Self-regenerating tubing bioreactor for removal of toxic substrates: Operational strategies in response to severe dynamic loading conditions.

A tubing TPPB (Two-Phase Partitioning Bioreactor) was operated with the objective of verifying the effective treatment of a phenolic synthetic wastewater with simultaneous polymeric tubing bioregeneration by introducing tubing effluent recycle and modifications to the Hydraulic Retention Time (HRT). 2,4-dichlorophenol (DCP) was employed as the target substrate and the bioreactor was operated for a 3 month period under severe loading conditions (from 77 to 384 mg/L d) with HRT in the tubing in the range of 2-4 h. Tubing effluent recycle (recycle flow rate/influent flow rate ratio = 0.3) was applied when a loss of performance was detected arising from the increased load. For HRT values of 3 and 4 h, almost complete DCP removal was achieved after a few days (1-5) of operation while for the 2 h HRT (i.e. in the most severe loading condition) the DCP removal was ≥97%. A beneficial effect on the process performance arising from recycle application was evident for all the operating conditions investigated, and was confirmed by statistical analysis. Essentially complete polymer bioregeneration was achieved when the bioreactor was operated at the lowest HRT (i.e. 2 h), combined with the application of tubing effluent recycle. The results of this study highlighted several advantages of the tubing TPPB configuration in a comparative analysis of different regeneration options, including the possibility of operating continuously with simultaneous bioregeneration and without the need for additional units or operational steps and extra-energy consumption.