Abstract
A cylindrical bioelectrochemical reactor (BER) containing carbon fiber textiles (CFT; BER + CFT) has characteristics of bioelectrochemical and packed-bed systems. In this study, utility of a cylindrical BER + CFT for degradation of a garbage slurry and recovery of biogas was investigated by applying 10% dog food slurry. The working electrode potential was electrochemically regulated at −0.8 V (vs. Ag/AgCl). Stable methane production of 9.37 L-CH4 · L−1 · day−1 and dichromate chemical oxygen demand (CODcr) removal of 62.5% were observed, even at a high organic loading rate (OLR) of 89.3 g-CODcr · L−1 · day−1. Given energy as methane (372.6 kJ · L−1 · day−1) was much higher than input electric energy to the working electrode (0.6 kJ · L−1 · day−1) at this OLR. Methanogens were highly retained in CFT by direct attachment to the cathodic working electrodes (52.3%; ratio of methanogens to prokaryotes), compared with the suspended fraction (31.2%), probably contributing to the acceleration of organic material degradation and removal of organic acids. These results provide insight into the application of cylindrical BER + CFT in efficient methane production from garbage waste including a high percentage of solid fraction.
Highlights
Recycling of the huge organic fraction in municipal solid wastes such as garbage and waste from the food industry has been long-awaited (Haruta et al 2005)
Potential on the cathodic working electrode was regulated at −0.8 V because we previously reported that stable methane production and decomposition of garbage slurry at a high organic loading rate (OLR) were observed in a small-scale thermophilic bioelectrochemical methanogenic reactor (250-mL working volume) regulated at −0.8 V (Sasaki et al 2010b)
The gas production rate in the bioelectrochemical reactor (BER) + carbon fiber textiles (CFT) increased as the OLR increased (Figure 3a)
Summary
Recycling of the huge organic fraction in municipal solid wastes such as garbage and waste from the food industry has been long-awaited (Haruta et al 2005). Anaerobic digestion using methane fermentation is an effective technology for recovering methane gas as a renewable energy source. It is a low-cost process and produces little residual sludge (Ahring 2003; Forster-Carneiro et al 2008). Thermophilic packed-bed systems have been reported to be one of the high-performance reactor designs (Sasaki et al 2007; Ueno et al 2007). In the packed-bed system, supporting materials were packed to retain microorganisms and thereby enable operation at a high organic loading rate (OLR) and short hydraulic retention time
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