A 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

1-18. (canceled)

19. A method for treating substrates for biogas production in anaerobic digesters, which comprises treating a substrate with an efficient amount of one or more proteolytic enzymes alone or in combination with at least one carbohydrase, wherein at least one of the one or more proteolytic enzymes has at least 60% amino acid identity to SEQ ID NO: 1 or to SEQ ID NO: 2; or to a 51 serine protease derived from Nocardiopsis dassonvillei subsp. dassonvillei, Nocardiopsis prasina, Nocardiopsis prasina (previously alba), Nocardiopsis sp., Nocardiopsis alkaliphila or Nocardiopsis lucentensis.

20. The method of claim 19, wherein the S1 serine protease is selected from the group consisting of proteases derived from Nocardiopsis dassonvillei subsp. dassonvillei DSM 43235, Nocardiopsis prasina DSM 15649, Nocardiopsis prasina DSM 14010, Nocardiopsis sp. DSM 16424, Nocardiopsis alkaliphila DSM 44657 or Nocardiopsis lucentensis DSM 44048.

21. The method of claim 19, wherein at least one of the one or more proteolytic enzymes is thermostable.

22. The method of claim 19, wherein at least one of the one or more proteolytic enzymes is acid stable.

23. The method of claim 19, wherein the substrate is a plant material.

24. The method of claim 23, 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.

25. The method of claim 19, wherein the substrate comprises liquid manure, agricultural byproducts or organic waste.

26. The method of claim 19, wherein the proteolytic enzyme is derived from Nocardiopsis dassonvillei subsp. dassonvillei DSM 43235, or has the amino acid sequence of SEQ ID NO: 1 or SEQ ID NO: 2.

27. The method of claim 19, wherein at least one carbohydrase is an amylase or a cellulase.

28. The method of claim 19, wherein at least one carbohydrase is a beta-glucanase or a xylanase.

29. The method of claim 19, wherein at least one carbohydrase is added and the at least one carbohydrase is selected from the group consisting of amylases, beta-glucanases, pectinases, xylanases, xyloglucanases, and combinations thereof.

30. The method of claim 29, wherein at least one carbohydrase is added in an amount of 0.1-500 mg enzyme protein/kg substrate.

31. The method of claim 19, wherein each of the one or more proteolytic enzymes is added in an amount corresponding to 0.1-500 mg enzyme protein/kg substrate.

32. The method of claim 19, wherein the reactor temperature is above 20 C. and below 70 C.

33. The method of claim 19, wherein the pH of the biogas fermenter is above 4.5 and below 9.0.

34. The method of claim 19, wherein the pH of the biogas fermenter is between 6.7 and 7.5.

35. The method of claim 19, wherein one or more proteolytic enzymes alone or in combination with at least one carbohydrase are added before, after or simultaneously with the substrate to the fermenter.

36. A method for producing biogas in anaerobic digester, wherein the substrate is treated using a method of claim 19.

37. The method of claim 36, wherein the amount of biogas produced per kg substrate is larger in comparison with a similar process without the enzyme treatment of the substrate.

Description

LEGEND OF THE FIGURES

[0146] FIG. 1: Degradation of corn silage in batch fermentations.

[0147] 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.

[0148] FIG. 2: Degradation of corn and sorghum silage in batch fermentations.

[0149] The influence of the combined carbohydrase and protease preparation on the degradation of a recalcitrant substrate is shown.

[0150] FIG. 3: Degradation of corn silage in batch fermentation.

[0151] 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.

[0152] FIG. 4: Increase of biogas yields caused by different proteases

[0153] It was shown that two of the protease preparations led to an increased biogas yield.

[0154] FIG. 5: The methane yield in the four reactors can be seen.

[0155] 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.