The performance of the waste stabilization pond system at Boujaad, Morocco

The wastewater stabilisation ponds system of the city of Boujaad was constr ucted and put into operation in 1992. The two main objectives of this plant are the prevention of pollution of water resources and the environment by means of wastewater discharges as well as the saving of fresh water by mean s of reuse of treated wastewater for irrigation purposes. Within the period of March 1997 to March 1998 a comprehensive analysis campaign of both the raw and the treated wastewater at a number of different sampling points has been carried out in order to evaluate the treatment efficiency of this was tewater treatment plant. The results of these investigations showed an aver age raw wastewater flow of 1600 m(3)/d, which is well below the design flow of 2500 m(3)/d. With respect to the physico-chemical treated wastewater quality and in comp arison with the French treated wastewater standards (1980) these results in dicated that 90 % of the wastewater samples showed BOD5-figures below the q uoted French standard, whereas 83 % of the samples showed COD-figures above the corresponding French treated wastewater standard. With average treated wastewater suspended solids contents of 56 mg/l the su spended solids removal rate has been determined as being in the range of 65 %. If compared to the anticipated Moroccan wastewater standards for direct was tewater discharge into receiving water bodies as stipulated in the Moroccan Standards Project the obtained wastewater analysis results showed COD- and BOD5 values below these foreseen Moroccan wastewater discharge standards. The analysis results of SS, TKN and total phosphorus (P-tot) showed figures slightly above these Moroccan standards. In view of the microbiological wa stewater characteristics the treated effluents of the Boujaad WSP respond t o the WHO directive with respect to wastewater to be used for restricted ir rigation (category B). Taking into consideration the CEC directive for wastewater generated by was tewater treatment plants and discharged to the environment, the efficiency of the Boujaad WSP is relatively low with respect to the SS-removal, the re moval of organic matter (expressed by BOD5 and COD) as well as the removal of nutrients (expressed by TKN and P-tot). This relatively low efficiency m ight basically be caused by the already highly diluted incoming raw wastewa ter, which again is caused by the effect of significant infiltration of gro undwater into the sewerage network. Besides the evaluation of the overall t reatment efficiency, detailed investigations of the performance of individu al ponds have been carried out as well.