Method for improving substrate degradation in agricultural biogas plants

Abstract

The invention relates to the use of at least one bacterial amylase and/or bacterial or fungal cellulase in combination with one or more protease(s) in substrates for anaerobic digestion processes for biogas production for improving degradation of maize, maize silages and/or other biogas substrates, in particular for improving gas yield, velocity and substrate conversion rate.

Claims

1. A method for treating a substrate for biogas production in an anaerobic digester, which comprises treating the substrate with an efficient amount of a protease, wherein the protease has at least 85% amino acid identity to SEQ ID NO: 1 or to SEQ ID NO: 2.

2. The method of claim 1, wherein the protease is an S1 serine protease.

3. The method of claim 2, wherein S1 serine protease is a Nocardiopsis S1 serine protease.

4. The method of claim 3, wherein the S1 serine protease is a Nocardiopsis alkaliphile, Nocardiopsis dassonvillei, Nocardiopsis lucentensis, or Nocardiopsis prasina S1serine protease.

5. The method of claim 4, wherein the S1 serine protease is obtained from Nocardiopsis alkaliphila DSM 44657, Nocardiopsis dassonvillei subsp. dassonvillei DSM 43235, Nocardiopsis lucentensis DSM 44048, Nocardiopsis prasina DSM 15649, Nocardiopsis prasinaDSM 14010, or Nocardiopsis sp. DSM 16424.

6. The method of claim 1, wherein the protease has at least 90% amino acid identity to SEQ ID NO: 1 or to SEQ ID NO: 2.

7. The method of claim 1, wherein the protease has at least 95% amino acid identity to SEQ ID NO: 1 or to SEQ ID NO: 2.

8. The method of claim 1, wherein the protease has the amino acid sequence of SEQ ID NO: 1 or SEQ ID NO: 2.

9. The method of claim 1, wherein the protease is thermostable.

10. The method of claim 1, wherein the protease is acid stable.

11. The method of claim 1, wherein the substrate is a plant material.

12. The method of claim 11, wherein the plant material is selected from the group consisting of maize, maize silage, corn silage, grass silage, triticale silage and other whole plant silage.

13. The method of claim 1, wherein the substrate comprises liquid manure, agricultural byproducts or organic waste.

14. The method of claim 1, further comprising treating the substrate with a carbohydrase.

15. The method of claim 14, wherein the carbohydrase is selected from the group consisting of amylases, cellulases, beta-glucanases, pectinases, xylanases, xyloglucanases, and combinations thereof.

16. The method of claim 14, wherein the carbohydrase is added in an amount of 0.1-500 mg enzyme protein/kg substrate.

17. The method of claim 1, wherein the protease is added in an amount of 0.1-500 mg enzyme protein/kg substrate.

18. The method of claim 1, wherein the treatment is at a temperature above 20 C. and below 70 C.

19. The method of claim 1, wherein the treatment is at a pH above 4.5 and below 9.0.

20. A method for producing biogas in an anaerobic digester, wherein the substrate is treated using a method of claim 1.

Description

LEGEND OF THE FIGURES

(1) FIG. 1: Degradation of corn silage in batch fermentations.

(2) The observed effect is attributed to the enzyme preparation only. A partial effect of the enzymes' stabilizing agent can be excluded as the negative control, for which enzyme stabilizer was used, did not influence the gas yield.

(3) FIG. 2: Degradation of corn and sorghum silage in batch fermentations.

(4) The influence of the combined carbohydrase and protease preparation on the degradation of a recalcitrant substrate is shown.

(5) FIG. 3: Degradation of corn silage in batch fermentation.

(6) The influence of the preparation with combined lead activities is shown. In order to illustrate the positive effects, carbohydrase:protease ratios ranging from 1:1 to 20:1 were tested.

(7) FIG. 4: Increase of biogas yields caused by different proteases

(8) It was shown that two of the protease preparations led to an increased biogas yield.

(9) FIG. 5: The methane yield in the four reactors can be seen.

(10) Accumulated methane production as a function of accumulated fed ODM, where the slope of the linear regression gives the methane yield. N1 is reference reactor, N21% protease added weekly based on total DM in the reactor, N31% protease added daily based on DM of substrate fed to a reactor, N45% protease added daily based on DM of substrate fed to a reactor.