Gulbin Erden Ayse Filibeli Department of Environmental Engineering, Dokuz Eylu ¨l University, Buca-Izmir, Turkey Research Article Effects of Fenton Pre-Treatment on Waste Activated Sludge Properties Fenton process was investigated for the purpose of biological sludge disintegration. The Box–Wilson experimental design was employed to evaluate the effects of major process variables (Fe(II) and H 2 O 2 concentrations) on both disintegration and dewatering performance of sludge. Results showed that 4g Fe(II)/kg total solids (TSs) and 60g H 2 O 2 /kg TS are efficient for floc disintegration. Fenton pre-treatment enhanced the biodegradability of sludge. For 4 g Fe(II)/kg TS and 60 g H 2 O 2 /kg TS, 19.4% higher methane production was achieved compared to raw sludge in biochemical methane potential assay. Fenton pre-treatment resulted in the release of organic sludge com- ponents into the liquid phase. For 4 g Fe(II)/kg TS and 60 g H 2 O 2 /kg TS, dissolved organic carbon and total nitrogen in sludge’s supernatant increased by 75.74 and 60.60%, respectively. Fenton pre-treatment enhanced the filterability of sludge and it can be applied for conditioning purpose before mechanical dewatering units. Keywords: Anaerobic biodegradability; Biological sludge; Box–Wilson experimental design; Fenton pre-treatment; Floc disintegration Received: June 1, 2010; revised: September 2, 2010; accepted: September 16, 2010 DOI: 10.1002/clen.201000199 1 Introduction Biological treatment of wastewater results in the generation of a considerable amount of waste activated sludge that has to be treated. Sludge treatment and disposal represents a decisive factor for design, operation, and costs of wastewater treatment especially for large treatment plants. Since the costs of sludge treatment are high, representing 50–60% of the total operating costs of the waste- water treatment [1], much attention has been focused on advanced sludge treatment processes to reduce the amount of sludge pro- duced and to improve the dewaterability of the sludge. In order to improve hydrolysis and anaerobic digestion performance, dis- integration was developed as the pretreatment process of sludge to accelerate the anaerobic digestion and to increase degree of stabilization [2, 3]. Increase of stabilization degree of sludge with disintegration process provides less sludge production, more stable sludge, and more biogas production comparing the classical anaerobic digestion [4]. Ultrasonic treatment [5–8], ozone oxidation [9–11], mechanical disintegration [12], alkaline treatment [13, 14], thermal treatment [15], and biological hydrolysis with enzymes [16, 17] were investigated for sludge disintegration purpose by sev- eral researchers in half-scale and lab-scale plants. Fenton process is one of the commonly used advanced oxidation techniques. Fenton’s reagent is a mixture of H 2 O 2 and ferrous iron. The ferrous iron initiates and catalyses the decomposition of H 2 O 2 , resulting in the generation of highly reactive hydroxyl (HO  ) radicals [18]. The HO  radical is the main oxidizing agent in the process capable of decom- posing a number of organic substances via oxidation. The rate and extent of the Fenton reactions are dependent on system parameters including, iron and hydrogen peroxide concentration, and solution pH. The application of Fenton process for sludge disinte- gration may cause two phenomena that solubilization and mineral- ization of sludge solids. Some part of activated sludge is mineralized to carbon dioxide and water while the other part of sludge is solubilized to biodegradable organics, which are easily accessible and can be digested much faster in later biological process than sludge in a particular phase. Takumura et al. [19] applied the similar advanced oxidation method of photo-Fenton reaction to biological sludge in a batch photo reactor for disintegration purpose and they noted that 4 g H 2 O 2 /L, 0.04 g Fe(II)/L application at pH 3 for 6 h reaction time is efficient for effective sludge’s solubilization. Neyens et al. [20] were applied Fenton process to thickened sludge and they noted that optimum activity is the presence of 25 g H 2 O 2 /kg dry solids (DSs), 1.67 g Fe(II)/kg DSs, pH 3, and at ambient tempera- ture and pressure. In these conditions Fenton process resulted in a considerable reduction of DSs and organic dry solids (ODS) contents in the filter cake of 20%, an improved dewaterability with a 30% reduction of the sludge volume, and a 30% increase of the cake DS- content when compared with the untreated sludge sample. Dewil et al. [21] were investigated the influence of Fenton process (25 g H 2 O 2 /kg DS, 1.67 g Fe 2þ /kg DS, pH 3) on mechanical drying performance of thickened activated sludge and DSs content of sludge cake increased from 22.5 to 40.3% with this application. In another study, Buyukkamaci [22] evaluated the effect of Fenton’s Correspondence: Dr. G. Erden, Department of Environmental Engineering, Dokuz Eylu ¨l University, Kaynaklar Campus, 35160, Buca- Izmir, Turkey E-mail: gulbin.erden@deu.edu.tr Abbreviations: BMP, biochemical methane potential; CST, capillary suction time; DD, disintegration degree; DOC, dissolved organic carbon; DS, dry solid; EC, electrical conductivity; EPS, extracellular polymeric substance; SRF, specific resistance to filtration; TN, total nitrogen; TS, total solid. 626 Clean – Soil, Air, Water 2011, 39 (7), 626–632 ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com