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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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biochemical oxygen demand, aeration, asb, 30 minutes, effluents, concentration, effluent, Suspended Solids, bod, demand loading

Total Suspended Solids (TSS) & Volatile Suspended Solids (VSS)

TSS testing measures the total concentration of suspended (non-soluble) solids in the aeration stabilization basin (ASB) or in effluents. The total suspended solids (TSS) data is critical in determining the operational behavior of a waste treatment system. It is usually a permitted test and solids must be kept at a minimum.

In order to test the total suspended solids, a well-mixed sample should be filtered through a weighed standard glass-fiber filter. The residue left on the filter is dried to a constant weight at a temperature between 103 °C and 105 °C. The increase in the weight of the filter represents the total suspended solids of the sample. Large floating particles or submerged agglomerates of nonhomogeneous materials from the sample may be excluded in the total suspended solids measurements if it is determined that their inclusion is not representative of the entire sample. The size of sampling should also be limited to a size that yields no more than 200 mg residue.

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