The yeast strain Candida tropicalis was used for the biodegradation of gaseous toluene. Toluene was effectively treated by a liquid culture of C. tropicalis in a bubble-column bioreactor, and the toluene removal efficiency increased with decreasing gas flow rate. However, toluene mass transfer from the gas-to-liquid phase was a major limitation for the uptake of toluene by C. tropicalis. The toluene removal efficiency was enhanced when granular activated carbon (GAC) was added as a fluidized material. The GAC fluidized bioreactor demonstrated toluene removal efficiencies ranging from 50 to 82% when the inlet toluene loading was varied between 13.1 and 26.9 g/m(3)/h. The yield value of C. tropicalis ranged from 0.11 to 0.21 g-biomass/g-toluene, which was substantially lower than yield values for bacteria reported in the literature. The maximum elimination capacity determined in the GAC fluidized bioreactor was 172 g/m(3)/h at a toluene loading of 291 g/m(3)/h. Transient loading experiments revealed that approximately 50% of the toluene introduced was initially adsorbed onto the GAC during an increased loading period, and then slowly desorbed and became available to the yeast culture. Hence, the fluidized GAC mediated in improving the gas-to-liquid mass transfer of toluene, resulting in a high toluene removal capacity. Consequently, the GAC bubble-column bioreactor using the culture of C. tropicalis can be successfully applied for the removal of gaseous toluene.
In this study, an organic solvent tolerant bacterial strain was isolated. This strain was identified as Pseudomonas sp. strain S5, and was shown to degrade BTEX (Benzene, Toluene, Ethyl-Benzene, and Xylene). Strain S5 generates an organic solvent-tolerant lipase in the late logarithmic phase of growth. Maximum lipase production was exhibited when peptone was utilized as the sole nitrogen source. Addition of any of the selected carbon sources to the medium resulted in a significant reduction of enzyme production. Lower lipase generation was noted when an inorganic nitrogen source was used as the sole nitrogen source. This bacterium hydrolyzed all tested triglycerides and the highest levels of production were observed when olive oil was used as a natural triglyceride. Basal medium containing Tween 60 enhanced lipase production to the most significant degree. The absence of magnesium ions (Mg2+) in the basal medium was also shown to stimulate lipase production. Meanwhile, an alkaline earth metal ion, Na+, was found to stimulate the production of S5 lipase.