Evaluation of the efficiency of wastewater treatment and the diversity of phytoplankton in a large-scale waste stabilization pond in an arid climate

Abstract

This study aimed to evaluate the effectiveness of a full-scale waste stabilization pond in treating domestic wastewater in a peri-urban area with arid climatic conditions. The experiment was conducted in the municipality of Saada, located 18 km west of Marrakech, Morocco. The wastewater treatment system consisted of two anaerobic ponds, four facultative ponds, and four maturation ponds arranged in series. The system treated an average inflow of 525 m³/day. In order to evaluate the efficiency of the treatment process, periodic sampling and analysis of physicochemical and bacteriological parameters were performed at the influent and effluent of each treatment stage. Phytoplankton monitoring was carried out in the three lagoons (anaerobic, facultative and maturation). The study found that maximum pollutant removal occurred during the warmer months of the year, and minimum removal occurred during the winter period. The highest removal percentages of TSS, COD, and NH₄⁺ were 72.66 %, 79.28 %, and 72.53 %, respectively. However, the removal of total phosphorus and its assimilable form (PO₄³⁻) did not exceed 40 % and 50 %, respectively. Fecal coliform removal reached an average removal of 2.71 log units at the outlet of the maturation pond. Phytoplankton parameters, based on qualitative and quantitative aspects of microalgae, indicated a dominance of cyanobacteria (46.87 %) and chlorophyceae (28.13 %), while diatoms were moderately present (12.50 %) in all ponds. This may indicate an unsatisfactory purification performance of the plant. The quantitative study also showed a great dominance of the species Chlorella, especially in the maturation pond.