Statistical analysis of optimum Fenton oxidation conditions for landﬁll leachate treatment Shrawan K. Singh, Walter Z. Tang ⇑ Department of Civil and Environmental Engineering, Florida International University, 10555 West Flagler Street, Miami, FL 33174, USA article info Article history: Received 30 May 2012 Accepted 7 August 2012 Available online 12 September 2012 Keywords: Fenton oxidation Landﬁll leachate Chemical oxidation Oxidation efﬁciency Hydrogen peroxide abstract Optimal operating conditions observed by peer reviewed publications for Fenton oxidation of raw and biological and coagulation treated leachates were reviewed and statistically analyzed. For the ﬁrst-stage Fenton oxidation, the optimal pH range of 2.5–4.5 was observed for raw and coagulation treated leachates with a median pH of 3.0, whereas, for biologically treated leachate the optimum pH range was 2.5–6.0 with a median pH of 4.2. Theoretically, the optimal ratio of H 2 O 2 /Fe 2+ should be the ratio of rate constants of the reactions between OH Å radical with Fe 2+ and H 2 O 2 , which is approximately 11; however, for leachate treatment, a median optimum relative dose of 1.8 (w/w) (3.0 M/M) was observed. Biologically treated leachate showed relatively lower optimum ratio of H 2 O 2 /Fe 2+ doses (median: 0.9 w/ w) as compared to raw (median: 2.4 w/w) and coagulation treated (median: 2.8 w/w) leachate. Median absolute doses of H 2 O 2 and Fe 2+ were 1.2 mg H 2 O 2 /mg of initial COD (COD 0 ) and 0.9 mg Fe 2+ /mg COD 0 , respectively and raw leachate required higher reagent doses compared to pretreated leachates. A univer- sal Fenton oxidation relationship between COD removal efﬁciency (g) and COD loading factor (L COD ) for landﬁll leachate treatment was developed. As L COD increases from 0.03 to 72.0, g varies linearly as g ¼ 0:733L COD  0:182: This robust linear relationship between L COD and g holds for Fenton oxidation of raw as well as biological and coagulation treated leachates. The relationship was validated using Leave-one-out cross validation technique and errors in predicting g using L COD were evaluated by apply- ing Monte Carlo Simulation. As a result, the relationship can be used as a universal equation to predict Fenton treatment efﬁciency for a given COD 0 loading in the range of 0.03–72.0 for landﬁll leachate treatment. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Landﬁlls are designed to dispose high quantities of waste at economical costs with potentially less environmental affects; how- ever, improper landﬁll management may pose serious environ- mental threats through discharge of high strength polluted wastewater also known as leachate. Although modern landﬁll engineering and operational practices minimize leachate genera- tion, proper leachate discharge remains one of the greater chal- lenges for landﬁll operators due to its complex chemical and changing characteristics over time. Multiple factors inﬂuence leachate characteristics such as waste age, climatic conditions, waste composition, landﬁll design, and operational practice; how- ever, selecting leachate treatment method, which is often a combi- nation of multiple processes, is mostly associated with the state of landﬁll stabilization. Leachate treatability is evaluated as a function of landﬁll age or by the ratio of Biochemical Oxygen Demand (BOD 5 ) to Chemical Oxygen Demand (COD) with values close to 1 representing young leachate and values of 0.1 or less described as stabilized leachate (Diamadopoulos, 1994). Young leachate majorly contains low molecular weight more biodegradable organic matter (OM) (Huo et al., 2008); thus are subjected to standard biological treatment processes. Once waste decomposition reaches the stable methano- genic phase, landﬁll leachate OM is dominated by biologically refractory OM (such as humic- and fulvic-like OM), reducing the effectiveness of biological treatment processes and necessitating other physico-chemical processes (Huo et al., 2008). The most common physico-chemical processes used for landﬁll leachate treatment are coagulation and ﬂocculation (Amokrane et al., 1997; Tatsi et al., 2003), activated carbon (AC) adsorption (Maranon et al., 2009; Singh et al., 2012), chemical oxidation (Rivas et al., 2004; Tizaoui et al., 2007), and membrane-based technolo- gies (Tabet et al., 2002; Trebouet et al., 2001). These physico-chem- ical processes are often used as a pretreatment or post-treatment steps prior to biological processes. Recently, an exponential increase in number of peer reviewed publications on landﬁll leachate treatment using chemical oxida- tion processes has been observed. Among them, a catalyst driven 0956-053X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2012.08.005 ⇑ Corresponding author. Tel.: +1 305 348 3046; fax: +1 305 348 2802. E-mail address: tangz@ﬁu.edu (W.Z. Tang). Waste Management 33 (2013) 81–88 Contents lists available at SciVerse ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman