Controlled absorption and release of an active agent by using EVAc beads. effect of various parameters

Transient performance of two-phase partitioning bioreactors treating a toluene contaminated gas stream

Two-phase partitioning bioreactors (TPPBs) consist of a cell-containing aqueous phase and an immiscible organic phase that sequesters and delivers toxic substrates to cells based on equilibrium partitioning. The immiscible organic phase, which acts as a buffer for inhibitory substrate loadings, makes it possible for TPPBs to handle high volatile organic compound (VOC) loadings, and in this study the performance of liquid n-hexadecane and solid styrene butadiene (SB) polymer beads used as partitioning phases were compared to a single aqueous phase system while treating transient loadings of a toluene contaminated air stream by Achromobacter xylosoxidans Y234. The TPPBs operated as well-mixed stirred tanks, with total working volumes of 3 L (3 L aqueous for the single-phase system, 2 L aqueous and 1 L n-hexadecane for the solvent system, and 2.518 L aqueous volume and 500 g of SB beads for the polymer system). Two 60-min step changes (7 and 17 times the nominal loading rates, termed "small" and "large" steps, respectively) were imposed on the systems and the performance was characterized by the overall removal efficiencies, instantaneous removal efficiency recovery times (above 95% removal), and dissolved oxygen recovery times. For the small steps, with a nominal loading of 343 g/m3/h increasing to 2,400 g/m3/h, the TPPB system using n-hexadecane as the second phase performed best, removing 97% of the toluene fed to the system compared with 90% for the polymer beads system and only 69% for the single-phase system. The imposed large transient gave similar results, although the impact of the presence of a second sequestering phase was more pronounced, with the n-hexadecane system maintaining much reduced aqueous toluene concentrations leading to significantly improved performance. This investigation also showed that the presence of both n-hexadecane and SB beads improved the oxygen transfer within the systems.

Biodegradation of a phenolic mixture in a solid-liquid two-phase partitioning bioreactor

A solid-liquid two-phase partitioning bioreactor (TPPB) in which the non-aqueous phase consisted of polymer (HYTREL) beads was used to degrade a model mixture of phenols [phenol, o-cresol, and 4-chlorophenol (4CP)] by a microbial consortium. In one set of experiments, high concentrations (850 mg l(-1) of each of the three substrates) were reduced to sub-inhibitory levels within 45 min by the addition of the polymer beads, followed by inoculation and rapid (8 h) consumption of the total phenolics loading. In a second set of experiments, the beneficial effect of using polymer beads to launch a fermentation inhibited by high substrate concentrations was demonstrated by adding 1,300 and 2,000 mg l(-1) total substrates (equal concentrations of each phenolic) to a pre-inoculated bioreactor. At these levels, no cell growth and no degradation were observed; however, after adding polymer beads to the systems, the ensuing reduced substrate concentrations permitted complete destruction of the target molecules, demonstrating the essential role played by the polymer sequestering phase when applied to systems facing inhibitory substrate concentrations. In addition to establishing alternative modes of TPPB operation, the present work has demonstrated the differential partitioning of phenols in a mixture between the aqueous and polymeric phases. The polymeric phase was also observed to absorb a degradation intermediate (arising from the incomplete biodegradation of 4CP), which opens the possibility of using solid-liquid TPPBs during biosynthetic transformation to sequester metabolic byproducts.

Theoretical treatment of pollutant transfer in a finite volume of food from a polymer packaging made of a recycled film and a functional barrier

The problem of pollutant transfer in food from a polymer packaging made of a recycled film and a functional barrier is studied from a theoretical point of view. In the present case, the process is controlled by Fickian diffusion through the two films of the polymer packaging in perfect contact and by convection into the food. A numerical model is built, taking all the facts into account: the diffusion of the pollutant through the two polymer films, a convective coefficient of mass transfer on the surface, a partition factor, the volume of the liquid and the thicknesses of the polymer films. The results are expressed by using dimensionless numbers so that they can be used for various cases, viz the kinetics of pollutant transferred into the food and the profiles of concentration of the pollutant through the packaging.