Higher Remediation Efficiency Research Articles

Contamination and remediation of contaminated firing ranges—an overview

Land and groundwater resources are fundamental pillars of sustainable human development. The negligent abandonment of ammunition and its fragments during range activities can result in severe contamination of range sites, thereby posing a significant risk to both the ecological environment and human health. Nevertheless, numerous uncertainties persist regarding the comprehension of range contaminated sites. In this study, the literature on the range of contaminated sites decommissioned after 2000 was systematically examined to consolidate basic information related to these sites, such as contaminant types, contamination status, and remediation measures. Considerable attention is devoted to investigating the advancement of diverse techniques, such as phytoremediation, chemical leaching, and solidification/stabilization, to remediate polluted areas within decommissioned firing ranges. Among the various types of remediation means, physical remediation and chemical remediation have higher remediation efficiency, but generally have higher costs and are prone to secondary pollution. Bioremediation is low cost and environmentally friendly, but has a long restoration cycle. The choice of remediation method should be based on actual needs. Additionally, this study puts forth prospective avenues for future research. Ultimately, this endeavor aims to attract the interest of scholars toward the remediation of contaminated sites within firing ranges, thereby making a valuable contribution to both human wellbeing and sustainable progress.

Potential mechanism of biochar enhanced degradation of oxytetracycline by Pseudomonas aeruginosa OTC-T

Extensive use of oxytetracycline (OTC) and the generation of its corresponding resistance genes have resulted in serious environmental problems. Physical-biological combined remediation is an attractive method for OTC degradation because of its high remediation efficiency, stability, and environmental friendliness. In this study, an effective OTC-degrading strain identified as Pseudomonas aeruginosa OTC-T, was isolated from chicken manure. In the degradation experiment, the degradation rates of OTC in the degradation systems with and without the biochar addition were 92.71–100 % and 69.11–99.59 %, respectively. Biochar improved the tolerance of the strain to extreme environments, and the OTC degradation rate increased by 20.25 %, 18.61 %, and 13.13 % under extreme pH, temperature, and substrate concentration conditions, respectively. Additionally, the degradation kinetics showed that biochar increased the reaction rate constant in the degradation system and shortened the degradation period. In the biological toxicity assessment, biochar increased the proportion of live cells by 17.63 % and decreased the proportion of apoptotic cells by 58.87 %. Metabolomics revealed that biochar had a significant effect on the metabolism of the strains and promoted cell growth and reproduction, effectively reducing oxidative stress induced by OTC. This study elucidates how biochar affects OTC biodegradation and provides insights into the future application of biochar-assisted microbial technology in environmental remediation.

Impacts of Modified Fly Ash on Soil Available Lead and Copper and Their Accumulation by Ryegrass

Fly ash (FA) is promising for environmental remediation, but how to modify the FA with high remediation efficiency through an environmentally friendly and low-cost modification method is scare. A modified FA (MFA) was prepared through a one-step hydrothermal modification with Ca(OH)2 and KH2PO4. Results indicated that irregular agglomerates occurred on the surface of the MFA and that the specific surface area increased by 1.94 times compared to that of FA. Compared to FA, glassy compositions in MFA were destroyed and amorphous Si/Al and alkaline aluminosilicate gels were formed. The soil application of 0.2–0.6% MFA significantly increased soil pH by 0.23–0.86 units compared to FA and decreased available lead (Pb) and copper (Cu) by 25–97.1% and 13.5–75%, respectively. MFA significantly decreased exchangeable Pb and Cu by 12.5–32% and 11.4–35.2%, respectively, compared to FA. This may be due to the high pH and specific surface area of MFA, which promoted to the formation of amorphous Si/Al, metal–phosphate precipitation, and complexation with functional groups. In addition, MFA slightly increased the biomass of shoots and roots and decreased the uptake of Pb and Cu by ryegrass. This study provides a new modification method for the utilization of FA in the heavy metal-contaminated soils.

