Microalgae-bacteria systems for surfactant and pathogen removal: assessing potentials and prospects for domestic sewage treatment

Abstract

The application of microalgae–bacteria systems for domestic wastewater treatment represents a promising strategy to simultaneously achieve pollutant removal and biomass production, aligning with the principles of the circular economy and nature-based solutions. However, consolidating this technology at full scale depends on understanding and optimizing operational parameters that ensure stable and predictable performance. The choice of anionic surfactants and pathogens as model contaminants is justified by their environmental and sanitary relevance. Thus, evaluating the removal of these pollutants allows assessing the robustness of the technology when addressing real sanitation challenges. In this thesis, critical variables were investigated, including feeding and mixing regime, hydraulic retention time, pH and carbon supplementation, in High Rate Algal Ponds (HRAPs) operated under tropical conditions. Additionally, different cultivation conditions were assessed; presence and absence of light; pH adjustment; CO2 supplementation; addition of an organic carbon source; combined anoxic–aerobic systems; and atmospheric aeration, as well as the mechanisms involved in the removal of surfactants and pathogens. The results showed that the combination of microalgae and bacteria achieved the highest efficiencies in anionic surfactant removal, reaching up to 97% under conditions with atmospheric aeration, controlled pH, and CO2 supplementation. Semi-continuous feeding regimes promoted higher biomass productivity and total suspended solids concentrations, whereas continuous regimes favored system stability and nutrient removal, albeit with lower Escherichia coli inactivation. Intermittent mixing in HRAPs maintained high surfactant and pathogen removal efficiencies, reduced energy demand, and did not compromise biomass quality. These findings reinforce the importance of integrated operational adjustments to improve the efficiency and sustainability of HRAPs, providing guidance for their design and large-scale application in tropical settings.