The present study was done to compare between two free biomass biological wastewater treatment processes (WWTP): (i) aerated lagoon AL which is an extensive process and (ii) activated sludge AS which is an intensive process. For the removal rates and exit concentrations of physical pollution (Total Suspended Solids TSS), biological pollution (Biochemical Oxygen Demand after 5 days BOD₅ and Chemical Oxygen Demand COD), nitrogen pollution (Nitrite and Nitrate) and phosphorus pollution (Orthophosphates) of both processes were collected and analyzed. The results showed that there is a satisfactory removal rate of TSS, BOD₅ and COD in accordance with Algerian and world health organization (WHO) effluent discharge standards for the case of AS process. While for AL process, removal rates of the three cited parameters were low and concentrations were higher than that of WHO discharge standards. In accordance with the nutriments (nitrogen and phosphorus), the removal rates are very low in the AL WWTP and very high in the AS WWTP. Generally, the residual concentrations remain very high in the treated effluent of both plants and could constitute a great risk of eutrophication and cause the formation of algal blooms in AL WWTP. According to these results, the AS is the most efficient process in Ouargla region.