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Stages of anaerobic digestion

Anaerobic digestion occurs in several stages, each facilitated by different groups of microorganisms. These stages include hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Here’s a brief overview of each stage:



  1. Hydrolysis: Large organic molecules such as carbohydrates, fats, and proteins are broken down into smaller molecules by enzymes called hydrolytic bacteria. This stage prepares the complex organic matter for further degradation.
  2. Acidogenesis: The products of hydrolysis (simple sugars, amino acids, and fatty acids) are converted into volatile fatty acids (VFAs), ammonia, carbon dioxide, and hydrogen by acidogenic bacteria. This stage is characterized by the production of acids and other compounds as the organic matter continues to break down.
  3. Acetogenesis: In this stage, acetogenic bacteria further break down the VFAs produced in the acidogenesis stage into acetic acid, hydrogen, and carbon dioxide. Acetogenesis is an essential step before methane production can occur.
  4. Methanogenesis: Methanogenic archaea convert the acetic acid, hydrogen, and carbon dioxide produced in the previous stages into methane (CH4) and carbon dioxide (CO2). This stage is where the majority of biogas production occurs, with methane being the primary component of biogas.

These stages are interconnected and depend on the presence of specific groups of microorganisms to efficiently break down organic matter and produce biogas. The overall process is sensitive to environmental factors such as temperature, pH, and substrate composition, which can influence the efficiency of biogas production.

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