Tracer test and hydraulics modeling of a large WWTP

Tracer tests with rhodamine WT were performed at the biggest wastewater treatment plant of Mexico (‘Dulces Nombres’ WWTP, 5 m³/s). The aim was to develop the hydraulics sub-model to represent the aeration tanks, in the context of a project for calibrating the activated sludge model N°1 (ASM1). The planning of the experiment was performed by pre-simulation in AQUASIM, which allowed determining the quantities of dye (8 L per reactor) and sampling schedule that were required. After the tests, the rhodamine concentration profiles of the outlet mixed liquors were fit with different alternative of tank mixing models. Simulating the tracer data allowed to estimate the unknown influent flows, as well as determine the best hydraulics model: 4 completely stirred tank reactors retro-connected through the RAS (return activated sludge).