Feasibility of operating a solid–liquid bioreactor with used automobile tires as the sequestering phase for the biodegradation of inhibitory compounds

• Used tire pieces absorbed high aqueous levels of DCP in a bioreactor.
• The DCP was released to cells based on metabolic demand and degraded.
• The tire-modified bioreactor greatly outperformed a conventional bioreactor.
• Waste polymers have significant potential for other biotreatment applications.

Finding new uses for waste or discarded material is an important environmental goal; being able to use a waste material to treat another waste is an even more attractive objective, and this was the purpose of the present work. We previously showed that used automobile tires have an affinity for a toxic contaminant, dichlorophenol (DCP), absorbing and releasing it based on concentration driving forces. Here we have exploited this phenomenon by using used tires as the sequestering phase in a Two-Phase Partitioning Bioreactor (TPPB) to treat otherwise-toxic levels of DCP, far out-performing single phase operation in a sequencing batch bioreactor. A comprehensive examination of substrate loading, reactor exchange ratio, and tire fraction used, demonstrated that the tire-TPPB system could handle a 40% higher influent substrate loading and an increase of the exchange ratio value from 0.5 (prohibitive for single phase operation) to 0.7. Such improvement was obtained with a tire fraction ≤9%, comparable to that for commercial polymers previously employed in TPPBs. This study has opened the door to the identification of other waste plastics suitable for use in TPPBs for the treatment of recalcitrant organic contaminants.

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