In daily operation, anaerobic reactors are one of the most important equipment in sewage systems. But do you understand the operating principle of anaerobic reactors? In fact, anaerobic reactions can be divided into four stages, namely hydrolysis, acidification, hydrogen production, acetic acid production, and methane production.

1. Hydrolysis stage

Purpose: Conversion of high molecular weight organic compounds into small molecular weight organic compounds

Because the molecular weight of high molecular weight organic compounds is relatively large and cannot penetrate cell membranes, they cannot be directly utilized by bacteria. Therefore, in the first stage, they are broken down into small molecules by bacterial extracellular enzymes. For example, cellulose is hydrolyzed by cellulase into disaccharides and glucose, starch is broken down by amylase into maltose and glucose, and protein is hydrolyzed by protease into short peptides and amino acids. The hydrolysis products of these small molecules can dissolve in water and be utilized by bacteria through the cell membrane.

2. Acidification stage

Objective: To convert the small molecule organic compounds generated in the previous stage into volatile acids

At this stage, the small molecule compounds mentioned above are transformed into simpler compounds within the cells of fermenting bacteria (i.e. acidifying bacteria) and secreted outside the cells. The main products of this stage include volatile fatty acids (VFA), alcohols, lactic acid, carbon dioxide, hydrogen, ammonia, hydrogen sulfide, etc. At the same time, acidifying bacteria also utilize some substances to synthesize new cellular substances. Therefore, insufficiently acidified wastewater will produce more residual sludge during anaerobic treatment.

3. Hydrogen production and acetic acid production stage

Objective: The products of acid producing bacteria are converted into acetic acid, hydrogen, and carbon dioxide by acetic acid bacteria.

At this stage, the products from the previous stage are further converted into acetic acid, hydrogen, carbonic acid, and new cellular substances.

The main reactions are as follows:

4. Methane production stage

Methanogenic bacteria can be divided into two populations: acetolytic bacteria and hydrogenotrophic bacteria.

During this stage, acetic acid, hydrogen, carbonic acid, formic acid, and methanol are converted into methane, carbon dioxide, and new cellular substances.

The main reactions are as follows:

The above are the four basic stages of anaerobic reactions. Wastewater undergoes different reactions at each stage, ultimately achieving the goal of removing COD and producing biogas. During the operation of the anaerobic reactor, webmasters can gain a deeper understanding of the pH value and the control role of VFA in these four different reaction stages. By mastering the basic principles, they can better control and operate the anaerobic reactor.

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