ANAEROBIC-DIGESTION OF ALKALINE BLACK LIQUOR USING AN UP-FLOW ANAEROBIC SLUDGE BLANKET REACTOR

The anaerobic digestion of alkaline black liquor from a cereal straw p ulping mill was studied in batch (serum bottles) and continuous system s (up-flow anaerobic sludge blanket reactor-UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alka line black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5-10 kg COD m-3 day-1, the UASB reactor achieved 50-60% COD removal efficienc ies. Gas production was 2-3 dm3 per dm3 of alkaline black liquor. Two different sludge types were examined in the reactor: granular and clus ter-like sludges. Sludge in a cluster, which involved many small granu les and flocs, tended to form larger aggregates and possessed good set tling ability.