Synergy between carbon sources and light in microalgal culture from the perspective of wastewater treatment in high rate algal ponds

Using solar light as an energy source in microalgae-based wastewater treatment is crucial for maintaining sustainability. To maintain treatment efficiency, microalgae need to exhibit resilience, especially during periods of reduced sunlight. Organic carbon, often abundant in wastewater, has been observed to enhance algal productivity and limit biomass loss under extreme light conditions. Microalgae have demonstrated the ability to adapt to different light levels, and carbon sources may play a significant role in this adaptation. However, microalgal growth modes can be influenced by various factors, including self-shading, affinity for organic carbon molecules, production of inorganic carbon through the oxidation of organic carbon, and nutrient consumption. Notwithstanding a lack of complete understanding regarding the synergy between carbon sources and light across diurnal cycles, further research in natural settings could still yield useful information regarding microalgal adaptation to dynamic solar conditions. This review concludes that a combination of laboratory-controlled studies, evaluating the relevance of different factors within the system, and outdoor, large scale operational high rate algal ponds (HRAPs) should be conducted to comprehensively investigate the complex mechanisms involved in HRAPs. This combined approach would contribute to optimizing the efficiency and sustainability of microalgae-based wastewater treatment processes.