Elsevier

Desalination

Volume 270, Issues 1–3, 1 April 2011, Pages 124-129
Desalination

Photo-Fenton mineralization of synthetic municipal wastewater effluent containing acetaminophen in a pilot plant

https://doi.org/10.1016/j.desal.2010.11.032Get rights and content

Abstract

The aim of this work was to study the mineralization of acetaminophen (ACTP) present in synthetic municipal wastewater effluent (S.E.) in a UV-A/C pilot plant using a homogeneous photo-Fenton oxidation process with continuous addition of H2O2 to the system.

The mineralization process was found to follow pseudo-first-order kinetics. Experimental kinetic constants were fitted using neural networks (NNs). The mathematical model reproduced the experimental data to within a 90% confidence level. At the optimum conditions (H2O2 flow rate = 50 mL/h, [Fe(II)] = 2 ppm, pH = 2.5 and temperature = 40 °C), 71.5%, 82.1% and 94% of COT, COD and BDO-5 were removed in 120 min respectively.

Determination of the hydrogen peroxide consumed and remaining in the water revealed that 5.8 mol of H2O2 were consumed per each mol of total organic carbon removed from solution. It was also confirmed that an excess of dissolved H2O2 is needed to achieve high mineralization rates, so continuous addition of peroxide is recommended for industrial application of this process.

Comparison experiments of scavenger-loaded conditions proved that the reaction takes place mainly through a radical and single oxygen mechanism (96.7%).The molecular pathway (0.7%) and direct photolysis (2.6%) are secondary.

Research Highlights

►Photo-Fenton process is an alternative for the mineralization of S.E. with ACTP. ►Under optimum conditions, 83% of COD and 71% of TOC are removed in 120 min. ►5.8 mol of H2O2 were consumed per mol of TOC removed. ►The reaction takes place mainly through a radical mechanism.

Introduction

The presence of pharmaceuticals has been documented and reported as an emerging environmental issue [1], [2], [3], [4].

Acetaminophen (ACTP), commonly named as paracetamol (N-acetyl-4-aminophenol) is a common analgesic and anti-inflammatory widely used for humans and animals. It has been reported to be present with a concentration up to 6 μgL 1 in European Sewage Treatment Plant (STP) effluents [2], up to 10 μgL 1 in natural waters in USA [5] and even more than 65 μgL 1 in the Tyne river [6]. The presence of trace pharmaceuticals in drinking water is also of public concern since little is known about chronic health effects associated with long-term ingestion [7].

ACTP can appear in the environment due to partial removal in STP, or due to its use for the control of brown tree snakes [8] or from manufacturing wastes [9].

The treatment of ACTP by chemical or electrochemical methods has already been reported [8], [10]. However, nowadays advanced oxidation processes (AOPs) have emerged as an important class of technologies for the destruction of pollutants in aqueous suspensions. AOP generates a powerful oxidizing agent, hydroxyl radical, which may completely destroy the pollutants in wastewater. Thus, acetaminophen solutions have been treated using ozonation/H2O2/UV [8], ozonation/UV/Fe+ 2/Cu+ 2 [11], UV/TiO2 [12], photo-Fenton under black light and solar irradiation [13] or solar/TiO2 and Solar/photo-Fenton processes [14].

The photo-Fenton process, which combines Fenton oxidation and UV–visible light, offers a cost-effective source of hydroxyl radicals and is easy to operate and maintain [15]. However, an industrial application of this technique requires a previous study with a pilot plant with continuous addition of reagents as well as demands a high degree of mineralization. This investigation presents a number of important advances such as:

  • a)

    Continuous addition of hydrogen peroxide rather than only at the beginning of the tests; this made it possible to increase the concentration of dissolved hydrogen peroxide in the water, enhancing the mineralization process,

  • b)

    A complete study of the mineralization process including the importance of each degradation mechanism and obtaining the optimum operation conditions;

  • c)

    Determination of the number of moles of H2O2 needed to remove each mol of Total Organic Carbon (TOC).

The experimental results were fitted using neural networks (NNs), which allowed the values of the mineralization constant to be estimated within the studied range as a function of the operating variables (H2O2 flow rate, initial concentration of Fe(II), pH, and temperature); the individual effect of each variable involved was also determined.

Section snippets

Materials

ACTP reagent grade was purchased from Sigma-Aldrich. Analytical-grade ferrous sulfate (FeSO4·7H2O) and 30% hydrogen peroxide (H2O2) were purchased from Merck and used as received. The pH of the wastewater was adjusted with H2SO4 and NaOH solutions.

Reagents used to prepare the synthetic municipal wastewater treatment plant effluent (S.E.) were purchased from Panreac: peptone, meat extract, urea, K2HPO4, CaCl2·2H2O, NaCl and Mg2SO4·7H2O.

Experimental runs

The UV pilot plant (FLUORACADUS-08/2.2), already described

NN fitting

The experimental results obtained for the mineralization constant were fitted with NNs with an average error lower than 10%. The equation and fitting parameters are shown in Table 2. N1 and N2 are general factors related to the first and the second neuron, respectively. W11 to W14 are the contribution parameters to the first neuron and represent the influence of each of the variables in the process (H2O2 flow rate, initial concentration of Fe(II), pH and temperature); W21 to W24 are the

Conclusions

  • The use of a homogeneous process with UV light can offer a practical alternative for the mineralization of S.E. with ACTP.

  • Under the optimum conditions (H2O2 flow rate = 50 mL/h, [Fe(II)] = 2 ppm, pH 2.5 and T = 40 °C) it is possible to degrade 83% of the COD, 71% of the TOC and 94% of BDO-5 in 120 min. 5.8 mol of H2O2 were consumed per mol of TOC removed.

  • The reaction takes place mainly through a radical and single oxygen mechanism (96%).The molecular pathway (0.7%) and direct photolysis (2.6%) are

Acknowledgement

Financial support from the JCCM, POII10-0114-3563 is gratefully acknowledged.

References (33)

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