A comparison of biogas production from dairy manure filtrate using conventional and fixed-film reactors.

The methane production capability of two laboratory-scale, 4-L, anaerobic reactors (conventional and fixed-film) receiving screened dairy manure and operated at35°C was compared. Dairy manure filtrate with 4.4% total solids (TS) and 3.4% volatile solids (VS) (average value) was prepared from 1:1 manure/water slurry. The feed material was added intermittently at loading rates ranging from 2.34 to 25.0 and 2.25 to778 g VS/L-day, for the conventional and fixedfilm reactor, respectively. Maximum methane production rate for the conventional reactor was 0.63 LCH4/Ldigesta-day achieved at a 6-day hydraulic retention time (HRT). For the fixed-film reactor, the maximum production rate was 6.20 L CH4/Lday when operated at a loading rate of 259 g VS/L-day at 3h HRT. The fixed-film reactor was capable of sustaining a loading of 778 g VS/L-day at 1 h HRT. The fixed-film reactor could be operated at shorter HRTs and higher loading rates thantheconventional reactor. Average biogas methane content from thefixed-film reactor (65.8%) was higher than from the conventional reactor (61.6%). Results indicate that a high potential reduction of required reactor volume is possible through applicationof a fixed-film concept.