Methane Production by Fermentor Cultures Acclimated to Waste from Cattle Fed Monensin, Lasalocid, Salinomycin, or Avoparcin

The ability of microorganisms to ferment waste from cattle fed monensin, lasalocid, or salinomycin to methane was determined. Continuously mixed anaerobic fermentors with 3-liter working volumes at 55°C were used; fermentors were fed once per day. Initially, all fermentors were fed waste without antibiotics at 6% volatile solids (VSs, organic matter) and a 20-day retention time (RT) for 60 days. Waste from animals fed monensin, lasalocid, or salinomycin at 29, 20, and 16.5 mg per kg of feed, respectively, was added to duplicate fermentors at the above VSs, and RT. Avoparcin (5 to 45 mg/liter) was not fed to animals but was added directly to duplicate fermentors. Lasalocid and salinomycin had minimal effects on the rate of methane production at RTs of 20 days and later at 6.5 days. Avoparcin caused an increase in organic acids from 599 to 1,672 mg/liter (as acetate) after 4 weeks, but by 6 weeks, acid concentrations declined and the rate of methane production was similar to controls at a 6.5-day RT. The monensin fermentors stopped producing methane 3 weeks after antibiotic addition. However, after a 6-month acclimation period, the microorganisms apparently adapted, and methane production rates of 1.65 and 2.51 liters per liter of fermentor volume per day were obtained with 6% VSs, and RTs of 10 and 6.5 days, respectively. This compares with 1.78 and 2.62 liters/liter per day for controls (P > 0.05). All fermentors that were fed waste containing antibiotics had lower pH values and ammonia and alkalinity concentrations, suggesting less buffering capacity and protein catabolism than in controls. Acclimation results obtained with fermentors at 35°C were similar to those for fermentors at 55°C. These studies indicate that waste from cattle fed these selected growth-promoting antibiotics can be thermophilically fermented to methane at RTs of 6.5 days or longer and VS concentrations of 6%, at rates comparable to waste without antibiotics.     

Effect of Dietary Monensin or Chlortetracycline on Methane Production from Cattle Waste

Wastes from feedlot cattle fed finishing diets containing either monensin, chlortetracycline, or no antibiotic were investigated as substrates for methane production. We used continuously mixed anaerobic fermentors with 3-liter working volumes at 35 and 55°C; these fermentors were fed once per day. Within a few days after waste from animals fed monensin was added, the volume of methane produced began to decrease in the 55°C fermentors. After 9 days of daily feeding, methane production was severely inhibited, the pH dropped from 7.6 to 5.9, and the concentration of volatile acids increased from 543 to 6,300 mg/liter (as acetate). Although additions of waste from cattle fed monensin were discontinued after 9 days, the fermentors did not resume gas production within 8 weeks. The addition of waste from cattle which had been fed chlortetracycline reduced the methane production rate approximately 20%; however, pH and volatile acid values were comparable to control fermentor values after 40 days. Similar effects were observed with the 35°C fermentors. In a batch fermentation experiment in which 50-g portions of volatile solids from waste of animals fed monensin, chlortetracycline, or no antibiotics were added to fermentors, monensin delayed the onset of methane production for about 40 days, but then these fermentors began to produce methane at a rate comparable to the control rate. The ultimate methane yields from the three types of waste after 180 days were not significantly different. These studies indicate that monensin has a detrimental effect on the conversion of feedlot wastes to methane, unless microorganisms can be adapted to the levels that are present in these wastes.     

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.     

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.     

Methane from cattle waste: Effects of temperature, hydraulic retention time, and influent substrate concentration on kinetic parameter (k)

The effects of temperature (35 and 55 degrees C), influent volatile solids (VS) concentration (S(0) = 43, 64, 82, 100, and 128 kg VS/m(3)) and hydraulic retention time (HRT = 4, 5, 8, 10, 15, and 25 days) on methane (CH(4)) production from cattle waste were evaluated using 3-dm(3) laboratoryscale fermentors. The highest CH(4) production rate achieved was 6.11 m(3) CH(4) m(-3) fermentor day(-1) at 55 degrees C, four days HRT, and S(0) = 100 kg VS/m(3). Batch fermentations showed an ultimate CH(4) yield (B(0)) of 0.42 m(3) CH(4)/kg VS fed. The maximum loading rates for unstressed fermentation were 7 kg VS m(-3) day(-1) at 35 degrees C and 20 kg VS m(-3) day(-1) at 55 degrees C. The kinetic parameter (K, an increasing K indicates inhibition of fermentation) increased exponentially as S(0) increased, and was described by: K = 0.8 + 0.0016 e(0.06S(0) ). Temperature had no significant effect on K for S(0) between 40 and 100 kg VS/m(3). The above equation predicted published K values for cattle waste within a mean standard error of 7%.     

