Enhancing plant-microbe associated bioremediation of phenanthrene and pyrene contaminated soil by SDBS-Tween 80 mixed surfactants

Impact mechanisms of various surfactants on the biodegradation of phenanthrene in soil: Bioavailability and microbial community responses

The present study was conducted to systematically explore the mechanisms underlying the impact of various surfactants (CTAB, SDBS, Tween 80 and rhamnolipid) at different doses (10, 100 and 1000 mg/kg) on the biodegradation of a model polycyclic aromatic hydrocarbon (PAH) by indigenous soil microorganisms, focusing on bioavailability and community responses. The cationic surfactant CTAB inhibited the biodegradation of phenanthrene within the whole tested dosage range by decreasing its bioavailability and adversely affecting soil microbial communities. Appropriate doses of SDBS (1000 mg/kg), Tween 80 (100, 1000 mg/kg) and rhamnolipid at all amendment levels promoted the transformation of phenanthrene from the very slow desorption fraction (Fvslow) to bioavailable fractions (rapid and slow desorption fractions, Frapid and Fslow), assessed via Tenax extraction. However, only Tween 80 and rhamnolipid at these doses significantly improved both the rates and extents of phenanthrene biodegradation by 22.1-204.3 and 38.4-76.7 %, respectively, while 1000 mg/kg SDBS had little effect on phenanthrene removal. This was because the inhibitory effects of anionic surfactant SDBS, especially at high doses, on the abundance, diversity and activity of soil microbial communities surpassed the bioavailability enhancement in dominating biodegradation. In contrast, the nonionic surfactant Tween 80 and biosurfactant rhamnolipid enhanced the bioavailability of phenanthrene for degradation and also that to specific degrading bacterial genera, which stimulated their growth and increased the abundance of the related nidA degradation gene. Moreover, they promoted the total microbial/bacterial biomass, community diversity and polyphenol oxidase activity by providing available substrates and nutrients. These findings contribute to the design of suitable surfactant types and dosages for mitigating the environmental risk of PAHs and simultaneously benefiting microbial ecology in soil through bioremediation.

Larger aggregate formed by self-assembly process of the mixture surfactants enhance the dissolution and oxidative removal of non-aqueous phase liquid contaminants in aquifer

Surfactants can transfer non-aqueous phase liquid (NAPL) contaminants to the aqueous phase, and enhance the removal of the latter in groundwater. However, the extensive use of surfactants causes secondary contamination and increases the non-target consumption of oxidants. It is pressing to develop a surfactant with high phase transfer efficiency and sound compatibility with oxidants to minimize the use of surfactants for groundwater remediation. The phase transfer capability of different surfactants and their binary mixtures, their enhanced KMnO4 oxidation performance for NAPL contaminants as well as influencing factors were investigated to solve the above-mentioned question. The results showed that Tween20, SDBS and BS-12 perform best in terms of phase transfer capability among nonionic, anionic and amphoteric surfactants respectively, and only SDBS and BS-12 produce a synergistic effect among the binary mixtures. The CMC of SDBS/BS-12 was lower than its ideal CMC value, and the self-assembly process of SDBS/BS-12 also formed larger aggregates, which improved the phase transfer performance. Compared to other single surfactants, the removal efficiency of petroleum hydrocarbons in the aquifer sediments was raised by 7.4-33.8 % using the mixed surfactant. The SDBS/BS-12 mixture was compatible with KMnO4 and boosted the reaction of NAPL contaminants with KMnO4 by transferring from the NAPL phase to the aqueous phase. As a result, the NAPL toluene and phenanthrene removal efficiency increased from 37 % and 29 % to 80 % and 86 % respectively. Natural organic matters inhibited the phase transfer efficiency of the SDBS/BS-12 mixture, whereas anions and monovalent cations enhanced the phase transfer capability of the mixture. High-valent cations led to precipitation in the SDBS/BS-12, which could be eliminated by adding Na2Si2O5. The SDBS/BS-12 mixture delivered the same phase transfer efficiency with the dosage of 1.73-23.07 % of other single surfactants, and its cost was equivalent to 0.25-41.7 % of the latter, thus embracing bright application prospects.

Optimizing the formulation of Erwinia bacteriophages for improved UV stability and adsorption on apple leaves

Fire blight is a bacterial disease that affects plants of the Rosaceae family and causes significant economic losses worldwide. Although antibiotics have been used to control the disease, concerns about their environmental impact and the potential to promote antibiotic resistance have arisen. Bacteriophages are being investigated as an alternative to antibiotics; however, their efficacy can be affected by environmental stresses, such as UV radiation. In this study, we optimized the formulation of Erwinia phages to enhance their stability in the field, focusing on improving their UV stability and adsorption using adjuvants. Our results confirmed that 4.5 % polysorbate 80 and kaolin improve phage stability under UV stress, resulting in an 80 % increase in PFU value and improved UV protection efficacy. Adsorption assays also demonstrated that polysorbate 80 and kaolin improved the absorption efficiency, with phages detected in plant for up to two weeks. These findings demonstrate the effectiveness of the auxiliary formulation of Erwinia bacteriophages against environmental stress.

