Abstract
In this study, a water–silicone oil biphasic system was developed to enhance the biodegradation of monochlorobenzene (CB) by Delftia tsuruhatensis LW26. Compared to the single phase, the biphasic system with a suitable silicone oil fraction (v/v) of 20% allowed a 2.5-fold increase in the maximum tolerated CB concentration. The CB inhibition on D. tsuruhatensis LW26 was reduced in the presence of silicone oil, and the electron transport system activity was maintained at high levels even under high CB stress. Adhesion of cells to the water–oil interface at the water side was observed using confocal laser scanning microscopy. Nearly 75% of cells accumulated on the interface, implying that another interfacial substrate uptake pathway prevailed besides that initiated by cells in the aqueous phase. The 8-fold increase in cell surface hydrophobicity upon the addition of 20% (v/v) silicone oil showed that silicone oil modified the surface characteristics of D. tsuruhatensis LW26. The protein/polysaccharide ratio of extracellular polymeric substances (EPS) from D. tsuruhatensis LW26 presented a 3-fold enhancement. These results suggested that silicone oil induced the increase in the protein content of EPS and rendered cells hydrophobic. The resulting hydrophobic cells could adhere on the water–oil interface, improving the mass transfer by direct CB uptake from silicone oil.
Highlights
Monochlorobenzene (CB) is a major volatile organic compound (VOC) emitted from the production of substances, such as nitrochlorobenzene, aniline, pesticides, adhesives, dyes, and drugs [1]
The air/oil partition coefficient obtained in this work was comparable with that obtained by Muñoz et al [22], who reported that the partition coefficient of α-pinene in silicone oil was 0.000183, and was considerably lower than the partition coefficient of hexane (0.0034) reported by Arriaga et al [35]
In addition to its great affinity for CB, silicone oil was demonstrated to be biocompatible with D. tsuruhatensis LW26 and non-biodegradable by D. tsuruhatensis LW26 under the tested experimental conditions
Summary
Monochlorobenzene (CB) is a major volatile organic compound (VOC) emitted from the production of substances, such as nitrochlorobenzene, aniline, pesticides, adhesives, dyes, and drugs [1]. It has been listed as a priority pollutant by the American Environmental Protection Agency given its recalcitrance against removal and its biotoxicity and carcinogenicity [2]. Various techniques have been developed to remove CB from off-gas emissions, including biological methods [3], adsorption [4], photochemical methods [5], and catalytic oxidation [6,7]. Biological techniques are more attractive than physical and chemical methods because of their low cost, reliability, and environmental friendliness [8]. Wang et al [10] observed that a prolonged recovery time was required after a transient loading operation, caused by the short-term increase in CB concentration when using a biofilter
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