Acetate Degradation at 70°C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70°C

Anaerobic acetate degradation at 70°C and at 55°C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70°C and less than 15 days was needed at 55°C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55°C up to 90% of the COD was removed. Batch assays showed that sludges from two 70°C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70°C. Both 70°C sludges, as well as the 55°C sludge, produced methane at temperatures of 37 to 73°C. The 55°C sludge exhibited shorter lag phases than the 70°C sludges and higher specific methane production rates between 37 and 65°C.     

Anaerobic digestion of cattle waste at mesophilic and thermophilic temperatures

Methanogenesis was studied using stirred, bench-top fermentors of 3-1 working volume fed on a semi-continuous basis with waste obtained from cattle fed a high grain, finishing diet. Digestion was carried out at 40 and 60°C. CH₄ production was 11.8, 18.3, 61.9 and 84.5% higher in the thermophilic than the mesophilic digestor at the 3, 6, 9 and 12 g volatile solids (VS) l^–1 reactor volume loading rates, respectively. When compared on an energetic basis CH₄ production was 7.4, 18.3, 72.9 and 107.3 kJ day higher in the thermophilic than the mesophilic digestor. CH₄ production decreased more rapidly with each increase in VS loading rate and decrease in retention time (RT) in the mesophilic than the thermophilic digestor. When expressed as l g^–1 VS fed or as kJ kJ^–1 fed, the amount of CH₄ was 49% less at the highest compared to the lowest loading rate in the mesophilic digestor. In the thermophilic digestor the decrease was only 16%. Propionate accumulated in the mesophilic digestor at the two highest loading rates, reaching concentrations of about 50 mM, but were only about 13 mM in the thermophilic digestor. Isobutyrate, isovalerate plus 2-methylbutyrate, and valerate also accumulated at the higher loading rates.     

Effect of mixing duration and vacuum on methane production rate from beef cattle waste

The effects of mixing duration and vacuum on methane production rates from anaerobically fermented beef cattle wastes were discussed. The results showed that continuously mixed fermentors produced significantly (P < 0.05) higher methane production rates than fermentors mixed two hours per day. However, the rates from the continuously mixed fermentors were only 8-11% higher than the intermittently mixed fermentors at six and four days hydraulic retention time (HRT), respectively. There was no significant difference between the vacuum and conventional fermentors at six days HRT, but there was a significant difference at four days HRT. The CH(4) production rate of the vacuum fermentors was 5% higher than the conventional fermentors at four days HRT. The results of these experiments compared well with predicted CH(4) production rates. These results suggest that there is little potential for increasing the fermentation rates of livestock wastes by increased mixing or vacuum.     

Methanosarcinaceae and Acetate-Oxidizing Pathways Dominate in High-Rate Thermophilic Anaerobic Digestion of Waste-Activated Sludge

This study investigated the process of high-rate, high-temperature methanogenesis to enable very-high-volume loading during anaerobic digestion of waste-activated sludge. Reducing the hydraulic retention time (HRT) from 15 to 20 days in mesophilic digestion down to 3 days was achievable at a thermophilic temperature (55°C) with stable digester performance and methanogenic activity. A volatile solids (VS) destruction efficiency of 33 to 35% was achieved on waste-activated sludge, comparable to that obtained via mesophilic processes with low organic acid levels (<200 mg/liter chemical oxygen demand [COD]). Methane yield (VS basis) was 150 to 180 liters of CH₄/kg of VS_added. According to 16S rRNA pyrotag sequencing and fluorescence in situ hybridization (FISH), the methanogenic community was dominated by members of the Methanosarcinaceae, which have a high level of metabolic capability, including acetoclastic and hydrogenotrophic methanogenesis. Loss of function at an HRT of 2 days was accompanied by a loss of the methanogens, according to pyrotag sequencing. The two acetate conversion pathways, namely, acetoclastic methanogenesis and syntrophic acetate oxidation, were quantified by stable carbon isotope ratio mass spectrometry. The results showed that the majority of methane was generated by nonacetoclastic pathways, both in the reactors and in off-line batch tests, confirming that syntrophic acetate oxidation is a key pathway at elevated temperatures. The proportion of methane due to acetate cleavage increased later in the batch, and it is likely that stable oxidation in the continuous reactor was maintained by application of the consistently low retention time.     

