ANDIG2 – Questions

1. A digester goes “sour” when fermenting bacteria are producing more organic acids than methanogens can convert into methane, causing the pH of the slurry to drop. When the pH drops below 6.8, methanogens die off and methane production ceases.

a. True.

b. False

2. Anaerobic conditions occur:

a. When oxygen is present.

b. When specific fermenting bacteria are present in the slurry.

c. In the absence of oxygen.

d. When the slurry is at pH 4.0 or higher.

3. Fermenting bacteria and methanogens do not need to work together to produce biogas.

a. True

b. False

4. Methanogens need organic acids produced by fermenting bacteria to generate methane.

a. True

b. False

5. The primary conversion route of complex organic compounds to methane formation is: complex organics→acidic acid→ methane.

a. True

b. False

6. A feedstock is any organic material with biogas production potential.

a. True

b. False

7. Anaerobic digestion increases odors and pathogen levels.

a. True

b. False

8. Volatile solids are the portion of the total solids (i.e. organic matter) that can be converted to gas.

a. True

b. False

9. Once a digester is “sour”, the best option is to:

a. Inoculate the slurry with enzymes to jump start biogas production.

b. Empty the digester and start over with fresh feedstocks and new digestate.

c. Stop feeding the digester and stir the slurry for a day.

d. Infuse biogas into the slurry to feed the methanogens and restart biogas production.

10. Stabilization is:

a. A biological process that, over time, makes the slurry less odorous and reduces pathogens that pose a health risk.

b. Shoring up the walls of a digester so that they do not fall over.

c. A necessary step to maximize the production of biogas.

d. Both a and c.

ANSWERS