Prato (Tuscany, Italy) is an important textile district which is one the more water-consuming industrial sector. In the past, the main water supply source of the city was the local groundwater, leading to a progressive depletion of this resource. For this reason, wastewater reclamation has played a key role for the industrial district since 1990s, through a refining plant managed by GIDA SpA. The plant is composed of the following sections: chemical decoloration, sand filtration, biological activated carbon (BAC) filtration and then disinfection with sodium hypochlorite and hydrogen peroxide. The most expensive section in term of operational cost is the BAC, due to the energy demand (required for the oxygen transfer) and the oxygen supply cost. Among the 5 BACs of the plant, two of them worked in parallel from 2012 until 2018, treating more than 3·106 m3 of water each, but one (filter A) having a doubled oxygen dosage than the other (filter B). In the present work, a study on the effect of different dosage on the performances of the plant has been carried out. Moreover, the concentration of the biomass and the amount of biomass removed with backwashing has been evaluated. A comparison between the filters A and B in terms of color, N_NH4+ and COD removal, shows typical different behaviors (Figure 1). A linear decrease of performance over the time can be seen for color, which is removed mainly by adsorption. On the contrary, ammonium removal, by means of biological processes, doesn’t show any tendency with a typical high variability due to influent concentration. COD removal shows an intermediate behavior, even if a clear fall is present after 1 million cubic meters. Comparing the average removal rates of these three parameters, the increase in oxygen dosage leads to an increase of 40% of ammonium removal, 10% of COD removal and 6% of color removal with respect to the low-oxygen filters. On the other hand, considering the costs for energy requirements and oxygen supply, costs for the two different dosages have been estimated to 0.033 €/m3 for filter A and 0.009€/m3 for filter B.