Method for simplified determination of the course of methane release from biomass samples during methane fermentation on a laboratory scale

Abstract

The proposed simplified method for the simplified determination of the course of methane release from biomass samples during methane fermentation in laboratory batch experiments by using a pretreated sample of biogenic material in a germ-containing inoculum, introducing the experimental setup into a mesophilic or thermophilic environment, determining the released gas volume and determining the methane content in the released fermentation gas, is characterized by the following: that the biogenic material sample is pretreated using biotechnological means, that parts of the fermentation residue of an active methane fermentation plant for biogenic material with a similar composition to the material sample to be evaluated are used as inoculum, that the mixture of the biogenic material sample to be evaluated and the selected inoculum is placed in a laboratory fermenter for batch methane fermentation, that the selected anaerobic mesophilic or thermophilic environment is maintained in the laboratory fermenter for the entire duration of the experiment, that the total mass of the filled laboratory vessel is determined at regular intervals, and that a gas sample is taken from the laboratory vessel and analyzed before or after the determination of the current total mass.

Description

Technical field of the invention

[0001] The invention relates to a method for the simplified determination of the methane release process from biomass samples during methane fermentation on a laboratory scale. Such a technical solution is required when using biotechnological techniques for bioenergy production. State of the art

[0002] Methane fermentation based on cultivated biomass may have had temporary market justification due to the perceived overproduction of agricultural products within the European Union. This led, for example, to the temporary subsidization of the so-called set-aside of agricultural production areas.

[0003] In Germany, as a result of political decision-making since the 1990s, the legal framework for promoting electricity generation from cultivated biomass has also been developed, particularly through the various versions of the Renewable Energy Sources Act (EEG).

[0004] As a result of these subsidies, a high-performing industry developed, which in Germany alone led to a stock of approximately 10,000 active methane fermentation plants with varying electrical outputs between 50 kW and 20 MW by 2022.

[0005] There are now a number of reasons that make a continuation of this development seem questionable.

[0006] Regardless, the development of various process and equipment technologies required a benchmark that would allow for comparative evaluation through laboratory tests even before results from fully realized plants were available. The VDI Guideline 4639 of the Association of German Engineers was clearly intended to fulfill this task.

[0007] The VDI 4639 (2016) standard sets out requirements for the execution and evaluation of preliminary laboratory tests on the methane fermentation of biogenic material samples, which are hardly feasible in the typically small plant operating structures.

[0008] Since even in high-performance research institutions there is too much room for discretion in the application of VDI 4630, the results obtained can at best be considered to have the quality of an indicative standard.

[0009] This assessment is explained in great detail in the dissertation by Thomas Fritz at the University of Rostock, dated December 2008.

[0010] The improved evaluation method presented in this dissertation at the University of Rostock (2008) eliminates a number of technical application problems, but does not yet enable practical evaluation of methane release processes for new biogenic material samples in small operational laboratories. Criticism of the state of the art

[0011] With the known methods for observing and quantitatively evaluating methane release in connection with laboratory-scale methane fermentation experiments, it is not yet possible to obtain precise statements about the methane release processes over a selected experimental period without sophisticated gas volume measurement technology and without direct access to qualified gas analysis technology. Object of the invention

[0012] The object of the invention is to overcome the shortcomings of the known prior art. In particular, the development of a technical solution for the reliable quality determination of small gas samples in the range of a few ml, such as those that can be regularly taken from conventional laboratory fermenters, is required without having to interrupt the undisturbed methane fermentation. Description of the invention

[0013] The invention is disclosed by claim 1, special embodiments of the invention are described in the dependent claims.

