BIO 301:TEMPERATURE IN NATURAL METHANE PRODUCTION COMPARED TO BIOREACTOR

METHANE PRODUCTIONSeth Shenton,

• About The Author• Brief Summary of Papers• Introduction: Relevance of Methane Produ

ction• Summary 1. Zeikus and Winfrey, 1976• The production of methane in a natural enviro

nment• Summary 2: Zinder et. al. 1984• The industrial production of methane• Comparison of Papers• Critique• References

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About the author I am a third year Biomedical science and

Molecular biology student, who graduates at the end of this semester. I chose BIO301 as an elective unit, so far I have found it challenging, fun and time consuming.

The reason the methanogenesis papers where chosen is they provide a good insight into the production of methane in a bioreactor and in a natural environment.

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Brief summary of the papers: Executive Summary

Paper one is that of methanobacterium in lake sediment, the temperature change effects the methane production, the optimum methane production in sludge in a natural environment was examined and the results showed higher temperature increased the resulting methane production to a certain point before becoming to high for functional growth, paper one also points out the effects of pressure on increased methane production.

Paper two shows temperature on bioreactors in methane production, the temperature sustained was up to 68 °C , the production dropped rapidly in comparison to 54 °C . Methane production in a bioreactor can withstand a higher temperature maximum than that of the natural methanobacterium.

These papers where chosen, as they came from the same journal, on the same topic at around a similar time. Both have a high level of applicability to modern production of methane and both contained the main factor of interest, the optimum temperature in methanogenesis.

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Introduction: Relevance of methane production The production of methane from waste is a viable way of

producing large amounts of energy as a replacement of natural resources that are declining rapidly (Weiland, 2006).

Methane is produced in natural environments, such as wetlands or underwater where anaerobic conditions are available (Valentine et. al, 1994). Methane production in the environment is of interest for optimum production of methane in bioreactors, the production of methane is currently a non-industrialised process, on any large scale.

The eventual possibility is that of a renewable energy, that is clean and an auxiliary to a carbon dioxide and organic waste effluent, it can be utilised in methane production and maximise the production of methane.

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Summary 1: Zeikus J.G. and Winfrey M.R. I: Temperature Limitation of Methanogenesis in Aquatic Sediments. Zeikus J.G. and

Winfrey M.R. 1976 Applied and Environmental Microbiology 31(1):99-107

Increased methanogenesis with increasing temperature, with the substrate, of the bacteria (Methanobacterium) in a natural aquatic environment. The effect of depth (pressure) on methane production was also measured which shows the relatively constant temperatures with distance, as well. The three sampling depths where 5 metres, 10 metres and 18 metres and the average of the replicates is displayed in figure 1 as the mMoles of CH4x10^3/g of sediment.

This Shows that in a natural environment the bacteria produce more methane in the seasons with the higher temperature than that of the lower temperature, as can be seen in figures 1 and 2 the increasing of temperature increases methane production until approximately 45 °C then there is a steep drop of methane production as the temperature increases.

At 18 metres the production of methane was highest in the methanobacterium, this is potentially due to the anaerobic environment in comparison to that of the other measurements of 10 and 5 metres.

In a more summarised view, temperature is directly correlated with production of methane in a natural environment; this occurs until maximum temperature is reached, then efficiency drops drastically.

Figure 1: This shows with increasing temperature and pressure of the aquatic environment within the area of the methanogens, there is an increase in the production of methane. The pH in these environments was a constant 7.1

Figure 2: Methane production over 16 days with two temperature deficits showing that 30 °C produces more Methane than that of the 16 °C bacterium.This data was acquired using radioactive C14 isotopes.

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The production of methane and its optimisation

The production of methane from sludge in a natural environment. The natural environment provide major insights into the production of methane in the environment and allows the optimization of the production of such a bacterial product.

The production of methane is seriously underestimated as a viable energy source of the future. The potential is there and figure 3 shows the current understanding of the production routes required for optimization of methane in a simplified form.

The substrate would preferentially be a waste of some form to minimise costs and maximise the appeal of using bacterium to produce energy.

The use of acetate as pathway in methane production is relatively common, as often the bacterium associated with waste disposal use acetate from degraded waste sludge, in figure 3 this process can be seen when the COD is converted to acetate (Fukuzaki et. al, 1990).

The hydrogen partial pressure must be low enough so as to allow acetogenesis to be thermodynamically favourable, over other potential pathways and bacteria (Angenent et. al, 2004)

Figure 3: The pathway of methanogenesis and the multifactorial elements involved in its production.Image from, Weiland. 2006.

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Summary 2: Zinder S.H. Anguish T. Cardwell S.C. II: Effects of Temperature on Methanogenesis in a Thermophilic (58 degrees Celsius) anaerobic digestor.

Zinder S.H., Anguish T., Cardwell S.C. 1984. Applied and Environmental Microbiology 47(4):808-813.

The use of the species methanobacterium to produce methane for commercial prospects has been considered viable for a long while. Using C14 isotopes in the precursor chemicals in an anaerobic digestor it was found that the use of temperatures of close to 60 °C was found to be optimal. The fact that such a high temperature was used, is particularly interesting from a commercial point of view. If the substrate the bacterium was grown on was heated above 65 °C the production of methane was reduced rapidly leading to a decrease in efficiency of the production and a build up of substrate (figure 5).

