This study includes two parts; the first one, concerns evaluation of the physicochemical and microbiological quality of the urban wastewater of the city of Fez, through a space-time dynamics. In turn, the second part deals with the contribution to the treatment of these effluents, by a new biodegradable reagent in the process of physicochemical treatment (coagulation flocculation). For this purpose, the sampling of urban wastewater was carried out 4 months (September, December, February and June 2019), at a rate of two samplings per period on 4 specific sites along the river Fez, the degree of contamination of which differs from one site to another, according to space and time. The diagnostic of these stations showed a high level of pollution that is difficult to biodegrade. Indeed, this pollution can cause negative effects not only on the environment but also on human’s health. In order to take long-term action against the low quality of water, and to replace certain inorganic coagulants, alternative processes for water treatment using cactus powder were set up. The characterization of results showed that the urban effluent has a high load in terms of electrical conductivity (EC), dissolved oxygen, chemical oxygen demand (COD), as well as concentrations of faecal coliforms, streptococci and staphylococci. In addition, the purifying power revealed that the removal rate of COD reaches maximum values of 38%and 58% forlimeand the mixture of lime with cactus powder, respectively.