[Ex-situ remediation of PAHs contaminated site by successive methyl-beta-cyclodextrin enhanced soil washing].

Polycyclic aromatic hydrocarbon (PAH) polluted sites caused by abandoned coking plants have attracted great attentions. This study investigated the feasibility of using methyl-beta-cyclodextrin (MCD) solution to enhance ex situ soil washing for extracting PAHs. Treatment with elevated temperature (50 degrees C) in combination with ultrasonication (35 kHz, 30 min) at 100 g x L(-1) was effective. It was found that 96.7% +/- 2.4% of 3-ring PAH, 89.7% +/- 3.2% of 4-ring PAH, 76.3% +/- 2.2% of 5 (+6)-ring PAH and 91.3% +/- 3.1% of total PAHs were removed from soil after five successive washing cycles. The desorption kinetics of PAHs from contaminated soil was determined before and after successive washings. The 400 h Tenax extraction of PAHs from soil was decreasing gradually with increasing washing times. Furthermore, the F(r), F(sl), k(r), k(sl) and k(vl) were significantly lower than those of CK (P < 0.01). Therefore, considering the removal efficiency and potential environmental risk after soil )ashing, successive washing three times was selected as a reasonable parameter. These results have practical implications for site risk assessment and cleanup strategies.

[Optimizing remediation conditions of non-thermal plasma for DDTs heavily contaminated soil].

A series of experiments were carried out in a non-thermal reactor to remove DDTs in heavily contaminated soil by dielectric barrier discharge (DBD). The study aims to investigate the effects of soil properties (including soil particle size and soil water content) and equipment working parameters (e. g. the plasma power, the processing time and discharge atmosphere) on the removal of DDTs from soil. The results showed that DDTs in soil were significantly degraded by the non-thermal plasma produced by dielectric barrier discharge. Removal rate of DDTs increased with increasing processing time. The removal efficiency of DDTs ranged from 95.3% to 99.9% in 20 minutes. The optimum conditions were as follows: 1 kW of the plasma power, 20 minutes of processing time in air discharge atmosphere, 0-0.9 mm soil particle size and 4.5% -10.5% of soil moisture content. The results also showed that o,p'-DDE might be the intermediate dechlorination and dehydrogenation product of the o,p'-DDT after the oxidization.

[In-situ remediation of polychlorinated biphenyls polluted soil by ecological controlling measures: a field trial].

A field experiment was conducted to study the remediation of agricultural soils polluted with polychlorinated biphenyls (PCBs) by several ecological controlling measures. After sequential stages of liming, plowing, planting alfalfa and paddy, a significant part of PCBs was removed from the soil, with an average removal rate of 86.9%. The treatment also decreased the toxic equivalency of dioxin-like PCBs in soil. Analysis of PCB congener composition showed that at stages of liming, plowing and alfalfa planting, the low-chlorinated biphenyls were removed; whereas at the stage of paddy planting, the high-chlorinated biphenyls were degraded. The ecological controlling measures had little influence on the microbial communities in soil. The results suggest that ecological control techniques could be widely applied in the remediation of agricultural soils with PCBs contamination.

Phytoremediation of oilfield sludge after prepared bed bioremediation treatment.

A field-scale experiment was carried out to compare the effectiveness of five plant species in the remediation of oily sludge. Alfalfa, tall fescue, and soybean substantially increased the removal rate of oil and grease (O&G) after 120 days of remediation. Of these, soybean treatment showed the highest removal rate of 34.2% compared with only 13.7% in the unplanted control plot. In addition to assisting with phytoremediation, soybean can also be used for energy production, for example in the production of biodiesel. Furthermore, microbial counts and community level physiological profiling using Biolog sole carbon source utilization tests were used to investigate the effect of plants on the microbial community of oily sludge. Plants selectively increased microbial counts in the rhizosphere and O&G concentrations of the sludge were negatively correlated with counts of TPH (total petroleum hydrocarbon) degraders. The acute biotoxicity of the sludge was also tested by the bacterial luminescence method and alfalfa treatments decreased the biological toxicity of the sludge compared with the unplanted control.

[Effects of Rhizobium meliloti on PCBs degradation and transformation in solution culture].

The capability of Rhizobium meliloti on degrading 2,4,4'-trichlorobiphenyl and 18 kinds of polychlorinated biphenyl congener mixtures was studied by shaking flask experiment. The results showed that the degradation capability of Rhizobium meliloti to 2, 4, 4'-trichlorobiphenyl increased gradually with the increasing concentration of 2, 4, 4'-trichlorobiphenyl. After 7 days, the degradation rates of 2, 4, 4'-trichlorobiphenyl under 1.0, 5.0 10.0, 25.0, 50.0 mg x L(-1) concentration of 2, 4, 4'-trichlorobiphenyl were 34.0%, 48.3%, 69.7%, 96.0%, 98.5% respectively. Meanwhile some new intermediate products were found in the solution culture. The capability of Rhizobium meliloti on degrading 18 kinds of polychlorinated biphenyls congener mixtures appeared in a trend from low to high, then decreased to a certain balance with the increasing concentration of the mixture. The highest degradation rate was 54.7%, and moreover, a transformation process from higher chlorinated PCBs congeners to lower chlorinated PCBs congeners emerged.

[Sorption behavior of PCB28 to phosphatidylcholine and triglyceride].

