Theoretical estimates of the heat of combustion of organic substrates or products can be very accurate. Theoretical evaluation and experimental measurements of heat evolution data will also be presented in detail.
Microcalorimetry
The heating is also arranged to operate continuously via a feedback control circuit so that any heat generated by microbial metabolism in the reaction vessel is continuously balanced by electrical heating of the reference balance. Similar to the adiabatic calorimeter, a double calorimeter is used in which the measuring element of the reaction vessel is compared with the measuring element of the same vessel.
Dynamic Calorimetry
If the incoming gas stream is saturated with water at the temperature of the culture broth, and is negligible. Dynamic calorimetry is therefore not as efficient to reliably determine the heat evolution during the end of the exponential culture growth phase when the rate of heat release can decrease drastically in a relatively short period of time or during other rapid metabolic changes.
Continuous Calorimetry
It is obvious from Eqs. the proportion of available electrons in the substrate that is included in the biomass. the proportion of available electrons in the substrate that are transferred to oxygen. the proportion of available electrons in the substrate used in product formation. part of the energy of the substrate that is evolved as heat. fraction of substrate energy converted to biomass. fraction of substrate energy converted to product. It is obvious from Eq. 44), that under aerobic conditions the proportion of substrate energy that is developed as heat is equal to the proportion of available electrons transferred to oxygen.
Relationships among Heat Evolution Data, Oxygen Consumption Data, Carbon Dioxide Respiration Data, and Substrate Consumption Data
Where me is defined as the energetic maintenance Eq. 75) can therefore be rewritten as follows: the specific consumption rate of organic substrate due to growth. the specific consumption rate of organic substrate due to cell maintenance. the specific consumption rate of organic substrate due to product formation. It is further noted that 1 mole of oxygen corresponds to 4 equivalents of an electron, i.e. the number of electrons required for the reduction of one molecule of oxygen:
Microbial Metabolic Heat Evolution as an Analytical Tool for Checking the Consistency of Biomass and Substrate Data
The good agreement between and therefore confirmed the validity of the biomass data and the heat evolution data selected during the experiment. It is important to note that Eq. 129), which included heat evolution data, can be used to check the consistency of experimental measurements of substrate utilization, oxygen consumption, and carbon dioxide respiration.
Indirect Estimation of Biomass Concentrations by Monitoring the Quantity of Heat Evolution
Both the rate of oxygen consumption and the rate of heat evolution can now be continuously monitored during the experiment. In a special case where product formation is related to growth, oxygen consumption data can be used together with heat evolution data to calculate the amount of products.
Indirect Estimation of Glucose and Ethanol Concentration during an Ethanol Biosynthesis Process
However, in some cases, the amount of non-cellular products can be predicted from heat evolution and oxygen consumption data. The amount of heat evolution is first calculated from the oxygen consumption data (112.8 U per g O2 equivalent).
What is the Meaning of an Energy Balance?
For sugar beet, the Battelle Institute2) - whose values are generally quite high - indicates an average value of 4.20 MJ kg-1 ethanol in the United States, against 3.5 MJ kg-1 of the official document cited10 ). When the plant for the utilization of cellulosic materials from municipal waste is far from such a place, the production of ethanol will be burdened with the transportation of raw materials.
Industrial Production
The high figure for production from whey is certainly due to the high dilution of the beer (2.5% vol.). In the industrial phase, these elements are mainly the energy necessary for the construction of the plant (genetically, with reference to the weight of steel) and for its maintenance.
Agricultural Refuse and other Vegetable Products (M)
It is interesting to note that, according to the same source, the energy consumption in the industrial phase of the production of ethanol from sugar cane should not exceed 66 % of this value. It is clear that the above data will be sufficient for the energy balance of the ethanol that is not used as fuel.
After Sezzi45), the energy savings in the production of gasoline at lower R.O.N. would generally be 2.5% of the net heat value of the fuel for gasolines blended with 10% ethanol and 5% for gasolines blended with 20% ethanol. According to Jawetz 49) the energy savings in the production of low-quality gasoline would be 6^-10.
