Thermophilic Methane Research Articles

多孔性セラミックスを用いた嫌気性固定床による高温メタン発酵

多孔性セラミックスを用いた嫌気性固定床による高温メタン発酵

Characterization of Xylan-utilizing Anaerobes from Mesophilic and Thermophilic Methane Sludge and Their Xylan Degrading Enzymes

Characterization of Xylan-utilizing Anaerobes from Mesophilic and Thermophilic Methane Sludge and Their Xylan Degrading Enzymes

Separation of the propionate degradation to improve the efficiency of thermophilic anaerobic treatment of acidified wastewaters

The degradation of propionate generally is limiting in the thermophilic methane digestion of acidified wastewaters. In this paper the propionate degradation in thermophilic systems is studied. A two-stage process is developed, in which the propionate degradation is spatially separated from other conversions in which hydrogen is involved. Significantly better results were obtained with the two-stage system as compared with a one-stage system with an equal total volume: loading rates of 20–50 kg COD m −3 day −1 showed a 10–13% better treatment efficiency in the two-stage system. It is concluded that the removal of the biogas evolved in the first degradation processes is the cause of the superior performance of the two-stage system.

The mechanism of ammonia inhibition in the thermophilic digestion of livestock wastes

This paper proposes a scheme for the inhibition of thermophilic methane digestion processes by high ammonia concentrations. Ammonia acts as a strong inhibitor of the formation of methane from H 2 and CO 2. It has only a minor effect on the formation of methane from acetate, as indicated by the independence of the specific growth rate of acetate-consuming methanogens from the ammonia concentration (up to 4500 mg NH 4 +-N per litre). On the basis of thermodynamic considerations it is shown that the inhibition of the hydrogen consumption leads to an inhibition of propionate breakdown. Accumulated propionate, in turn, acts as an inhibitor of the acetate-consuming methanogens. This scheme explains the discrepancy between the observed acetate accumulation in thermophilic methane digestion systems with high ammonia levels and the independence of acetate mediated methanogenesis from high ammonia concentrations under laboratory conditions.

Characterization of xylan-utilizing anaerobes from mesophilic and thermophilic methane sludge and their xylan degrading enzymes.

A mesophilic and three thermophilic clostridial species were newly isolated as potent xylan utilizing bacteria from mesophilic and thermophilic methane sludge, respectively. The mesophilic strain, X-4, had a characteristic fermentation pattern of xylan, producing ethanol and acetic acid in addition to hydrogen and carbon dioxide. The thermophiles, XY-6, XY-10 and XY-23, were strains of the typical butyric acid fermentation type. The utilization of xylan by mesophilic strain X-4 was evident at late exponential or early stationary growth phase followed by an increase in production of xylanase in the culture fluid, while xylan was fermented by the thermophilic strains from the beginning of their cultivation. Cell-bound xylanase was detected in the three thermophilic strains. Enzyme secreted into the medium (supernatant xylanase) was detected in strains XY-6 and XY-10 but not in strain XY-23. The actions of xylanase preparations from X-4 and XY-6 were characterized, indicating that cell-bound β-xylosidases we...

Thermophilic anaerobic digestion of screened dairy manure

Three 6-litre reactors were used to examine fermentation stability and and methane production rates at mesophilic (35°C) and thermophilic (55°C) temperatures using screened dairy manure with mean feed strengths of 3.4% and 5.2% VS. All reactors produced gas reliably at hydraulic retention times (HRT's) ranging from 16 days down to as low as 1·5 days. The maximum thermophilic methane production rates for both feed strengths were higher than that for the mesophilic reactor using 3·4% VS feed. These thermophilic maxima were seen to occur at 2 days HRT for the 3·4% VS feed and at 4 days HRT for the 5·2% VS feed, while the mesophilic maximum rate was observed at 10 days HRT (3·4% VS feed). Net energy calculations, based on equal maintenance heating requirements for all reactors, showed the highest value of approximately 4·2 MJ kg −1 TS per day for the mesophilic reactor at 10 days HRT.

Nutritive value of methane fermentation residue in diets fed to feedlot steers.

Nutritive value of the methane fermentation residue (MFR) from the effluent of a large scale thermophilic methane generator was determined in diets fed to feedlot steers. The MFR contained 22.2% dry matter and 21.9% crude protein (dry basis). Two diets containing 10.6% (dry basis) MFR were formulated using the Urea Fermentation Potential (UFP) system such that in one diet N was in excess (-1.6 UFP) while in the other diet energy was in excess (+2.6 UFP). These two diets were compared in a California Net Energy trial with a feedlot diet (-.3 UFP) containing the same ingredients except the MFR. Six steers were fed in a replicated 3(2) Latin square metabolism trial and 70 steers were fed in a 118-d comparative-slaughter, feedlot trial. Digestibilities of dry matter, organic matter, crude protein, acid detergent fiber, ash, total digestible nutrients (TDN) and metabolizable energy were depressed (all P less than .05) in the MFR-containing diets. Steers fed the MFR-containing diets had lower (P less than .05) rates of gain and increased (P less than .05) feed requirements per unit gain. Net energies for maintenance and gain were slightly lower for the MFR-containing diets than the control diet. Crude protein digestibility for the MFR calculated by difference, for the -UFP and the +UFP diets were 37.8 and 50.7%, while corresponding values for TDN were 28.8 and 12.8%, respectively. Concentrations of potentially toxic elements in kidney, liver and muscle as well as flavor and tenderness of steaks were not affected by feeding MFR.

Bioconversion of Macrocystis pyrifera to methane

AbstractMethane production by anaerobic digestion of kelp is a relatively new approach to augmenting the national gas supply. Digestion of the giant marine kelp Macrocystis pyrifera, investigated in a series of bench‐scale experiments at the Institute of Gas Technology (IGT), is reported. Conducted with both untreated and chemically pretreated plants, the tests have evaluated the effects of major limits on bioconversion of kelp, including temperature, indigenous salt concentration, external nutrients, inocula source, loading, residence time, manner of mixing and frequency of feeding. A detailed chemical characterisation of the kelp samples is presented. Raw‐kelp digestion was not limited by nitrogen or phosphorus. Temperature ranges of 35–40°C and 50–55°C were found to be optimum for mesophilic and thermophilic digestion of raw kelp. The mesophilic methane yield in the semicontinuous mode was about 4.5 SCF/lb (280.94 cm3 g−1) of volatile solids (VS) added compared with a thermophilic methane yield of 2.4 SCF/lb (149.83 cm3 g−1) of VS added. The mesophilic organisms could be acclimatised to a salt concentration that has a conductivity of 43 000 μmho cm−1 without any deleterious effect. Thermophilic methanogens were more sensitive to high salt concentrations than the mesophilic organisms. Raw kelp had an estimated ultimate biodegradability of 80%. Mannitol and algin were the most biodegradable components.

Biomethanation of Minnesota reed sedge peat

The high moisture content of peat, the occurrence in peat of large concentrations of fermentable organics of plant origin, the use of hydraulic peat mining techniques, and the possibility of recycling digested peat residue to the peat bogs are factors that support the position that biological gasification methods can be effectively utilized. Chemical characterization work indicated that peat is rich in organic matter, has all the essential elements needed for biological gasification, and should, in theory, be digestible. However, the chemical analyses also point to three possible impediments to vigorous digestion of peat: (1) The presence in peat of large concentrations of cellulose, hemicellulose, lignin, and other complex substances of low biodegradabilities; (2) The nonavailability of such essential elements as nitrogen, phosphorus, etc., that are mostly organically bound; and (3) The toxicities arising because of nitrates and other inhibitors. The work reported here consisted of exploratory digestion runs designed to study the effects of such factors as digestion mode, inoculum source, temperature, loading, detention time, feed particle size, and chemical pretreatment on peat digester gas yield, production rate, and gas quality. Work with Minnesota Reed Sedge Peat showed that it could be digested in both batch and continuous modes with or without external nutrient additions. A thermophilic temperature of 55°C effected higher gas yields than other mesophilic or thermophilic test temperatures. A thermophilic (55°C) methane yield of 0.14 std m 3/kg (2.2 SCF/lb) VS (volatile solids) added was obtained with raw as-received peat during batch digestion for about 86 days, compared with a methane yield of 0.11 std m 3/kg (1.7 SCF/lb) VS added observed during semicontinuous thermophilic (55°C digestion at a 60-day detention time and 0.80 kg VS/m 3-day (0.05 lb VS/ft 3-day) loading. Subsequent batch digestion showed that particle size reduction and acid or alkali treatment could cause a three fold increase in methane production over that obtained with raw untreated peat. This suggests that a methane yield of up to 0.31 std m 3/kg (5 SCF/lb) VS added — which is about 60% of the maximum theoretical yield — may be obtained by optimizing the digestion and feed pretreatment conditions.

