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.     

Effect of Temperature and Retention Time on Methane Production from Beef Cattle Waste

The effect of temperature and retention time on the rate of methane production from waste of beef cattle fed a finishing diet was investigated by using continuously mixed 3-liter working volume anaerobic fermentors. The temperatures ranged from 30 to 65°C with 5°C increments between fermentors. The fermentors were fed once per day with 6% volatile solids (organic matter). Retention time for each temperature was varied from 18 to 2.5 days. After 3-volume turnovers, samples were obtained on 4 consecutive days. The highest methane production rate (liters/liter of fermentor per day) and methane yield at that rate (liters/gram of volatile solids) were 1.27 and 0.19 at 9 days and 30°C, 1.60 and 0.16 at 6 days and 35°C, 2.28 and 0.23 at 6 days and 40°C, 2.42 and 0.24 at 6 days and 45°C, 2.83 and 0.14 at 3 days and 50°C, 2.75 and 0.14 at 3 days and 55°C, 3.18 and 0.14 at 2.5 days and 60°C, and 1.69 and 0.17 at 6 days and 65°C. Volatile solids degradation at these retention times and temperatures was between 46 and 54%. The concentrations of volatile acids in the 30 to 55°C fermentors were generally below 2,000 mg/liter, with the exception of the 3-day retention time. The 60 and 65°C fermentors were usually above this level for all retention times. These studies indicate potential rates of methane production from the fermentation of untreated waste of beef cattle fed high-grain finishing diets. This information should serve as preliminary guidelines for various kinetic analyses and aid in economic evaluations of the potential feasibility of fermenting beef cattle waste to methane.     

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.     

The action of polyether ionophorous antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) in vivo and in vitro: study by light and electron microscopy

The effect of three polyether antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) was studied in vivo and in vitro by means of light and electron microscopy. It was found that these three drugs act against free merozoites, which are destroyed by bursting of the cell border (i.e. pellicle), endoplasmic reticulum and internal organelles even after very short exposure times (20 min) in media containing 1 ppm, 10 ppm or 100 ppm of these drugs. Sporozoites, however, survived these drug concentrations during an exposure time of 30 min (this would be sufficient to penetrate host cells and start development). Intracellular stages, which were situated in a parasitophorous vacuole within an intact host cell, were not attacked, apparently because these drugs are almost incapable of penetrating host cells. On the other hand, parasites (such as differentiated schizonts, gamonts) located within degenerating host cells showed slight disintegration, which did not necessarily led to their death. From these results it becomes clear why these polyether antibiotics have to be fed daily. Doses of 70 ppm salinomycin, 125 ppm monensin and 125 ppm lasalocid were found to bring about an equivalent protective effect against an infection with 40,000 Eimeria tenella oocysts.     

Effect of Monensin and Lasalocid-Sodium on the Growth of Methanogenic and Rumen Saccharolytic Bacteria

It is thought that monensin increases the efficiency of feed utilization by cattle by altering the rumen fermentation. We studied the effect of monensin and the related ionophore antibiotic lasalocid-sodium (Hoffman-LaRoche) on the growth of methanogenic and rumen saccharolytic bacteria in a complex medium containing rumen fluid. Ruminococcus albus, Ruminococcus flavefaciens, and Butyrivibrio fibrisolvens were inhibited by 2.5 μg of monensin or lasalocid per ml. Growth of Bacteroides succinogenes and Bacteroides ruminicola was delayed by 2.5 μg of monensin or lasalocid per ml. Populations of B. succinogenes and B. ruminicola that were resistant to 20 μg of either drug per ml were rapidly selected by growth in the presence of each drug at 5.0 μg/ml. Selenomonas ruminantium was insensitive to 40 μg of monensin or lasalocid per ml. Either antibiotic (10 μg/ml) inhibited Methanobacterium MOH, Methanobacterium formicicum, and Methanosarcina barkeri MS. Methanobacterium ruminantium PS was insensitive to 40 μg of monensin or 20 μg of lasalocid per ml. The methanogenic strain 442 was insensitive to 40 μg of monensin but sensitive to 10 μg of lasalocid per ml. The results suggest that monensin or lasalocid acts in the rumen by selecting for succinate-forming Bacteroides and for S. ruminantium, a propionate producer that decarboxylates succinate to propionate. The selection could lead to an increase in rumen propionate formation. Selection against H₂ and formate producers, e.g. R. albus, R. flavefaciens, and B. fibrisolvens, could lead to a depression of methane production in the rumen.     