Sorption behaviors of PCB28 to phosphatidylcholine (PC)and triglyceride (TG) were studied. Results showed that sorption equilibrium could be achieved in 8 h for PCB28, and the sorption amount on PC was higher than that of TG when the initial PCB28 concentration is in the range of 50-250 microg x L(-1). As the initial PCB28 concentration increases, the absolute sorption amount and relative sorption amount on PC and TG enhances. And linear isotherm is suggested as the most appropriated fitting type, sorption constants K(d) calculated from linear isotherm for PC and TG are 38.84 L x g(-1) and 20.14 L x g(-1) respectively, which suggested that PC had a higher sorption ability to PCB28 than that of TG, and the fatty acid chain length might be important factors to influence the sorption mechanism of PC and TG.

[Phytoremediation of polychlorinated biphenyls contaminated soil by leguminosae-gramineae intercropping: a field trial].

Phytoremediation of polychlorinated biphenyls (PCBs) contaminated soil by leguminosae (alfalfa) and gramineae (ryegrass and tall fescue) was studied in a field trial. All planted treatments had significantly higher PCBs removal efficiency compared with those of unplanted control after 270 days of in-situ phytoremediation. Alfalfa monoculture received the highest removal efficiency of soil PCBs by 59.6%. Analysis of PCBs congeners composition showed that the percentage of di-chlorinated biphenyl decreased in all planted treatments. Alfalfa produced the maximum biomass among the 3 plants. Total PCBs concentration in alfalfa roots reached 355.1 microg/kg, which was significantly higher than those in ryegrass and tall fescue. The phytoextraction efficiency of different treatment was in order of alfalfa > alfalfa-ryegrass-tall fescue > alfalfa-ryegrass > ryegrass > alfalfa-tall fescue > tall fescue. The results suggest that alfalfa may be an ideal candidate for the phytoremediation of PCBs contaminated soil.

Enhanced removal of polychlorinated biphenyls from alfalfa rhizosphere soil in a field study: the impact of a rhizobial inoculum.

Polychlorinated biphenyls (PCB) are persistent pollutants in soil environments where they continue to present considerable human health risks. Successful strategies to remediate contaminated soils are needed that are effective and of low cost. Bioremediation approaches that include the use of plants and microbial communities to promote degradation of PCB have significant potential but need further assessment under field conditions. The effects of growth of alfalfa (Medicago sativa L.) and inoculation with a symbiotic nitrogen fixing bacterium (Rhizobium meliloti) on the removal of polychlorinated biphenyls (PCB) from rhizosphere soil were evaluated in a field experiment. The initial PCB content of the soil ranged from 414 to 498 microg kg(-)(1). PCB removal for the rhizosphere soil was enhanced in the planted treatments, an average of 36% decrease in PCB levels compared to a 5.4% decrease in the unplanted soil, and further enhanced when plants were inoculated with the symbiotic Rhizobium (an average of 43% decrease) when evaluated at 90 days after planting. Plant biomass production was higher in the inoculated treatment. The total PCB content was increased from 3.30 microg kg(-)(1) to 26.72 microg kg(-)(1) in plant shoots, and from 115.07 microg kg(-)(1) to 142.23 microg kg(-)(1) in roots in the inoculated treatment compared to the planted treatment. Increased colony forming units (cfu) of total heterotrophic bacteria, biphenyl-degrading bacteria and fungi were observed in the rhizosphere of inoculated plants. PCB removal from the rhizosphere soil was not significantly correlated with the direct PCB uptake by the plants in any of the treatments but was significantly correlated with the stimulation of rhizosphere microflora. Changes in the soil microbial community structure in the planted and inoculated treatment were observed by profiling of bacterial ribosomal sequences. Some bacteria, such as Flavobacterium sp., may have contributed to the effective degradation of PCB and deserve further investigation.

[Combined remediation effects of arbuscular mycorrhizal fungi-legumes-rhizobium symbiosis on PCBs contaminated soils].

The combined remediation effects of dual inoculation with an arbuscular mycorrhizal fungus (AM) and rhizabium (Rhizobium meliloti) with a host plant (alfalfa) on PCBs contaminated soils was studied using pot experiments. The results showed that alfalfa had a clear role in PCBs removal in soils compared with treatments without alfalfa and inoculated microorganisms, PCBs concentration in lightly and heavily polluted soils decreased 15.8% and 23.5%, respectively. After planting alfalfa with single incubation of Glomus caledonium, PCBs concentration decreased 14.8% and 24.1% from lightly and heavily polluted soils, decreased 20.6% and 25.5% for single incubation of Rhizobium meliloti, respectively. After dual incubation with Glomus caledonium and Rhizobium meliloi, PCBs concentration in lightly and heavily polluted soils decreased 23.2% and 26.9%. We also observed that soil microbial communities in alfalfa rhizosphere soils had a higher carbon utilization rate, improving the functional diversity of the soil microbial community. The results suggest that dual incubation of Glomus caledonium and Rhizobium meliloti has great potential in remediation of PCBs contaminated soils.

[Spatial distribution of soil PCBs congeners in typical area of Yangtze River Delta region].

191 surface farmland soil samples were collected from an area of 27 km2 in typical polluted county of the Yangtze River Delta region and analyzed for concentrations of 16 kinds of polychlorinated biphenyls. The results of statistical analysis indicated that the concentrations of PCBs in the soils ranged from 0.01-484.5 ng/g, with the average concentration of 35.52 ng/g. In farmland soils tri- and tetra-chlorinated biphenyls were the main congeners, and some proportional penta- and hexachlorinated biphenyls also existed. The spatial analysis showed that the PCBs concentrations were stronger correlated in a given spatial range, and indicated that in the farmland soil PCBs spatial distribution pattern had an extent relationship with the activities of dismantling electronic wastes, burning plastic cable and line, wastewater irrigation and some pollution enterprises position in this typical region.