Increase in Nutrient Concentrations in Reactor Effluent

Toxicity in the activated sludge process is one of several reasons for an unstable biomass that is responsible for increases in the quantities of ionized ammonia (NH4+) and orthophosphate (H2PO47HPO42-) in the filtrate of an aeration tank effluent (Table 19.16). Bacteria degrade BOD in order to obtain energy and carbon for cellular activity and growth (MLVSS). In order to maintain adequate cellular activity and growth, nitrogen and phosphorus in the form of ionized ammonia and orthophosphate, respectively, are removed from the bulk solution of the aeration tank during the degradation of BOD. However, during a toxic event in the aeration tank, decreased cellular activity occurs as a result of damage to bacterial enzyme systems.

Decreased enzymatic activity results in decreased degradation of BOD and decreased MLVSS production. With less MLVSS production occurring, decreased quantities of nutrients are removed from the bulk solution. Therefore, increased quantities of nutrients leave the aeration tank.The ionized ammonia and orthophosphate that are not used in the aeration tank can be found in the filtrate of the aeration tank effluent.

TABLE 19.16 Operational Conditions Responsible for Increased Concentrations of Ionized Ammonia and Orthophosphate in the Filtrate of an Aeration Tank

Nutrient

TABLE 19.16 Operational Conditions Responsible for Increased Concentrations of Ionized Ammonia and Orthophosphate in the Filtrate of an Aeration Tank

Nutrient

Operational Condition

Ionized Ammonia

Orthophosphate Ions

Decrease organic loading

X

X

Die-off of large numbers of bacteria (lack of

X

X

substrate or endogenous respiration)

Excess ionized ammonia in influent

X

Excess orthophosphorus in influent

X

Increased HRT (solubilization of nutrients)

X

X

Loss of nitrification

X

Toxicity

X

X

FIGURE 19.4 Toxic "attack" upon a bacterial cell. Depending upon the form of the toxic waste, toxicity "attacks" critical cellular structures and important cellular activities. Critical cellular structures attacked include the cell wall, cell membrane, fibrils, and genetic material. Important cellular activities attacked include enzymatic activity and the regulation of genetic materials.

FIGURE 19.4 Toxic "attack" upon a bacterial cell. Depending upon the form of the toxic waste, toxicity "attacks" critical cellular structures and important cellular activities. Critical cellular structures attacked include the cell wall, cell membrane, fibrils, and genetic material. Important cellular activities attacked include enzymatic activity and the regulation of genetic materials.

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