Experimental study on remediation of petroleum-contaminated soil by combination of freeze-thaw and electro-osmosis

Electro-osmosis has been well recognized as a technique for the remediation of petroleum-contaminated soil, however seasonally freezing and thawing adds the complexity of petroleum mobility in cold regions. To investigate the influence of freeze-thaw on the electroosmotic removal of petroleum and explore the enhancement of freeze-thaw on the electroosmotic remediation efficiency in remediating the petroleum-contaminated soils, a set of laboratory tests were performed in three types of treatment modes, freeze-thaw (FT), electro-osmosis (EO) and freeze-thaw combined electro-osmosis (FE). The petroleum redistributions as well as the moisture content changes after the treatments were evaluated and compared. The petroleum removal rates of the three treatments were analyzed, and the underlying mechanisms were elaborated. The results indicated that the overall efficiency of the treatment mode regarding petroleum removal from soil followed the order of FE > EO > FT, corresponding to 54%, 36% and 21% in maximum, respectively. A considerable amount of water solution with surfactant was driven into contaminated soil during FT process, but the petroleum mobilization primarily occurred inside of the specimen. A higher remediation efficiency was yield in EO mode, but the induced dehydration and cracks leaded to the dramatical depression in the efficiency in further process. It is proposed that the petroleum removal is closely related to the flow of water solution with surfactant that is favorable to the solubility and mobilization of the petroleum in soil. Thus, the water migration induced by freeze-thaw cycles substantially improved the efficiency of the electroosmotic remediation in FE mode that gave the best performance for the remediation of the petroleum-contaminated soil.

Research progress of bio-slurry remediation technology for organic contaminated soil.

Bio-slurry remediation technology, as a controllable bioremediation method, has the significant advantage of high remediation efficiency and can effectively solve the problems of high energy consumption and secondary pollution of traditional organic pollution site remediation technology. To further promote the application of this technology in the remediation of organically polluted soil, this paper summarizes the importance and advantages of bio-slurry remediation technology compared with traditional soil remediation technologies (physical, chemical, and biological). It introduces the technical infrastructure and its technological processes. Then, various factors that may affect its remediation performance are discussed. By analyzing the applications of this technology to the remediation of typical organic pollutant-(polycyclic aromatic hydrocarbons(PAHs), polychlorinated biphenyls(PCBs), total petroleum hydrocarbons(TPH), and pesticide) contaminated sites, the following key features of this remediation technology are summarised: (1) the technology has a wide range of applications and can be used in a versatile way in the remediation projects of various types of organic-contaminated soil sites such as in clay, sand, and high organic matter content soil; (2) the technology is highly controllable. Adjusting environmental parameters and operational conditions, such as nutrients, organic carbon sources (bio-stimulation), inoculants (bio-augmentation), water-to-soil ratio, etc., can control the remediation process, thus improving the restoration performance. To sum up, this bio-slurry remediation technology is an efficient, controllable and green soil remediation technology that has broad application prospects.

Monitoring TPH biodegradation in soil around Ray oil refinery by natural attenuation, biostimulation and bioaugmentation treatments

In this study, total petroleum hydrocarbons (TPHs) decontaminating mechanisms for soils around the Rey refinery complex (South of Tehran, Iran) was investigated. Natural attenuation, biostimulation and bioaugmentation (separately and in combination) methods were evaluated TPHs and soil microbial respiration in 210 days, using laboratory treatments The modified methods were applied through 13 different treatments, including improving the environmental conditions for native bacteria (natural attenuation for treatments 1-8), adding non-native bacterial complex (bioaugmentation for treatment 9) and intensifying and stimulating growth while adding non-native bacterial complex (biostimulation-bioaugmentation for treatments 10-13). Although, overall of the treatments, a significant decreasing TPHs concentration were observed over the time, biostimulation-bioaugmentation treatments had the highest amount of TPHs decomposition, the highest rate of bio-respiration, the lowest half-life times (t1/2), and the highest remediation efficiency and biodegradation constants rate. Among natural attenuation treatments, modifiers with manure and sawdust had the greatest effect on reducing the TPHs concentration and the highest rate of bio-respiration. The first-order kinetic model was fitted to the data related to biodegradation in a satisfactory manner. The results showed that there was a strong and positive linear correlation between decreasing TPHs concentration and microbial respiration in all modifiers. Although for the bacterial treatments and at the early stages of inoculation, the rate of total respiration was low, but as the time passed and with adaptation of the effective inoculated bacteria to contaminated soil, the respiration rate gradually was increased. Due to its low cost and low environmental risk, the proposed bioremediation technique for oil contaminated soil can be recommended to the region.

