Development of a partitioning bioscrubber process for the treatment of waste gases containing toxic volatile organic compounds.

摘要

A two-phase partitioning bioscrubber (TPPB) has been developed for the removal and biodegradation of toxic volatile organic compounds (VOCs) from industrially-derived waste gases. TPPBs are characterized by a cell-containing aqueous medium, as well as a second, immiscible organic liquid phase with a high affinity for the target VOC which provides protection from high concentrations of toxic compounds through equilibrium partitioning, and enhanced rates of VOC absorption. Achromobacter xylosoxidans Y234 was selected to degrade benzene while n-hexadecane, with a nominal organic phase volume fraction of 0.33, served as the organic phase in the 3 L bioscrubber.;Cellular maintenance energy had an important impact, ultimately leading to pseudo-steady-state operation. With the culture in a 'maintenance state', in which substrate was directed towards essential energy generation rather than biosynthesis, net biomass accumulation became zero. Translation of this effect into an operating policy which encourages pseudo-steady-state operation greatly simplified operating protocols by eliminating medium exchanges, reduced costs, and minimized waste generation. This novel protocol was demonstrated during a prolonged treatment period (30 days) where a constant benzene elimination capacity of 141 +/- 12 g/m3-h was attained with >99% removal efficiency.;The presence of the organic phase greatly reduced effluent benzene concentrations during and after transient perturbations in the feed gas, particularly for large fluctuations. Parametric sensitivity analysis revealed that both the volume fraction and Henry's Law coefficient of the organic phase can greatly influence performance. It was also found that microorganisms which best thrive under dilute substrate concentrations will make ideal biocatalysts in the TPPB.;Overall, this thesis has continued to advance the TPPB towards becoming a viable alternative for waste gas treatment by demonstrating its high performance potential under industrially-relevant conditions while also streamlining its operating requirements and reducing labor and material costs.;The fundamental constituent phenomena comprising the TPPB were studied to investigate their individual contributions to its overall performance and aided in developing a mechanistic, mathematical model. Oxygen transfer rates in the two-phase partitioning bioscrubber were enhanced by using an organic phase with a high equilibrium solubility of oxygen. Empirical models of oxygen mass transfer coefficients in aqueous medium and n-hexadecane were developed as a function of the operating conditions, as well as a combined model of oxygen absorption in the two-phase partitioning bioscrubber.