Pentachlorophenol aerobic removal in a sequential reactor: start-up procedure and kinetic study.

This study has demonstrated the applicability of a simple technology such as the sequencing batch reactor (SBR), operated with suspended biomass, to the aerobic biodegradation of a highly toxic compound, the pentachlorophenol (PCP). An enrichment of a microbial consortium, originated from the biomass of an urban wastewater treatment plant, was performed and 70 days were sufficient to achieve removal efficiencies of ∼90% with the compound fed as only carbon and energy source Once completed the start-up period, the SBR was operated with the acclimatized biomass for 60 days at a feed concentration of PCP in the range of 10-20 mg L(-1). Improved performance was observed at increased influent concentration and the reached removal efficiency for the highest concentrations was stable at values≥90%. Kinetic and stoichiometric characterization of the acclimated biomass was performed with biodegradation tests carried out in the bioreactor during the reaction phase. The classical and a modified four-parameter forms of the Haldane equation were applied to model the substrate inhibited kinetics. Both models provided reliable predictions with high correlation coefficients (>0.99). The biomass characterization was completed with the evaluation of the growth yield coefficient, Y (0.075 on chemical oxygen demand base) and endogenous respiration rate, b (0.054 d(-1)). The aerobic SBR, operated in the metabolic mode with a mixed culture, showed superior performance in comparison to continuous systems applied in the same range of PCP influent loads and achieved removal rates are suitable for application.

Treatment of substituted phenol mixtures in single phase and two-phase solid-liquid partitioning bioreactors.

The biological treatment of phenolics is constrained by the inherent cytotoxicity of these compounds. One method to alleviate such toxicity is to add a sequestering phase to absorb, and subsequently release, the substrate(s) to the micro-organisms; such a system is termed a Two Phase Partitioning Bioreactor. Here we have compared the performance of a TPPB, relative to single phase operation, in which a small volume (5%, v/v) of beads of the polymer Hytrel 8206 was used to treat aqueous mixtures of 2,4-dimethylphenol and 4-nitrophenol. Hytrel 8206 was selected from a range of polymers that were tested for their partition coefficients (PCs) for the target molecules, with the more hydrophobic compound (2,4-dimethylphenol) having a higher PC value (201) than 4-nitrophenol (143). Significantly increased removal rates for both substrates were demonstrated in TPPB mode relative to single phase operation. Additionally, the differential release of the compounds to the aqueous phase and their distinct PC values changed the kinetic pattern of the biotreatment system, smoothing out the cellular oxygen demand. Release of the substrates by the polymer over 60 operating cycles was virtually complete (>97%) demonstrating the reusability and robustness of the use of polymers in overcoming cytotoxicity of phenolic substrates.