PHASE-SEPARATION DURING ANAEROBIC FERMENTATION OF SOLID SUBSTRATES INAN INNOVATIVE PLUG-FLOW REACTOR

Separation of the liquefaction-acidification and gasification phases o f anaerobic digestion was studied in a simple, plug-flow reactor (PFR) charged with 3 to 10 wt% solids-content feed slurries. The unmixed PF R had zigzagging parallel channels with floors sloping towards the out let. Steady-state runs were conducted at hydraulic retention times of 32 to 13 days and organic loading rates (OLRs) of 0.84 to 6.84 kg-VS/m (3)-d. Phase separation was first observed when the OLR was 2.05 kg-VS /m(3)-d. Longitudinal pH and volatile fatty acid (VFA) profiles at thi s OLR showed a lowest pH of 6.10 and a highest VFA accumulation of 150 0 mg/l. The acidogenic phase predominated within the first 50 cm from the inlet, and the methanogenic phase prevailed in the remainder of th e PFR. At an OLR of 6.84 kg-VS/m(3)-d the pH dropped to 4.4, and the V FA accumulated to 9600 mg/l with the acidogenic phase extending to 83 cm from the PFR inlet. Unlike a CSTR digester, the PFR always recovere d from the initial sour digestion and afforded high VS reductions of 7 8 to 63% corresponding to methane yields of 0.36 to 0.28 m(3)/kg-VS ad ded. (C) 1997 IAWQ. Published by Elsevier Science Ltd.