GERMAN DEMOCRATIC REPUBLIC                                               PATENT SPECIFICATION

 

[SEAL] (12) Economic Patent                                                               (19) DD (11) 245 861 A1

 

Granted pursuant to §17 subs. 1 of the Patent Act                                                                                         4(51) C 02 F 11/04

                                                                                                                                                                                             C 02 F 3/28

 

OFFICE FOR INVENTIONS AND PATENTS  

Published in the version submitted by the applicant

 

 

(21) WP C 02 F / 286 845 1 (22) February 6, 1986                           (44) May 2, 1987

 

 

(71)         Academy for the Agricultural Sciences of the GDR, Institute for Fertilization Research, 1500 Potsdam, Templiner Strasse 21, DD

 

(72)         Vollmer, Gerd-Rainer, Dr. rer. nat.; Franz, Johann, Dr. Agr. Grad. Agr.; Franzke, Gudrun, Grad. Chem., DD

 

 

(54)         Method for Producing Biogas from Liquid Swine Manure

 

 

(57) The invention relates to a method for generating biogas from liquid swine manure or waste products of similar composition. According to the known methods of anaerobic fermentation of liquid manure, sizeable fractions of the organic substance are not accessible to methane formation and/or are converted microbially into methane and carbon dioxide only at a low rate of decomposition. An increase in the conversion rate is possible by separating the biogas reactors into an acidiogenic and a methanogenic digestion tower and/or by operating two reactors for the two stages or by the transition to the thermophilic temperature range. However, thermophilic methods have not been used to date because of the lower net energy production and the instability of the process. The object of the invention is to increase the biogas yield per ton of employed organic substance with a simultaneous increase in the conversion rate. In this case it is not necessary to increase the construction costs in order to increase the biogas formation rate. This object is achieved by culturing additionally to the microorganism population, present in the biogas reactor, a bacterium that is able to make otherwise inaccessible component contents of the organic substance of the substrate accessible to a microbial utilization and, thus, to increase the energy production. The invention can be used in swine production plants as well as production plants with waste products of similar composition.

                                                                                                                                                                                                  3 pages

 

ISSN 0433-6461

 

Claims of the Invention:

 

1.         Method for producing biogas from liquid swine manure and from straw-containing materials and other lignocellulose containing wastes, characterized in that additionally to the microorganism population, present in the biogas reactor, a bacterium is cultured that is able to microbially decompose otherwise non-recyclable component contents of the organic substance of the substrate; that a fermentation temperature ranging from 29 deg. C to 40 deg. C, preferably 33 deg. C to 35 deg. C, is maintained; that the pH value ranges from 7.0 to 8.5; that the average treatment period ranges from 5 to 25 days, preferably 10 to 20 days.

 

2.         Method for producing biogas from liquid swine manure as well as straw-containing materials and other lignocellulose containing wastes, characterized in that the additional bacterium Ruminococcus flavefaciens is cultured from fresh bovine or ovine rumen content.

 

Applicable Field of the Invention

 

The invention relates to a method for producing biogas from liquid swine manure while simultaneously reducing undesired content materials.

The invention belongs in the field of technical microbiology and can be used in plants of industrial animal production as well as in plants, which accumulate liquid swine manure.

 

Characteristics of the Prior Art Technical Solutions

 

In addition to the known conventional one stage method for recycling liquid manure, in particular two stage methods as well as methods in the thermophilic temperature range have been developed for increasing the methane yield relative to a unit of reactor volume and relative to the employed quantity of organic material.

Whereas the thermophilic methods have not established themselves to date owing to the inadequate net energy production and the unstable process control, two stage methods have already had an impact on the practice. These two stage methods work on the principle of separating the acid stage from the methane stage. Thus, it is possible to achieve a significantly higher fermentability than with the known one stage methods.

In a fermenter, described in the DE 2 939 169, the methane generating reactor is additionally assigned an acid reactor, in which the waste water to be treated is subjected to pre-acidification before the actual methane generation. The acid reactor is filled periodically; the retention time is 3 days, during which it is necessary to raise the temperature. According to one method (DE 3 102 739), the acid and the methane ferment separately in that in the reactor chamber the acid phase and the methane phase are divided in the inverse ratio to the decomposition rates in the process stages - acid plus acetic acid formation / methane formation - preferably of about 1:10. The separation is realized in a round fermentation tank with a circular ring chamber.

In the method, described in the DE 2 621 524, the separation is coupled with a return of the acid formers for pre-digesting the organic substance. That is, there is a separating device between the acid reactor and the methane reactor. All of the invention specifications that claim a fermentation process having two stages or multi-stages run according to this basic principle of separating the acid and the alkaline fermentation either by means of two independent reactors or by splitting one reactor into two chambers.

(DE-OS 2821 796, US-PS 4022665, US-PS 4318993, US-PS 4040953, US-PS 4053395, US-PS 4067801, CH-PS 495302, GB-AS 2013170).

In this context these methods give volume ratios between the acid reactor and the methane reactor of 1:5 up to 1:10. Hence, these methods have the drawback that between 10% and 20% of the reactor volume cannot be utilized for the actual methane fermentation; and/or that additional reactors have to be built. The method (US-PS 4 401 565) attempts to reduce the costs for the pre-digestion by a vacuum treatment before or in the reactor.

In both the conventional one stage fermentation and in the two stage fermentation of liquid swine manure, this method cannot access sizeable quantities of the organic substance for the methane formation, because the mixed population of acid formers does not include any microorganisms that are able to digest the lignocellulose.

 

Object of the Invention

 

The object of the invention is to produce biogas from liquid swine manure or similar substrates at a biogas yield and biogas formation rate that is high in relation to the employed organic substance. Furthermore, the object is simultaneously to reduce the environmentally noxious content materials of the liquid manure.

 

Presentation of the Essence of the Invention

 

The object of the invention is to utilize maximally the organic content materials, present in the liquid swine manure, at a high biogas production rate for microbial methane generation.

The invention achieves this object by culturing additionally to the mixed population, present in the biogas reactor, a bacterium that is able to digest the content materials of the liquid swine manure that are otherwise inaccessible for the methane fermentation and, thus, to obtain them for the production of biogas. In this way a maximum microbial biogas synthesis with simultaneous maximum decomposition of the organic content materials of the liquid manure is achieved so that there is no need for a pre-digestion through separation into two stages.

Ruminococcus flavefaciens from ovine rumens is used as the bacterium and adapted to the liquid swine manure. This bacterium is able to digest the lignin enveloped cellulose in the solid materials of the liquid swine manure and, in so doing, is able to simultaneously multiply. In the solution to the problem of the invention, the Ruminococcus flavefaciens is cultured in the biogas reactor that ferments the liquid swine manure, a process that is possible only under stable process conditions (concentration of water vapor volatile carboxylic acids below 800 mg/l). In this case the reactor should not be charged with fresh liquid swine manure for 24 hours before and after the addition of the ovine rumens.

In the solution to the problem of the invention, already known elements of anaerobic fermentation technologies are modified and improved in such a way that a higher efficiency of the process is realized.

The fundamental idea of the invention is to achieve an increase in the specific biogas yield while simultaneously increasing the biogas formation rate without any additional construction costs and, thus, to realize in an acceptable way the object of the invention not only in principle, but also with respect to the material and energy budget and, hence, economically.

In the method, according to the invention, the utilization of the content materials of the liquid manure is carried out by means of a one stage fermentation. In this case the digestion of the component contents of the organic substance is supported by culturing an appropriate bacterium in the biogas reactor.

The fermentation process is characterized by

-           a temperature ranging from 29 deg. C to 40 deg. C, preferably 33 deg. C to 35 deg. C;

-           a pH value between 7.0 and 8.5;

-           an average retention time between 5 and 25 days, preferably 10 to 20 days;

-           a concentration of water vapor volatile carboxylic acids below 2 g/l, preferably below 1.5 g/l.

The significant advantages of the method over currently applied methods for generating biogas are:

-           increase in the biogas yield per ton of employed organic dry substance and, thus, an increase in the efficiency of the method;

-           increase in the biogas formation rate and, thus, a decrease in the retention time of the liquid manure in the biogas reactor (decrease in investments for the construction of reactors).

-           no additional construction costs for tanks for acidic fermentation.

 

Embodiment

 

The liquid swine manure, which is used within the scope of the example of the method, originates from an industrial swine breeding facility. The magnitude and the methods of the animal husbandry, including the applied feeding regime, necessitate a composition of the raw liquid manure that remains constant within certain limits. The liquid manure, delivered from the swine production facilities, can be characterized by the following material characteristic values: TS [total solids] 33.0 g/l, oTS [organic total solids] 24.6 g/l, CFS [fixed solids] 5.2 g/l, NK 2.7 g/l, NH4+ 1.53 g/l. Ruminococcus flavefaciens is cultured from fresh ovine rumens in the biogas reactor. The fermentation runs at a temperature of 33 deg. C, a pH value of 7.8 and a concentration of water vapor volatile carboxylic acids of 800 mg/l. For an average retention time of 20 days the fermenter sequence is characterized by the following material characteristic values: TS 20.5 g/l, oTS 13.0 g/l, CFS 0.8 gl/l, NK 2.7 g/l, NH4+ 2.2 g/l.

The specific biogas yield is 0.58 m3/kg of oTS [organic total solids]; the biogas formation rate is 0.7 m3/m3 x d [day]. The fermentation of the corresponding liquid manure, on which the Ruminococcus flavefaciens was not cultured, is 0.40 m3/kg of oTS [organic total solids]; the biogas formation rate is 0.55 m3/m3 x d [day]. The methane content in the biogas is 70%. The decomposition of BSBb [bis(hydroxybutyl) succinate] is over 90%.