Treatment of Waters Contaminated by Phenol and Cresols in Circulating Packed Bed Bioreactors—Biodegradation and Toxicity Evaluations

Biodegradation of phenol, o -cresol, and p -cresol was evaluated in continuous flow circulating packed bed bioreactors. Effect of loading rate on the removal rate of phenolic compounds was assessed by varying the influent concentration and flow rate. Regardless of the nature of phenolic compounds at a constant concentration, increase of loading rate caused the removal rate to pass through a maximum and then decline. Influent concentrations of 100 and 300 mg L −1 did not affect the removal rates of phenol and p -cresol, but higher rates were obtained at 500 mg L −1 . With o -cresol, increase of influent concentration from 100 to 300 mg L −1 enhanced the removal rate but no further enhancement was observed at 500 mg L −1 . The maximum removal rates for phenol, o -cresol, and p -cresol were 67.6–97.8, 38.7–73.8, and 77.2–107.2 mg L −1 h −1 at loading rates of 96.7–171.1, 61.6–163.9, and 87.4–183.9 mg L −1 h −1 (hydraulic residence time 2.9, 1.7–1.8, 1.2–2.8 h), respectively. Toxicity examination of untreated influents singled out phenol as the least toxic compound, while o -cresol and p -cresol showed similar toxicities. Treatment of influent containing 100 mg L −1 of phenolic compound led to the highest decrease in toxicity (> 93%) for all three compounds. With influent concentrations of 300 mg L −1 or higher, the decrease in toxicity of treated effluent was highest for phenol, followed by p -cresol, and then o -cresol. Finally, the observed patterns revealed that the toxicity of treated effluent was affected by the extent of biodegradation, as well as the toxic nature of phenolic compound under treatment.