As part of environmental preservation and sustainable water resource management actions, particularly in a semi-arid region, an annual monitoring program was carried out in 2024 to assess the treatment performance and environmental compliance of the Djelfa city wastewater treatment plant. This approach aimed to assess the effectiveness of the biological treatment and to identify possible optimization needs, in accordance with national regulatory requirements and WHO recommendations. The study focused on the main physicochemical parameters, including pH, temperature, electrical conductivity, turbidity, suspended solids (SS), chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), ammonium (NH₄⁺), nitrates (NO₃⁻) and phosphates (PO₄³⁻), in order to evaluate the removal efficiencies and quality of the treated effluents. The results obtained highlight generally satisfactory performance, with yields of 91 to 92% for suspended solids and BOD₅, 83 to 84% for COD and 55 to 66% for phosphates. Regarding nitrogen, ammonium was reduced by 57 to 61%, while nitrates recorded a marked increase (200 to 236%), demonstrating the effectiveness of the nitrification process. Overall, the quality of the treated effluents complies with Algerian discharge standards and international recommendations. However, the fluctuations observed in nitrogen and phosphorus nutrient concentrations reflect certain limitations in the nitrification/denitrification and phosphorus removal processes, suggesting the need for operational adjustments to enhance the stability and efficiency of the biological treatment.