The effect of petroleum levels on some soil biological properties under phytoremediation and bioaugmentation

With the development of industries and excessive use of petroleum compounds, petroleum pollution has become a serious threat to the environment. The aim of this study was to the effect of petroleum levels on the biological activities of soil affected by phytoremediation and bioaugmentation. A surface soil sample was collected from the polluted areas around Bandar Abbas Oil Refinery Company, and the petroleum-degrading bacteria were isolated. M. yunnanensis (native) was selected among the isolated colonies for further experiment. The used soil in this study was a surface soil collected from Baghu region of Bandar Abbas, Sothern Iran, and treatments were added to soil samples. To evaluate removal of petroleum levels (0, 4, and 8%) from the soil by phytoremediation (control, sorghum, barley, and bermudagrass) and bioaugmentation (control, A. brasilense (non-native) and M. yunnanensis) and bioaugmented phytoremediation, a factorial pot experiment with completely randomized design and three replications was performed. The results demonstrated that sorghum and bermudagrass were more resistant than barley to the toxic effects of petroleum. Positive effect of bacteria on dry weight in polluted soil was greater than in the non-polluted soil. The degradation of petroleum reaches 77% in sorghum + M. yunanesis + 4% petroleum. Plants had stronger ability to degrade total petroleum hydrocarbon (TPH), while bacteria could better degrade polyaromatic hydrocarbons (PAHs). Application of bacteria and plants stimulated soil biological characteristics (dehydrogenase, arylsulfatase, lipase, bacterial population, and respiration) in polluted soil. Among measured enzymes, dehydrogenase exhibited a stronger response to petroleum levels. Four-percent level had greater irritating effect on soil biological properties. Plants and bacteria rely on differences in biological properties to attain synergy in petroleum degradation. Results indicated that M. yunnanensis has a high ability to remove petroleum from soil, and plants enhance the efficiency of this bacterium.

Bioremediation of Polycyclic Aromatic Hydrocarbons in Contaminated Soils Using Vermicompost

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils are reported in many literatures. Composting, in addition to bioremediation, can simultaneously increase soil organic matter content and soil fertility and is thus regarded as one of the most cost-effective methods of soil remediation. In this study, biodegradation of phenanthrene (PHE) and pyrene (PYR) is reported by microbial consortia enriched by vermicompost. After soil samples preparation and grinding, the samples were contaminated with 100, 200, and 300 mg/kg of PHE and PYR concentrations and inoculated with three concentrations (2, 4, and 6 wt.%) of vermicompost. PHE and PYR concentrations were analyzed by HPLC during bioremediation. After 70 days, two highly capable microbial consortia were used to remove the pollutants in bioaugmentation conditions. Analysis of their microbial composition revealed that the consortia contain several Proteobacteria phylum bacterial species, and the most common genera were Pseudomonas and Citrobacter. Decontamination rates for PHE and PYR were estimated to be 89% and 83% over 45 days, respectively. Biodegradation kinetics revealed that microbial degradation followed a first-order kinetics. This study provides clear evidence on the biodegradation of PHE and PYR, paving the way for the development of bioremediation technologies for the recovery of polluted ecosystems.

In situ phytoremediation of polycyclic aromatic hydrocarbon-contaminated agricultural greenhouse soil using celery

Although celery has been established as an effective plant in the remediation of organic pollutant-contaminated soil, few studies have investigated the associated biological processes in rhizosphere and the effect of celery on agricultural field remediation in situ. In this study, a polycyclic aromatic hydrocarbon (PAH)-contaminated agricultural greenhouse was used as the experimental site, and three celery species (Apium graveolens L., Oenanthe javanica (Blume) DC., Libanotis seseloides (Fisch. & C.A. Mey. ex Turcz.) Turcz.) were applied for in situ remediation. After 90 days, the PAH dissipation rate of the L. seseloides treatment was highest (50.21%), and most of the PAHs were limited to its roots (translocation factor 0.516). This suggested that L. seseloides is a potential species for phytoremediation coupled with agro-production. The culturable microbial population and invertase activity results strongly supported that O. javanica is suitable for the establishment of exogenous bacteria-celery co-remediation techniques. Pearson's correlation analysis showed that the polyphenol oxidase (PPO) activity was highly significantly positively correlated with the PAH dissipation rate (r = 0.984, P < 0.01), and we suggest that PPO can be used as a microecological index during PAH remediation.

