ENVIRONMENTAL BIOTECHNOLOGY Efficient treatment of garbage slurry in methanogenic bioreactor packed by fibrous sponge with high porosity Kengo Sasaki & Daisuke Sasaki & Masahiko Morita & Shin-ichi Hirano & Norio Matsumoto & Naoya Ohmura & Yasuo Igarashi Received: 29 October 2009 / Revised: 23 January 2010 / Accepted: 25 January 2010 / Published online: 17 February 2010 # Springer-Verlag 2010 Abstract Adding a supporting material to a methanogenic bioreactor treating garbage slurry can improve efficiency of methane production. However, little is known on how characteristics (e.g., porosity and hydrophobicity) of the supporting material affect the bioreactor degrading garbage slurry. We describe the reactor performances and microbial communities in bioreactors containing hydrophilic or hydrophobic sheets, or fibrous hydrophilic or hydrophobic sponges. The porosity affected the efficiency of methane production and solid waste removal more than the hydrophilic or hydrophobic nature of the supporting material. When the terminal restriction fragment length polymorphism technique was used at a lower organic loading rate (OLR), microbial diversities in the suspended fraction were retained on the hydrophobic, but not the hydrophilic, sheets. Moreover, real-time quantitative polymerase chain reaction (PCR) performed at a higher OLR revealed that the excellent performance of reactors containing fibrous sponges with high porosity (98%) was supported by a clear increase in the numbers of methanogens on these sponges, resulting in larger total numbers of methanogens in the reactors. In addition, the bacterial communities in fractions retained on both the hydrophobic and hydrophilic fibrous sponges differed from those in the suspended fraction, thus increasing bacterial diversity in the reactor. Thus, higher porosity of the supporting material improves the bioreactor performance by increasing the amount of methanogens and bacterial diversity; surface hydrophobicity contributes to maintaining the suspended microbial community. Keywords Supporting material . Methane fermentation . Garbage . Porosity . Hydrophobicity Introduction In Japan, the large amount of organic solid wastes (e.g., garbage) produced every year is coped with by dumping it in landfills or incinerating it, both of which produce environ- mental problems (Haruta et al. 2005; Ueno et al. 2007). Consequently, there is now a great deal of the social interest in the recycling of organic solid wastes. Anaerobic digestion using methane fermentation is one approach to addressing this problem, as it has minimal environmental impact and reduces sludge production, and its end products can be used as an energy source (Farhadian et al. 2007). The up-flow anaerobic sludge blanket (UASB) process is the most popular anaerobic system for wastewater treatment; how- ever, UASB is not adapted for treatment of waste with organic solids (Ueno et al. 2007). Anaerobic biological reactors utilized for the treatment of organic solid wastes include a two-stage system (phase separation in an acido- genic process and a methanogenic processes) and a packed- bed system (Angelidaki et al. 2006; Sasaki et al. 2007; Ueno et al. 2007). Because of its higher loading rate and greater biogas yield, the packed-bed system has recently gained much attention (Tatara et al. 2004, 2008; Umaña et al. 2008). K. Sasaki : M. Morita (*) : S.-i. Hirano : N. Matsumoto : N. Ohmura Biotechnology Sector, Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba-ken 270-1194, Japan e-mail: masahiko@criepi.denken.or.jp D. Sasaki : Y. Igarashi Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan Appl Microbiol Biotechnol (2010) 86:1573–1583 DOI 10.1007/s00253-010-2469-7