Toxicity of phenol towards anaerobic biogranules

Toxity of phenol towards upflow anaerobic sludge blanket (UASB) biogranules treating wastewater containing different substrates was investigated. Under shock-loading conditions, the specific methanogenic activity (SMA) of the biogranules decreased with the increase of phenol concentration. The C1.50 (i.e. the concentration at which bioactivity was 50% of the control) was 1750, 1000 and 1700 mg-phenol litre−1 for acetate-, propionate- and benzoate-degrading biogranules, respectively. Under continuous-loading conditions, however, phenol toxicity was not progressive. Instead, phenol had a threshold toxicity level for each type of biogranules: 1050–1600, >850 and 1100–1700 mg litre−1 for benzoate-, propionate- and acetate-degrading biogranules, respectively. Below these threshold levels, phenol was not inhibitive to the activity of biogranules; but above them, the inhibition was nearly 100%. Phenol toxicity was neither cumulative nor permanent. Once the phenol concentration in wastewater was lowered to levels below the threshold, biogranules were able to gradually regain 100% of their activity. Lowering substrate concentration expedited the recovering process.