Incorporation of biofilm activity in river biodegradation modeling: a case study for linear alkylbenzene sulphonate (LAS)

A mathematical model was constructed which considers both biofilm and suspended biomass activity in relation to the biodegradation of individual chemicals in rivers. To calibrate this model for the surfactant LAS (linear alkylbenzene sulphonate), experimental data were obtained in a lab-scale artificial river system, which allowed to collect accurate and reproducible river biodegradation data next to the required river characteristics. Biofilm processes were shown to be by far the most significant removal mechanism of LAS in the considered system which had a high surface area to volume ratio. The biodegradation model could be fitted to the data using realistic parameter values. Subsequently, the model was corroborated by comparing its predictions to a field study in the Red Beck, a small Yorkshire river. Only easy to collect or default data were used as model parameters. The predicted LAS first-order removal rate coefficient (without any calibration using the field data) was 0.25 h−1, which is less than 20% slower than removal measured in the field.