Biodegradation of phenol by using free and immobilized cells of Acinetobacter sp. XA05 and Sphingomonas sp. FG03

https://doi.org/10.1016/j.bej.2008.12.001Get rights and content

Abstract

Strain XA05 and FG03 with high biodegradation activity of phenol were isolated from the activated sludge and phenol-contaminated soils in Northwest of China, respectively. DNA sequencing and homologous analysis of 16s rRNA gene identified that XA05 belonged to an Acinetobacter sp. and FG03 was closely related to the Sphingomonas sp. Strain XA05 and FG03 were mixed at the ratio of 1:1, and polyvinyl alcohol (PVA) was used as a gel matrix to immobilize mixed cells of two strains by repeated freezing and thawing. The removal efficiency of phenol by free and immobilized cells and factors affecting phenol degradation were investigated, the stability of the immobilized cells was also reported. Experimental values indicated that both free suspended and immobilized cells showed high phenol degradation efficiencies, higher than 95% within 35 h with an initial concentration of 800 mg/l phenol, and the immobilized cells showed better performance than that of the suspended cells.

Introduction

Phenol is now one of the most common toxic environmental pollutants, which mainly originated from industrial processes, such as oil refineries, coking plants, industrial resin manufacturing, petroleum-based processing plants, pharmaceuticals, plastic, and varnish industries, etc. [1], [2]. Phenol is hazardous to aquatic life, plants, and many other organisms, and acts as a substrate inhibitor in the biotransformation [3]. Thus, elimination of phenol effectively is necessary to preserve the environment and the health of human beings.

Efficient treatment methods are available for the degradation of phenol, and compared with physico-chemical methods [4], [5], the biodegradation method of phenol reduction is universally preferred, because of lower costs and the possibility of complete mineralization [6], [7], [8], [9]. In this sense, biological treatment of phenol contamination has therefore gained an increasing attention in pollution prevention [10], [11], [12], [13], and a large number of phenol-degrading bacteria have been isolated and characterized at the physiological and genetic level [14], [15], [16].

However, the use of free bacterial cells for wastewater treatment in activated sludge processes creates problems such as solid waste disposal. Immobilized microorganisms have been showed to be effective to treat phenol-containing wastewater with little sludge production and have been receiving increasing attention [17], [18], [19].

The purpose of this investigation has been to study biodegradation of phenol by using free and immobilized cells of Acinetobacter sp. XA05 and Sphingomonas sp. FG03 strains. Factors of affecting phenol biodegradation process and stability of immobilized cells were also investigated.

Section snippets

Materials and growth conditions

Samples of activated sludge were obtained from Xi’an Beishiqiao Wastewater Treatment Facility, Xi’an China; Samples of phenol-contaminated soils were collected at a site near Fugu Coking Plant, North of Shaanxi province in China. Phenol with greater than 99% purity and PVA with an average degree of polymerization of 2400–2500 were purchased from Shanghai Chemical Factory. All other chemicals used were of the highest purity available. Mineral medium (MM) was used for the enrichment and isolation

Isolation and identification of phenol-degrading strain

By enrichment culture, several bacterial isolates capable of growth on phenol as the sole carbon and energy source were isolated from activated sludge and phenol-contaminated soils in China, respectively. Each isolate was tested for their ability to utilize phenol at concentrations from 200 to 1000 mg/l in liquid minimal medium. The strain XA05 (isolated from activated sludge) and FG03 (isolated from phenol-contaminated soil) were selected for detailed studies because of their high

Discussion

Phenol and its derivatives are distributed either as natural or artificial mono-aromatic compounds in various environmental sites as major pollutants. These compounds are toxic and persistent. Development of improved technologies capable of degrading persistent and recalcitrant compounds becomes necessary. Compared with physico-chemical methods, biodegradation method of phenols reduction is universally preferred, because of lower costs and the possibility of complete mineralization [9].

Conclusion

  • (1)

    Two new phenol-degrading bacteria with high biodegradation activity and high tolerance of phenol, strain XA05 and strain FG03 were isolated from the activated sludge and contaminated soil, respectively. From 16s RNA gene sequence analysis, it was determined that the strain XA05 and FG03 belongs to the genus Acinetobacter and genus Sphingomonas and is hereby named Acinetobacter sp. XA05 and Sphingomonas sp. FG03, respectively.

  • (2)

    Cells of strain XA05 and FG03 were mixed at the ratio of 1:1, and the

Acknowledgements

The authors would like to thank Dr. M. Nikolausz (Department of Bioremediation, Helmholtz Centre for Environmental Research - UFZ) for assistance in microbial identiation methods. This work was supported by the Foundation of Educational Department of Shaanxi Province (06JK267) and Science and Technology Program of Xi’an (YF07196) and Basic Research Program of Xi’an University of Architecture and Technology (JC0507).

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