The Streeter-Phelps (DO sag) equation models:
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Wastewater treatment plant efficiency only
DO deficit in a river over time after organic discharge — models deoxygenation and reaeration rates
Rainfall intensity-duration-frequency
Flocculation kinetics in treatment plant
Correct Answer
B. DO deficit in a river over time after organic discharge — models deoxygenation and reaeration rates
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Streeter-Phelps (1925): D = (kL_0/(k_r − k_d)) × (e^(−k_d·t) − e^(−k_r·t)) + D_0·e^(−k_r·t). Models dissolved oxygen deficit D(t) in a river after a point discharge. kd = deoxygenation rate, kr = reaeration rate. Critical (minimum) DO occurs at time tc = (1/(kr−kd))·ln[(kr/kd)·(1 − D0(kr−kd)/(kd·L0))]. Used for river assimilative capacity studies.
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