A coupled RTD and mixed-order kinetic model to predict high rate algal pond wastewater treatment under different operational conditions: Performance assessment and sizing application

Abstract

A coupled residence time distribution (RTD) and mixed-order model was developed to simulate the performance of a pilot high rate algal pond (HRAP) for wastewater treatment under different operational conditions requiring simple influent and effluent wastewater characteristics as input data. The model showed potential in general assessment of the HRAP system performance, successfully capturing the magnitude as well as general trend of COD, TKN, TN and TP concentrations with acceptable accuracy (Nash-Sutcliffe Efficiency (NSE) value up to 0.99). However, due to the common limitation of black box model type, the detailed agreement between model and experimental data was highly varied, sometime unsatisfactory performance (NSE < 0) was obtained, especially for highly complex processes like TKN or TN removal. Besides, general information on the dynamics of algal bacterial processes under different operational conditions could be revealed by analyzing calibrated reaction order n and reaction rate constant kn values with higher n value corresponding to higher complexity of the process and higher kn values associating with higher removal rate. Moreover, the model could also be used as a quick and convenient support for HRAP design and construction by providing estimated hydraulic retention time (HRT) values required for single HRAP system treating wastewater in different case studies. Further validation with outdoor HRAP system is necessary to increase the accuracy of the model prediction.