Impact of light intensity on purple phototrophic bacteria mixed cultures: experimental insights and biokinetic modelling

Developing kinetic models is crucial for understanding and optimizing purple phototrophic bacteria (PPB) growth in photobioreactors (PBR). Given the significant role of radiation transfer, integrating light into PPB kinetic models is fundamental for enhancing PBR design and operation. In this study, batch experiments were conducted under monochromatic light intensity conditions ranging from 10 to 60 W·m−2 to assess the influence of this parameter on a mixed PPB culture. An existing biokinetic model was adapted to incorporate the light dependence of PPB growth using a Monod-type light function, which included light attenuation based on experimentally measured mass extinction coefficients. Microbiological characterizations evidenced the selective pressure of light on the PPB mixed culture, and the developed model could effectively describe the population behavior. Estimated parameters were validated in a continuous PBR operated at 40 W·m−2, demonstrating the model ability to predict biomass growth and substrate consumption, and to support technological upscaling.