Biodegradation Study of Phenol by Burkholderia sp. PS3 and Bacillus pumilus OS1 Isolated from Contaminated Soil

摘要

Water pollution by phenols is a major environmental problem in present days. Phenol is a highly hazardous and toxic substance emitted to the environment by the effluent from various industries. Environmental Protection Agency has set the limits for concentration of phenol in wastewater discharge are 0.5 mg/l for surface waters and 1 mg/l for the sewerage system Therefore, industrial effluents containing phenol require proper treatment before being discharged into the environment. There are various methods available for removal of phenol from wastewater. Among these, Biological treatment of phenolic effluent is attractive than that of other alternatives as it is cost effective and produces non toxic end products. Biodegradation of phenol mainly depends on the efficiency of the microbe, concentration of media components and the physiological conditions. In the present study two different phenol contaminated soils (one with effluent from paper mill and the other with crude oil) has been chosen to isolate highly efficient microbes. Aerobic bacterial strains PS3 and OS1 have been isolated from the soil contaminated with paper mill effluent and crude oil respectively. Strain PS3 has been found to tolerate 1500 mg/l of phenol, while the strain OS1 tolerate up to 1250 mg/l of phenol. On the basis of morphological, biochemical and molecular characteristics, strain PS3 and strain OS1 have been identified as Burkholderia sp. PS3 and Bacillus pumilus OS1 respectively. Optimization studies on growth and degradation has been carried out by using Plackett-Burman Design and central composite design (CCD) to evaluate optimum values of medium components and physiological conditions. Most significant factors have been screened using Plackett-Burman design from nine important variables. Temperature, pH, phenol concentration and inoculum size have been found significant for Burkholderia sp. PS3 while pH, temperature, phenol concentration, inoculum size and (NH4)2SO4 concentration have been found significant for Bacillus pumilus OS1. These factors have been optimized by central composite design with correlation coefficient of 0.9679 and 0.9827 for strain PS3 and OS1 respectively. For Burkholderia sp. PS3, maximum phenol degradation of 99.96% has been predicted at pH - 7.18, temperature - 28.9○C, phenol - 297.9 mg/l and inoculum size - 5.04% (v/v). A maximum phenol degradation of 99.99% has been predicted for Bacillus pumilus OS1 at pH - 7.07, temperature - 29.3○C, phenol - 227.4 mg/l, inoculum size - 6.3% (v/v) and (NH4)2SO4 - 392.1 mg/l. The predictedudxviii optimum degradations have been validated by experiments and the experimental degradation has been found to be 99.88% and 99.90% for Burkholderia sp. PS3 and Bacillus pumilus OS1 respectively.