Characterization of nano zero-valent iron (nZVI) and its application in sono-Fenton process to remove COD in palm oil mill effluent M.R. Taha a , A.H. Ibrahim b, * a Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia, 43600, Malaysia b School of Environmental Engineering, Universiti Malaysia Perlis, 01000, Malaysia Introduction The purification of wastewater has been a global issue for quite some time. In general, a wastewater treatment process is required before any industrial wastewater is emitted into any water bodies. Stringent rules and regulations that must be met periodically by the industries have indirectly resulted in the installation of better treatment processes. Meanwhile, many researchers have being carrying out studies to enhance available wastewater treatment technologies, including the utilization of nanotechnology. The application of nanotechnology had a significant impact on wastewater treatment processes. Nanomaterial such as nano zero- valent iron (nZVI) has been widely used to treat polluted groundwater and also effectively used as an absorbent for various pollutants. It has also be used to treat groundwater containing arsenic (V) [1] and to remove nitrate from wastewater [2]. Furthermore, nZVI was also successfully used as a permeable reactive barrier (PRB) to remove nitrate from polluted groundwa- ter [3]. Besides that, nZVI has also been utilized as catalyst in wastewater treatment process. Weng [4,5] used nZVI as catalyst in Fenton/ultrasound process to decolorize dyes such as Direct Blue (DB15) and Reactive Black (RB5). The combination of ultrasound with the Fenton process (sono- Fenton) is one of the most advanced oxidation processes (AOPs) used to treat organic pollutants in wastewater. In the conventional Fenton process, FeSO 4 is utilized as a major source of Fe 2+ [6,7]. Formed Fe 2+ will react with certain oxidizing agents (i.e. hydrogen peroxide) to produce hydroxyl radical (OH  ). The reaction is presented in Eq. (1): Fe 2þ þ H 2 O 2 ! Fe 3þ þ OH  þ OH  (1) In this process, OH  will attack organic molecules by radical addition, hydrogen abstraction, electron transfer, and radical combination [8]. Respectively, the reactions can be described as follows: R þ OH  ! ROH (2) R þ OH  ! R  þ H 2 O (3) R n þ OH  ! R n1 þ OH  (4) OH þ OH  ! H 2 O 2 (5) Generally, after completion, the reaction between OH  with organic compounds will produce water (H 2 O), carbon dioxide (CO 2 ) and salts. Combination of ultrasound with the Fenton process is one of the innovations that has improved the efficiency of the Fenton process. Bremner [9] combined the Fenton process with ultrasound to degrade phenols in aqueous, while Chakinala Journal of Environmental Chemical Engineering 2 (2014) 1–8 A R T I C L E I N F O Article history: Received 11 September 2013 Received in revised form 8 November 2013 Accepted 22 November 2013 Keywords: Nano zero-valent iron (nZVI) Sono-Fenton Palm oil mill effluent (POME) A B S T R A C T Nano zero-valent iron (nZVI) has received great attention for its capability to treat wastewater. One of its applications is in an advanced oxidation process (AOP) called the sono-Fenton process. This study presents the characterization of the nZVI particle by its particle size, scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, X-ray diffraction (XRD), energy dispersive X- ray (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. Results show that the average size of nZVI is 49 nm and it has two layers. The outer layer (shell) is comprised of iron oxides (i.e. FeO) while the core is elemental iron (Fe). At pH 2, nZVI was found to be a good replacement for iron sulfate (FeSO 4 ) as a ferrous iron (Fe 2+ ) source in the sono-Fenton process. In addition, the removal process of organic pollutants from diluted palm oil mill effluent (POME) was also accelerated by ultrasound, particularly at higher intensity and longer sonication time. Eighty percent (80%) of the chemical oxygen demand (COD) was removed in 2 h instead of 24 h by silent degradation. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +60 125353897; fax: +60 389216147. E-mail addresses: dmrt@eng.ukm.my (M.R. Taha), haqiibrahim@gmail.com (A.H. Ibrahim). Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jec e 2213-3437/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jece.2013.11.021