Self-regenerating polymeric tubing bioreactor for removal of toxic substrates: operational strategies to face long-term severe dynamic loading conditions

A tubing TPPB (Two-Phase Partitioning Bioreactor) was operated with the objective of verifying the effective treatment of a phenolic syntheticwastewaterwith 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 bioreactorwas operated for a 3month period under severe loading conditions (from77 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 removalwas achieved after a fewdays (1-5) of operationwhile for the 2 h HRT (i.e. in themost severe loading condition) the DCP removalwas >=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 achievedwhen the bioreactorwas operated at the lowest HRT (i.e. 2 h), combinedwith 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.