Co-biodegradation of Phenol, o-Cresol, and p-Cresol in Binary and Ternary Mixtures: Evaluation of Bioreactor Performance and Toxicity of Treated Effluents

Co-biodegradation of phenol and cresols in binary and ternary mixtures was investigated in circulating packed-bed bioreactors (CPPBs). Effects of composition (phenol: 500 mg L-1, o-cresol and p-cresol: 100-500 mg L-1), phenolic loading rate (2-508 mg L-1 h(-1)), and bioreactor residence time (1-54 h) on the removal efficiency and removal rate of phenols and effluent toxicity were evaluated. In the binary mixtures, maximum phenol removal rate with 100, 300, and 500 mg L-1 p-cresol was 87.2, 89.2, and 90.7 mg L-1 h(-1) at residence times of 4.0, 3.6, and 2.7 h, respectively. The corresponding values with o-cresol were 117.7, 76.6, and 68.9 mg L-1 h(-1) at residence times of 4.2, 4.6, and 4.4 h. Increase of p-cresol or o-cresol concentration in the binary mixture with phenol enhanced the cresol removal rate, with the highest removal rates for p-cresol and o-cresol being 121.3 and 70.3 mg L-1 h(-1), respectively. In the ternary mixture, increase of p-cresol or o-cresol concentration enhanced their removal rate and presence of each compound inhibited the biodegradation of the other. Cresols, specially o-cresol, impacted the biodegradation of phenol negatively. Consistent with the trend for biodegradation of individual phenols, the highest removal rate was achieved with p-cresol, followed by phenol, and o-cresol (135.3, 129.2, and 108.0 mg L-1 h(-1)). Effluents were less toxic than the influents, but the toxicity was not eliminated in the effluents obtained under maximum removal rate of phenolic compounds. This implies that removal efficiency is more influential than removal rate in eliminating the toxicity.

Automated summary

The co-biodegradation of phenol and cresols in binary and ternary mixtures was investigated using circulating packed-bed bioreactors. The study found that increasing the concentration of o-cresol and p-cresol enhanced their removal rate, but negatively affected the biodegradation of phenol. The removal efficiency had a greater impact on eliminating toxicity than the removal rate.