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 = 2.3-40 mg L-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 x 10(-8) cm(2) s(-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 x 10(-2) mgDCP mgVSS(-1) h(-1), K-I = 35 mgDCP L-1 and K-s = 18 mgDCP L-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 130 mg L-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 500 min for a feed of 320 mg L-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.