Terminal Reactions in the Anaerobic Digestion of Animal Waste

An anaerobic mesophilic digestor was operated using beef cattle waste (diluted to 5.75% volatile solids) as substrate; retention time was 10 days with daily batch feed. Volatile solids destruction was 36%. Daily gas production rate was 1.8 liters of gas (standard temperature and pressure) per liter of digestor contents (0.99 liters of CH₄ per liter of digestor contents). Acetate turnover was measured, and it was calculated that 68% of the CH₄ was derived from the methyl group of acetate. When the methanogenic substrates acetic acid or H₂/CO₂ were added to the digestor on a continuous basis, the microflora were able to adapt and convert them to terminal products while continuing to degrade animal waste to the same extent as without additions. The methanogenic substrates were added at a rate at least 1.5 times the microbial production rate which was measured in the absence of added substrates. Added acetate was converted directly to CH₄ by acetoclastic methanogens; H₂ addition greatly stimulated acetate production in the digestor. A method is described for the measurement of acetate turnover in batch-fed digestors.     

Evidence for the Existence of Psychrophilic Methanogenic Communities in Anoxic Sediments of Deep Lakes

In order to obtain evidence for the existence of psychrophilic methanogenic communities in sediments of deep lakes that are low-temperature environments (4 to 5°C), slurries were first incubated at temperatures between 4 and 60°C for several weeks, at which time they were amended, or not, with an additional substrate, such as cellulose, butyrate, propionate, acetate, or hydrogen, and further incubated at 6°C. Initial methane production rates were highest in slurries preincubated at temperatures between 4 and 15°C, with maximal rates in slurries kept at 6°C. Hydrogen-amended cultures were the only exceptions, with the highest methane production rates at 6°C after preincubation at 30°C.     

Radiation Resistance and Injury of Yersinia enterocolitica

The D values of Yersinia enterocolitica strains IP134, IP107, and WA, irradiated at 25°C in Trypticase soy broth, ranged from 9.7 to 11.8 krad. When irradiated in ground beef at 25 and −30°C, the D value of strain IP107 was 19.5 and 38.8 krad, respectively. Cells suspended in Trypticase soy broth were more sensitive to storage at −20°C than those mixed in ground beef. The percentages of inactivation and of injury (inability to form colonies in the presence of 3.0% NaCl) of cells stored in ground beef for 10 days at −20°C were 70 and 23%, respectively. Prior irradiation did not alter the cell's sensitivity to storage at −20°C, nor did storage at −20°C alter the cell's resistance to irradiation at 25°C. Added NaCl concentrations of up to 4.0% in Trypticase soy agar (TSA) (which contains 0.5% NaCl) had little effect on colony formation at 36°C of unirradiated Y. enterocolitica. With added 4.0% NaCl, 79% of the cells formed colonies at 36°C; with 5.0% NaCl added, no colonies were formed. Although 2.5% NaCl added to ground beef did not sensitize Y. enterocolitica cells to irradiation, when added to TSA it reduced the number of apparent radiation survivors. Cells uninjured by irradiation formed colonies on TSA when incubated at either 36 or 5°C. More survivors of an exposure to 60 krad were capable of recovery and forming colonies on TSA when incubated at 36°C for 1 day than at 5°C for 14 days. This difference in count was considered a manifestation of injury to certain survivors of irradiation.     

