Guillaume Darracq

Removal of Hydrophobic Volatile Organic Compounds in an Integrated Process Coupling Absorption and Biodegradation { Selection of an Organic Liquid Phase

Since usual processes involve water as absorbent, they appear not always really efficient for the treatment of hydrophobic volatile organic compound (VOC). Recently, absorption and biodegradation coupling in a two-phase partitioning bioreactor (TPPB) proved to be a promising technology for hydrophobic compound treatment. The choice of the organic phase, the non-aqueous phase liquid (NAPL) is based on various parameters involved in both steps of the process, hydrophobic VOC absorption in a gas–liquid contactor, and biodegradation in the TPPB. VOC solubility and diffusivity in the selected NAPL, as well as NAPL viscosity, seems to be the main parameters during the absorption step, while biocompatibility, namely the absence of toxic effect of the NAPL towards microorganisms, non-biodegradability and VOC partition coefficient between NAPL and water were revealed as the key factors during the biodegradation step. The screening of the various NAPL available in the literature highlighted two families of compounds matching the required conditions for the proposed integrated process, silicone oils and ionic liquids.

Absorption and biodegradation of hydrophobic volatile organic compounds: determination of Henry's constants and biodegradation levels.

Biodegradation of three volatile organic compounds (VOCs) was studied. Toluene, dimethylsulphide (DMS), and dimethyldisulphide (DMDS) were introduced into flasks filled with emulsions of Di-2-EthylHexylAdipate (DEHA) in water, containing biomass (activated sludge). The VOC concentrations were analysed in the gas, organic and aqueous phases, and compared to the initial VOC quantities introduced in order to deduce their consumption by biomass. Toluene and DMDS were completely consumed, and then removed from the gas and the organic phases, except when DEHA and water are in the same volume ratio, which appears to be extreme environmental conditions for bacterial growth. The high DMS volatility resulted in an important gas loss, leading to a lower amount of DMS available for activated sludge growth. For all the VOC experiments, some components, characteristics of the DEHA degradation, including 2-ethylhexanal, 2-ethylhexanol, 2-ethylhexanoic acid and adipic acid, were identified.

Activated Sludge Acclimation for Hydrophobic VOC Removal in a Two-Phase Partitioning Reactor

The effect of activated sludge acclimation on the biodegradation of toluene and dimethyldisulphide (DMDS) in the presence of a non-aqueous phase liquid, polydimethylsiloxane (PDMS), in a two-phase partitioning bioreactor was characterized. The influence of the presence of PDMS, at a ratio of 25% (v/v), and acclimation of activated sludge on two hydrophobic VOC biodegradation was studied. Activated sludge were acclimated to each VOC and in the presence of the non-aqueous phase liquid, namely in the emulsion of PDMS in water. Using acclimated cells, 97.9% and 108.7% improvement of the mean biodegradation rates were recorded for toluene and DMDS, respectively, if compared to the values recorded in the absence of acclimation. While and in agreement with the lower solubility in water of DMDS if compared to toluene, a most significant effect of PDMS addition on the rate of DMDS removal was recorded, 87.0% and 153.6% for toluene and DMDS, respectively. In addition and if both biomass acclimation and PDMS addition were considered, overall improvements of the removal rates were 204% and 338% for toluene and DMDS.