermentation is increasingly used in South China to produce biogas and the first steps have been taken in introducing small solar collectors.

Unified Basis for Biological Treatment Design and Operation

A unified basis for design and operation of biological waste treatment systems employing suspensions of microorganisms is developed from microbial kinetic concepts and continuous culture of microorganisms theory. Biological solids retention time, θ c , average time period a unit of biological mass is retained in the system, is suggested as an independent parameter for process design and control. Steady-state kinetic models are presented for three process configurations, i.e., completely mixed reactor without solids recycle, completely mixed reactor with solids recycle, and plug flow reactor with solids recycle. Reported values of kinetic coefficients are tabularized for: (1) aerobic treatment of carbonaceous wastes; (2) aerobic biological nitrification; (3) anaerobic methanogenic fermentation of carbonaceous wastes. These coefficient values are substituted into the models to determine lower limits, i.e., minimum values of θ c , for each process. Minimum values of θ c of models are compared with θ c values for actual treatment systems.