Abstarct: One of the main branches of research in the field of photocatalytic treatment of water pollutants is the application of photocatalysts in the second generation of photoreactors called fixed-bed photoreactors, in which the light source includes the UV spectrum irradiated on a fixed-bed coated with photocatalytic materials. The pollutants in the water during the flow of water on the surface of the specimens are degraded due to a series of photocatalytic oxidation-reduction reactions. Although many reactors with different specifications and shapes have been built so far, the demand to develop and improve the conditions of these reactors is still in progress. In this study, cement composite was used as a matrix to immobilize and expose TiO2 particles in the substrate to perform the photocatalytic reaction in a photoreactor with a fixed bed. Also, for the first time, a relatively high volume of 5000 ml of contaminated water was used on a lab scale to evaluate the reactor's purification performance. The effect of the characteristics of the cement matrix of the fabricated composites on the photocatalytic activity of their surface was investigated. Moreover, the effect of the acid treatment process on increasing the efficiency of the degradation rate of the two pollutants methylene blue (MB) and nitrate individually and simultaneously with the initial concentrations of 4, 8, and 12 mg/L for MB pollutant and initial concentrations of 60, 80 and 100 mg/L nitrate pollutant were investigated. To evaluate the influence of bed characteristics on the photocatalytic treatment process, 6 different mix designs with two ratios of water to cementitious materials of 0.28 and 0.42 as well as 0, 5, and 10 percent of silica fume as a mineral admixture were fabricated, and tested. Standard tests were performed to determine the mechanical characteristics of the composites, including compressive strength, flexural strength, and abrasion resistance, and spectrophotometric tests were performed to evaluate the variation of MB and nitrate degradation rates over the fabricated specimens as a photocatalytic bed. The results of this study showed that improving the mechanical properties of the composite does not necessarily lead to the improvement of the photocatalytic activity. Specimens within the normal strength category, 5 and 10 percentages of silica fume (specimens 2 and 3), while maintaining the quality of the matrix in composite cement, gained the highest photocatalytic performance in the degradation of MB. In the case of specimen 2, the degradation rate was at least 10.4% higher than that of the competent group. In addition, in the series of high-performance composites, specimen no. 6 showed the highest amount of denitrification among the designs with a denitrification rate constant of at least 1.02×10-3 min-1 in various flow rates and with the highest initial concentration. In addition, specimen 3 with the MB degradation rate of 2.57×10-3 min-1 obtained the maximum MB degradation rate constant in the complex pollution case. The microstructural evaluation also proved the role of acid treatment in increasing the contact surface and density of TiO2 particles on the composite surface. baxsed on the existing definitions of pollutant removal efficiency and according to the scale of the performed tests, a new comparison was made by taking into account the initial volume of polluted water, the power consumption of the lamp, and the decomposition rate. It can be seen that the system tested in this study without the use of nanomaterials and with much lower energy consumption, can remove higher amounts of pollutants compared to other studies.