Integrated assessment of irrigation water quality and wastewater reuse under hydrochemical, microbiological, and metal contamination constraints in a Mediterranean semi-arid basin

Abstract

Abstract Water scarcity in semi-arid Mediterranean regions increasingly drives wastewater reuse for agriculture. In northeastern Algeria, the Middle Seybouse basin faces pressures from urban effluents and agricultural runoff, which can impair water quality and threaten ecosystems, soils, crops, and public health. Studies on the environmental impacts of the Guelma wastewater treatment plant (WWTP) are lacking. This study provides the first multiparametric assessment of Guelma WWTP effluent and its irrigation suitability. Seasonal samples were collected in 2024 from three sites: WWTP effluent, the Seybouse river mixing zone, and a downstream station. Physicochemical parameters, nutrients, bacteriological indicators, and heavy metals (Cr, Cd, Fe, Pb, Zn) were analyzed. Irrigation suitability was assessed using sodium adsorption ratio (SAR), sodium percentage (Na%), residual sodium carbonate (RSC), magnesium hazard (MH), permeability index (PI), Kelly’s ratio (KR), and the irrigation water quality index (IWQI), while seasonal and spatial variations were explored with analysis of variance (ANOVA) and principal component analysis (PCA). Results showed seasonal variability, with ranges of total suspended solids = 5–124 mg/L, 5-day biological oxygen demand (BOD₅) = 5.6–36 mg/L, chemical oxygen demand (COD) = 28–169 mg/L, electrical conductivity (EC) ≈ 1271 µS/cm, and total dissolved solids (TDS) ≈ 635 mg/L. IWQI (range: 46–74) indicated generally good to moderate irrigation suitability, though seasonal sodicity risks were noted. Treated wastewater could support irrigation of salt-tolerant crops using drip irrigation and soil management. These results provide guidance for water managers, policymakers, and farmers to safely reuse treated wastewater and reduce environmental and health risks