engleski

Small-scale field experiment for bioremediation of polychlorinated biphenyl-contaminated soil

The main objective of our study was to propose a remediation method for enhancing PCB transformation in contaminated soil of the transformer station TS 110/35 kV Zadar, Croatia, damaged during warfare operations in 1991. Two fundamental approaches for enhancing biodegradation of accumuaccumulated PCBs in contaminated soils have been comprised in our small-scale biodegradation experiment, i.e. i) stimulation of the growth of contaminant degraders within indigenous soil microflora (biostimulation) and ii) introduction of microbial cultures of known PCB-degradation capacity (bioaugmentation). Two cultures were chosen as seed cultures: i) mixed culture originating from PCB-contaminated soil of the transformer station area (TSZ7) and ii) a pure culture isolated from this mixed culture (strain Z6, identified as Rhodococcus erythropolis using 16S rDNA gene sequence comparison). These cultures showed substantial growth and PCB-degradation activity in the presence of biphenyl as supplemental carbon source. Based on growth kinetics studies of the selected cultures and biotransformation experiments in which the factors that affect PCB biodegradation were studied, a plan for a small-scale-field experiment was established. It comprised of three pots filled with well homogenized soil of the transformer station. Each pot was equipped with a small irrigation system operated by a peristaltic pump. Plots were divided into two parts ; one was filled with earthworms Lumbricus rubellus (Annelida, Oligochaeta, Lumbricidae). Earthworms were used to improve the dispersal of soil inoculants, to transport microbial inoculants into deeper layers and to increase soil aeration. To facilitate natural changes of environmental conditions, experimental pots were held in a semi-opened room (protected from rain and wind). The soil PCB bioaugmentation treatment employed repeated inoculations with the selected cultures along with the addition of surfactant soya lecithin, for enhancing PCB bioavailability (1 g/kg), xylose as supplemental carbon source (1 g/kg) and carvone as inducer of PCB catabolism (50 mg/kg). The biostimulation treatment included only the addition of carbon source, inducer and surfactant. Amendment and inoculation of the soil was carried out weekly to maintain augmented culture density as well as soil moisture. Soil samples were collected every month and analysed for PCBs by capillary gas chromatography with mass spectrometric detection. The changes in PCB congener mass fractions in soil were quantified against a standard solution of Aroclor 1248. Gradual decrease of PCB mass fractions in soil observed in all experimental pots, and a slightly higher decrease of some PCB congeners in the pots bioaugmented with xylose-grown, carvone-induced, mixed bacterial culture TSZ7 during a four-month treatment is considered as a promising indication of partial soil decontamination. Furthermore, a simple design of our small-scale-field experiment should facilitate its application in field conditions.

PCB; bioremediation; small-scale experiment

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