Lag Phase Of Growth

During lag phase of growth, bacteria are active but do not reproduce. The bacteria are synthesizing enzymes to degrade substrates in their new environment. The

Bacterial Population (MLVSS)

Increasing

Bacterial Population (MLVSS)

Increasing

Increasing

FIGURE 9.3 Bacterial growth curve, continuous culture or continuous reactor. In a continuous culture, substrates are provided continuously (e.g., an on-line aeration tank).

Increasing

MCRT (days)

FIGURE 9.3 Bacterial growth curve, continuous culture or continuous reactor. In a continuous culture, substrates are provided continuously (e.g., an on-line aeration tank).

degradation of substrates provides the carbon and energy needed for reproduction. Lag phase of growth occurs in biological treatment units during start-up and recovery from toxicity. Sudden shock loadings with substrates not previously contained in the wastewater can produce a short lag phase of growth for a few hours. This is due to the fact that bacteria do not have the appropriate enzymes synthesized to degrade the new substrates in the shock loading condition. If the bacteria have the ability to synthesize the enzymes when expose to the new substrates, the enzymes are produced (substrate-induced enzyme synthesis).

In addition to the synthesis of enzymes, bacteria are adjusting to their new environment in the biological treatment unit. For example, the biological treatment unit possesses different biological, chemical, and physical conditions than the environment (soil, water, or gastrointestinal tract of humans) where the bacteria previously had inhabited. The length of lag phase of growth is determined by (1) the conditions of the new environment and (2) the species of bacteria present. Bacteria in a minimal nutrient environment take longer to adjust than bacteria in a rich nutrient environment. Some bacteria adjust quickly in one hour, while other bacteria take several days to adjust.

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