Phytoremediation of pyrene-contaminated soils: A critical review of the key factors affecting the fate of pyrene

Soil contamination by pyrene has increased over the years due to human-related activities, urgently demanding for remediation approaches to ensure human and environment safety. Within this frame, phytoremediation has been successfully applied over the years due to its green and cost-effectiveness features. The scope of this review includes the main phytoremediation mechanisms correlated with the removal of pyrene from contaminated soils and sediments to highlight the impact of different parameters and the supplement of additives on the efficiency of the treatment. Soil organic matter (SOM), plant species, aging time, environmental parameters (pH, soil oxygenation, and temperature) and bioavailability are among the main parameters affecting pyrene removal through phytoremediation. Phytoextraction only accounts for a small part of the entire phytoremediation process, but the addition of surfactants and chelating agents in planted soils could increase pyrene accumulation in plant tissues by 20% as a consequence of the increased pyrene bioavailability. Rhizodegradation is the main phytoremediation mechanism involved due to the activity of bacteria capable of degrading pyrene in the root area. Inoculated-planted soil treatments have the potential to decrease pyrene accumulation in shoots and roots by approximately 30 and 40%, respectively, further stimulating the proliferation of pyrene-degrading bacteria in the rhizosphere. Plant-fungi symbiotic association results in an enhanced accumulation of pyrene in shoots and roots of plants as well as a higher biodegradation. Finally, pyrene removal from soil can be improved in the presence of amendments, such as natural non-ionic surfactants, biochar, and bacterial mixtures.

A salt resistant biosurfactant produced by moderately halotolerant Pseudomonas aeruginosa (AHV-KH10) and its application for bioremediation of diesel-contaminated sediment in saline environment

A halotolerant bacterial strain was isolated from oily-contaminated sites of Persian Gulf, which characterized as Pseudomonas aeruginosa (AHV-KH10) by 16S rRNA gene sequencing. This strain was used for bioremediation of diesel-contaminated sediments. Biosurfactant production was initially screened by using oil displacement test and drop-collapse method, followed by measurement of surface tension (ST) of growth medium. Produced biosurfactant was a rhamnolipid type biosurfactant and lowered the ST to 33.4 mN/m at the given critical micelle concentration (CMC) of 75 mg/L. Addition of 3 CMC rhamnolipid, inoculums size of 15 mL, biodegradation in slurry phase and salinity level of 6% led totally to a diesel biodegradation rate of 70% for initial concentration of 1000 mg/kg after 35 days. The maximum diesel removal occurred at the salinity content of 6% indicating the moderately halo-tolerant characteristics of isolated strain. Evaluation of bacterial growth showed a biomass yield of 0.33 mg _VSS/mg _diesel in selected conditions. The field performance of Pseudomonas aeruginosa AHV-KH10 was proved through the removal of the TPH content in unwashed sediment, which varied from 2390 to 1875 mg/kg within four months.

The Utility of Electrochemical Systems in Microbial Degradation of Polycyclic Aromatic Hydrocarbons: Discourse, Diversity and Design

Polycyclic aromatic hydrocarbons (PAHs), especially high molecular weight PAHs, are carcinogenic and mutagenic organic compounds that are difficult to degrade. Microbial remediation is a popular method for the PAH removal in diverse environments and yet it is limited by the lack of electron acceptors. An emerging solution is to use the microbial electrochemical system, in which the solid anode is used as an inexhaustible electron acceptor and the microbial activity is stimulated by biocurrent in situ to ensure the PAH removal and avoid the defects of bioremediation. Based on the extensive investigation of recent literatures, this paper summarizes and comments on the research progress of PAH removal by the microbial electrochemical system of diversified design, enhanced measures and functional microorganisms. First, the bioelectrochemical degradation of PAHs is reviewed in separate and mixed PAH degradation, and the removal performance of PAHs in different system configurations is compared with the anode modification, the enhancement of substrate and electron transfer, the addition of chemical reagents, and the combination with phytoremediation. Second, the key functional microbiota including PAH degrading microbes and exoelectrogens are overviewed as well as the reduced microbes without competitive advantage. Finally, the typical representations of electrochemical activity especially the internal resistance, power density and current density of systems and influence factors are reviewed with the correlation analysis between PAH removal and energy generation. Presently, most studies focused on the anode modification in the bioelectrochemical degradation of PAHs and actually more attentions need to be paid to enhance the mass transfer and thus larger remediation radius, and other smart designs are also proposed, especially that the combined use of phytoremediation could be an eco-friendly and sustainable approach. Additionally, exoelectrogens and PAH degraders are partially overlapping, but the exact functional mechanisms of interaction network are still elusive, which could be revealed with the aid of advanced bioinformatics technology. In order to optimize the efficacy of functional community, more advanced techniques such as omics technology, photoelectrocatalysis and nanotechnology should be considered in the future research to improve the energy generation and PAH biodegradation rate simultaneously.

