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floc, asb, figure 1, Aerated Stabilization Basins, consumption, concentration, growth phase, amount of time, blue food, bod, bacterial cells, bacterial growth curve

Biological Growth Curve in Aerated Stabilization Basins

Bacteria are present throughout an aerated stabilization basin (ASB), though their form and concentration may differ in the different areas of the ASB. At the front end of the ASB, where the influent enters and there is the highest concentration of biochemical oxygen demand (BOD), bacterial concentrations are higher and bacteria are dispersed as they are busy consuming the BOD. At the back end of the system, where BOD is sparse, bacteria form floc and settle out. The bacterial growth curve, as seen in Figure 1, characterizes the different growth stages of bacteria in relation to the amount of food (BOD) available.

Bacterial growth curvebbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbFigure 1: The Bacterial Growth Curve

The growth rate of the bacteria in the ASB is directly proportional to the amount of BOD available. Figure 1 shows the growth rate of the bacteria over time. The blue curve represents the amount of BOD available for consumption. The red curve represents the amount of bacterial mass in the bulk water. There are four distinct phases of bacterial growth: lag phase, log phase, declining growth phase and endogenous respiration phase.

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floc, aeration, filamentous bacteria, abundance, heterotrophic organisms, Aerated Stabilization Basins, filament, activated sludge, aerator, filamentous organisms, aeration basin, effluent, carbon compounds, filaments

Filamentous Bacteria in Aerated Stabilization Basins Part 2

Concern or Curiosity?

Part 2 – Thiothrix and Type 021N

Mike Foster, Principal Consultant – Environmental Business Specialists, LLC
Paul Klopping, Principal Consultant – Callan & Brooks

ThiothrixIn part one of this series, we discussed the differences between activated sludge and aerated stabilization basins (ASBs) with regard to filamentous bacteria and filamentous bulking. We also talked about one of the most common filaments found in ASBs, Haliscomenobacter hydrossis. In this article, we will discuss three other filament species found in aerated stabilization basins – Type 021N, Thiothrix, Beggiatoa.

These three filaments all share a common metabolic trait – mixotrophy. These organisms can grow on a number of organic compounds heterotrophically, but also may gain energy for growth from the simultaneous oxidation of inorganic, reduced sulfur compounds (e. g. H2S). Thus the presence of reduced sulfur compounds in wastes being treated may give these filamentous organisms a growth advantage over other strictly heterotrophic organisms (i.e. floc formers). It should be noted that actual energy capture from sulfur oxidation has not been vigorously proven, as yet, and that true autotrophy does not occur, as organic carbon compounds are always required for growth.

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