Temperatures near 65 °C lead to inhibition of the methanobacterium , as shown in smaller experiments substrate that was incubated at 65 °C produced approximately 25% of the methane than that of the substrate and environmental conditions that where maintained at 58 °C .

Different strains of the methanosarcina have different optimal temperatures, considering the evolutionary relatedness this is curious from a commercial perspective and for optimisation of the process.

With an increased temperature the cost of production goes up, a particular strain of methanogen that is capable of reaching an optimised temperature at a lower one would be commercially viable.

 

In a short summary the methanogens in a bioreactor could withstand higher temperatures (~10 °C) than those in a normal environment (45 °C), though the maximum temperature that lead to death was not significantly increased form that of optimum production. Temperature is one of the most fundamental elements in optimization of methanogenesis

Figure 4: this shows the temperature and the production rate of the methane and the optical density leading to the number of microbes in the specific culture at the specific temperature at any one time. This graph shows a clearly distinct optimal zone of around 60-70 degrees Celsius where both the temperature and the OD continue to increase.

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Figure 5: Over a period of days the temperature and production rates where monitored. After an increase of 6 °C the production rate of the methanogens was reduced, giving rise to substrate, which stabalised when the temperature was returned to 58 °C

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The industrial production of methane and other uses The production in a bioreactor requires

optimisation of feed input and temperature. The pH plays an important, as does the pressure the culture works at (Zeikus and Winfrey, 1976).

The potential for the use of bioreactors as more than just a energy production, it provides a way of clean energy from waste.

Figure 6 shows the possible production using bioreactors, the possible routes of not only producing methane from waste but other products, lead to an expanded horizon in the renewable energy and sources field.

Figure 6 The potential production pathways of organic waste material, this figure shows that more than one viable product can be achieved with the right system.Image from: http://www.e-inst.com/biomass-to-biogas/. Accessed 27/09/12

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Comparison of Papers Zinder et. al, concluded that growth with high temperatures for the

microorganisms yielded better productivity, but when compared to Zeikus and Winfrey the temperature that was optimal in a natural environment is lower than that of the commercial one.

Zeikus and Winfrey however found that the pH of 7.1 found in the natural aquatic environments was sufficient of growth where a lower pH of 6.7 was found to be optimal in a commercial bioreactor for methane production.

Both articles indicate that the production of methane occurs well at high temperature, before sharply dropping off past optimum temperatures.

The methanogenic bacteria work particularly well at high pressure of 18 metres and constant temperature. The pressure of 18 metres is over that of 2 atmospheres (Zeikus and Winfrey, 1976), this provides a possible way of increasing the production rate of methane in a bioreactor, as always the costs of a pressurised bioreactor against the potential productivity must be weighed up.

The production of biogas if of great interest to scientists as it allows the implementation of renewable energy that can provide energy for a large market.

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Critique Both papers how similarities between natural sludge fed

bacterium and bioreactors. Both show increases in temperature increase production until maximum point is reached, which is beyond a thermally stable point leading to a decrease in methane production and eventual death of the organisms. What appears most interesting is the variability of the maximum production rate temperature in an artificial environment and a natural one.

The pH in these environments are both similar, in the natural environment the pH was 7.1 compared to a pH of 6.7.

The optimization of such a process appears to be slightly different in the natural environment and that of a bioreactor, even though the same species of methanobacterium (Zinder et. al, 1984. Zeikus and Winfrey, 1976).

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References: Angenent L.T., Karim K., Al-Dahhan M.H., Wrenn B.A., guez-Espinosa R.D. 2004. Production of

bioenergy and biochemicals from industrial and agricultural wastewater. Trends in Biotechnology 22(9): 477-485

Fukuzaki S., Nishio N., Nagai S. 1990. Kinetics of the Methanogenic Fermentation of Acetate. Applied and Environmental Microbiology 56(10):3158-3163

P. Weiland. 2006. Biomass Digestion in Agriculture: A Successful Pathway for the Energy Production and Waste Treatment in Germany. Engineering in Life Sciences 6(3):302-309

  Ma X., Novak P.J., Michael J. Semmens M.J., Clapp L.W., Hozalskib R.M. 2006. Comparison of

pulsed and continuous addition of H2 gas via membranes for stimulating PCE biodegradation in soil columns. Water Research 40(6):1155-1166

Valentine D.W., Holland E.A., Schimel D.S. 1994. Ecosystem and Physiological controls over methane production in northern wetlands. Journal of Geophysical Research 99(1): 1563

Zeikus J.G. and Winfrey M.R. 1976. Temperature Limitation of Methanogenesis in Aquatic Sediments. Applied and Environmental Microbiology 31(1):99-107

Zinder S.H., Anguish T., Cardwell S.C. 1984. Effects of Temperature on Methanogenesis in a Thermophilic (58 degrees Celsius) anaerobic digestor. Applied and Environmental Microbiology 47(4):808-813.

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