Bioremediation of PAH-contaminated shooting range soil using integrated approaches

Serious contamination of polycyclic aromatic hydrocarbons (PAHs) occurs at outdoor shooting ranges due to the accumulation of clay target fragments containing coal tar or petroleum pitch. These contaminated sites are characterized with high-molecular-weight PAHs that are low in bioavailability and recalcitrant to bioremediation. We evaluated the effectiveness of different remediation strategies, used individually or in combinations, to decontaminate PAHs in a shooting range soil. The treatments included vegetation with bermudagrass [Cynodon dactylon (L.) Pers] or switchgrass [Panicum virgatum]), bioaugmentation of Mycobacterium vanbaalenii PYR-1, and addition of surfactants (Brij-35, rhamnolipid biosurfactant, or Brij-35/sodium dodecyl sulfate mixture). The initial total PAH concentration in the shooting range soil was 373 mg/kg and consisted of primarily high-molecular-weight PAHs (84%). Planting of bermudagrass and switchgrass resulted in 36% and 27% ∑₁₆PAH reduction compared to the non-vegetated control, respectively. Bermudagrass enhanced soil dehydrogenase activity and both vegetation treatments also increased polyphenol oxidase activity. Bioaugmentation of M. vanbaalenii PYR-1 had a significant effect only on the dissipation of high-molecular-weight PAHs, leading to a 15% decrease (∑₁₀PAH) compared to the control. In the non-vegetated soil, Brij-35/sodium dodecyl sulfate mixture increased PAH degradation compared to the no surfactant control. The increased PAH biodegradation in the vegetated and bioaugmented treatments improved lettuce [Lactuca sativa] seed germination, suggesting reduced toxicity in the treated soils. Phytoremediation using bermudagrass or switchgrass with bioaugmentation of M. vanbaalenii PYR-1 was an effective in situ remediation option for shooting range soils with heavy PAH contamination.

Combination of rhamnolipid and biochar in assisting phytoremediation of petroleum hydrocarbon contaminated soil using Spartina anglica

Biochar (BC) and rhamnolipid (RL) is used in bioremediation of petroleum hydrocarbons, however, the combined effect of BC and RL in phytoremediation has not been studied until now. In this paper, the phytoremediation of petroleum hydrocarbon-contaminated soil using novel plant Spartina anglica was enhanced by the combination of biochar (BC) and rhamnolipid (RL). Samples of petroleum-contaminated soil (10, 30 and 50 g/kg) were amended by BC, BC+ RL and rhamnolipid modified biochar (RMB), respectively. After 60 day's cultivation, the removal rate of total petroleum hydrocarbons (TPHs) for unplanted soil (UP), planted soil (P), planted soil with BC addition (P-BC), planted soil with BC and RL addition (P-BC + RL) and planted soil with addition of RMB (P-RMB) were 8.6%, 19.1%, 27.7%, 32.4% and 35.1% in soil with TPHs concentration of 30 g/kg, respectively. Compared with UP, the plantation of Spartina anglica significantly decreased the concentration of C_8-14 and tricyclic PAHs. Furthermore, the application of BC and RMB alleviated the toxicity of petroleum hydrocarbons to Spartina anglica via improving plant growth with increasing plant height, root vitality and total chlorophyll content. High-throughput sequencing result indicated that rhizosphere microbial community of Spartina anglica was regulated by the application of BC and RMB, with increase of bacteria and plant mycorrhizal symbiotic fungus in biochar and RMB amended soil.

The effects of anionic and non-ionic surfactant on anaerobic co-digestion of sludge, food wastes and green wastes

Surfactants are widely used and discharged into wastewater treatment plants, which might influence the anaerobic digestion (AD) treatment of municipal waste. In this study, the effects of typical anionic surfactants sodium dodecyl benzene6 sulfonate (SDBS) and non-ionic surfactants APG, on mesophilic anaerobic co-digestion of sludge, food waste, and green waste were investigated. Results indicated that at 5 mg/g, the biogas production was inhibited in SDBS supplemented systems while stimulated in APG-added reactors, with the methane yield of 146.58 L/g VS consumed. At 15 mg/g, the biogas production in both SDBS and APG supplemented reactors was both inhibited. It means the negative or positive effect of APG on AD depends on the dose of APG supplementation. The 16S rRNA gene analysis demonstrated the microbial community structure in the digester was changed due to the addition of surfactant. Bacteroidia significantly increased with the addition of APG and SBDS, while the increase of Clostridia only occurred in APG-added system. The variation of microbial Communities' structure in APG and SDBS-added digesters might give an explanation for the different efficiencies in these two systems. Thus, the effects of surfactants on the efficiency of AD should be considered during the disposal of municipal organic waste.

