Cellulose pulp mill effluent treatment in an upflow anaerobic sludge blanket reactor

The performance of a bench scale upflow anaerobic sludge blanket reactor (UASB) was evaluated for the treatment of diluted black liquor from a Kraft pulp plant. The reactor was monitored over a 635 day period of continuous operation. In the first experimental phase, the hydraulic and organic load rate were changed while, in the second phase, these operational parameters were kept constant to observe the long-term changes in the reactor behaviour. The average chemical oxygen demand removal efficiency during the entire experiment was 80% and, due to the low growth of biomass, it was not necessary to waste the sludge. The microbial consortium became acclimated to the substrate, even though black liquor is potentially toxic for methanogenic cells. The anaerobic biomass presented a good recovery capacity after a thermal shock and subsequent acidification. The UASB reactor was stable, easy to operate with low maintenance and operational costs. (C) 2002 Elsevier Science Ltd. All rights reserved.