In this work, we investigated the photocatalytic degradation of p-nitrophenol using a cobalt (Co)-doped ZnO photocatalyst. The Co-doped ZnO photocatalyst was first prepared through a simple wet impregnation method and subsequently characterized using various qualitative and quantitative techniques. Response surface methodology (RSM) was employed for experimental design and optimization of photocatalytic process. The effects including initial concentration of 4-Nitrophenol [4-NP] in , catalyst dosage, pH and irradiation time were investigated, and RSM suggested a seconddegree polynomial model for abatement of p-nitrophenol from aqueous phase. Under optimized conditions (pH = 5; Irradiation time = 180 min; catalyst dosage = 30 mg; [4-NP] in = 30 mg/L), up to 82% degradation was achieved, signifying the efficacy of the prepared photocatalyst. Moreover, the real case study was employed by incorporating Co-doped ZnO nanocomposite for treatment of real paper wastewater and results showed a considerable photocatalytic activity of Co-ZnO nanocomposites on paper wastewater.