Mixed-surfactant-enhanced phytoremediation of PAHs in soil: Bioavailability of PAHs and responses of microbial community structure

The present study was conducted to explore the mechanisms of surfactant-enhanced phytoremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs), focusing on the bioavailability of PAHs and microbial diversity. We investigated the remediation efficiencies of phenanthrene and pyrene after the addition of mixed surfactants (sodium dodecyl benzene sulfonate (SDBS) and Tween 80) of different ratios (1:1, 1:2, and 2:1) at the concentration of 100 mg/kg to soils cultured with ryegrass (Lolium multiflorum L.). The fractions of phenanthrene and pyrene were determined using a sequential extraction method, and the microbial diversity was evaluated using 16S rRNA gene high-throughput sequencing. The results showed that mixed surfactants could enhance the remediation efficiencies of PAHs, and mainly occurred in the initial 21 days. Mixed surfactants at the ratio of 1:1 (HM1) showed the best remediation efficiency in enhancing the dissipation of pyrene in 21 days. Mixed surfactants showed little effects on the removal of phenanthrene. In general, HM1 significantly decreased the bioavailable, bound and residual fractions of pyrene; additionally, higher abundances of PAH-degradation bacteria and degradation-related genes were observed. Pearson correlation analysis among PAH degraders, degradation-related genes and bioavailable fraction of PAHs was performed. Our results indicated that mixed surfactants could promote the transformation of pyrene from the bound and residual fractions to bioavailable fractions and enhance the abundances of PAH degradation bacteria and PAH degradation-related genes, thereby enhancing the degradation of pyrene.

Effects of mixed surfactants on the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in crops and the bioremediation of contaminated farmlands

Given the widespread contamination of polycyclic aromatic hydrocarbons (PAHs) in farmland, it is necessary to develop a technology to ensure the safety of agricultural productions and remediate the contaminated soils. In this study, a series of mixed surfactants were utilized to reduce the uptake of PAHs by crops in farming period and enhance the plant-microbe associated biodegradation in fallow period. During the farming period, the mixtures of cetyltrimethyl ammonium bromide (CTMAB) and Tween 80 were attached on soil by cationic-exchange and hydrogen bond, respectively, which increased soil organic matter to partition the bio-available fraction of PAHs. The maximum reduction of phenanthrene and pyrene was 88.6% and 94.9% for chrysanthemum (Chrysanthemum coronarium L.), and 90.6% and 91.9% for raphanus (Raphanus sativus L.), respectively. During the fallow period, sodium dodecyl benzene sulfonate (SDBS) reduced the adsorption loss of Tween 80 on soil to enhance desorption of PAHs. The mixtures of SDBS and Tween 80 increased the water-soluble fraction of PAHs in soils, modified bacterial community structure, and enriched the functional genes involved cell motility and signal transduction. Removal efficiencies of phenanthrene and pyrene in soils were high to 86.7% and 90.7%. This systematic technology provided an effective solution to remediate and plant on PAH-contaminated farmlands.

Surfactant-enhanced bioremediation of DDTs and PAHs in contaminated farmland soil

Field-scale bioremediation of dichlorodiphenyl trichloroethanes (DDTs) and polycyclic aromatic hydrocarbons (PAHs) contaminated farmland soil from the Shenyang North New Area of China was studied using the bacteria Arthrobacter globiformis. The additive effects of different concentrations of biosurfactant rhamnolipids (RLs) and anionic-nonionic mixed surfactant (SDBS-Tween 80) were evaluated. DDT and PAH removal rates by A. globiformis after 150 days of remediation were 52.1% and 21.9%, respectively. At the optimum RL concentration of 5 mg kg^-1, DDTs and PAHs had removal rates of 64.3% and 35.6%, respectively, at 150 days. This was 60.7% and 29.3% higher than the control; 36.9% and 19.8% higher than soil with RL-5 alone; and 12.2% and 13.8% higher than the A. globiformis treatment alone. RL-5 can enhance soil enzyme activity and A. globiformis reproduction during the DDT and PAH biodegradation processes. This study illustrates a highly efficient, low-cost in situ soil bioremediation technology that could have practical utility.

