Production Of Rhamnolipid Biosurfactant And Its Effect On The Biodegradation Of Phenol By Microorganisms

Phenol with higher toxic and recalcitrant to degradation is widely present in industrial waste water. There are many methods of phenol wastewater treatment. The phenol removal by biodegradation, with high efficiency, low cost and no secondary pollution, become the most common phenol wastewater treatment methods. For the feature of solubilization and adsorption surfactant can enhanced the biodegradation of hydrophobic organic contaminants. However, this effect of surfactants on biodegradation of phenol is not clear. In this paper, the influence of the two synthetic surfactans, cetyl trimethylammonium bromide(CTAB) and Triton X-100, and a biosurfactant, dirhamnlipid, on phenol degradation by Candida tropicalis CICC 1463 was systematically studied. Aimed to explore the degradation of bacteria, surfactants and the interaction of substrate degradation.First the rhamnolipid biosurfactant was produced by aerobic fermentation using a Pseudomonas aeruginosa strain. It was separated from the culture by acid precipitation and purified by column chromatography until monorhamnolipid and dirhamnolipid were obtained. HPLC-MS examination showed that both of the rhamnolipids contained three main components and they were used in the following studies. Next Critical micelle concentration(CMC) of the monorhamnolipid and dirhamnolipid in mineral salt medium (MSM) around neutral pH was investigated as the support for studies on microbial adsorption of them. The results showed that their critical micellar concentrations in MSM at pH 6.5 were 75μM and 106μM, respectively.Then the influence of the dirhamnlipid and two different types of synthetic surfactans on biodegradation of phenol by Candida tropicalis was studied. The objective was to explore the degradation of bacteria, surfactants and the interaction of substrate degradation. Result of the experiment showed that different influence of different types of surfactants on phenol degradation. At the beginning of degradation the yeast population decayed, phenol metabolization and bacterial growth did not occur simultaneously, which indicated the toxicity of phenol and formation of intermediate product. CTAB was toxic to C.tropicalis, and it restrained phenol removal. The phenol degradation were accelerated by Triton X-100 of low concentrations, and the complete gradation was achieved. When Triton X-100 concentration was increased, decay of the yeast in the intial phase was weakened, but phenol removal and bacterial growth were lagged. The biosurfactant diRL enhanced phenol degradation and growth of the C. tropicalis markedly, and the effect increased with increasing of diRL concentration. The diRL concentration also decreased gradually during the fermentation. These results indicated that diRL could reduce phenol toxicity to a great extent and favor the bacterial growth as co-substrate.