This article is devoted to the experimental procedure followed for the treatment of industrial waste colored by coagulation flocculation. The amount of water used and therefore the volume of the effluent and its pollution rate vary considerably depending on the production step. The variations of the COD, of the effluents of different stages of the process of manufacturing the leather are evoked in this work. A screening study is done in order to identify the most influential factors in COD as a response. Analytical methods and techniques will be presented. Several factors such as pH, the nature of the coagulant, the concentration of the coagulant, the concentration of the flocculating agent, the concentration of the ash and the type of flocculantare taken into account in this study to determine their effects on The COD.