Enhancing the performance of anaerobic digestion of dairy manure through phase-separation

Anaerobic digestion (AD) is an effective way to convert animal manures into profitable by-products while simultaneously reducing the pollution of water, air, and soil caused by these wastes. Conventional high-rate anaerobic reactors cannot effectively process animal manures with high solids-containing wastes. The two-phase configuration for AD has several advantages over conventional one-phase processes, e. g., increased stability of the process, smaller size and cost efficient process configurations. In the present study, the experiments were carried out in a two-phase system composed of an acidogenic reactor and a methanogenic reactor, and in a one-phase system composed of only a methanogenic reactor. The reactors were operated as unmixed (without an external mixing aid), unsophisticated, and daily-fed mode. It was found that the two-phase configuration was more efficient than the one-phase system. The biogas production in the two-phase system at a hydraulic retention time (HRT) of 8.6 days (only methanogenic phase) was calculated to be 42\% higher at an organic loading rate (OLR) of 3.5 g VS/L \textperiodcentered day than that of the one-phase with a HRT of 20 days. This translates into significant performance improvement and reduced volume requirement. This finding represents a further step in the achievement of wider use of simple anaerobic reactor configurations for waste treatment in rural areas. \textcopyright 2008 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim.