Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe On the critical use of zero valent iron nanoparticles and Fenton processes for the treatment of tannery wastewater Giorgio Vilardi ⁎ , Luca Di Palma, Nicola Verdone Sapienza University of Rome, Dept. of Chemical Engineering Materials Environment, Via Eudossiana 18, 00184 Rome, Italy ARTICLE INFO Keywords: Heterogeneous-Fenton Tannery wastewater Intensified-process Cr(VI) nZVI ABSTRACT The use of iron nanoparticles in the heterogeneous Fenton oxidation treatment of tannery wastewater was in- vestigated. A comparison with the conventional oxidation process, involving Fe(II) addition was performed. The main operating parameters influence, such as pH, temperature and reagents amount, on total phenolic species, total organic compounds, Cr(VI) content and chemical oxygen demand reduction was investigated. Heterogeneous Fenton oxidation resulted more efficient and fast with respect to the conventional process, but a higher amount of iron was required in the process. In this case, the optimal conditions were assessed at H 2 O 2 / COD (w/w) = 0.5, nZVI/H 2 O 2 (w/w) = 0.75 and pH = 3, achieving a total Cr(VI) removal as well as a re- markable TOC, COD and phenols degradation efficiency (up to 70, 73 and 88%, respectively). The best results were obtained with the combination of the two processes, fixing the optimal conventional Fenton operating parameters (H 2 O 2 /COD (w/w) = 0.75, Fe(II)/H 2 O 2 (w/w) = 0.15 and pH = 2.5), adopting a nZVI/H 2 O 2 (w/w) ratio equal to 0.2. In such conditions, that also allowed to reduce the catalyst amount used with respect to the Heterogeneous Fenton process, a noticeable TOC, COD and phenols removal efficiency (81.15, 87.44 and 94.04%, respectively) was achieved. In addition, the iron sludge production of such combined process was close to that obtained in the conventional one. 1. Introduction Leather tanning industry represents one of the most present activ- ities in the Mediterranean area and it is well known that produces huge amount of liquid waste [1]. About 1218 tanneries are sited on the Italian territory contributing for 65% of the overall EU leather pro- duction, considering that nearly one out of three skins traded between international operators is from Italy [2]. About 2110 Mm 2 of leather is produced annually in the world generating approximately 40 million L of Cr-polluted wastewater every year [3], since 100–110 L of water are necessary to tan 1 m 2 of hides [2]. Chromium tanning process remains still the widest employed process with respect to vegetable one [4], because of better leather quality and stability, besides the less time required from the former tanning process [5]. The high concentrations of low-biodegradable compounds in tannery wastewater represents a serious technological and environmental challenge for the operators, because chrome tanning process, hide pre-treatment and post-treatment require the use of several chemicals, such as chromium salts, bicarbo- nate salts, inorganic and organic acids and surfactants [6]. Tannery wastewater (TW) is characterized by high values of chemical oxygen demand (COD 3–10 g L -1 ), biological oxygen demand (BOD 0.5–4gL -1 ), total dissolved solids (TDS of 5–15 g L -1 ), total suspended solids (TSS of 500–300 mg L -1 ), Cr(VI) (5–20 mg L -1 ) and Cr(III) (50–300 mg L -1 ) content, and phenolic compounds concentration (100–500 mg L -1 ), with strong odor and dark brown color [7,8]. The complex TW composition has led researchers to develop combined and integrated processes to remove the most toxic and stable compounds before the final treating in biological reactors [7–12]. Chemical coa- gulation, flocculation, membrane filtration (MF) and advanced oxida- tion processes (AOPs) are the main solutions proposed and used [13–20]. Membrane processes demonstrated to be noticeably effective towards chromium recovery from Tannery wastewaters [21], con- sidering also the significant simultaneous COD and polyphenols re- moval efficiencies obtained in various studies [22,23]. Regarding the latter processes, instead, they have raised notable interest because of their flexibility, effectiveness and relatively low-cost [24,25]. AOPs consist of a wide class of methods capable of generating radical species such as OH%, able to oxidize recalcitrant pollutants [26], generally through a radical mechanism characterized by large kinetic rate con- stant values (10 6 –10 9 M -1 s -1 ), 10 6 –10 12 times faster than ozone use [27]. Fenton is an effective AOP for the degradation of toxic organic pollutants in wastewater [28–30], based on the production of highly https://doi.org/10.1016/j.jwpe.2018.01.011 Received 27 November 2017; Received in revised form 12 January 2018; Accepted 19 January 2018 ⁎ Corresponding author. E-mail address: giorgio.vilardi@uniroma1.it (G. Vilardi). Journal of Water Process Engineering 22 (2018) 109–122 2214-7144/ © 2018 Elsevier Ltd. All rights reserved. T