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 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.