Tratamento de águas residuárias via biotecnologia de microalgas: avaliação de diferentes estratégias de operação de lagoas de alta taxa para melhoria da produção e composição de biomassa

Abstract

Wastewater treatment is essential to ensure water quality and protect public health by promoting the removal of pollutants prior to discharge into the environment. However, conventional systems often exhibit high energy demand, significant operational costs, and limited nutrient recovery, which has driven the search for more sustainable alternatives based on resource recovery. In this context, microalgae have emerged as a promising strategy due to their ability to produce O2 via photosynthesis, capture CO2, and assimilate nutrients present in wastewater, thereby contributing to the development of more sustainable treatment systems and to the conversion of waste into value-added biomass. Given that treatment efficiency and the biochemical profile of microalgal biomass are strongly influenced by the operational strategy adopted, this study was structured into two complementary approaches, aiming to evaluate different configurations of high-rate algal ponds (HRAPs) and their impacts on effluent treatability and on the metabolic steering of the biomass. In the first part of the study, microalgae cultivation was evaluated in high-rate algal ponds (HRAPs) operated in two stages, aiming to assess pollutant removal efficiency and the production of biomass and bioactive compounds of interest. The system was operated in batch mode for 15 days, under nutrient-rich conditions favorable to microalgal growth in the first stage and stress conditions in the second stage. The genus Desmodesmus exhibited high abundance in both stages. During the first stage, higher productivities of total biomass (4.26 g m-2 d -1 ) and algal biomass (0.07 g m-2 d -1 ) were observed, along with high removal efficiencies of ammoniacal nitrogen [NH4 + (92%)], phosphate [PO4 3- (92%)], and nitrate [NO3 - (95%)]. In the second stage, lower nutrient removal efficiencies were observed; however, a high chemical oxygen demand (COD) removal of approximately 91% was achieved, along with greater lipid accumulation (68.8%) compared to the first stage (45.1%). In the second part of the study, microalgae cultivation in series was evaluated using four HRAPs arranged sequentially as a wastewater polishing system, with a hydraulic retention time (HRT) of 3 days in each HRAP. The highest productivities of total biomass (19.56 g m-2 d -1 ) and algal biomass (0.18 g m-2 d -1 ) were observed in HRAP 4, along with the highest contents of carbohydrates (11.7%), proteins (21.5%), and lipids (18.2%). The highest removals of NH4 + (73%), COD (47.8%), and PO4 3- (34.9%) occurred in HRAP 1, while the highest NO3 - removal was recorded in HRAP 4 (76%). Escherichia coli removal occurred progressively along the series, with average efficiencies of 90% in each HRAP and complete absence in the final effluent of HRAP 4. Collectively, the four HRAPs arranged in series enhanced wastewater treatability, microalgal growth, and the biochemical composition of the biomass. Overall, the results reinforce the potential of integrating high-rate algal ponds into wastewater treatment systems, demonstrating that the choice of operational strategy directly influences treatment efficiency, biomass productivity, and the metabolic allocation of microalgal biomass.