Degradation Process And Mechanism Of Phenolic Compounds From Petrochemical Wastewater By Bacterial Strains

As an important industrial raw materials and by-products of many industrial enterprises, phenolic compounds are now common industrial pollutants with features of a wide range and detrimental. Petrochemical wastewater is one of the most serious sources in all pollution sources of phenolic compounds. The method of microorganism biodegradation is an economic and effective way to treat phenolic wastewater. As the biodegradable characteristics of phenolic wastewater, to find efficient phenol-degradation bacteria becomes a major research question. Current bioremediation researches mostly concentrate on microbial degradation of single target phenolic compound, which over-simplifies the natural status, because the pollutants, commonly existing in complex mixtures, often affect the biodegradation kinetics each other.Based on the above issues, this paper studied the process and mechanism of biodegradation of mixed phenols. We use traditional enrichment, screening, purification methods to select 10 degrading bacteria of 8 kinds of phenolic compounds from a soil sample polluted by phenol wastewater. In the 10 strains on the degradation of mixed phenols, we found that Pseudomonas sp. XQ23 has the best performances. XQ23 can degrade all the 10 mixed phenols except for 2,6-dimethylphenol and 2,4,6-trimethylphenol in 24 hours with the total phenol concentration 400 mg/L. In the degrading experiments for single phenols, Pseudomonas sp. XQ23 can degrade phenol, 2-methylphenol, 3-methylphenol, 4-methylphenol, 3-ethylphenol and 2,3-dimethylphenol, partially degrade 2,5-dimethylphenol, but not 3,5-dimethylphenol,2,4-dimethylphenol,2,6-dimethylphenol and 2,4,6-trimethylphenol. Experiments illustrate that the mixture of phenolic compounds promote strain XQ23's degradation on 3,5-dimethylphenol, 2,4-dimethylphenol and 2,5-dimethylphenol. Furthermore, we found that there were no differences for the degradation of phenols by XQ23 on a crude phenol product and a simulation of the product by pure phenols, indicating that the degradation of mixed phenolic compounds can well simulate real crude phenol products.The 10 strains were identified by 16s rDNA sequence analysis and phylogenetic analysis. Among them seven strains belong to Pseudomonas strains, two are Sphingobacterium strains, and one is Bacillus strain. The phenol degradation abilities have corelation with taxonomy. Strain XQ23's characteristics of temperature, pH, dissolved oxygen, salinity, and generations were tested. The results showed that XQ23 is an aerobic bacterium. It has good tolerance on salinity (growth in 42.40 g/L salt). The optimum growth temperature is 30oC, pH is 6. After 12 generations of serial cultivation in rich medium, the degradation ability of phenolic compounds has not changed.