Comparative investigation on a hexane-degrading strain with different cell surface hydrophobicities mediated by starch and chitosan.

Bioremediation usually exhibits low removal efficiency toward hexane because of poor water solubility, which limits the mass transfer rate between the substrate and microorganism. This work aimed to enhance the hexane degradation rate by increasing cell surface hydrophobicity (CSH) of the degrader, Pseudomonas mendocina NX-1. The CSH of P. mendocina NX-1 was manipulated by treatment with starch and chitosan solution of varied concentrations, reaching a maximum hydrophobicity of 52%. The biodegradation of hexane conformed to the Haldane inhibition model, and the maximum degradation rate (ν max) of the cells with 52% CSH was 0.72 mg (mg cell)-1·h-1 in comparison with 0.47 mg (mg cell)-1·h-1 for cells with 15% CSH. The production of CO2 by high CSH cells was threefold higher than that by cells at 15% CSH within 30 h, and the cumulative rates of O2 consumption were 0.16 and 0.05 mL/h, respectively. High CSH was related to low negative charge carried by the cell surface and probably reduced the repulsive electrostatic interactions between hexane and microorganisms. The FT-IR spectra of cell envelopes demonstrated that the methyl chain was inversely proportional to increasing CSH values, but proteins exhibited a positive effect to CSH enhancement. The ratio of extracellular proteins and polysaccharides increased from 0.87 to 3.78 when the cells were treated with starch and chitosan, indicating their possible roles in increased CSH.

[Removal of Volatile Sulfur Odor by the Biotrickling Filter].

The biodegradation of gas-phase mixtrue of dimethyl sulfide (DMS) and 1-propanethiol (PT) was examined in a biotrickling filter (BTF), inoculated with a microbial consortium composed of activated sewage sludge, and pure strains of Alcaligenes sp. SY1 and Pseudomonas putida. S-1. BTF could be successfully started up within only 11 days when the inlet concentrations of DMS and PT were both 50 mg·m-3 and EBRT was 30 s, with 90% removal efficiency (RE) of DMS and 100% RE of PT. In the steady state, the maximum elimination capacities of DMS and PT were 8.7 g·(m3·h)-1 and 12.4 g·(m3·h)-1, respectively. The presence of PT with a concentration up to 51 mg·m-3 showed an antagonistic removal pattern for DMS, but the opposite did not occur. Meanwhile, the BTF showed high efficiency in the biodegradation of H2S. When the concentration of H2S was as high as 230 mg·m-3, the RE of H2S could reach 98%. However, H2S showed a declining effect on the removal of DMS when the concentration exceeded 115 mg·m-3.