Anaerobic Digestion Stages
The anaerobic digestion process and production of methane is divided into stages. Three stages often are used to illustrate the sequence of microbial events that occur during the digestion process and the production of methane (Figure). These stages are hydrolysis, acid forming, and methanogenesis. The anaerobic digestion process proceeds efficiently if the degradation rates of all three stages are equal. If the first stage is inhibited, then the substrates for the second and third stages will be limited and methane production decreases. If the
third stage is inhibited, the acids produced in the second stage accumulate. The inhibition of the third stage occurs because of an increase in acids and, consequently, loss of alkalinity and decrease in pH. The most common upsets of anaerobic digesters occur because of inhibition of methane-forming bacteria—the third stage. The anaerobic digestion process contains different groups of bacteria. These groups work in sequence, with the products of one group serving as the substrates of another group. Therefore, each group is linked to other groups in chainlike fashion, with the weakest links being acetate production and methane production.
STAGE 1—HYDROLYSIS STAGE
STAGE 2—ACID-FORMING STAGE
STAGE 3—METHANOGENESIS STAGE
The anaerobic digestion process and production of methane is divided into stages. Three stages often are used to illustrate the sequence of microbial events that occur during the digestion process and the production of methane (Figure). These stages are hydrolysis, acid forming, and methanogenesis. The anaerobic digestion process proceeds efficiently if the degradation rates of all three stages are equal. If the first stage is inhibited, then the substrates for the second and third stages will be limited and methane production decreases. If the
third stage is inhibited, the acids produced in the second stage accumulate. The inhibition of the third stage occurs because of an increase in acids and, consequently, loss of alkalinity and decrease in pH. The most common upsets of anaerobic digesters occur because of inhibition of methane-forming bacteria—the third stage. The anaerobic digestion process contains different groups of bacteria. These groups work in sequence, with the products of one group serving as the substrates of another group. Therefore, each group is linked to other groups in chainlike fashion, with the weakest links being acetate production and methane production.
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| Anaerobic Digestion Stages |
STAGE 2—ACID-FORMING STAGE
STAGE 3—METHANOGENESIS STAGE
