Comparative Analysis of Livestock Wastewater Reuse Under Summer and Winter Conditions at a Scale-Down Microalgae Culture

Microalgae-based wastewater treatment systems are an environmentally friendly technology for reuse of polluted water produced in livestock farming. Since pollution removal depends on light availability, the performance should be evaluated under different seasonal conditions, even in reduced lab scale systems. This study evaluates the treatment of livestock digestate in an experimental High-Rate Algae Pond (HRAP) that recreates outdoor conditions. Chemical and biological pollution removal were analyzed, as well as the response of photosynthetic activity of the culture. Pollutant removal varied between seasons, while summer was characterized by higher nitrogen and phosphorus removal (81 and 69%, respectively), on the other hand, winter presented higher elimination of organic matter (91%) and pathogens. In this sense, P. aeruginosa removal was notably higher in winter (100%) than in summer (50%). Higher light penetration and increased photosynthetic efficiency in winter, along with greater fluctuations in pH and dissolved oxygen concentrations, contributed to higher levels of pathogen decay. Photosynthetic response tests indicated higher oxygen production per unit biomass in winter, suggesting physiological adaptations to lesser light conditions. This adaptation was correlated with the relative high pH and dissolved oxygen values registered. The findings highlight the adaptation and robustness of algae cultures as a solution for wastewater treatment and reuse in the primary sector.