Journal of Hazardous Materials 142 (2007) 258–265 Effects of insufficient air injection on methanogenic Archaea in landfill bioreactor Bulent Mertoglu a,∗ , Baris Calli a , Nuray Guler a , Bulent Inanc b , Yuzo Inoue b a Department of Environmental Engineering, Marmara University, 34722 Goztepe, Istanbul, Turkey b National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan Received 7 June 2006; received in revised form 3 August 2006; accepted 8 August 2006 Available online 12 August 2006 Abstract In this study, methanogenic Archaea diversity in an aerated landfill bioreactor filled with co-disposed incineration bottom ashes and shredded incombustible wastes was monitored and analyzed as a function of time using molecular techniques. Besides, the effects of insufficient air injection on the bioreactor performance and methanogenic diversity were evaluated thoroughly. Results indicated that rapid bio-stabilization of solid waste are possible with aerated landfill bioreactor at various oxygen and oxidation reduction potential levels. Slot-blot hybridization results of leachate samples collected from aerated landfill bioreactor showed that archaeal and bacterial activities increased as stabilization accelerated and bacterial populations constituted almost 95% of all microorganisms. The results of slot-blot hybridization and phylogenetic analysis based on 16S rRNA gene revealed that Methanobacteriales and Methanomicrobiales were dominant species at the beginning while substituted by Methanosarcina-related methanogens close to the end of the operation of bioreactor. © 2006 Elsevier B.V. All rights reserved. Keywords: Landfill; Aeration; Incineration ash; Methanogen; Molecular methods 1. Introduction A bioreactor landfill is a sanitary landfill site that uses enhanced microbiological processes to transform and stabilize the readily and moderately decomposable organic waste con- stituents within 4–8 years. The need for long-term monitoring and maintenance can be reduced if the decomposition rate is accelerated. Various enhancement techniques have been devel- oped to enhance decomposition of organic and inorganic matter by adding supplemental water/leachate, possibly air and some nutrients to the waste [1–3]. Landfills in Japan currently receive municipal solid waste incineration (MSWI) residues and shredded low-organic wastes as main inputs [4]. The incineration residues and other shredded incombustible low-organic wastes originating especially from recycling activities are not completely stable and need further stabilization and monitoring [5]. There are only few studies ∗ Corresponding author at: Faculty of Engineering, Department of Environ- mental Engineering, Marmara University, 34722 Goztepe, Istanbul, Turkey. Tel.: +90 216 3474090; fax: +90 216 3480293. E-mail address: bmertoglu@eng.marmara.edu.tr (B. Mertoglu). evaluating the full-scale landfill bioreactor performances filled with co-disposed MSWI residues and shredded incombustible wastes [6,7]. However, microbial populations responsible for bio-stabilization of such a waste have not been discussed any- where before. Within a landfill environment, a complex sequence of physi- cally, chemically and biologically mediated events occur simul- taneously [8]. All stages in the aerobic and anaerobic degra- dation of solid waste that involved in landfills are monitored and evaluated according to the composition of landfill gas and characteristics of landfill leachate. Although much is known about the basic metabolism in landfill ecosystem, little is known about the microorganisms responsible for these processes. Only a few percent of Bacteria and Archaea have been isolated and almost nothing is known about their interactions [9]. In order to fully understand and characterize the microbial communities and activities, knowledge of their structure and diversity is nec- essary [10]. Molecular techniques give available information about the waste decomposition in aerobic and anaerobic processes using oligonucleotides and primers, designed to be specific for Archaea and Bacteria [11,12]. At present, ribosomal RNA 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.08.008