Progress in modeling of high-rate algal ponds

The objective of this paper is to present experimental methodologies developed in the field of process engineering facilitating the quantification of the main processes involved in high rate algal ponds (HRAPs). The model presented is based on the River Waters Quality Model No. 1. The hydrodynamic system is particularly simple and the reactor is modeled with a series of perfectly mixed recirculation reactors. For the calibration of the model, one must go through the study of the main axes of this model. The hydrodynamics of the reactor fitting Voncken’s model: circulation time (Tc), recirculation flow rate, water velocity (Vc), Peclet’s number, etc.), the gas–liquid transfer processes for oxygen but also for NH3, CO2 and the photosynthesis-related biochemical processes were monitored. The simulation is conducted in a HRAPs pilot plant using the WEST program. The oxygenation factor was optimized and set by a series of experimental data obtained on the pilot station located in Marrakech. The obtained result show a strong link between concentration of algae and dissolved oxygen concentrations with maximum levels reached after 500 h. The maximum concentration of algae and oxygen are in the order of 500 and 16 g m–3, respectively. This is one more element to judge the consistency of our model. Additionally, the simulation of heterotrophic biomass, algae biomass, nitrogen concentration, chemical oxygen demand removal efficiency and oxygen concentrations vs. time in the HRAPs with the classical cycles due to day/night conditions show that the influence of light is clearly marked on the oxygen and algae concentrations. The methodology adopted to characterize the gas transfer coefficient is suitable for piston reactors with recirculation.