Nutrient removal performance within the biological treatment of the Marrakech wastewater treatment plant and characterization of the aeration and non-aeration process

The strategy for controlling and monitoring aerobic/anoxia cycles at the level of the 4 biological treatment basins of the wastewater treatment plant of Marrakech is mainly based on the measurements provided by the dissolved oxygen (DO) and redox potential (oxidation–reduction potential) sensors (ORP). In this work, the comparison of the ammonium (NH4+) of the 24 h balance with the daily average values of DO and ORP for each basin showed that when the oxygen concentration is low, the NH4+ concentration is high. The maximum NH4+ value of around 10.3 mg N/L is obtained on the day when the DO concentration is almost zero at the level of one of the 4 basins, which is basin B1. Moreover, knowing that the influent flow is unstable, the punctual monitoring of these parameters at the exit of each basin showed that during the mornings the punctual concentrations of NH4+ are generally low in comparison to NO3– concentrations which are high and the measurements of DO and ORP which correspond are important. Conversely, the results obtained during afternoons with high values of NH4+ correspond to low values of DO, ORP and NO3–. This shows that the need for oxygen also fluctuates during the day. In real-time control, the use of key parameters obtained from temporary readings of the DO and ORP profiles provide valuable information on the biological nitrification–denitrification process: The DO breakpoint indicates the disappearance of NH4+ during the aerobic phase (end of nitrification), called DO elbow are break points on ORP profiles; the ORP knee on the ORP profile signifies the control point where the nitrate has been effectively reduced during the non-aeration cycle (the nitrate knee), The oxygen-uptake rate which can reflect the activity of micro-organisms… In this work, given the large amount of information provided by the system, these key parameters are used to accurately interpret some aeration/non-aeration cycles within the four basins.