Effect of Inoculum Addition Modes and Leachate Recirculation on Anaerobic Digestion of Solid Cattle Manure in an Accumulation System

The effect of both leachate recirculation (at 40 and 50 °C) and the mode of inoculum addition (at 50 °C) on the performance of a non-mixed accumulation (i.e. fed batch) system treating solid cattle wastes was investigated, using laboratory scale reactors at a filling time of 60 days. A relatively high methane production rate (MPR) and low stratification of intermediates occur with leachate recirculation. The leachate recirculation volume flow and methane production rate are smaller at 40 °C than at 50 °C: 0·31 and 0·7 l [CH4] l−1 [reactor] day−1, respectively. The increased MPR at higher temperature is at one hand caused by the increase of microbial activity, at the other hand by the lower viscosity causing the increased leachate recirculation volume. Dividing the inoculum in equal doses and distributing them with the feed positively affects the system behaviour as compared to adding the same inoculum amount at the reactor bottom at the start only. Without addition of inoculum a very poor system performance was observed. The average MPR was 0·2, 0·4 and 0·5 l [CH4] l−1 [reactor] day−1 for the reactor without inoculum, inoculum addition at the reactor bottom and inoculum addition in different equal doses, respectively.