Effects of Temperature on Methanogenesis in a Thermophilic (58°C) Anaerobic Digestor

The short-term effects of temperature on methanogenesis from acetate or CO₂ in a thermophilic (58°C) anaerobic digestor were studied by incubating digestor sludge at different temperatures with ¹⁴C-labeled methane precursors (¹⁴CH₃COO⁻ or ¹⁴CO₂). During a period when Methanosarcina sp. was numerous in the sludge, methanogenesis from acetate was optimal at 55 to 60°C and was completely inhibited at 65°C. A Methanosarcina culture isolated from the digestor grew optimally on acetate at 55 to 58°C and did not grow or produce methane at 65°C. An accidental shift of digestor temperature from 58 to 64°C during this period caused a sharp decrease in gas production and a large increase in acetate concentration within 24 h, indicating that the aceticlastic methanogens in the digestor were the population most susceptible to this temperature increase. During a later period when Methanothrix sp. was numerous in the digestor, methanogenesis from ¹⁴CH₃COO⁻ was optimal at 65°C and completely inhibited at 75°C. A partially purified Methanothrix enrichment culture derived from the digestor had a maximum growth temperature near 70°C. Methanogenesis from ¹⁴CO₂ in the sludge was optimal at 65°C and still proceeded at 75°C. A CO₂-reducing Methanobacterium sp. isolated from the digestor was capable of methanogenesis at 75°C. During the period when Methanothix sp. was apparently dominant, sludge incubated for 24 h at 65°C produced more methane than sludge incubated at 60°C, and no acetate accumulated at 65°C. Methanogenesis was severely inhibited in sludge incubated at 70°C, but since neither acetate nor H₂ accumulated, production of these methanogenic substrates by fermentative bacteria was probably the most temperature-sensitive process. Thus, there was a correlation between digestor performance at different temperatures and responses to temperature by cultures of methanogens believed to play important roles in the digestor.     

Biomass adaptation over anaerobic co-digestion of sewage sludge and trapped grease waste

The feasibility of sewage sludge co-digestion using intermediate waste generated inside a wastewater treatment plant, i.e. trapped grease waste from the dissolved air flotation unit, has been assessed in a continuous stirred lab reactor operating at 35 °C with a hydraulic retention time of 20 days. Three different periods of co-digestion were carried out as the grease waste dose was increased. When the grease waste addition was 23% of the volatile solids fed (organic loading rate 3.0 kg_COD m⁻³ d⁻¹), an increase in methane yield of 138% was reported. Specific activity tests suggested that anaerobic biomass had adapted to the co-substrate. The adapted inoculum showed higher acetoclastic methanogenic and β-oxidation synthrophic acetogenic activities but lower hydrogenotrophic methanogenic activity. The results indicate that a slow increase in the grease waste dose could be a strategy that favours biomass acclimation to fat-rich co-substrate, increases long chain fatty acid degradation and reduces the latter’s inhibitory effect.     

