Re-use of automobile tires as the partitioning phase in a solid-liquid partitioning bioreactor applied to the removal of substituted phenols

Waste tires in small pieces (3-4 mm) were utilized as the sorption phase in a TPPB for the biodegradation of 2,4-dichlorophenol (DCP) and 4-nitrophenol (4NP). These compounds are extensively used in the chemical industry and are found in many industrial effluents. Both compounds are toxic, being characterized by EC50 values of 2.3-40 mg/L and 64 mg/L for DCP and 4NP, respectively. Since a higher inhibitory effect on microorganisms is exerted by DCP the experimental tests were focused on strategies to reduce its negative impact on microbial activity. Sorption tests for DCP and 4NP were first performed to verify the related uptake rates by the tires, and results demonstrated that the tires had a higher affinity for DCP. A mixed culture acclimatized to the two phenolic compounds was then utilized in biodegradation tests in the TPPB reactor operated in sequencing batch mode. Biodegradation kinetics were investigated for DCP in single compound tests and for the binary mixture DCP-4NP. In single compound tests a significant reduction in DCP toxicity, and a concomitant enhancement in substrate removal efficiency (92%) was clearly seen for the TPPB case, with practically negligible biodegradation in the conventional single phase reactor. Finally, for the mixture we verified that the single phase system was not able to appreciably remove the DCP at a feed concentration of 150 mg/L for both compounds while a significant biodegradation was obtained in the TPPB operated with 10% v/v tires.