Optimizing the Composition of Bioactive Coatings to Support Toluene Removal

Abstract

The potential of bioactive coatings as an innovative biotechnology to overcome the mass-transfer limitations of conventional technologies when treating indoor air pollutants, especially hydrophobic volatile organic compounds (VOCs), was herein assessed. Bioactive coatings consist of active microorganisms entrapped in a polymer matrix, which needs to be porous to facilitate effective gas pollutant and nutrient exchange. To increase porosity, two additives, sucrose and glycerol mixtures (Suc/Gly) and halloysite nanotubes (HNTs), were included in the bioactive coatings at two concentration levels. The toluene removal performance of the different bioactive coatings was studied in batch mode at low (~300 mg m-3) and high (~3000 mg m-3) toluene concentrations. Overall, low HNTs concentration coatings supported optimum toluene removals, comparable to biofilm controls at both toluene concentrations. High HNTs concentration coatings and low Suc/Gly concentration coatings achieved good toluene removals, especially when supplemented at 300 mg m-3, eventually outperforming biofilm controls at the end of high toluene concentration experiments. High Suc/Gly concentration supported a limited toluene removal in both experiments, which was attributed to a preferential consumption of sucrose over toluene. These findings were corroborated by ESEM/conventional SEM imaging, revealing a certain degree of porosity in the HNTs bioactive coatings, visible at both the surface and internal levels. On the contrary, more homogeneous surfaces were observed in the Suc/Gly bioactive coatings, where total polymer coalescence was partially hindered by the addition of Suc/Gly. These results paved the way towards the implementation of bioactive coating in larger bioreactors for real-life indoor air purification.