Improved BOD Modelling Using the FOLD Approach for Wastewater Treatment Design

ABSTRACT Accurate modelling of biochemical oxygen demand (BOD) is critical for wastewater treatment system design. This study aims to compare the classical first‐order model with the fractional‐order logistic decay (FOLD) model in predicting BOD kinetics. The models were applied to two types of experimental datasets: respirometric and dilution. Parameters were estimated using nonlinear least squares and integrated into design equations for activated sludge and aerated lagoon systems to compute retention time, reactor volume and blower horsepower. The FOLD model consistently produced higher design estimates and superior statistical fit ( R 2 , RMSE, AIC and BIC), especially with respirometric data. Paired t ‐tests showed statistically significant differences ( p < 0.05) across all design parameters based on respirometric input, whereas dilution data showed less significant variation. The FOLD model more effectively captures complex BOD decay dynamics and is recommended for use in designs utilizing high‐resolution, time‐series BOD data.