Chemosphere 74 (2008) 797–803 0045-6535/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2008.10.028 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere 1. Introduction The management of municipal solid wastes (MSW) may cre- ate serious environmental and economic problems. In the devel- oped countries, the trend is to divert a large part of urban refuse away from landfills to controlled bioreactors, providing improved control over operating conditions and allowing the process to be manipulated to achieve more efficient digestion of waste. The concerns on the long term management issues of landfills favor bioreactor practices, which promote short stabilization times and minimize environmental impact (Chugh et al., 1999; O’Keefe and Chynoweth, 2000). Organic fraction of MSW has high energy content. Due to its composition, organic fraction of MSW can also be considered as an optimal substrate for acidogenic fermentation (Traverso et al., 2000). In general, the beneficial product formation through anaer- obic digestion (AD) has been focused on methane only, which is the final product in the methanogenic anaerobic process (Hwang et al., 2004). However, AD must not be seen solely as a biogas pro- duction process. In addition to biogas, AD may generate other intermediary and valuable products, such as solvents and volatile fatty acids (VFAs), which can be marketed along with methane. Furthermore, earlier reports indicated that conversion of the MSW can be achieved as VFA production by acidogenic step of AD. The VFA would be extracted and converted to products, such as methyl or ethyl esters for commercial purposes (Ten Brummeler et al., 1991; D’Addario et al., 1993). The aim would be to obtain the maximum concentration of VFA in the liquid phase (Argelier et al., 1998). Using organic fraction of MSW acidogenic fermentation, the yields obtainable in terms of VFA and light alcohols, are up to the 40% of the influent total chemical oxygen demand (tCOD) which is a promising result (Traverso et al., 2000). Leaching bed reactors (LBRs) were designed mainly to treat the high-solids organic wastes and to recover biogas at high rates. LBRs also constitute a promising option for dry AD of organic frac- tion of MSW. The results of the organic fraction of MSW studies resulted in the development of two-phase processes including LBRs (Ghosh, 1985; Chugh et al., 1999; Vieitez et al., 2000). The concept of an LBR (also known as percolating anaerobic or dry AD) is basically a one-stage column reactor operated in batch mode, through which leachate (or liquor) is collected at the bottom of the reactor. The solubilisation of complex solid-state organic wastes to simple organic compounds (known as liquefaction/hydrolysis) by hydrolytic microorganisms and their acidification to VFAs and alcohols efficiently by acidogens take place in LBRs. The concept of a two-stage leaching bed and methanogenic reactor has been used effectively for AD of organic fraction of MSW (Chugh et al., 1999; Vieitez et al., 2000), fruit and vegetable wastes (Mtz-Viturtia et al., 1995), food wastes (Ghanem et al., 2001; Han et al., 2002), animal manure (Demirer and Chen, 2008) as well as biohydrogen production by anaerobic fermentation of food waste (Han and Shin, 2004). However, to the author’s best knowledge no study is cited in the literature for the hydrolysis/acidification of Performance of leaching bed reactor converting the organic fraction of municipal solid waste to organic acids and alcohols E. Dogan a , T. Dunaev b , T.H. Erguder a , G.N. Demirer a, * a Department of Environmental Engineering, Middle East Technical University, Ankara 06531, Turkey b Department of Civil and Environmental Engineering, Villanova University, Villanova 19085, PA, USA article info abstract Article history: Received 16 April 2008 Received in revised form 16 October 2008 Accepted 17 October 2008 Available online 29 November 2008 A lab-scale leaching bed reactor (LBR) was operated to (1) investigate the potential of in-vessel solid-state anaerobic digestion of the organic fraction of municipal solid waste (MSW) and (2) examine the feasibility of using LBRs for hydrolysis/liquefaction and acidification of organic fraction of MSW for maximum total volatile fatty acid (tVFA) and alcohol production. A hydrolysis efficiency of 60% was achieved in the LBR, which was mainly affected by the solids content of organic fraction of MSW, the amount of water addition into the LBR and the channeling through the waste bed. The net mass of tVFA produced was 7000 mg at the end of 80 d. The main individual VFAs produced were acetic and butyric acids and the main alcohol was ethanol. The variations in the by-products of acidification were mainly due to the nature of feed and pH variations in the LBR. LBRs achieved rapid hydrolysis and acidification of organic fraction of MSW, con- sequently, high hydrolysis yield, chemical oxygen demand removal and tVFA production. © 2008 Elsevier Ltd. All rights reserved. Keywords: Solid-state anaerobic digestion Leaching bed reactor Total volatile fatty acids Acetic acid Butyric acid Ethanol * Corresponding author. Tel.: +90 312 210 58 67; fax: +90 312 210 26 46. E-mail address: goksel@metu.edu.tr (G. Demirer).