THE INFLUENCE OF ENVIRONMENTAL TEMPERATURE ON THE UTILIZATION OF FOOD ENERGY IN BABY CHICKS

1. An optimum of environmental temperature is to be expected for the utilization of food energy in warm blooded animals if their food intake is determined by their appetite. 2. Baby chicks were kept in groups of five chicks in a climatic cabinet at environmental temperatures of 21°, 27°, 32°, 38°, and 40°C. during the period of 6 to 15 days of age. The intake of qualitatively complete food was determined by their appetite. Food intake, excretion, and respiratory exchange were measured. Control chicks from the same hatch as the experimental groups were raised in a brooder and were given the same food as the experimental chicks. The basal metabolism of each experimental group was determined from 24 to 36 hours without food at the age of 16 days. 3. The daily rate of growth increased with decreasing environmental temperature from 2.74 gm. at 40°C. to 4.88 gm. at 21°C. This was 4.2 to 6.5 per cent of their body weight. 4. The amount of food consumed increased in proportion to the decrease in temperature. 5. The availability of the food, used for birds instead of the digestibility and defined as See PDF for Structure showed an optimum at 38°C. 6. The CO₂ production increased from 2.95 liters CO₂ per day per chick at 40°C. to 6.25 liters at 21°C. Per unit of the 3/4 power of the body weight, 23.0 liters CO₂ per kilo^3/4 was produced at 40°C. and 43.4 liters per kilo^3/4 at 21°C. The CO₂ production per unit of 3/4 power of the weight increased at an average rate of approximately 1 per cent per day increase in age. The R.Q. was, on the average, 1.04 during the day and 0.92 during the night. 7. The net energy is calculated on the basis of C and N balances. A maximum of 11.8 Cal. net energy per chick per day was found at 32°C. At 21°C. only 6.9 Cal. net per day per chick was produced and at 40°C. an average of 6.7 Cal. 8. The composition of the gained body substance changed according to the environmental temperature. The protein stored per gram increase in body weight varied from 0.217 to 0.266 gm. protein and seemed unrelated to the temperature. The amount of fat per gram gain in weight dropped from a maximum of 0.153 gm. at 32°C. to 0.012 gm. at 21°C. and an average of 0.107 gm. at 40°C. The energy content per gram of gain in weight had its maximum of 2.95 Cal. per gm. at 38°C. and its minimum of 1.41 Cal. per gm. at 21°C. at which temperature the largest amount of water (0.763 gm. per gm. increase in body weight) was stored. 9. The basal metabolism increased from an average of 60 Cal. per kilo^3/4 at an environmental temperature of 40°C. to 128 Cal. per kilo^3/4 at 21°C. No indication of a critical temperature was found. 10. The partial efficiency, i.e. the increase in net energy per unit of the corresponding increase in food energy, seemed dependent on the environmental temperature, reaching a maximum of 72 per cent of the available energy at 38°C. and decreasing to 57 per cent at 21°C. and to an average of 60 per cent at 40°C. 11. The total efficiency, i.e. the total net energy produced per unit of food energy taken in, was maximum (34 per cent of the available energy) at 32°C., dropped to 16 per cent at 21°C., and to an average of 29 per cent at 40°C.     

Impact of Inoculum Preparation and Storage Conditions on the Response of Escherichia coli O157:H7 Populations to Undercooking and Simulated Exposure to Gastric Fluid

This study evaluated the impact of inoculum preparation and storage conditions on the response of Escherichia coli O157:H7 exposed to consumer-induced stresses simulating undercooking and digestion. Lean beef tissue samples were inoculated with E. coli O157:H7 cultures prepared in tryptic soy broth or meat decontamination runoff fluids (WASH) or detached from moist biofilms or dried biofilms formed on stainless steel coupons immersed in inoculated WASH. After inoculation, the samples were left untreated or dipped for 30 s each in hot (75°C) water followed by lactic acid (2%, 55°C), vacuum packaged, stored at 4 (28 days) or 12°C (16 days), and periodically transferred to aerobic storage (7°C for 5 days). During storage, samples were exposed to sequential heat (55°C; 20 min) and simulated gastric fluid (adjusted to pH 1.0 with HCl; 90 min) stresses simulating consumption of undercooked beef. Under the conditions of this study, cells originating from inocula of planktonic cells were, in general, more resistant to heat and acid than cells from cultures grown as biofilms and detached prior to meat inoculation. Heat and acid tolerance of cells on meat stored at 4°C was lower than that of cells on nondecontaminated meat stored at 12°C, where growth occurred during storage. Decontamination of fresh beef resulted in injury that inhibited subsequent growth of surviving cells at 12°C, as well as in decreases in resistance to subsequent heat and acid stresses. The shift of pathogen cells on beef stored under vacuum at 4°C to aerobic storage did not affect cell populations or subsequent survival after sequential exposure to heat and simulated gastric fluid. However, the transfer of meat stored under vacuum at 12°C to aerobic storage resulted in reduction in pathogen counts during aerobic storage and sensitization of survivors to the effects of sequential heat and acid exposure.     

Temperature Adaptations in the Terminal Processes of Anaerobic Decomposition of Yellowstone National Park and Icelandic Hot Spring Microbial Mats

The optimum temperatures for methanogenesis in microbial mats of four neutral to alkaline, low-sulfate hot springs in Yellowstone National Park were between 50 and 60°C, which was 13 to 23°C lower than the upper temperature for mat development. Significant methanogenesis at 65°C was only observed in one of the springs. Methane production in samples collected at a 51 or 62°C site in Octopus Spring was increased by incubation at higher temperatures and was maximal at 70°C. Strains of Methanobacterium thermoautotrophicum were isolated from 50, 55, 60, and 65°C sites in Octopus Spring at the temperatures of the collection sites. The optimum temperature for growth and methanogenesis of each isolate was 65°C. Similar results were found for the potential rate of sulfate reduction in an Icelandic hot spring microbial mat in which sulfate reduction dominated methane production as a terminal process in anaerobic decomposition. The potential rate of sulfate reduction along the thermal gradient of the mat was greatest at 50°C, but incubation at 60°C of the samples obtained at 50°C increased the rate. Adaptation to different mat temperatures, common among various microorganisms and processes in the mats, did not appear to occur in the processes and microorganisms which terminate the anaerobic food chain. Other factors must explain why the maximal rates of these processes are restricted to moderate temperatures of the mat ecosystem.     

Metabolic Activity of Fatty Acid-Oxidizing Bacteria and the Contribution of Acetate, Propionate, Butyrate, and CO2 to Methanogenesis in Cattle Waste at 40 and 60°C

The quantitative contribution of fatty acids and CO₂ to methanogenesis was studied by using stirred, 3-liter bench-top digestors fed on a semicontinuous basis with cattle waste. The fermentations were carried out at 40 and 60°C under identical loading conditions (6 g of volatile solids per liter of reactor volume per day, 10-day retention time). In the thermophilic digestor, acetate turnover increased from a prefeeding level of 16 μM/min to a peak (49 μM/min) 1 h after feeding and then gradually decreased. Acetate turnover in the mesophilic digestor increased from 15 to 40 μM/min. Propionate turnover ranged from 2 to 5.2 and 1.5 to 4.5 μM/min in the thermophilic and mesophilic digestors, respectively. Butyrate turnover (0.7 to 1.2 μM/min) was similar in both digestors. The proportion of CH₄ produced via the methyl group of acetate varied with time after feeding and ranged from 72 to 75% in the mesophilic digestor and 75 to 86% in the thermophilic digestor. The contribution from CO₂ reduction was 24 to 29% and 19 to 27%, respectively. Propionate and butyrate turnover accounted for 20% of the total CH₄ produced. Acetate synthesis from CO₂ was greatest shortly after feeding and was higher in the thermophilic digestor (0.5 to 2.4 μM/min) than the mesophilic digestor (0.3 to 0.5 μM/min). Counts of fatty acid-degrading bacteria were related to their turnover activity.     

Effects of Temperature and Carbon-Nitrogen (C/N) Ratio on the Performance of Anaerobic Co-Digestion of Dairy Manure,Chicken Manure and Rice Straw: Focusing on Ammonia Inhibition

Anaerobic digestion is a promising alternative to disposal organic waste and co-digestion of mixed organic wastes has recently attracted more interest. This study investigated the effects of temperature and carbon-nitrogen (C/N) ratio on the performance of anaerobic co-digestion of dairy manure (DM), chicken manure (CM) and rice straw (RS). We found that increased temperature improved the methane potential, but the rate was reduced from mesophilic (30∼40°C) to thermophilic conditions (50∼60°C), due to the accumulation of ammonium nitrogen and free ammonia and the occurrence of ammonia inhibition. Significant ammonia inhibition was observed with a C/N ratio of 15 at 35°C and at a C/N ratio of 20 at 55°C. The increase of C/N ratios reduced the negative effects of ammonia and maximum methane potentials were achieved with C/N ratios of 25 and 30 at 35°C and 55°C, respectively. When temperature increased, an increase was required in the feed C/N ratio, in order to reduce the risk of ammonia inhibition. Our results revealed an interactive effect between temperature and C/N on digestion performance.     

Unexpected Errors in Gas Chromatographic Analysis of Methane Production by Thermophilic Bacteria

Unexpected errors in methane measurement by gas chromatography occurred when samples at thermophilic temperatures were analyzed. With a standard curve prepared at room temperature (25°C), stoppered bottles incubated and sampled at 37 to 85°C showed more methane upon analysis than bottles incubated at 25°C: values at 50, 63, and 85°C were 109, 126, and 125%, respectively, of the 25°C value. All variation between 4 and 50°C can be explained by the temperature difference between culture bottle and sampling syringe, and the variation of methane concentration can be predicted by the gas law. Between 50 and 63°C, there was a more dramatic rise than predicted by theory. These variations are important to consider if thermophilic methane production is to be measured accurately. Methods to avoid errors are discussed.