Organic contamination and remediation in the agricultural soils of China: A critical review

Soil pollution is a global problem in both developed and developing countries. Countries with rapidly developing economies such as China are faced with significant soil pollution problems due to accelerated industrialization and urbanization over the last decades. This paper provides an overview of published scientific data on soil pollution across China with particular focus on organic contamination in agricultural soils. Based on the related peer-reviewed papers published since 2000 (n=203), we evaluated the priority organic contaminants across China, revealed their spatial and temporal distributions at the national scale, identified their possible sources and fates in soil, assessed their potential environmental risks, and presented the challenges in current remediation technologies regarding the combined organic pollution of agricultural soils. The primary pollutants in Northeast China were polycyclic aromatic hydrocarbons (PAHs) due to intensive fossil fuel combustion. The concentrations of organochlorine pesticides (OCPs) and phthalic acid esters (PAEs) were higher in North and Central China owing to concentrated agricultural activities. The levels of polychlorinated biphenyls (PCBs) were higher in East and South China primarily because of past industrial operations and improper electronic waste processing. The co-existence of organic contaminants was severe in the Yangtze River Delta, Pearl River Delta, and Beijing-Tianjin-Hebei Region, which are the most populated and industrialized regions in China. Integrated biological-chemical remediation technologies, such as surfactant-enhanced bioremediation, have potential uses in the remediation of soil contaminated by multiple contaminants. This critical review highlighted several future research directions including combined pollution, interfacial interactions, food safety, bioavailability, ecological effects, and integrated remediation methods for combined organic pollution in soil.

Removal of hydrophobic volatile organic compounds with sodium hypochlorite and surfactant in a co-current rotating packed bed

A co-current flow rotating packed bed was applied to remove volatile organic compounds (VOCs) by sodium hypochlorite (NaClO) and surfactant (sodium dodecyl benzene sulfonate, SDBS) from air stream. Xylene was used as a model VOC herein. The effect of pH, concentration of NaClO and SDBS solution, liquid flow rate, gas flow rate and rotational speed on xylene removal efficiency and overall mass transfer coefficient (K_Ga) were discussed. Then, a correlation for K_Ga of the co-current rotating packed bed was proposed by fitting the experimental data of K_Ga and independent variables of liquid/gas ratio, rotational speed, pH, NaClO concentration and treatment time, which was in good agreement with the experimental data (the deviation≤±30%).

Interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and organic soil washing agents

Understanding interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and soil-washing agents can help in choosing efficient agents which are able to desorb and solubilize PAHs. This study investigated interaction mechanisms between pyrene and four washing agents including: two dissolved organic matters (DOM) F-DOM and CRC-DOM, and two commercial bio-based surfactants BBE-1000 and Supersolv using fluorescence spectroscopy combined with multivariate curve resolution alternating regression (MCR-AR). The efficiencies of these washing agents in removing PAHs from the soil were tested in a soil washing experiment. Pyrene showed π-π interactions with F-DOM and no interaction with CRC-DOM. This could be attributed to the more aromatic structures in F-DOM compared to CRC-DOM. The two DOMs were inefficient in soil washing which might be attributed to the relatively weak effect of π-π interactions in releasing PAHs from the soil. Interaction mechanisms between pyrene and the bio-based surfactants were elucidated with MCR-AR, which resolved three spectroscopically active species from pyrene emission spectra as a function of pyrene and bio-based surfactants concentrations. These species resembled pyrene emission in a polar and nonpolar microenvironment, respectively and of an excimer. Concentration profiles retrieved by the model for the three species showed that, below the critical micelle concentration (CMC), Supersolv created more nonpolar interactions with pyrene compared to BBE-1000. In soil washing, Supersolv showed the highest efficiency in extracting PAHs from the soil. This highlighted the importance of nonpolar interactions in desorbing PAHs from soils, which could then be solubilized in micelles. This study demonstrated the potential of fluorescence spectroscopy combined with the MCR-AR model for selecting efficient soil-washing agents.

Polycyclic aromatic hydrocarbons (PAHs) enrich their degrading genera and genes in human-impacted aquatic environments

Bacterial degradation is an important clearance pathway for organic contaminants from highly human-impacted environments. However, it is not fully understood how organic contaminants are selected for degradation by bacteria and genes in aquatic environments. In this study, PAH degrading bacterial genera and PAH-degradation-related genes (PAHDGs) in sediments collected from the Pearl River (PR), the Pearl River Estuary (PRE) and the South China Sea (SCS), among which there were distinct differences in anthropogenic impact, were analyzed using metagenomic approaches. The diversity and abundance of PAH degrading genera and PAHDGs in the PR were substantially higher than those in the PRE and the SCS and were significantly correlated with the total PAH concentration. PAHDGs involved with the three key processes of PAH degradation (ring cleavage, side chain and central aromatic processes) were significantly correlated with each other in the sediments. In particular, plasmid-related PAHDGs were abundant in the PR sediments, indicating plasmid-mediated horizontal transfer of these genes between bacteria or the overgrowth of the bacteria containing these plasmids under the stresses of PAHs. Our results suggest that PAH degrading bacteria and genes were rich in PAH-polluted aquatic environments, which could facilitate the removal of PAHs by bacteria.

