Chemical Engineering Journal 157 (2010) 80–85 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Oil sludge treatment by photocatalysis applying black and white light Otidene Rossiter Sá da Rocha a,∗ , Renato F. Dantas b , Marta Maria Menezes B. Duarte b , Marcia Maria Lima Duarte a , Valdinete Lins da Silva b a Federal University of Rio Grande do Norte, Chemical Engineering Department, Avenida Senador Salgado Filho, 3000, 59072-970 Natal, Brazil b Federal University of Pernambuco, Chemical Engineering Department, Avenida Artur de Sá, s/n, 50740-521 Recife, Brazil article info Article history: Received 9 June 2009 Received in revised form 22 October 2009 Accepted 26 October 2009 Keywords: Petroleum waste Advanced oxidation Heterogeneous photocatalysis Hydrocarbons Polycyclic aromatic hydrocarbons abstract Soil contamination by non-aqueous phase liquid compounds (NAPLs), mainly from petroleum hydrocar- bons, has been a matter of great concern, especially due to aromatic and polycyclic aromatic hydrocarbon contamination, which can pose a health risk due to its carcinogenic and mutagenic properties. In this study, oil sludge treatment was carried out using heterogeneous photocatalysis (H 2 O 2 /UV/TiO 2 ). A 2 3 factorial design experimental plan was used, applying black and white light reactors; in addition the effects of hydrogen peroxide (H 2 O 2 ) concentration, TiO 2 mass and irradiation time were evaluated using TOC removal as a response. Heterogeneous photocatalysis provided efficient degradation and mineraliza- tion of a large part of the organic matter. Moreover, the method also proved to be an alternative treatment for removing PAH from oil sludge, eliminating 100% of all PAH content from the oil sludge sample after 96 h of irradiation. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Oil spills cause significant environmental and economic damage to a wide variety of natural resources. The degree of this damage depends on where the spill occurs, type and discharge volume, season and environmental conditions [1,2]. In recent decades, soil contamination by non-aqueous phase liquid compounds, specifi- cally oil hydrocarbons from oil spills has been a matter of great concern [3,4]. This concern is justified because polycyclic aromatic hydrocarbons (PAH), an oil contaminant, pose a risk to human health due to its carcinogenic and mutagenic properties [5–8]. According to Faria and Rosa [9], the complexity of PAH mixtures depends on their emission sources. Generally, these mixtures have a wide variety of PAH at different concentrations. Thus, the knowl- edge of the presence of these compounds in environmental samples and the search for suitable treatment methods are of great interest to governments worldwide. Although the remediation for PAH- contaminated soil has been extensively investigated by various research groups, especially in terms of biological treatment, few works were found in the literature on treating PAH with advanced oxidation processes (AOPs) [10,11]. PAH concentrations of ng L -1 have been detected in soil, water and plant samples [12,13]. In addition, due to their physical–chemical properties and their wide environmental distri- bution, the risk of contamination by these substances is significant. ∗ Corresponding author. Tel.: +55 81 2126 8711; fax: +55 81 2126 7278. E-mail address: otidene@eq.ufrn.br (O.R.S. da Rocha). Indeed, because of their lipophilic nature, PAH and their derivatives can be absorbed by the skin, ingested or inhaled, and quickly spread throughout the organism [8]. Advanced oxidation processes are defined as processes that can generate radicals in a sufficient amount to oxidize most of the complex chemicals present in environmental matrices. Hydroxyl radicals (*OH) are powerful oxidizing reagents with an oxidation potential of 2.8 V [14]. Furthermore, they react with most organic and many inorganic compounds, exhibiting faster oxidation reac- tion rates than those of conventional oxidants [15]. The main advantage of these processes is that the contaminant is destroyed and not transferred to another phase [16,17]. Among the AOPs, het- erogeneous photocatalysis stands out as a promising technology in the treatment of environmental pollutants [18–21]. The photocat- alytic oxidation enables the utilization of near UV and sunlight for irradiation, thus, resulting in a considerable saving especially for large-scale operations [22]. These processes entail a photochemical degradation of a lot of compounds present in wastewater, capable of achieving total mineralization at mild conditions of tempera- ture and pressure [23]. In these processes, the chemical reactions are characterized by a free radical mechanism, thus radicals such as “*OH and *HO 2 ” can be produced by the homogeneous radia- tions degradation of oxidizing compounds like hydrogen peroxide (H 2 O 2 ) and ozone. Another method to achieve and at the same time enhance the production of free radicals is the photocatalytic oxi- dation mechanism occurring at the surface of semiconductors e.g., TiO 2 [24]. The aim of this work was to study the oil sludge treatment by photocatalysis using titanium dioxide (TiO 2 ) as catalyst, hydrogen 1385-8947/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2009.10.050