Use of potassium depletion to assess adaptation of ruminal bacteria to ionophores.

When mixed ruminal bacteria from cattle fed timothy hay were suspended in a medium containing a low concentration of potassium, monensin and lasalocid catalyzed a rapid depletion of potassium from cells. The ionophore-mediated potassium depletion was concentration dependent, and it was possible to describe the relationship with saturation constants. Mixed ruminal bacteria never lost more than 50% of their potassium (Kmax = 46%), and the concentrations of monensin and lasalocid needed to cause half-maximal potassium depletion (Kd) were 178 and 141 nM, respectively. When cattle were fed 350 mg of monensin per day, the ratio of ruminal acetate to propionate decreased from 4.2 to 2.9, and the Kd of monensin was eightfold greater than the value for mixed ruminal bacteria from control animals. Monensin supplementation also caused a twofold increase in the Kd of lasalocid. Lasalocid supplementation (350 mg per day) had no effect on the ruminal acetate-to-propionate ratio, but it caused a twofold increase in the Kd values of monensin and lasalocid. Increases in Kd occurred almost immediately after ionophore was added to the ration, and the Kd values returned to their prefeeding values within 14 days of withdrawal. Ionophore supplementation had no effect on the Kmax values, and approximately 50% of the population was always highly ionophore resistant. Because the Kd values of even adapted ruminal bacteria were low (< 1.5 microM), it appears that a large proportion of the ruminal ionophore is bound nonselectively to feed particles or ionophore-resistant bacteria.     

Effect of monensin and 2-bromoethanesulfonic acid on fatty acid metabolism and methane production from cattle manure

Summary The effect of monensin and 2-bromoethanesulfonic acid (BESA) on methane production from cattle manure and on volatile fatty acids metabolism was tested. At 10 days retention time 0.81 biogas per liter cattle manure and day were produced. Methanogenesis was inhibited 20% by 3 mM BESA per liter and 45% by 2–5 mg monensin per liter. When the digestion was inhibited with either of the both drugs, the acetate pool increased drastically. Like in untreated fermentations the propionate pool increased in BESA-inhibited fermentations for several hours after substrate addition. After 24 h however it did not decrease to the low level reached in non-inhibited fermentations. When monensin was the inhibitor, the propionate pool did not change for 15 h, but then decreased with the same rate as in the control experiment. Adaptation processes or detoxification may be responsible for the delayed degradation.The degradation of low concentrations of buty-rate to acetate and the turn over rates of the butyrate pool are almost identical in cattle manure containing BESA, monensin, or no inhibitor. The turn over of ¹⁴C-acetate from butyrate degradation is delayed in BESA and monensin inhibited fermentations.From the data presented it can be concluded, that BESA mainly inhibits the methanogens, while monensin seems to inhibit both, methanogenic and nonmethanogenic organisms. However, a fast adaptation to or detoxification of the antibiotic seems to occur.     

Effect of Aeration on Growth and Aflatoxin Production by Aspergillus flavus in Submerged Culture

Aspergillus flavus ATCC 15517 produced up to 212 mg per liter of total aflatoxin in submerged culture in aerated (3,000, 6,000, 9,000, and 12,000 ml/min) and agitated medium in 14-liter fermentors with 10 liters of medium consisting of 2% yeast extract and 10% sucrose. Aflatoxin production increased with time. A maximum of 212 mg/liter was produced at 9,000 ml/min aeration, whereas the yield decreased substantially at the lower aeration rates. Two other strains of A. flavus synthesized aflatoxin in smaller quantities.     