Thermophilic methanogenesis in a hot-spring algal-bacterial mat (71 to 30 degrees C).

Algal-bacterial mats which grow in the effluent channels of alkaline hot springs provided an environment suitable for studying natural thermophilic methane producing bacteria. Methane was rapidly produced in cores taken from the meat and appeared to be an end product of decomposition of the algal-bacterial organic matter. Formaldehyde prevented production of methane. Initial methanogenic rate was lower and methanogenesis became exponential when samples were permitted to cool before laboratory incubation. Methanogenesis occurred and methanogenic bacteria were present over a range of 68 to 30 degrees C, with optimum methanogenesis near 45 degrees C. The temperature distribution of methanogenesis in the mat is discussed relative to published results on standing crop, primary production, and decomposition in the thermal gradient. The depth distribution of methanogenesis was similar to that of freshwater sediments, with a zone of intense methanogenesis near the mat surface. Methanogenesis in deeper mat layers was very low or undetectable despite large numbers of viable methanogenic bacteria and could not be stimulated by addition of anoxic source water, sulfide, or a macronutrient solution.

Thermophilic methane production from cattle waste.

Methane production from waste of cattle fed a finishing diet was investigated, using four 3-liter-working volume anaerobic digestors at 60 degrees C. At 55 degrees C a start-up culture, in which waste was the only source of bacteria, was generated within 8 days and readily adapted to 60 degrees C, where efficiency of methanogenesis was greater. Increasing the temperature from 60 to 65 degrees C tended to drastically lower efficiency. When feed concentrations of volatile solids (VS, organic matter) were increased in steps of 2% after holding for 1 months at a given concentration, the maximum concentrations for efficient fermentation were 8.2, 10.0, 11.6, and 11.6% for the retention times (RT) of 3, 6, 9, and 12 days, respectively. The VS destructions for these and lower feed concentrations were 31 to 37, 36 to 40, 47 to 49 and 51 to 53% for the 3-, 6-, 9-, and 12-day RT digestors, respectively, and the corresponding methane production rates were about 0.16, 0.18, 0.20, and 0.22 liters/day per g of VS in the feed. Gas contained 52 to 57% methane. At the above RT and feed concentrations, alkalinity rose to 5,000 to 7,700 mg of CaCo3 per liter (pH to 7.5 to 7.8), NH3 plus NH4+ to 64 to 90 mM, and total volatile acids to 850 to 2,050 mg/liter as acetate. The 3-day RT digestor was quite stable up to 8.2% feed VS and at this feed concentration produced methane at the very high rate of 4.5 liters/day per liter of digestor. Increasing the percentage of feed VS beyond those values indicated above resulted in greatly decreased organic matter destruction and methane production, variable decrease in pH, and increased alkalinity, ammonia, and total volatile acid concentrations, with propionate being the first to accumulate in large amounts. In a second experiment with another lot of waste, the results were similar. These studies indicate that loading rates can be much higher than those previously thought useful for maximizing methanogenesis from cattle waste.