Acta

ARTICLE pubs.acs.org/IECR

Wastewater Ozonation Catalyzed by Iron
Anaid Cano Quiroz, Carlos Barrera-Díaz,* Gabriela Roa-Morales, Patricia Balderas Hernndez, a Rubí Romero, and Reyna Natividad
Centro Conjunto de Investigacin en Química Sustentable UAEM-UNAM, Carretera Toluca-Atlacomulco Km 14.5, Toluca, Estado de o Mxico, C.P. 50200 Mxico e e ABSTRACT: The effectiveness of ozone andintegrated ozone catalyzed processes with iron plates on industrial wastewater treatment was evaluated. Both processes were tested at different pH values of the industrial wastewater. Ozonation, under optimal conditions of pH 7 and treatment time of 60 min, reduced the chemical oxygen demand (COD) by 45%, color by 82%, and the turbidity by 55%. The addition of iron plates inside the reactor greatlyimproved the reduction of COD (80%), color (90%) and turbidity (99%). Thus, it was concluded that the ozonation process catalyzed with iron plates noticeably improves wastewater quality. Additional advantages of the process are that there is no sludge generation and it occurs readily at pH 7.

1. INTRODUCTION Water availability is a problem that people face in different regions of the world since manyindustries generate effluents that contain pollutants which should be eliminated before being discharged.1 Previous studies show that conventional treatment methods (i.e., biological, physical, and chemical) applied to the industrial effluents treatment have limited success since wastewater contains very stable refractory and toxic compounds.2 Another main drawback of these processes is that they areassociated with the production of a large amount of sludge, which requires treatment before final disposal. Recently, studies have paid more attention to the treatment of refractory or toxic polluting agents contained in the effluents. The new way of approaching the elimination of these contaminants is through advanced oxidation processes (AOPs).3 AOPs are defined as the processes in which thehydroxyl radical is the main implied oxidant. It has been reported that these technologies are capable of degrading a wide variety of refractory compounds from stabilized lixiviation, and they are an excellent alternative for treating residual waters of high resistance. Indeed, AOPs exhibit a high efficiency, especially when they are compared to processes involving conventional chemical oxidation.4-7 Twoof the most simple and most representative advanced oxidation processes are the oxidation by ozone and by the use of the Fenton reagent. Although ozone is a powerful oxidant, a total organic compound mineralization is not likely to be achieved by ozonation only.8 Therefore, the combination of ozone with other technologies, such as UV, ultrasound, electrocoagulation, and flotation, allows theincrease of the pollutants removal yield.9-12 On the other hand, Fenton oxidation combines hydrogen peroxide with iron in acidic conditions. These reagents promote the organic pollutants oxidation by generating hydroxyl radicals. Albeit this AOP is very useful for the removal of aromatic compounds due to their fast reaction with hydroxyl radicals, there are occasions in which complete mineralization isnot attained. This is mainly due to the formation of Fe (III) compounds, which contribute to the generation of carboxyl acids that are very difficult
r 2010 American Chemical Society

to destroy by means of this oxidant.13,14 Even the Fenton based processes (i.e., Electro-Fenton and Foto-Fenton) require one to maintain an acidic pH which makes the addition of chemicals into reacting solutionunavoidable.15-17 Another attempt to improve ozonation removal efficiency is the use of metals or their oxides to catalyze ozonation.18-21In this context, the advantages of the use of Fe (III) based catalysts have been reported for the oxalic acid degradation.21 In such a study, a complete mineralization was attained and an interesting mechanism was proposed. It was suggested that mineralization occurs...