Influence of delta-hexachlorocyclohexane (δ-HCH) to Phytophthora ×alni resistant Alnus glutinosa genotypes − Evaluation of physiological parameters and remediation potential

Hexachlorocyclohexanes (HCHs) are persistent organochlorine pesticides with the adverse effects on human health and the environment. The effect of delta-isomer of hexachlorocyclohexane (δ-HCH) on germination, growth parameters and physiological parameters was studied in different Alnus glutinosa (L.) Gaertn. progeny of resistant genotypes to pathogen Phytophthora ×alni. Two experiments were performed: a short-term experiment to determine the effect of δ-HCH on total germination (GT), germination energy (GE), speed of germination (SG), shoot length and biomass of seedlings, and a long-term experiment devoted to remediation aspects. In addition, changes in the hormonal system of alders were monitored in both cases. Significant differences were found between the treated and control group in most of the evaluated characteristics. Also, the content of studied phytohormones differs between groups. Furthermore, the obtained results indicate genetically determined variability in response to δ-HCH. Of the six tested, the Březové and Tuřany progeny seem to be suitable candidates for phytoremediation because of the adaptation to stress conditions or high remediation efficiency. The rest of tested progeny seems to be unsuitable due to higher mortality, lower remediation efficiency and higher levels of stress hormones resulting in significant decrease in biomass and plant height. Moreover, results indicate the role of the plant as a remediation accelerator, probably through released exudates, and a positive effect on the soil microbiome as the presence of plants increased the remediation efficiency by 20.85 – 35.89%. The obtained research findings may be helpful in better understanding the processes involved in removing these pesticides from the soil. Further research should be focused on rhizosphere microbiome, mechanism of in-plant isomerization and metabolites identification.

Determination of the efficiency of combination therapies on the bioremediation of petroleum spill aquatic ecosystem

Environmental degradation resulting from petroleum spills had become a major menace in most petroleum rich regions of the world. The remediation potential of individual green materials and their combinations were quantified in this study. Stimulated petroleum spill water was remediated with water lettuce, activated charcoal, rice husks and their combinations, within an experimental period of 40 days. The total petroleum hydrocarbons (TPH) value of the contaminated water and remediated contaminated water was determined in accordance with American Public Health Association’s (APHA) approved procedures. Findings of this study depicted that the amendments used were able to reduce the TPH concentration of the contaminated water; with activated charcoal tending to have higher remediation efficiency than rice husk. The results revealed that the TPH concentration of the contaminated water treated with only water lettuce, declined from 3897 to 1296 mg/L; while the TPH value of contaminated water treated with water lettuce and activated charcoal (C2 and C3), dropped from 3897 to 535 mg/L and 382.33 mg/L respectively, depending on the charcoal quantity employed. It was also observed that the TPH of the contaminated water treated with water lettuce and rice husk (C4 and C5), dropped from 3897 to 864 mg/L and 680 mg/L respectively, depending on the quantity of rice husks used for the bioremediation program. Additionally, the study’s findings revealed that the TPH of the contaminated water remediated with the combination of water lettuce, charcoal, rice husk and cassava starch (C6 and C7) declined from 3897 to 392 mg/L and 223 mg/L respectively. The study’s findings had depicted that agricultural waste materials can be harnessed to remediate petroleum spill sites, and the remediation efficiency can be optimized through combined remediation methods/materials.

Combined apatite, biochar, and organic fertilizer application for heavy metal co-contaminated soil remediation reduces heavy metal transport and alters soil microbial community structure

