The aim of this study is to valorize the bottom ash generated by the thermal power plant in the cardboard manufacturing wastewater treatment by infiltration percolation process and to study the purifying effect of the crushed bottom ashes used instead of the fly ash which is already recycled in the cement industry. For this purpose, different coastal sands of the area of the city of El Jadida, combined with bottom ash (by-products of a local power plant), are used to filter wastewater from a cardboard manufacturing plant. The chemical and mineralogical composition of bottom ash are produced respectively by X-ray fluorescence and X-ray diffraction. The wastewater samples were collected during a complete cycle of production of the cardboard. The heavy metals content before and after filtration was obtained by atomic emission spectrometry, with inductively coupled plasma (ICP-AES). The main parameters analyzed were: total suspended solids (TSS), organic matter COD, BOD5, the potential hydrogen pH and heavy metals (iron, zinc and arsenic). The results are very conclusive and respect the essence of control required by Moroccan regulations (law 1606-06) related to discharges from the papermaking and cardboard industry.