Simultaneous Cr(Ⅵ) Reduction And Phenol Degradation In Pure Cultures Of Pseudomonas Aeruginosa

Chromium and its compounds are widely used in many industries and a large quantity of Cr(Ⅵ)-containing wastes are released into environment. Chromium, especially hexavalent chromium has posed great threat on environmental safety and human health. The reduction of quite toxic hexavalent chromium into less toxic trivalent chromium is the key for the detoxification of chromium. Many bacterial species have been found to be able to reduce Cr(Ⅵ) and microbial remediation has been regarded as a promising approach for the treatment of chromium pollution.However, in the previous studies, glucose or malate were used as carbon and energy source.In fact, a wide range of organic pollutants including phenol, naphthalene, and trichloroethylene (TCE) has been found at high concentrations in water containing Cr(Ⅵ). In these organic pollutants, phenol widely occurs in the Cr(Ⅵ) contaminated sites. Organic acid which can be used as carbon source for Cr(Ⅵ) reduction by some microorganism was detected during phenol degradation. This paper demonstrated the feasibility of simultaneous Cr(Ⅵ) reduction and phenol degradation using pure cultures of bacteria—P. aeruginosa.This paper demonstrated Cr(Ⅵ) reduction by P. aeruginosa through the bacterium or through filtrates of cultures and the parameters affecting Cr(Ⅵ) reduction by P. aeruginosa were thoroughly investigated, such as initial Cr(Ⅵ) concentration, initial phenol concentration and cells inoculum amount. The results demonstrated that P. aeruginosa can effectively reduce Cr(Ⅵ) and degrade phenol in the premise of P. aeruginosa having the biological activity; the ratio of Cr(Ⅵ) reduction by the incubated strain was lower than the ratio of Cr(Ⅵ) reduction by the incubating strain; the initial Cr(Ⅵ) concentration can affect Cr(Ⅵ) reduction and phenol degradation. The percent of Cr(Ⅵ) reduction and the percent of phenol degradation decreased with increasing initial Cr(Ⅵ) concentration.Cr(Ⅵ) can inhibit Cr(Ⅵ) reduction and phenol degradation when its concentration exceed 20mg/L. The rate of Cr(Ⅵ) reduction reached the maximum when the Cr(Ⅵ) concentrations was 20 mg/L and the average rate began to decrease at Cr(Ⅵ) concentrations higher than 20 mg/L, whereas the rate of phenol degradation decreased with increasing initial Cr(Ⅵ) concentration. The initial phenol concentration also has an impact on Cr(Ⅵ) reduction and phenol degradation, phenol degradation enhanced Cr(Ⅵ) reduction when the initial phenol concentration was lower than 100mg/L, and the rate of Cr(Ⅵ) reduction and the rate of phenol degradation reached the maximum as the phenol concentration was 100mg/L. With the cells inoculum amount from 0.5%-5%, the increase of cells inoculum amount leaded to the increase of Cr(Ⅵ) removal rate and phenol degradation rate. The relation between cells growth and Cr(Ⅵ) reduction and phenol degradation was detected. It was observed that the cells growth of P. aeruginosa and Cr(Ⅵ) reduction and phenol degradation were well correlated. The rate of Cr(Ⅵ) reduction and phenol degradation increased with increasing the amount of inocula. A good correlation between cumulative Cr(Ⅵ) reduced and cumulative phenol degraded with correlation coefficients ranging between 0.939 and 0.976. The reduction product of Cr(Ⅵ) and metabolites of phenol were analyzed, the results indicated that Cr(Ⅲ) was the predominant product of Cr(Ⅵ) reduction in cultures, and organic acid was detected during the course of phenol degradation, and total organic acids accounted for approximately 100% total measured TOC after phenol was almost completely degraded. P. aeruginosa utilized some organic acid intermediates to reduce Cr(Ⅵ), which may enhance the rate of phenol degradation thereby increasing biological activity in cultures.