Optimizing the composition of bioactive coatings to support toluene removal

The potential of bioactive coatings as an innovative biotechnology to overcome the mass-transfer limitations of conventional technologies when treating air pollutants, especially hydrophobic volatile organic compounds, was herein assessed. Bioactive coatings consist of active microorganisms entrapped in a polymer matrix, which needs to be porous to facilitate an effective gas pollutant 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 removals of the different bioactive coatings were 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 (>95%), comparable to biofilm controls at both toluene concentrations. High HNTs concentration coatings and low Suc/Gly concentration coatings achieved toluene removals over 95% after 7 toluene injections at low toluene concentration. At high toluene concentrations, these coatings eventually outperformed the biofilm controls. High Suc/Gly concentration coatings supported a limited toluene removal (4 and 1 injection at low and high toluene concentrations, respectively), attributed to a preferential consumption of sucrose over toluene. These findings were corroborated by ESEM/conventional SEM imaging, revealing 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 air purification. Bioactive coatings were developed to increase mass transfer for toluene removal. HNTs and Sucrose/Glycerol were used as additives to increase coating porosity. Toluene removals >95% achieved by both HNT and low Sucrose/Glycerol coatings. Sucrose favored uptake hindered toluene removal in high Sucrose/Glycerol coatings. Porous bioactive coating structures were confirmed by ESEM and conventional SEM.