Effect of monensin on the specific activity of ammonia production by ruminal bacteria and disappearance of amino nitrogen from the rumen.

When unadapted mixed ruminal bacteria (312 mg of protein per liter) were treated with monensin (5 mM) in vitro, the rates of ammonia production from enzymatic digests of casein, gelatin, and soy protein (0.5 g of N per liter) were decreased from 46 +/- 2 to 24 +/- 1, 20 +/- 1 to 7 +/- 1, and 40 +/- 2 to 18 +/- 2 nmol/mg of protein per min, respectively. Monensin also caused a decrease in ammonia production in vivo. Nonlactating dairy cows which were fed 0.56 kg of timothy hay 12 times per day had a steady-state ruminal ammonia concentration of 2.7 +/- 0.1 mM, and the ammonia concentration decreased to 1.2 +/- 0.2 mM when monensin (350 mg/day) was added to the diet. The decrease in ammonia production was associated with a 10-fold reduction (4.1 x 10(6) versus 4.2 x 10(5)/ml) in the most probable number of ammonia-producing ruminal bacteria that could use protein hydrolysate as an energy source. Monensin had little effect on the most probable number of carbohydrate-utilizing ruminal bacteria (6.5 versus 7.0 x 10(8)/ml). The addition of protein hydrolysates (560 g) to the rumen caused a rapid increase in the ammonia concentration, but this increase was at least 30% lower when the animals were fed monensin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of type of ionophore and carrier on in vitro ruminal dry matter disappearance,gas production,and fermentation end products of a concentrate substrate

Effects of ionophore type and carrier on in vitro ruminal digestion and fermentation patterns of a concentrate substrate were evaluated at various incubation times. Treatments were: control (no ionophore); lasalocid sodium commercial premix (Bov); lasalocid sodium mycelium cake (LasBio); laidlomycin sodium salt (LaidNa); laidlomycin propionate commercial premix (LaidPro); monensin sodium salt (Mon); and monensin sodium commercial premix (Rum). The Bov, LasBio, Mon, and Rum treatments supplied 4 μg of ionophore/mL of culture volume, whereas the LaidNa and LaidPro treatments supplied 1.33 μg of ionophore/mL. Total gas and methane production did not differ among treatments at any of the incubation times (P>0.09). Similarly, in vitro dry matter disappearance (IVDMD) was not affected by treatment (P>0.28) at 6, 18, and 24 h of incubation; however, IVDMD (P=0.03) was greater for ionophores than for the control at 12 h of incubation. Molar proportions of acetate (P<0.01), acetate:propionate (P<0.01), and total volatile fatty acid (VFA) concentrations (P<0.01) were decreased and propionate was increased (P<0.001) for the average of all ionophore-containing substrates compared with the control. Total VFA were decreased by Bov, LaidNa, and Rum, contrasted with their specific counterparts (LasBio, LaidPro, and Mon, respectively; P<0.05). Differences were detected among ionophore types for acetate (lasalocid vs. laidlomycin; P<0.05), propionate (lasalocid vs. monensin; P<0.05), and butyrate (monensin vs. lasalocid or laidlomycin; P<0.05). Capture of metabolic hydrogen in end products of fermentation was greater for ionophore-containing treatments (P<0.01) than for the control. These data suggest limited unique effects of ionophore type or carrier on IVDMD, total gas production, and methane; however, VFA proportions varied among ionophore types and carriers, which deserves further study.     

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.     

The effect of salinomycin and lasalocid on laboratory cultures ofEnterococcus fœcium andStaphylococcus gallinarum strains

The growth ofEnterococus fœcium strains CCM 4231 and EF 26, andStaphylococcus gallinarum SG 31 was inhibited by salinomycin and lasalocid at concentrations of 25 and 50 mg/L.Staphylococcus gallinarum was more sensitive to the additives used than were enterococci. Maximum inhibition (90%) was measured after the growth with the SG 31 strain in the presence of both ionophores. Growth of organisms was more inhibited by salinomycin at 25 mg/L (67.5%) than at 50 mg/L (63%). The inhibitory effect in enterococcal strains reached after the addition of salinomycin and lasalocid (on average) 63 and 58%, respectively. The CCM 4231 strain was more inhibited by salinomycin as well as by lasalocid than was the EF 26 strain.     

Heterotrophic Growth and Production of Xanthophylls by Chlorella pyrenoidosa

The growth and level of xanthophylls of several representative species of green algae were investigated as a possible source of pigmentation for the egg yolk and broiler markets. Chlorella pyrenoidosa 7-11-05 was selected for fermentation studies because of its high level of xanthophylls and wide temperature range for growth. The heterotrophic metabolism was preferred because of the ease of adaptability to present fermentation equipment. When used as the sole carbon source, glucose was the only sugar, among many tested, that gave appreciable growth in illuminated shaken flasks. A dry cell weight of 90 g per liter and total xanthophylls of 450 mg per liter were obtained from 190 g per liter of glucose monohydrate in 168-hr illuminated shaken flasks. Higher levels of glucose decreased yields. In combination with glucose, monosaccharides, such as fructose and galactose, were readily assimilated. The 7-11-05 strain was adapted to galactose as the sole carbon source after six vegetative passages. Light of the proper intensity and duration stimulated total xanthophylls approximately 35%. The effect on dry cell weight and total xanthophylls of seven antibiotics added at various levels in shaken flasks was studied. Erythromycin was essentially stable throughout the fermentation and nontoxic up to 25 μg/ml, with only slight toxicity at higher levels. Both erythromycin and ristocetin were effective in controlling a high incidence of bacterial contamination in 30-liter fermentors. With the higher agitation and aeration rates possible in 30-liter fermentors, dry cell weights in excess of 100 g per liter and total xanthophylls of 467 to 512 mg per liter were readily obtained from 230 to 260 g per liter of glucose in 162-hr illuminated batch-type fermentations. Continuous-feed runs yielded a dry cell weight of 302 g per liter and total xanthophylls of 650 mg per liter from 520 g per liter of glucose. The type of Chlorella cell produced was an important consideration with respect to the availability of the xanthophylls in pigmenting egg yolks and broilers.     

Some growth and metabolic characteristics of monensin-sensitive and monensin-resistant strains of Prevotella (Bacteroides) ruminicola.

New strains with enhanced resistance to monensin were developed from Prevotella (Bacteroides) ruminicola subsp. ruminicola 23 and P. ruminicola subsp. brevis GA33 by stepwise exposure to increasing concentrations of monensin. The resulting resistant strains (23MR2 and GA33MR) could initiate growth in concentrations of monensin which were 4 to 40 times greater than those which inhibited the parental strains. Resistant strains also showed enhanced resistance to nigericin and combinations of monensin and nigericin but retained sensitivity to lasalocid. Glucose utilization in cultures of the monensin-sensitive strains (23 and GA33) and one monensin-resistant strain (23MR2) was retarded but not completely inhibited when logarithmic cultures were challenged with monensin (10 mg/liter). Monensin challenge of cultures of the two monensin-sensitive strains (23 and GA33) was characterized by 78 and 51% decreases in protein yield (milligrams of protein per mole of glucose utilized), respectively. Protein yields in cultures of resistant strain 23MR2 were decreased by only 21% following monensin challenge. Cell yields and rates of glucose utilization by resistant strains GA33MR were not decreased by challenge with 10 mg of monensin per liter. Resistant strains produced greater relative proportions of propionate and less acetate than the corresponding sensitive strains. The relative amounts of succinate produced were greater in cultures of strains 23, GA33, and 23MR2 following monensin challenge. However, only minor changes in end product formation were associate with monensin challenge of resistant strain GA33MR. These results suggest that monensin has significant effects on both the growth characteristics and metabolic activities of these predominant, gram-negative ruminal bacteria.     

