Optimisation of the degradation of 4-nitrophenol by Fenton's process

Abstract

Processes optimisation is one of the main issues to take into account for the design of new chemical processes applied to wastewater treatment plants (WWTPs). Particularly, it can be achieved using design of experiments (DoE) tools, and can represent progress in the process performance and cost reduction. In this work, an advanced oxidation process (AOP), namely Fenton's process, is applied to degrade a nitrophenol model compound, i.e., 4-nitrophenol (4NP), in a lab-scale batch reactor. To optimise the process parameters (such as the temperature of the reaction - T, and the initial concentrations of hydrogen peroxide – [H2O2] – and ferrous ion – [Fe2+]), DoE was applied, namely central composite design (CCD) and response surface methodology (RSM). The 4NP degradation and mineralisation were evaluated as process outputs. The maximum 4NP and TOC removals (100 and 49.2%, respectively) and a non-toxic effluent (determined by the inhibition of Vibrio fischeri bacteria) were achieved after 60 min of reaction using the optimum conditions provided by the model (T = 70.2 °C, [H2O2] = 2.945 g/L and [Fe2+] = 5.9 mg/L). Some strategies, i.e. gradual addition of H2O2 and UV/visible radiation application, were still adopted to increase the mineralisation. However, the complete removal of 4NP and 80% of mineralisation was achieved when the Fenton process was assisted with UV/visible radiation. The lumped kinetic model (LKM) proposed, and used for the first time to describe the mineralisation of 4NP by Fenton's reaction, described well the profile of the residual carbon (i.e., the fraction of carbon not mineralised) during the treatment time for these experiments.