[0014] The inventive objective can then be achieved if the selected mesophilic or thermophilic environment in a laboratory fermenter can be maintained by placing it in a climate chamber or a temperature-controlled water bath. Further requirements then consist only of the availability of a laboratory balance for determining the mass loss between two successive observation points. Furthermore, the laboratory fermenter should be equipped with a cover, for example, a flexible closure, that allows a gas sample to be taken from the gas chamber of the laboratory fermenter using an injection needle. Finally, a standard portable gas detector is required, as is essential for ensuring personal safety in technical plants for methane fermentation. Character description Fig. Figure 1 shows the schematic interaction of the elements of an arrangement for the laboratory evaluation of methane release processes according to the invention. Examples of implementation

[0015] The invention will be explained in more detail with examples of its embodiment. Example 1:

[0016] Example 1 shows the sequence of steps for conducting experiments to determine methane release during methane fermentation of biogenic samples according to the Fig. 1 shown. a) Provision of biofiltrate as inoculum 2 from an active plant for the methane fermentation of predominantly crude fiber-rich input materials; In such biosubstrates, the methanogens required for the metabolism of the lignocellulosic crude fiber components and also, in small quantities, methanogens with significantly shorter generation times for the utilization of crude fat, crude protein and simple hydrocarbons may be expected. b) Determination of the amount of organic dry matter contained in the respective subset of inoculum 2; c) Taking two subsets for the fermentation experiments; d) Provision of an initial subset for batch fermentation in a climate chamber with mesophilic environmental conditions at 40°C; e) Addition of the biogenic material sample 1 to be evaluated at a concentration of 3.5 g oTS per liter of the available second subset of the inoculum 2 for batch fermentation in a climate chamber with mesophilic environmental conditions at 40 °C; f) Daily parallel removal of the unstirred laboratory fermenters 4 from the climate chamber, accepting the resulting thermal shock effects on the active methanogens and determining the mass losses to an accuracy of 0.01 g; g) Daily extraction of gas samples 5 from the laboratory fermenters 4 in the amount of 1 to 2 ml and determination of the proportion of methane in the sum of the contents of methane and carbon dioxide attributable to the gas sample; h) Calculation of the gas density of the released gas volume attributable to the day of the experiment; i) Calculation of the volume of methane released from both laboratory fermenters 4; j) Determination of the difference in methane volume from laboratory fermenter 4 with the cocktail of inoculum 2 and material sample 1 and laboratory fermenter 4 with inoculum 2; k) Determination of the volume difference of the released methane and its allocation to the amount of organic dry matter added to the cocktail of the material sample to be evaluated 1 in 1 CH4 / g oTS; l) Summing of the daily determined specific methane yields; m) Recording of the curves of the accumulated methane yields and the daily determined methane content in the released process gas over at least 50 treatment days; n) Determination of the specific methane yields attributable to the biogenic material sample 1 used up to the 25th day of treatment and use of this value for the dimensioning of the technical system. Example 2:

[0017] Example 2 refers to the explanation of the procedure for obtaining sufficiently accurate data for determining the density of the gas sample 5 taken from the individual laboratory fermenter 4.

[0018] For this purpose, the flexible cover of the laboratory fermenter 4 is pierced with the injection needle and an indeterminate volume of process gas between 1 and 2 ml is taken from the gas space of the laboratory femmeter 4.

[0019] The gas circuit 6, which is open at the gas outlet of the continuously active mobile gas warning device 7 during this procedure, is purged with drawn-in ambient air 8.

[0020] The gas circuit 6 is then closed. Now, the extracted gas sample 5 is inserted into the gas circuit 6 via an injection point in front of a moisture and dirt filter.

[0021] The mobile gas warning device 7 must have at least sensors for the determination of methane and carbon dioxide, each in the form of values ​​in vol%.

[0022] The information on the potentially measurable concentrations of the trace gases ammonia, hydrogen, carbon monoxide and hydrogen sulfide carried with gas sample 5 is unnecessary for the required density determination of the gas sample.

[0023] Taking into account the carbon dioxide content of the atmosphere, which has increased to 0.04 vol% in the last 25 years, the volume of the injected gas sample 5 is determined as the sum of the measured methane content and the measured value for carbon dioxide reduced by 0.04 vol%.

