Question

Which process occurs during the acidogenesis stage of anaerobic digestion?

• A. Hydrolysis of complex organic compounds
• B. Production of organic acids and volatile fatty acids
• C. Conversion of organic acids to methane and carbon dioxide
• D. Formation of methane gas by methanogens

Hint:

• Acidogenesis is the second stage in anaerobic digestion, following hydrolysis.
• During acidogenesis, bacteria ferment soluble organic compounds (sugars, amino acids) into:
  • Volatile Fatty Acids (VFAs) like acetic, propionic, butyric acid.
  • Alcohols.
  • CO$_2$ and H$_2$.
• The term "acidogenesis" itself refers to the generation of these acids.

Answer 1

The Correct Option is B

Anaerobic digestion involves several sequential biological stages: Option (A) Hydrolysis: Complex organic polymers (carbohydrates, proteins, lipids) are broken down by extracellular enzymes produced by hydrolytic bacteria into simpler, soluble monomers and oligomers (sugars, amino acids, fatty acids). Option (B) Acidogenesis (or Acid Formation): In this stage, acidogenic bacteria (fermentative bacteria) further metabolize the products of hydrolysis. They convert these simple organic molecules into a mixture of volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, and valeric acid. Other products can include alcohols (like ethanol), lactic acid, carbon dioxide (CO$_2$), and hydrogen gas (H$_2$). This is why it's called "acidogenesis" - acid generation. Option (C) Acetogenesis: Acetogenic bacteria convert the longer-chain VFAs (like propionic and butyric acid) and alcohols produced during acidogenesis into acetate, H$_2$, and CO$_2$. Acetate is a primary substrate for methanogens. Option (D) Methanogenesis: Methanogenic archaea convert acetate, and H$_2$/CO$_2$ (and other simple C1 compounds) into methane (CH$_4$) and CO$_2$. Option (a) describes the hydrolysis stage. Option (b) accurately describes the acidogenesis stage, where organic acids (VFAs) are produced. Option (c) describes parts of acetogenesis (conversion of some organic acids to acetate, H2, CO2) and methanogenesis (conversion of acetate to methane and CO2). Option (d) describes the methanogenesis stage. \[ \boxed{\text{Production of organic acids and volatile fatty acids}} \]