Evaluation of the efficiency of remediation of oil-contaminated soils by sorption-biological methods in laboratory conditions

The article is devoted to the use of the sorption-biological method of remediation of oil-contaminated soils. The object of the study was sod-podzolic soil with chronic oil pollution with an oil content of 2217 +/- 10 mg/kg. A strain of saprophytic bacteria Bacillus pumilus KM with established carbohydrate-oxidizing activity, high adhesive ability and absence of virulence factors was selected as a biodestructive microorganism. Bentonite from the Dash-Salakhli deposit (Azerbaijan) was used as a natural sorbent with a high sorption capacity. For research, 1% of the suspension of the daily culture of bacteria, 0.5 or 1% of the sorbent was added to the soil samples. The effectiveness of remediation was assessed by changes in the phytotoxicity of soil samples on the test culture Raphanus sativus L., the seeds of which were treated with soil extracts. For this purpose, the length of the root and ground parts of the seedlings was measured, and the number of germinated seeds in the control and experimental samples was recorded. The greatest efficiency of reducing phytotoxicity was established for soil samples containing 1% bentonite or 1% bacterial suspension. On the 4th day of the experiment, the root part of the test object was absent, but the length of the ground parts of the plant exceeded the control values by 5.8 and 5.6 times, respectively. Similar results were obtained on the 12th day of the experiment: when processing these samples of soil extracts, the intensity of root formation exceeded the control values by 3.9 and 3.3 times, the length of the ground part by 2.0 and 1.9 times, respectively. 30 days after the introduction of bacteria and sorbent into soil samples, the greatest intensity of reduction in soil phytotoxicity was established for similar samples. On the 4th day of the experiment, the length of the ground part exceeded the control values by 4.9 and 4.4 times, and on the 12th day - by 1.9 and 1.8 times, respectively. The formation of the root part of the plants occurred on day 12 and their length also exceeded the control by 5.9 and 5.3 times. The highest seed germination energy of the test object was characterized by soil extraction of the sample in which bacteria B. pumilus KM and sorbent were kept for 30 days. The most intense decrease in the toxicity index of soil samples was observed with the introduction of 1% sorbent or in the presence of 1% strain of B. pumilus KM for 30 days. When introducing bacteria B. pumilus KM or bentonite into soil samples, the dynamics of changes in the phytotoxicity of soils depends on the concentration of the introduced sorbent and the duration of circulation of destructive microorganisms.