[0024] The gas quality is then determined by the proportion of the methane content to the previously determined total.

[0025] The proportion of carbon dioxide in the injected gas sample 5 is determined with sufficient accuracy by subtracting the methane content from the calculated total. Using the known gas densities, the previously determined mass of released gas can now be recorded as the gas volume with the gas quality indicated by the methane content. Reference symbol list 1 material sample 2 inoculum 3 Mixture (fermentation substrate) 4 laboratory fermenters 5 Gas test 6 Gas cycle 7 Mobile gas detector 8 Ambient air 9 Fermentation residue

Claims

[1] Method for the simplified determination of the course of methane release from biomass samples during methane fermentation in a laboratory batch test by using a pretreated sample of biogenic material in a germ-containing inoculum, introducing the test mixture into a mesophilic or thermophilic environment, determining the released gas volume and determining the methane content in the released fermentation gas, characterized by , that the biogenic material sample (1) is pretreated by biotechnological means, that parts of the fermentation residue (9) of an active methane fermentation plant for biogenic material with a similar composition to the material sample to be assessed are used as inoculum (2), that the mixture (3) of the biogenic material sample to be evaluated and the selected inoculum is filled into a laboratory fermenter (4) for batch methane fermentation, that the selected anaerobic mesophilic or thermophilic environment is maintained in the laboratory fermenter (4) for the entire duration of the test, that the total mass of the filled laboratory vessel (4) is determined at regular intervals, that a gas sample is taken from the laboratory vessel (4) and analysed before or after determining the current total mass, [2] Method according to claim 1, characterized by that the biogenic material sample (1) to be assessed is continuously circulated as bulk material at temperatures between 20 and 70 °C for a period of between 5 and 15 minutes in an oxygen-containing atmosphere. [3] Method according to one of claims 1 and 2, characterized by that the material sample to be assessed (1) is pre-hydrolysed aerobically in suspended form with the inoculum by introducing fine bubbles of air or technical oxygen for a period of between 15 and 60 minutes. [4] Method according to one of claims 1 to 3, characterized by that in the selected inoculum (2) a dry matter content of 5 to 18 mass%, preferably between 8 and 12 mass%, is set. [5] Method according to claims 1 to 4, characterized by that the material sample (1) is fed to the laboratory fermenter (4) in a quantity ratio of between 2.0 and 5.0 g, preferably between 2.8 and 3.5 g of the organic dry matter contained in the material sample (1) per liter of the suspension volume contained in the laboratory fermenter (4). [6] Method according to claims 1 to 5, characterized by that a conventional fermentation tube with mineral oil as a barrier liquid is used for the gas removal from the laboratory fermenter (4). [7] Method according to claims 1 to 6, characterized by , that to determine the gas quality, a gas sample (5) of between 1 and 5 ml is taken from the laboratory fermenter (4), that the methane content is determined in the gas sample taken (5), that the density of the gas sample taken (5) is calculated from the determined methane content, that the volume of methane released between the last observation points is determined from the determined mass loss and the calculated density of the extracted gas, that the specific methane yield related to the organic dry matter of the biogenic material sample used (1) is calculated from the determined methane volume, that in addition to the cumulative methane yields plotted over the observation points, the course of the methane content in the released fermentation gas is also recorded, that the taken gas sample (5) is introduced into a gas circuit (6) filled with 20 to 50 ml of ambient air, that at least the volume fractions of methane and carbon dioxide of the mixture of ambient air and the gas sample (5) in the gas circuit (6) are measured, that a conventional mobile gas warning device (7) for monitoring the lower explosion limit for methane is used to measure the methane and carbon dioxide contents in the gas circuit (6). [8] Method according to claim 7, characterized by that the volume of the gas circuit (6) can be varied so that the volume of methane injected into the gas circuit (6) is preferably measured at a concentration between 3 and 4% of the volume of the gas circuit (6). [9] Method according to claim 7, characterized by . that the gas circuit (6) is opened after each measurement and flushed with ambient air (8).

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