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Notes: Abstract In order to conclude about the feasibility of using water-immiscible organic solvents in biological waste-gas treatment, a theoretical study was done in which different types of organic-solvent-containing systems are compared with systems where the pollutant is transferred directly to the water phase. For each system the total equipment volume needed to remove 99% of a pollutant from a waste-gas stream is calculated. Three different pollutants with a different solubility in water are considered: Hexane (m gw =71), dichloromethane (m gw =0.1) and acetone (m gw =0.0016), withm gw the partition coefficient (kg/m3 gas/kg/m3 water) of the pollutant between the gas and the water phase. From the results it is concluded that the use of organic solvents is only advantageous in case the specific area for mass transfer between solvent and water is large enough to compensate for the additional transport resistance introduced by the solvent, and secondly if the solvent shows a sufficiently high affinity for the pollutants.

Notes: Abstract   For a mass-transfer-limited system, it was demonstrated that the volumetric ethene transfer coefficient (k l a) from gas to water could be enhanced by dispersing adequate amounts of a water-immiscible organic liquid, namely the perfluorocarbon FC40, in the aqueous phase. When 26% (v/v) FC40 was dispersed in a culture of Mycobacterium parafortuitum an enhancement of k l a, calculated on a total liquid volume basis, of 1.8 times was found. Steady-state experiments in the absence of microorganisms, however, showed a 1.2-fold enhancement of k l a at 18.5% (v/v) FC40. At all FC40 volume fractions tested, enhancement factors with cells were higher than enhancements without cells; apparently the microorganisms or their excretion products affected the interfacial areas or characteristic phase dimensions.

Notes: Abstract  In order to conclude about the feasibility of using water-immiscible organic solvents in biological waste-gas treatment, a theoretical study was done in which different types of organic-solvent-containing systems are compared with systems where the pollutant is transferred directly to the water phase. For each system the total equipment volume needed to remove 99% of a pollutant from a waste-gas stream is calculated. Three different pollutants with a different solubility in water are considered: Hexane (m gw =71), dichloromethane (m gw =0.1) and acetone (m gw =0.0016), with m gw the partition coefficient (kg/m3 gas/kg/m3 water) of the pollutant between the gas and the water phase. From the results it is concluded that the use of organic solvents is only advantageous in case the specific area for mass transfer between solvent and water is large enough to compensate for the additional transport resistance introduced by the solvent, and secondly if the solvent shows a sufficiently high affinity for the pollutants. List of symbols a specific area for mass transfer [m-1] a p packing material specific area [m-1] C pollutant concentration [kg . m-3] D pollutant diffusivity [m2 . s-1] d stirrer diameter [m] d p bubble, droplet or packing material diameter [m] g acceleration of the gravity [m . s-2] Gr Grashof number: g*d 3* p Δρ*(ρ/μ)2/ρ [dimensionless] H height [m] K overall mass-transfer coefficient [m . s-1] k partial mass-transfer coefficient [m . s-1] m gw partition coefficient of the pollutant in the system gas/water [kg/m3 gas/kg/m3 water] m gs partition coefficient of the pollutant in the system gas/solvent [kg/m3 gas /kg/m3 solvent] sw partition coefficient of the pollutant in the system solvent/water: m gw /m gs [kg/m3 solvent /kg/m3 water] P power input per unit mass of fluid [W . kg-1] Q flow [m3 . s-1] Re Reynolds number: ρ*ν*d p /μ [dimensionless] Sc Schmidt number: μ/ρ*D [dimensionless] Sh Sherwood number: k*d p /D [dimensionless] T tank diameter [m] t time [s] v bs bubble rising velocity [m . s-1] v s superficial velocity [m . s-1] V volume [m3] φ void fraction [dimensionless] ɛ hold-up [dimensionless] ρ density [kg . m-3] μ dynamic viscosity [kg . m-1s-1] δ film thickness [m] σ interfacial tension [kg . s-2] Δρ density difference [kg . m-3] τ residence time [s] Subscripts c coalescence layer in to the equipment out from the equipment g gas phase s solvent phase w water phase

Notes: Summary A new technique is presented to determine gas-to-water overall volumetric mass transfer coefficients (k l a) in a stirred-tank reactor containing solvent-in-water dispersions. The compound to be transferred from the gas to the water was toluene; the water-immiscible organic solvent was FC40, a perfluorocarbon. The k l a was determined in steady-state conditions in the absence of biological consumption. Toluene removal was achieved by passing a continuous flow of toluene-free water through the reactor. When solvent was present it was separated from the water at the reactor outlet by means of a small settler and recycled back to the vessel. The k l a was found to increase with the FC40 volume fraction. An enhancement of 1.9 times on an aqueous-phase-volume basis was found at 15 % (v/v) FC40.