Simultaneous Degradation of Toxic and Volatile Substrates by Two Phase Partitioning Bioreactor Systems: Performance Characterization and Rational Polymer Selection
Poleo, Eduardo E.
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The degradation of toxic and volatile contaminants in aqueous streams is considered a challenge using conventional bioremediation strategies. At moderate concentrations, toxic contaminants induce microbial inhibition, which results in an overall decrease of reaction rates. On the other hand, volatile compounds are often stripped out of solution into the atmosphere during aeration in conventional wastewater treatments, and are not treated. The addition of a second non-aqueous phase with affinities for the contaminants can reduce aqueous concentrations to sub-inhibitory levels and also decrease contaminant volatilization, while still allowing controlled release of contaminants back to the microbial population; such systems have been denoted as Two Phase Partitioning Bioreactor (TPPB). The current work examined and compared the performance of solid-liquid TPPB to a liquid-liquid TPPB and a single phase system. The systems were compared in the simultaneous degradation of phenol and butyl acetate, two substrates known for their relatively high levels of toxicity and volatility, respectively. The solid-liquid TPPB, using 2 polymers selected heuristically, showed an improvement of 40 and 54 % in phenol degradation rates compared to the single phase and the liquid-liquid systems. Additionally, the solid-liquid system presented a 55 and 11 % enhancement in the amount of butyl acetate degraded. At higher initial substrate concentration the solid-liquid TPPB showed an improvement in the phenol degradation rate and the amount of butyl acetate degraded of 44 and 94 % respectively, compared to the single phase system. In order to rationalize polymer screening for solid-liquid TPPBs, selection criteria based on first principles were developed, and were based on consideration of polymer accessibility and polymer-solute thermodynamic affinity. Polymer accessibility was evaluated by considering glass transition temperature (Tg) and degree of crystallinity, while polymer-solute thermodynamic affinity was assessed using three different methods, Hildebrand solubility parameters, Hansen Solubility Parameters (HSP) and activity coefficients at infinite dilution. It was found that the HSP method gave the best trends and its predictions had better agreement with the experimental results. Consequent biodegradation experiments with a single, rationally selected polymer, and a mixture of waste polymers, demonstrated the superior performance of rational selected polymers.