Study on the performance of the wastewater stabilisation pond of Boujaâd, Morocco

The wastewater stabilisation ponds system of the city of Boujaâd was constructed and put into operation in 1992. The main objectives of this plant are to prevent pollution of water resources and the environment by wastewater discharges, and to save fresh water by reusing treated wastewater for irrigation purposes. Within the period March 1997–March 1998 a comprehensive analysis of both the raw and the treated wastewater at a number of different sampling points was carried out in order to evaluate the treatment efficiency of the plant. The results of these investigations showed an average raw wastewater flow of 1600 m³/d, which is well below the design flow of 2500 m³/d. With average treated wastewater suspended solids (SS) content of 56 mg/l the SS removal rate has been determined to be about 65%. If compared to the anticipated Moroccan wastewater standards for direct wastewater discharge into receiving water bodies as stipulated in the anticipated Moroccan Standards (AMS 1996) the wastewater analysis results showed COD and BOD₅ values below these foreseen Moroccan wastewater discharge standards. The analysis results of SS, TKN and total phosphorous (P_tot) were slightly above these Moroccan standards. In view of the microbiological wastewater characteristics the treated effluents of the Boujaâd wastewater stabilisation ponds (WSP) respond to the WHO directive with respect to wastewater to be used for unrestricted irrigation (category A). Taking into consideration the CEC directive for wastewater generated by wastewater treatment plants and discharged to the environment, the efficiency of the Boujaâd WSP is relatively low with respect to SS removal, the removal of organic matter (expressed by BOD₅ and COD) and the removal of nutrients (expressed by TKN and P_tot). This relatively low efficiency may be caused by the already highly diluted incoming raw wastewater, which again is caused by the effect of significant infiltration of groundwater into the sewerage network.