Soil amendments are used extensively to remediate soils contaminated with heavy metals. However, the effects of soil amendments on heavy metal bioavailability, plant yield, and bacterial community structure in tropical farmland soils remain largely unknown. In the present study, seaweed organic fertilizer (S), apatite (A), biochar (B), and seaweed organic fertilizer-apatite-biochar mixtures (SAB) were applied at different rates to assess their influence on cadmium (Cd), lead (Pb), and chromium (Cr) bioavailability in contaminated farmland soils, using different component ratios and doses in maize field plots, and maize yield. Effects on soil bacterial community structure were also evaluated based on high-throughput sequencing. Following addition of 2 % S + A + B combined amendment at a ratio of 1:0.5:1.5 (2%S1A0.5B1.5), soil pH and electrical conductivity (EC) were elevated, and bioavailable Cd, Pb, and Cr concentrations were reduced in potted soils, leading to higher heavy metal immobilization. Under field conditions, soil pH, EC, organic matter, ammonium‑nitrogen, available phosphorus, available potassium, and crop productivity were all increased considerably, whereas soil Cd and Cr bioavailability were lower in the combined amendment treatments than in the control treatments. Particularly, application of a 2.49 t·ha−1 combined amendment (0.83 t·ha−1 S + 0.41 t·ha−1A + 1.25 t·ha−1B,1:0.5:1.5) decreased Cd, Pb, and Cr concentrations in maize grain by 68.9 %, 68.9 %, and 65.7 %, respectively. Species abundance and evenness in bacterial communities increased in field soils subjected to combined amendments, with shifts in community structure and function mostly driven by changes in soil pH, organic matter content, and nutrient availability. Overall, the results suggest that 1.5%S1A0.5B1.5 is the optimal treatment for remediating heavy metal co-contaminated soil, and thereby, improving maize yield and quality. Combined organic and inorganic amendments achieve high remediation efficiency, mainly by improving chemical properties, reducing heavy metal bioavailability, and altering bacterial community structure and function in heavy metal contaminated farmland soils.

Solubilization of residual dodecane by surfactants in porous media: The relation between surfactant partition and solubilization

One-dimensional flow column experiments are conducted to specifically compare the transport behavior of three surfactants (sodium dodecyl benzene sulfonate (SDBS), Triton X-100, rhamnolipid) and a solvent n-propanol and their solubilization on dodecane in porous media. Compared to pentafluorobenzoic acid (PFBA), the low adsorption or partition loss of n-propanol incurred no retardation, shouldering or retention in breakthrough curves. While for surfactants, all the breakthrough curves exhibited retardation, shouldering or retention to different degrees in the presence of dodecane phase. Compared to the anionic SDBS with no significant bulk partition to non-aqueous phase liquid (NAPL), the non-ionic Triton X-100 with partition induced significant retardation and shouldering in breakthrough curves. The retention loss of solubilized aggregates resulted in obvious retention of rhamnolipid at different pore-water velocities. The increase of pore-water velocity could promote the transport of surfactants and the dodecane-surfactant aggregates. The elution of dodecane in the presence of surfactants showed a significant relation to the partition behaviors of surfactants and a characteristic of the rate-limited solubilization. In contrast, the n-propanol, which is basically a non-reactive solvent, exhibited the rapid equilibrium dissolution of dodecane. The results indicated that in remediation of field sites contaminated by hydrophobic organic contaminants (HOCs), the surfactants should be rationally selected, and a favorable pore-water velocity should be used to obtain a high remediation efficiency and to reduce the retention loss of surfactants as well.

Efficient Inorganic/Organic Acid Leaching for the Remediation of Protogenetic Lead-Contaminated Soil

In this study, inorganic acid and organic acid were used to leach and remediate superheavy, lead-contaminated protogenetic soil with a lead pollution level of 8043 mg∙kg−1. Among the compounds studied, HCl and citric acid (CA) presented the best effects, respectively. Under the optimal experimental conditions, the remediation efficiency of 0.05 mol∙L−1 CA reached 53.6%, while that of 0.2 mol∙L−1 HCl was 70.3%. According to the lead morphology analysis, CA and HCl have certain removal ability to different fractions of lead. Among them, the removal rates of acid-soluble lead in soil by HCl and CA are 93% and 83%, and the soil mobility factor (MF) value decreased from 34.4% to 7.74 % and 12.3%, respectively, indicating that the harm of lead in soil was greatly reduced. Meanwhile, the leaching mechanisms of CA and HCl were studied. The pH values of the soil after leaching with HCl and CA were 3.88 and 6.97, respectively, showing that HCl leaching has caused serious acidification of the soil, while the process of CA leaching is more mild. CA has a relatively high remediation efficiency at such a low concentration, especially for the highly active acid-soluble fraction lead when maintaining the neutrality of the leached soil. Hence, CA is more suitable for the remediation of lead-contaminated soil.

Remediation of oil-contaminated soil using Fe/Cu nanoparticles and biosurfactants

ABSTRACT Oil (or petroleum), consisting of a mixture of hydrocarbons, can leak from oil exploration, production, and use. Due to their complex mixture and interaction with the subsurface soil and water, they are hard to treat and can become a significant environmental concern. Rhamnolipid and sophorolipid biosurfactants, biologically produced surfactants, can be used to remove petroleum hydrocarbons. Nanoparticles have gained attention as promising materials for soil remediation. In this study, suspensions of Fe-Cu nanoparticles and biosurfactants were employed for the remediation of oil-contaminated soil. The results showed that these suspensions displayed a high oil removal rate from contaminated soil, which followed the first-order reaction. For batch experiments, the oil remediation efficiency was up to 84%. Optimum conditions to achieve the highest oil remediation performance included a rhamnolipid biosurfactant: nanoparticle ratio of 10:1 (wt%: wt%), pH 7, room temperature, and shaking speed of 60 rpm for 60 min. The remediation rate was improved by higher temperature and lower ionic strength. In the presence and absence of nanoparticles, rhamnolipid biosurfactant demonstrated a higher remediation efficiency than sophorolipid biosurfactant and ultraplex surfactant. The presence of other surfactants decreased the treatment productivity by 9-14% compared to using only rhamnolipid biosurfactant. Nanoparticles were reused with a remediation efficiency of 59% after three cycles by rhamnolipid biosurfactant. These results suggested that biosurfactants/Fe-Cu nanoparticle suspension showed promise for the remediation of oil-contaminated soil.

Pore-scale simulation of adaptive pumping remediation in heterogeneous porous media

Spilled petroleum hydrocarbons pose a long-term threat to surrounding soil and groundwater, so the design of related remediation methods exhibits a growing global concern. Numerous innovative methods have been developed based on Pump-and-Treat (P&T) technology, which is the most commonly used decontamination method. Understanding the pore scale remediation mechanism of adaptive pumping is essential to the development of a decontamination scheme. In this study, the phase-field method was used to capture the evolution of the two-phase interface in a pore scale heterogeneous model during the period of adaptive pumping, and the influences of displacement patterns and wettability on remediation efficiency were investigated systematically. The results demonstrate that the model has the shortest dimensionless breakthrough time under mix-wet conditions, while it has the longest dimensionless breakthrough time under water-wet conditions. Compared with positive pumping, the growth of the ultimate remediation efficiency of adaptive pumping reaches the maximum (11.39%) under mix-wet conditions with Ca = −4.7, M = −2. The remediation mechanism of the adaptive pumping includes increasing the swept area near the boundary, extending the maintenance time of the driving pressure difference, and expanding the interfacial area between the injected fluid and the contaminant. These mechanisms indicate that a higher remediation efficiency can be obtained when adaptive pumping is applied combined with some innovative decontamination approaches, such as chemically enhanced flushing technology and in situ thermal treatment technology.

Environmental Impacts and Immobilization Mechanisms of Cadmium, Lead and Zinc in Geotechnical Composites Made from Contaminated Soil and Paper-Ash

Paper-ash is used for remediation of heavily contaminated soils with metals, but remediation efficiency after longer periods has not been reported. To gain insights into the mechanisms of immobilization of cadmium (Cd), lead (Pb), and znic (Zn), a study was performed in the laboratory experiment in uncontaminated, artificially contaminated, and remediated soils, and these soils treated with sulfate, to mimic conditions in contaminated soil from zinc smelter site. Remediation was performed by mixing contaminated soil with paper-ash to immobilize Cd, Pb, and Zn in the geotechnical composite. Partitioning of Cd, Pb, and Zn was studied over one year in seven-time intervals applying the sequential extraction procedure and complementary X-ray diffraction analyses. This methodological approach enabled us to follow the redistribution of Cd, Pb, and Zn over time, thus, to studying immobilization mechanisms and assessing the remediation efficiency and stability of newly formed mineral phases. Cd, Pb, and Zn were effectively immobilized by precipitation of insoluble hydroxides after the addition of paper-ash and by the carbonization process in insoluble carbonate minerals. After remediation, Cd, Pb, and Zn concentrations in the water-soluble fraction were well below the limiting values for inertness: Cd by 100 times, Pb by 125 times, and Zn by 10 times. Sulfate treatment did not influence the remediation efficiency. Experimental data confirmed the high remediation efficiency and stability of insoluble Cd, Pb, and Zn mineral phases in geotechnical composites.