Surfactant-enhanced remediation of polycyclic aromatic hydrocarbons: A review

Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic and carcinogenic organic compounds that are widely present in the environment. The bioremediation of PAHs is an economical and environmentally friendly remediation technique, but it is limited because PAHs have low water solubility and fewer bioavailable properties. The solubility and bioavailability of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension; this method is called surfactant-enhanced remediation (SER). The SER of PAHs is influenced by many factors such as the type and concentration of surfactants, PAH hydrophobicity, temperature, pH, salinity, dissolved organic matter and microbial community. Furthermore, as mixed micelles have a synergistic effect on PAH solubilisation, selecting the optimum ratio of mixed surfactants leads to effective PAH remediation. Although the use of surfactants inhibits microbial activities in some cases, this could be avoided by choosing an optimum combination of surfactants and a proper microbial community for the targeted PAH(s), resulting in up to 99.99% PAH removal. This article reviews the literature on SER of PAHs, including surfactant types, the synergistic effect of mixed micelles on PAH removal, the impact of surfactants on the PAH biodegradation process, factors affecting the SER process, and the mechanisms of surfactant-enhanced solubilisation of PAHs.

Tween 80 surfactant-enhanced bioremediation: toward a solution to the soil contamination by hydrophobic organic compounds

The occurrence of hydrophobic organic compounds (HOCs) in the soil has become a highly significant environmental issue. This problem has been exacerbated by the strong sorption of HOCs to the soils, which makes them unavailable for most remediation processes. More and more works show that surfactant-enhanced biological technologies offer a great potential to clear up HOCs-contaminated soils. This article is a critical review of HOCs removal from soils using Tween 80 (one of the mostly used nonionic surfactants) aided biological remediation technologies. The review begins with a discussion of the fundamentals of Tween 80-enhanced desorption of HOCs from contaminated soils, with special emphasis on the biotoxicity of Tween 80. Successful results obtained by Tween 80-enhanced microbial degradation and phytoremediation are documented and discussed in section 3 and section 4, respectively. Results show Tween 80-enhanced biotechnologies are promising for treating HOCs-contaminated soils. However, considering the fact that most of these scientific studies have only been conducted at the laboratory-scale, many improvements are required before these technologies can be scaled up to the full-scale level. Moreover, further research on mechanisms related to the interaction of Tween 80 with degrading microorganisms and the plants is in high demand.

Influence of multiwalled carbon nanotubes and sodium dodecyl benzene sulfonate on bioaccumulation and translocation of pyrene and 1-methylpyrene in maize (Zea mays) seedlings

Influence of multiwalled carbon nanotubes with outer diameters > 50 nm (MW) and a surfactant sodium dodecyl benzene sulfonate (SDBS) on bioaccumulation and translocation of pyrene and 1-methylpyrene (1-CH₃-pyrene) in maize seedlings in single-(F1) and bi-(F2) compound systems was investigated. Pyrene concentration in shoots was detected in all treatments in F1 and F2, ranging in 10.43-60.28 ng/g and 21.46-40.21 ng/g, respectively, and its translocation factors (TFs) ranged in 0.12-0.19 and 0.07-0.16. However, no 1-CH₃-pyrene in shoots was detected from F1 and F2, indicating almost 100% suppression on its translocation from roots to shoots. SDBS at 100 mg/kg significantly enhanced pyrene bioaccumulation in roots and shoots by 43.5% and 77.4% in F1, and 21.7% in roots in F2, while showed insignificant effect on shoot concentration in F2. In contrast, SDBS at 100 mg/kg exerted no significant effect on root 1-CH₃-pyrene concentration in F1 and F2. With increasing amendment level of MW from 50 to 3000 mg/kg, both pyrene and 1-CH₃-pyrene concentrations in roots and shoots sharply decreased, indicating an increasing suppression on their bioaccumulation and translocation in plant. As for 3000 mg/kg MW + 100 mg/kg SDBS, root concentrations of pyrene and 1-CH₃-pyrene in F1 were significantly reduced by 53.4% and 100%, while shoot concentration of pyrene was not affected, generally consistent with the trend of the corresponding bioaccumulation factors (BCF_root) and TFs. As for F2 with the same treatment, root 1-CH₃-pyrene concentration declined by 68.6%, whereas pyrene bioaccumulation in roots and shoots was insignificantly affected, which were also in agreement with their BCF_root and TFs. Results of this work highlight the combined impacts of soil amendment with carbon nanotubes and surfactant on bioaccumulation and translocation of pyrene and 1-CH₃-pyrene in maize seedlings in multi-pollutant exposure systems, which is important for soil pollution control and food safety assessment.

Surfactant enhanced pyrene degradation in the rhizosphere of tall fescue (Festuca arundinacea)

The present study was conducted to evaluate the effect of two non ionic surfactants (Tween 80 and Triton X-100), a biosurfactant (Lecithin), and randomly methylated-β-cyclodextrins (RAMEB) on the remediation of pyrene from soil planted with tall fescue (Festuca arundinacea). Soils with pyrene concentration of about 243 mg kg(-1) was grown with tall fescue and were individually amended with 0, 200, 600, 1000, and 1500 mg kg(-1) of Tween 80, Triton X-100, biosurfactant, and RAMEB. The results show that all surfactants significantly increased plant biomass compared to unamended soil. Dehydrogenase activity was also stimulated as a result of surfactant addition. Only 3.9 and 3.2 % of pyrene was decreased in the uncovered and covered abiotic sterile control, suggesting that microbial degradation was the main removal mechanism of pyrene from soil. In the planted treatment receiving no surfactant, the remediation of pyrene was 45 % which is significantly higher than that of corresponding unplanted control soil, suggesting that the cultivation of tall fescue alone could enhance the overall remediation of pyrene in soil. All surfactants had significantly higher rates of pyrene remediation compared to the unamended planted soil. Generally, RAMEB displayed the highest remediation rates, i.e., 64.4-79.1 % followed by the Triton X-100, i.e., 60.1-74.8 %. The positive impact of surfactants on pyrene remediation could possibly be because of their capacities to increase its bioavailability in soil. The evidence from this study suggests that the addition of surfactants could enhance phytoremediation of PAHs polluted soil.

Evaluating bioavailability of organic pollutants in soils by sequential ultrasonic extraction procedure

Under current retrospective risk assessment framework, the total concentrations of organic pollutants in soils have been employed as the standard for over 30 years. The total concentrations reflect the overall accumulation in soils but tend to be overly conservative for assessing the ecological risks, where the bioavailability plays an important role. In this study, the bioavailability of organic pollutants in soils was evaluated using a stepwise and tiered classification method, namely the sequential ultrasonic extraction procedure (SEUP). The water-soluble and acid-soluble fractions extracted by the SEUP were the bioavailable fractions. The reliability and environmental relevance of the speciation method were examined with representative organic pollutants using the root uptake methods and the semipermeable membrane devices (SPMDs). The plant uptake amounts corrected with weight were highly correlated with the bioavailable fractions (R(2) > 0.75). The amounts of the bioavailable fractions were negatively correlated with the logKow values (R(2) ranging from 0.71 to 0.77) of the organic pollutants and the contents of soil organic matter (R(2) ranging from 0.68 to 0.96). As a refinement of the current risk assessment framework, the SUEP that has proved to be a reliable and convenient is thus highly recommended for evaluating the bioavailability of organic pollutants in soils.

Effectiveness of biostimulation through nutrient content on the bioremediation of phenanthrene contaminated soil

Bioremediation has shown its applicability for removal of polycyclic aromatic hydrocarbons (PAHs) from soil and sediments. In the present study, the effect of biostimulation on phenanthrene removal from contaminated soil via adding macro and/or micronutrients and trace elements was investigated. For these purposes three macro nutrients (as N, P and K), eight micronutrients (as Mg, S, Fe, Cl, Zn, Mn, Cu and Na) and four trace elements (as B, Mo, Co and Ni) in 11 mineral salts (MS) as variables were used. Placket-Burman statistical design was used to evaluate significance of variables (MS) in two levels of high and low. A consortium of adapted microorganisms with PAHs was used for inoculation to the soil slurry which was spiked with phenanthrene in concentration of 500 mg/kg soil. The optimal reduction resulted when a high level of macro nutrient in the range of 67-87% and low level of micro nutrient in the range of 12-32% were used with the nitrogen as the dominant macronutrient. The Pareto chart showed that NH4NO3 was the most effective variable in this experiment. The effect of elements on phenanthrene biodegradation showed following sequence as N > K > P > Cl > Na > Mg. Effectiveness of the other elements in all runs was less than 1%. The type and concentration of nutrient can play an important role in biodegradation of phenanthrene. Biostimulation with suitable combination of nutrient can enhance bioremediation of PAHs contaminated soils.