Continuous high-solids anaerobic co-digestion of organic solid wastes under mesophilic conditions
2011
Kim, Dong-Hoon | Oh, Sae-Eun
With increasing concerns over the limited capacity of landfills, conservation of resources, and reduction of CO₂ emissions, high-solids (dry) anaerobic digestion of organic solid waste (OSW) is attracting a great deal of attention these days. In the present work, two dry anaerobic co-digestion systems fed with different mixtures of OSW were continuously operated under mesophilic conditions. Dewatered sludge cake was used as a main seeding source. In reactor (I), which was fed with food waste (FW) and paper waste (PW), hydraulic retention time (HRT) and solid content were controlled to find the maximum treatability. At a fixed solid content of 30% total solids (TS), stable performance was maintained up to an HRT decrease to 40d. However, the stable performance was not sustained at 30d HRT, and hence, HRT was increased to 40d again. In further operation, instead of decreasing HRT, solid content was increased to 40% TS, which was found to be a better option to increase the treatability. The biogas production rate (BPR), CH₄ production yield (MPY) and VS reduction achieved in this condition were 5.0m³/m³/d, 0.25m³ CH₄/g CODₐddₑd, and 80%, respectively. Reactor (II) was fed with FW and livestock waste (LW), and LW content was increased during the operation. Until a 40% LW content increase, reactor (II) exhibited a stable performance. A BPR of 1.7m³/m³/d, MPY of 0.26m³ CH₄/g CODₐddₑd, and VS reduction of 72% was achieved at 40% LW content. However, when the LW content was increased to 60%, there was a significant performance drop, which was attributed to free ammonia inhibition. The performances in these two reactors were comparable to the ones achieved in the conventional wet digestion and thermophilic dry digestion processes.
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