2,4-Dichlorophenol removal in a solid–liquid two phase partitioning bioreactor (TPPB): kinetics of absorption, desorption and biodegradation

The applicability of a sequencing batch two phase partitioning bioreactor (TPPB) to the biodegradation of a highly toxic compound, 2,4-dichlorophenol (DCP) (EC50=2.3–40mgL−1) was investigated. A kinetic study of the individual process steps (DCP absorption into the polymer, desorption and biodegradation) was performed and, based on favourable absorption/desorption characteristics (DCP diffusivity of 6.6×10−8cm2s−1), the commercial polymer Tone P787 (Dow Chemical), was utilized as the sequestering phase for TPPB operation. Batch kinetic biodegradation tests were performed in both single- and two-phase modes, and the Haldane equation kinetic parameters were estimated (k=1.3×10−2mgDCPmgVSS−1h−1, KI=35mgDCPL−1 and Ks=18mgDCPL−1), confirming the highly toxic nature of DCP. Consistent with these findings, operation of the single-phase system showed that for an initial DCP concentration of 130mgL−1 the biomass was completely inhibited and DCP was not degraded, while the two-phase system achieved near-complete DCP removal. In sequencing batch mode the TPPB had a removal efficiency of 91% within 500min for a feed of 320mgL−1, which exceeds the highest concentration previously degraded. These results have confirmed the effectiveness of the use of small amounts (5%, v/v) of inexpensive commercial polymers as the partitioning phase in TPPB reactors for the treatment of a highly toxic substrate at influent loads that are prohibitive for conventional single-phase operation, and suggest that similar detoxification of wastewater influents is achievable for other target cytotoxic substrates.