Influence of seed inoculum on the start-up of an anaerobic baffled reactor

The start-up and performance of two ten litre, eight compartment anaerobic baffled reactors (ABRs) were studied under mesophilic conditions (35 degrees C). Two reactor seeding strategies were evaluated; one using a granular sludge from a plant treating pulp and paper mill effluents (ABR1) and one with a digested seed sludge (ABR2) with comparable total and volatile solids levels. The same start-up strategies were adopted in both systems, using a constant organic feed strength (4g 1(-1) COD as a synthetic sucrose/protein wastewater) coupled to a systematic halving of hydraulic retention time (HRT) when semi-steady state was reached in the reactors. The use of granular sludge as an inoculum resulted in a dramatic reduction in overall start-up time of the reactor compared to digested sludge, resulting in high COD removals after only a short period as well. as a stable start-up. However, the long term stability of the granules was shown to be linked strongly to the available nutrients. An overly rapid increase in OLR resulted in the failure of ABR2 due to the lack of sufficient acetoclastic and lithotrophic methanogens. Studies of the particle size distribution in ABR2, with a digested sludge inoculum, confirm the previous findings that the largest flocs form in the middle compartments of the ABR.