Wastewaters discharged into surface waters highly impacted humans and living aquatic organisms particularly when the treatment applied to reduce chemical and biological pollution is not appropriated. Biological treatment systems are often applied for the treatment of domestic wastewaters. These systems are limited when applied to the treatment of hospital wastewaters. In this study, we evaluated the efficiency of natural lagoon system, applied to treat combined wastewaters from hospital and from residences of nursing students. Results show that the lagoon system remove 98% of COD, 87% of BOD, 95% of TSS and 92% of total nitrogen. Arsenic and copper are removed (40%), but lead and cadmium concentrations increase in the effluent. Globally, the concentrations of nutrients and heavy metals, in the effluents, are inferiors to the limit values proposed by the Ivorian guidelines for water pollution. However, the reuse of effluents for irrigation of crops likely to be eaten uncooked is not recommended because of the high concentration of fecal bacteria (1.00 x 10⁵ CFU E. coli. 100 mL^-1. The disinfection process must be implemented after biological treatment to ensure the elimination of pathogenic microorganisms present in the effluent and sludge, before their reuse in agriculture.

Keywords: Wastewater Pollution; Lagoon System; Fecal Bacteria; Water Reuse; Biosolids;