Immobilization strategies for bioaugmentation of anaerobic reactors treating phenolic compounds

Degradation of phenol, ortho- and para-cresol was investigated in upflow an aerobic sludge bed (UASB) reactors bioaugmented with a methanogenic enrichm ent consortium able to degrade a mixture of phenolic compounds, in comparis on to a reactor, which was inoculated only with anaerobic granules. The var iables studied were the enrichment-to-inoculum ratio and the enrichment imm obilization method : 1) natural attachment of free cells to the granules, a nd 2) encapsulation within alginate beads. The increase of the percentage o f enrich ment from 2 to 5 % improved considerably the startup of the reacto rs. Going from 5 to 10% had no effect on the removal of the phenolic compou nds. Following a period of continuous operation at a hydraulic retention ti me of 3 days, the bioaugmented reactors showed specific activities on pheno l, ortho- and para-cresol, at least twofold higher than those of the contro l reactor. This increase was attributed to the immobilization of phenol, or tho- and para-cresol-degrading bacteria on the granules.