The anaerobic production of biogas from complex organic matter is a multi-step biological process. Understanding the correct sequence of these steps is crucial.

Biogas Production Steps Sequence

The process involves four distinct microbial stages:

• Hydrolysis: This initial step breaks down large, complex organic polymers (like carbohydrates, fats, and proteins) into smaller, soluble monomers (sugars, amino acids, fatty acids). Microbes secrete extracellular enzymes to achieve this breakdown.
• Acidogenesis: The soluble monomers produced during hydrolysis are then fermented by acidogenic bacteria. They convert these monomers into volatile fatty acids (VFAs) such as acetic acid, propionic acid, and butyric acid, along with ammonia, hydrogen sulfide, and carbon dioxide.
• Acetogenesis: In this stage, acetogenic bacteria further process the intermediate products from acidogenesis. They convert VFAs and other compounds into acetic acid, hydrogen gas ($H_2$), and carbon dioxide ($CO_2$).
• Methanogenesis: This final step is carried out by methanogenic archaea. They utilize the acetic acid, hydrogen, and carbon dioxide produced in the previous stages to generate methane ($CH_4$) and more carbon dioxide. This mixture of gases is the biogas.

Therefore, the correct sequence is Hydrolysis $\to$ Acidogenesis $\to$ Acetogenesis $\to$ Methanogenesis.

Final Answer Selection

Based on the established sequence of anaerobic digestion:

The correct sequence is: