An innovative mesophilic continuous-feed anaerobic plug-flow reactor was employed to study system performance with solid feeds from 3% to 16% TS and hydraulic retention times from 32.0 to 13.1 days. The reactor performance under high-solid feeds (>10% TS) corresponding to phase separation along the longitudinal distance of the plug-flow reactor was discussed. The two-phase plug-flow reactor (TPPFR) always recovered from acidogenic conditions prevailing at the head end of the TPPFR, and the methanogenic phase was dominant within the remainder of the TPPFR. As the feed solids concentration increased to greater than 16% (loading capacity of the feed solids concentration) and as the acidogenic phase was extended, the methanogenic bacteria could not recover from the “sour” digestion as shown by the decreased gas/or methane production rate. With same feeds and under same operating conditions, the performance of the plug-flow reactor with phase separation is much better than that of the conventional single-phase continuously stirred-tank reactor (CSTR) in terms of efficiency and overall bioconversion.

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