Preliminary Physicochemical Assessment of Aquaculture Effluents for Irrigation Reuse in the Brazilian Semi-Arid

Abstract Aquaculture effluents are increasingly recognized as a strategic resource for agricultural water reuse, especially in semi-arid regions, where water scarcity and fertilizer costs intensify pressure on production systems. Within a circular economy framework, these effluents may simultaneously supply water and nutrients; however, their physicochemical composition must be carefully assessed, since excessive salt loading may impair soil quality and threaten long-term agricultural sustainability. This study performed a preliminary physicochemical assessment of raw and diluted aquaculture effluents to determine their potential for irrigation reuse in the Brazilian semi-arid, with emphasis on salinity, sodicity, ionic composition, nutrient-related parameters, and trace elements. The experiment was conducted at the Federal Rural University of the Semi-Arid (UFERSA), Mossoró, northeastern Brazil, from October 2022 to December 2023. Five treatments were evaluated: T1 (100% freshwater), T2 (75% freshwater + 25% effluent), T3 (50% freshwater + 50% effluent), T4 (25% freshwater + 75% effluent), and T5 (100% effluent). Samples were analyzed for pH, electrical conductivity (EC), major ions, nutrients, and trace elements, while sodium adsorption ratio, magnesium hazard, residual sodium carbonate, and hardness were also determined. Dilution with freshwater partially improved irrigation suitability but increasing effluent proportion intensified hydrochemical restrictions. Although effluents supplied relevant amounts of Ca 2+ , Mg 2+ , N, and P, reuse potential was mainly limited by salinity, particularly EC and Cl − , whereas sodicity remained secondary. Multivariate analysis identified EC, Ca 2+ , Mg 2+ , Cl⁻, HCO₃ − , P, SAR, Mn, Zn 2+ , and N as the main drivers of water quality variation, supporting irrigation reuse under controlled dilution, drainage, and continuous monitoring protocols. Graphical Abstract