Ethanol in the Engine .1 Ethanol — Gasoline Blends
Using ethanol in an Otto engine without changing the compression ratio means giving up the advantage that is most characteristic of ethanol itself, that is, high octane number. Since the experimental thermal efficiency is improved by 10% with ethanol and the theoretical with gasoline by only 3.8%, the advantage given by ethanol at a compression ratio of 12 is obvious.
An Evaluation of Non-renewable Energy Savings
According to Pimentel56, the theoretical ratio (ethanol consumption/gasoline consumption) will be 1.09 in the case of ethanol at 96% (net calorific value 25.1 MJkg-1), taking into account both the different efficiency and the different density. The same evaluation is significantly less favorable in the case of ethanol without gasoline.
Gasoline from Ethanol
2, Committee Series of Energy Tables, U.S. Govn't Printing Office, Washington, D.C. van die DECHEMA Meeting, Frankfurt a/M, Junie 1980. Sweetener and Alcohol Conf., London 1980. et al.: Preprints of the IVth Alkohol Brandstof Tegnologie Internat.
Growth, Products, and Application
Taxonomy
This is not necessary for autotrophic growth in 6 5 ) virtually all the thermoacidophiles capable of leaching metals from ores require yeast extract for heterotrophic growth 166). However, resazurin color is not only dependent on the redox potential of the solution; it is also used as a pH indicator, changing from violet at pH 5.8 to orange at pH 3.8.
Maximal Specific Growth Rate
Although this is good for qualitative decisions, it should always be evaluated in combination with the effect of inhibitor concentration on specific growth rate (for quantitative characterization). If the methane formation rate is not limited by H2 and CO2, the methane yield is independent of the growth rate (Yp/X = 0.63 mol g-1 or Yx/P = 1.6 g mol-1) in Methanobacterium thermoautotrophicum (Marburg strain) , but Yp/X decreases to 0.33 mol g-1 (or Yx/P increases to 3 g mol-1) if H2 or C02 limit growth. This can be explained by a tighter coupling of growth and methanogenesis under substrate-limiting conditions; but the reasons for this are not yet known 54).
Saturation Parameter K s
Mixed cultures of Sulfolobus acidocaldarius and Ferrolobus leached 38 % of Cu from chalcopyrite containing 0.31 % Cu in 161 days at an average rate of 21 mg 1-1 d-1. Apparent Ks values for both H2 and C02 were measured for Methanobacterium thermoautotrophicum (Marburg strain) and expressed as vol% of gas in the supplied atmosphere: KS,H2 = 20% and Ks,CO2.
Maintenance of Thermophiles
An example of uncoupling maintenance under non-energy-limiting conditions has been described for Methanobacterium thermoautotrophicum. And if primary products are to be produced, high maintenance would be desirable because more products and less biomass can be produced.
Substrate Limitation of Growth
Assuming a simultaneity of growth rate and death rate in the optimal and supraoptimal growth range, so that μobserved = μ(T) — kd(T) — compare2 1 2 ) — the validity range of Arrhenius' law is extended up to maximum growth temperature;. The increased production capacity can be explained by .. a) the ability of C. thermocellum cellulase to degrade β-1,4-xylans and -glucans, b) the ability of C.
Thermostable Enzymes from Thermophiles
Hydrogenase, as pure enzyme or as part of an enzyme system, can play an important role as specific catalyst in the stereospecific production of chiral chemicals such as hydrogenations of Δ2-enoates or in the reduction of α,P-unsaturated carbonyls, the regeneration of coenzymes in isolated enzyme systems, or biological H2 production.. various artificial electron acceptors; however, its thermal stability is limited, i.e. the enzyme is slowly inactivated at 70 °C, although the highest activity was measured at 95 °C 3 0 0. Significant reduction of organic matter (as measured as chemical oxygen demand, biological oxygen demand ( BOD5), and total organic matter) were observed to be directly associated with the heat generation. The yield was calculated as 14.6 kJ g-1 of degraded chemical oxygen demand 324).
Instrumentation
Heat Transfer
If an inexpensive means of cooling thermophilic cultures is desired (and sufficient), one could flow dry gas to the reactor and remove the appropriate heat of vaporization from the reactor. This simple way of stripping products, either with air or with (inert) gas, provides a potential method to reduce the product concentration in the reactor.
Mass Transfer
Simple and inexpensively operating reflux coolers could then remove the heat from the system, but recycle water and products, if volatile, back to the reactor or into any sampling vessel if desired. As a consequence, its concentration in the culture vessel was reduced to non-inhibitory values (v/v)196). This is of particular interest for the cultivation of thermophiles on highly concentrated media, since 'concentration limitation' l4) is reported to be the most serious drawback of thermophilic product formation at present (compare Sects.
Stability of Organisms
Equilibrium states are independent of time and the experimenter can select and preset the specific growth rate of the organism. Although many of the expected benefits of thermophilic processes can currently be considered realistic, some of them have been overestimated and some disadvantages probably underestimated.
Technical Realization of Thermophilic Biotechnology
Especially in recent years, the great technical potential of thermophilic microorganisms has been shown by studies on the formation of thermostable enzymes, immobilization of thermophilic whole cells and enzymes, the production of chemicals, solvents and fuels, and the utilization of abundant renewable substrates by thermophiles. From the point of microbial diversity, rapid development and prosperity of thermophilic biotechnology can be expected.
Regulation and Metabolic Control
In general, it cannot be expected that both anaerobic and aerobic thermophiles will compete for the future value of thermophilic biotechnology, but that they will contribute equally due to the higher metabolic rates of the aerobes and the different product spectrum of the anaerobes49). At present, only 'concentration limitation' appears to be a problem, as most thermophilic wild types have been shown to be inhibited at lower product or substrate concentrations than comparable mesophilic (production) strains.
Genetic Means
The production of H2 from formate by E. coli and some other bacteria prevents acidification and inhibits the growth of micro-organisms 32'130). The metabolism of glucose and some other sugars by these bacteria is related to the production of H2 and CO2 in the ratio of 2.3-3.0.
Purple Bacteria
Evidence for the production of H2 by purple bacteria in light is more extensive 8>. The rate at which purple bacteria produce hydrogen in the light is usually greater than in the dark.
Green Bacteria
Certain purple bacteria as well as some chemotrophic microorganisms develop H2. at high rate in the presence of some artificial electron donors. For example, cells of Th. roseopersicina in the presence of methyl viologen and dithionite develops H2 corresponding to 400 ml h_ 1 g_ 1 dry biomass 21).
Cyanobacteria
The oxygen-inactivated Th. roseopersicina hydrogenase recovers like that of sulfate-reducing bacteria 400,449) in the presence of reducing agents (Na2S204) and under anaerobic conditions 380). On the other hand, microorganisms are known to synthesize hydrogenase in the presence of some organic compounds regardless of the availability of H2.
Nitrogenase
The following data provide evidence for the role of glutamine synthetase in the regulation of nitrogenase synthesis. Together with the regulation of synthesis, the activity of nitrogenase can change, depending on the conditions of N2-fixing bacteria.
Interrelationship between Hydrogenase and Nitrogenase
According to recent results, inhibition of nitrogenase activity of R. rubrum in the presence of NH4+ is determined by the conversion of this enzyme to an inactive regulated form. Thus, from the available data it can be concluded that the coordinated activity of nitrogenase and hydrogenase is physiologically important for microorganisms, thereby increasing their N2-fixing activity.
Applications of Hydrogenases and Nitrogenase
The maximum efficiency of energy conversion in the system containing chloroplasts and hydrogenases was calculated to be approximately 25%5 9. In: Hydrogenases: Their Catalytic Activity, Structure and Function (Schlegel, H., Schneider, K. eds.), p . . of the workshop on biosolar conversion.
