Phycoremediation: assessment of the efficiency in removing organic compounds and nutrients commonly found in domestic effluents

Phycoremediation is emerging as a promising alternative for treating effluents, receiving significant attention in recent years. The microalgae’s ability to efficiently remove contaminants from wastewater and survive in adverse conditions makes them excellent candidates for tertiary wastewater treatment. The main objective was to evaluate three species in monocultures of photosynthetic microalgae (Chlorella vulgaris, Desmodesmus subspicatus, and Raphidocelis subcapitata) in relation to the removal of organic compounds and nutrients generally present in domestic effluents. The effluent utilized was characterized by a chemical oxygen demand (COD) of 600 mg·L-1, total nitrogen concentration of 24 mg·L-1, and phosphate concentration of 10 mg·L-1, prepared in mineral water and evaluated at two distinct microalgal densities (105 and 107 algae·mL-1). After 96 hours, the species showed an increase in dry biomass production, with an increase of 17.3 and 11.4 times in the initial densities of 105 algae·mL-1 and 107 algae·mL-1, respectively. Controls using mineral water, which provided essential minerals for microalgal growth, and culture medium demonstrated biomass production increases of 2-fold and 8.7-fold, respectively. The reduction in COD was directly related to algae density, with greater reductions observed in bioassays with 107 algae mL-1. However, the COD reduction exceeded 78% in all bioassays. The highest nitrogen removal (80%) was recorded in the bioassay with C. vulgaris (107 algae mL-1), while D. subspicatus demonstrated higher phosphate removal (34%). On average, nitrogen and phosphate removal across all bioassays reached 68% and 21%, respectively. These results highlight the potential of microalgae as a polishing step in decentralized wastewater treatment systems.