Comparative study of three Pteris vittata-crop intercropping modes in arsenic accumulation and phytoremediation efficiency

Intercropping of Pteris vittata , an arsenic (As) hyperaccumulator, with crops is a method to realize the “production while remediation” of contaminated farmlands. However, the soil As remediation effects and the related mechanisms of P. vittata intercropping with different crops are rarely reported. In this study, by use of soil microplot experiment and root zone separation technique, the intercropping modes of P. vittata with maize ( Zea mays L.), ramie ( Boehmeria nivea (L.) Gaudich.) and castor ( Ricinus communis L.) were designed to investigate the As and nutrient uptake and accumulation, antioxidant enzyme response, soil As fractionation, and the remediation effects of As contaminated soil by P. vittata -crop intercropping. The results showed that the intercropping increased As content of P. vittata by 3.1–25.3%, decreased As content of maize grains and leaves of ramie and castor by 70.9%–95.6%, 29.2%–32.0% and 18.8%–32.0%, respectively, indicating higher remediation efficiency by P. vittata -crop intercropping. The intercropping increased the total nutrient contents (NPK) of the three crops by 2.0%–91.1%, promoted plant biomass by 3.7%–111.0%, increased the transpiration rate by 4.9%–68.9%, and decreased the malondialdehyde (MDA) content by 7.0%–31.8%. Analysis also showed that the intercropping enhanced soil pH value and available As content in P. vittata rhizosphere. The proportion of iron-bound As was enhanced in P. vittata rhizosphere soil but decreased in three crops rhizosphere soil. The analysis of soil microbial diversity showed that the intercropping decreased the abundance of chloroflexi , increased the abundance of proteobacteria and actinobacteria . In summary, the P. vittata -crop intercropping had a positive significance for improving As remediation effect of P. vittata and reducing the As content in crops. Those modes could be applied in the practice of heavy metal contamination remediation along with crop production in farmland. • Crop intercropping increased soil pH values and As availability in the rhizosphere of P. vittata . • Intercropping could improve soil As phytoremediation efficiency through increasing As content and accumulation in P. vittata . • Intercropping with P. vittata significantly reduced As contents in maize grains and leaves of ramie and castor. • P. vittata intercropping increased the growth, photosynthesis and nutrient contents of maize, ramie and caster. • The intercropping modes promoted microbial diversity.

Iron Sulfide Enhanced the Dechlorination of Trichloroethene by Dehalococcoides mccartyi Strain 195.

Iron sulfide (FeS) nanoparticles have great potential in environmental remediation. Using the representative species Dehalococcoides mccartyi strain 195 (Dhc 195), the effect of FeS on trichloroethene (TCE) dechlorination was studied with hydrogen and acetate as the electron donor and carbon source, respectively. With the addition of 0.2 mM Fe2+ and S2–, the dechlorination rate of TCE was enhanced from 25.46 ± 1.15 to 37.84 ± 1.89 μmol⋅L–1⋅day–1 by the in situ formed FeS nanoparticles, as revealed through X-ray diffraction. Comparing the tceA gene copy numbers between with FeS and without FeS, real-time polymerase chain reaction (PCR) indicated that the abundance of the tceA gene increased from (2.83 ± 0.13) × 107 to (4.27 ± 0.21) × 108 copies/ml on day 12. The transcriptional activity of key genes involved in the electron transport chain was upregulated after the addition of FeS, including those responsible for the iron–sulfur cluster assembly protein gene (DET1632) and transmembrane transport of iron (DET1503, DET0685), cobalamin (DET0685, DET1139), and molybdenum (DET1161) genes. Meanwhile, the reverse transcription of tceA was increased approximately five times on the 12th day. These upregulations together suggested that the electron transport of D. mccartyi strain 195 was enhanced by FeS for apparent TCE dechlorination. Overall, the present study provided an eco-friendly and effective method to achieve high remediation efficiency for organohalide-polluted groundwater and soil.

Research progress in the enhancement technology of soil vapor extraction of volatile petroleum hydrocarbon pollutants.

