Mechanistic model for the reclamation of industrial wastewaters using algal-bacterial photobioreactors.

A mechanistic model describing the steady-state biodegradation of inhibitory pollutants by algal-bacterial consortia in enclosed chemostat photobioreactors was developed. The modelwasthenvalidated againstexperimentaldataonsalicylate removal by a Chlorella Sorokiniana/Ralstonia basilensis consortium cultivated without external O2 supplied in an enclosed chemostat photobioreactor under various conditions of photon flux radiation, salicylate inlet concentrations, temperatures, and hydraulic retention times (HRT). A satisfactory fit of experimental data was achieved in both the fitting and validation data sets (11% of average relative error). The model was thus capable of describing satisfactorily the influence of the HRT and the combined increase of light input and temperature on salicylate removal efficiency (RE). The potential inhibitory effect of salicylate was considered into the model structure based on the influence of salicylate concentration on microalgae photosynthetic activity. Only four adjustable parameters were necessary when using this modeling approach, which significantly reduces the number of experimental kinetic and stoichiometric coefficients needed for process description. Variables such as reactor geometry and light absorption characteristics of the biomass were grouped into a single parameter, which highly simplifies photobioreactor modeling. Being based on stoichiometric, thermodynamic, and mass balances analysis, this model can be extended to the removal of any organic pollutant in industrial wastewaters and to any photobioreactor configuration. It therefore provides an important tool to assess the feasibility of pollutant biodegradation under full photosynthetic oxygenation (i.e., no external O2 supply) and to optimize photobioreactors by establishing the conditions under which complete pollutant removal can be achieved. The model herein developed also provides a tool to better understand the complex relationships between microalgae, bacteria, light, and pollutant concentration, which will promote the development of algal-bacterial processes as a cost-effective alternative for wastewater reclamation and algae production from wastewater.