The action of salinomycin-Na and lasalocid-Na on chloroquine- and mepacrine-resistant line of Plasmodium berghei K 173-strain in Wistar rats

Salinomycin-Na and lasalocid-Na, two ionophorous antibiotics known for their anticoccidial activity, exhibit in vivo blood schizontocidal action on the Plasmodium berghei Keyberg 173 RC/M line that has a high level of resistance to chloroquine and mepacrine. Salinomycin was found to have a greater effect than lasalocid on asexual stages of this line. Trophozoites and schizonts were no longer found after a single dose of 20 mg/kg or five doses of 1.25 mg/kg of salinomycin whereas a single dose of 40 mg/kg or five doses of 20 mg/kg of lasalocid showed no marked effect on parasitaemia within 96 h of starting treatment in rats. Some toxicological data show that lasalocid, however, is better tolerated in domestic animals than salinomycin. Early morphological changes in asexual blood stages were membrane-coiling in the cytoplasm followed by vacuolization and disruption of the cell membrane or pellicle after treatment with both compounds. In particular mature schizonts were totally destroyed showing enormously large vacuoles. Toxicological data and blood schizontocidal activity indicate the narrow safety margin in P. berghei infected rats, and place salinomycin in the 'markedly toxic' group of antimalarial compounds.     

Some growth and metabolic characteristics of monensin-sensitive and monensin-resistant strains of Prevotella (Bacteroides) ruminicola.

New strains with enhanced resistance to monensin were developed from Prevotella (Bacteroides) ruminicola subsp. ruminicola 23 and P. ruminicola subsp. brevis GA33 by stepwise exposure to increasing concentrations of monensin. The resulting resistant strains (23MR2 and GA33MR) could initiate growth in concentrations of monensin which were 4 to 40 times greater than those which inhibited the parental strains. Resistant strains also showed enhanced resistance to nigericin and combinations of monensin and nigericin but retained sensitivity to lasalocid. Glucose utilization in cultures of the monensin-sensitive strains (23 and GA33) and one monensin-resistant strain (23MR2) was retarded but not completely inhibited when logarithmic cultures were challenged with monensin (10 mg/liter). Monensin challenge of cultures of the two monensin-sensitive strains (23 and GA33) was characterized by 78 and 51% decreases in protein yield (milligrams of protein per mole of glucose utilized), respectively. Protein yields in cultures of resistant strain 23MR2 were decreased by only 21% following monensin challenge. Cell yields and rates of glucose utilization by resistant strains GA33MR were not decreased by challenge with 10 mg of monensin per liter. Resistant strains produced greater relative proportions of propionate and less acetate than the corresponding sensitive strains. The relative amounts of succinate produced were greater in cultures of strains 23, GA33, and 23MR2 following monensin challenge. However, only minor changes in end product formation were associate with monensin challenge of resistant strain GA33MR. These results suggest that monensin has significant effects on both the growth characteristics and metabolic activities of these predominant, gram-negative ruminal bacteria.     

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.     

High-Efficiency Conversion of Pyruvate to Acetoin by Lactobacillus plantarum during pH-Controlled and Fed-Batch Fermentations

The influence of pH on the type and concentration of metabolites produced from pyruvate by Lactobacillus plantarum ATCC 8014 was examined in pH-controlled fermentors at pH values of 4.5 to 6.5. Specific growth rates, cell dry weights, and diacetyl concentrations were highest at pH 5.5, with values of 0.78 h⁻¹, 190 mg/liter, and 1.2 mM, respectively. While the conversion efficiency (millimoles of acetoin formed per millimoles of pyruvate utilized) was highest (94.6%) at pH 4.5, acetoin levels were similar (20 mM) between pH 4.5 and 5.5. Feeding stationary-phase cells exogenous pyruvate increased acetoin levels to 78 mM.     

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.