At present, volatile petroleum hydrocarbon pollution in soil is still widespread and serious in China. Among the treatment methods for contaminated soil, soil vapor extraction technology is widely used in in situ remediation of volatile petroleum hydrocarbon-contaminated soil due to its simple equipment, easy installation, convenient operation and high remediation efficiency. In this paper, the present situation of volatile organic compounds (VOCs) contaminated by petroleum hydrocarbons is reviewed. The effects of soil permeability, pollutant characteristics, soil moisture content, ambient temperature, and gas extraction flow rate on soil vapor extraction are discussed. Moreover, five different types of soil vapor extraction enhancement technologies, characteristics, research and applications are introduced, and the development prospect of soil remediation industry is presented.

Effects of surfactant injection position on the airflow pattern and contaminant removal efficiency of surfactant-enhanced air sparging

Surfactant-enhanced air sparging (SEAS) is an effective remediation technique for VOCs-contaminated soil. In this study, three types of tests are performed to investigate the effects of the surfactant injection position on the airflow pattern, contaminant removal efficiency, and airflow path control. The three tests are conventional air sparging (CAS), entire SEAS (ESEAS), where the surfactant is incorporated into the entire contaminated soil, and local SEAS (LSEAS), where the surfactant is injected locally at different positions. With increasing distance between the injection position and the central axis, the LSEAS test results approach the results measured in the CAS test. When the surfactant is injected directly at the central axis, a high contaminant removal rate of 89% is obtained, which is even higher than that obtained for the ESEAS test. As the injection position moves away from the central axis, the removal rate decreases. Furthermore, when the injection position is close to the sparging point, the surfactant can successfully control the airflow path. Based on the test results, a critical distance between the surfactant injection position and sparging point exists where high remediation efficiency can be achieved. This optimal surfactant injection position is specific to each contamination site.

Remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil with double dielectric barrier discharge plasma technology: Influencing parameters

A double dielectric barrier discharge (DDBD) plasma reactor was used for the remediation of simulated contaminated soil by a mixture of two, three and four rings PAHs i.e. naphthalene (Nap), phenanthrene (Phe) and pyrene (Pyr). Various influencing parameters such as peak-to-peak applied voltage, soil moisture, oxygen to nitrogen ratio (O2:N2) of carrier gas and soil depth in the reactor were investigated. The results illustrate that with an initial PAH concentration of 100 mgkg−1 the remediation efficiency increased by 27–30% when the applied voltage was increased from 28 to 40 kV. When the moisture content had been raised from 1.7% to 4% the remediation efficiency of Nap, Phe and Pyr increased from 89.55, 84.51 and 83.36% to 96.32, 89.08 and 88.59% respectively. However, further increase in moisture content decreased the PAHs remediation efficiency. With increasing oxygen to nitrogen ratio, the remediation efficiency of PAHs increased up to 20%. Higher oxygen concentrations in DDBD reactor has beneficial effect due to the generation of increased oxygenated species such as ozone, atomic oxygen and nitrogen oxides in discharge zone. When the soil thickness in the reactor was increased from 1 mm to 3 mm – due to decreased penetration of active species into the deeper zone of the soil – the remediation efficiencies decreased by 10%. Compared to ozonation the treatment of PAHs in the DDBD reactor resulted in higher remediation efficiencies. This is due to the generation of more active species in case of DDBD plasma treatment. The study demonstrates that DDBD plasma is a promising technology for remediation of heavily contaminated sites of PAHs due to its high remediation efficiency and robustness.

Inoculation of Cd-contaminated paddy soil with biochar-supported microbial cell composite: A novel approach to reducing cadmium accumulation in rice grains

Bioremediation of heavy metal-contaminated soil using metal-resistant microbes is a promising remediation technology. However, as exogenous bacteria sometimes struggle to survive and grow when introduced to new soils, it is important to develop appropriate carriers for microbial populations. In this study, we report a novel approach to remediating Cd-contaminated rice paddy soil using biochar-supported microbial cell composites (BMCs) produced from agricultural waste (cornstalks). Pot experiments showed that amendment with BMC was more efficient at reducing root and grain Cd content than pure bacteria, while improving soil Cd fractionation toward more stabilized and less labile forms. Bacteria in the BMC medium grew more readily with more abundant metabolites than those raised in free cells, probably because biochar provides shelter via porous structures (as confirmed by scanning electron microscopy) as well as additional nutrients. Overall, the improved long-term production of microbial biomass caused by BMC inoculation results in a higher remediation efficiency. Our results demonstrate the feasibility of using biochar as an appropriate carrier for metal-tolerant bacteria to remediate Cd-contaminated paddy fields.