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.

Recent progress on in-situ chemical oxidation for the remediation of petroleum contaminated soil and groundwater.

Accidental oil leaks and spills can often result in severe soil and groundwater pollution. In situ chemical oxidation (ISCO) is a powerful and efficient remediation technology. In this review, the applications and recent advances of three commonly applied in-situ oxidants (hydrogen peroxide, persulfate, and permanganate), and the gap in remediation efficiency between lab-scale and field-scale applications is critically assessed. Feasible improvements for these measures, especially solutions for the 'rebound effect', are discussed. The removal efficiencies reported in 108 research articles related to petroleum-contaminated soil and groundwater were analyzed. The average remediation efficiency of groundwater (82.7%) by the three oxidants was higher than that of soil (65.8%). A number of factors, including non-aqueous phase liquids, adsorption effect, the aging process of contaminants, low-permeability zones, and vapor migration resulted in a decrease in the remediation efficiency and caused the residual contaminants to rebound from 19.1% of the original content to 57.7%. However, the average remediation efficiency of ISCO can be increased from 40.9% to 75.5% when combined with other techniques. In the future, improving the utilization efficiency of reactive species and enhancing the contact efficiency between oxidants and petroleum contaminants will be worthy of attention. Multi-technical combinations, such as the ISCO coupled with phase-transfer, viscosity control, controlled release or natural attenuation, can be effective methods to solve the rebound problem.

Surfactant-enhanced remediation of oil-contaminated soil and groundwater: A review.

Oil leakage, which is inevitable in the process of extraction, processing, transportation and storage, seriously undermines the soil and groundwater environment. Surfactants can facilitate the migration and solution of oil contaminants from nonaqueous phase liquid (NAPL) or solid phase to water by reducing the (air/water) surface tension, (oil/water) interfacial tension and micellar solubilization. They can effectively enhance the hydrodynamic driven remediation technologies by improving the contact efficiency of contaminants and liquid remediation agents or microorganism, and have been widely used to enhance the remediation of oil-contaminated sites. This paper summarizes the characteristics of different types of surfactants such as nonionic, anionic, biological and mixed surfactants, their enhancements to the remediation of oil-contaminated soil and groundwater, and examines the factors influencing surfactant performance. The causes of tailing and rebound effects and the role of surfactants in suppressing them are also discussed. Laboratory researches and actual site remediation practices have shown that various types of surfactants offer diverse options. Biosurfactants and mixed surfactants are superior and worth attention among the surfactants. Using surfactant foams, adding shear-thinning polymers, and combining surfactants with in-situ chemical oxidation are effective ways to resolve tailing and rebound effects. The adsorption of surfactants on soils and aquifer sediments decreases remediation efficiency and may cause secondary pollution, Therefore the adsorption loss should be noticed and minimized.

Accumulation of Cu, Cd, Pb, Zn and total P from synthetic stormwater in 30 bioretention plants.

The uptake and distribution of four heavy metals, including copper (Cu), cadmium (Cd), lead (Pb) and zinc (Zn), and those of total phosphorus (TP) in 30 plants in North China were investigated through pot trial experiments. Accumulation and distribution of heavy metals or TP were associated with plant species, tissues, metal elements and pollutant loading. The highest amount of heavy metal and TP accumulation was found in the whole plants of Hylotelephium erythrostictum (Miq.) H. Ohba (C1) and Chlorophytum laxum R. Br. (L4), respectively. Considering the biological concentration factor, translocation factor, retention factor and biomass indices, C1 is the suitable plant for Cd and Cu uptake, whereas Hosta plantaginea (Lam.) Aschers (L3) and Viola verecunda A. Gray (V1) are the suitable plants for Pb removal. Rehmannia glutinosa (Gaetn.) Libosch. ex Fisch. (S1) and L4 can be chosen for Zn and TP removal, respectively. Cluster analysis was applied to select suitable plants for heavy metal and TP removal. Results showed that C1, L4 and Pennisetum alopecuroides (L.) Spreng (G1) have a good capability of accumulating heavy metals and TP. Results demonstrated that the plant species rather than the families considerably influenced the accumulation of pollutants.

Ranking media for multi-pollutant removal efficiency in bioretention.

Bioretention is an effective best management practice for urban stormwater. This study aims to provide guidance for selecting the best bioretention medium in terms of pollutant removal capacity. Fuzzy set theory was applied with the improved analytic hierarchy process (IAHP) for weight determination, thus forming the fuzzy synthetic evaluation model, to assess the comprehensive efficiencies of certain sand media. This work is the first to use this method to study bioretention. Results demonstrated that the fuzzy synthetic evaluation model was a rational choice for the selection of bioretention media. The studied media were ranked by pollutant removal capacity as follows: Media III > Media V > Media I > Media VI > Media II > Media VII > Media IV. Media I had the best comprehensive removal efficiency and infiltration rate in bioretention. Moreover, the removal rates for Cd2+, Zn2+ and Pb2+ were excellent (>80%), those for Cu2+ and NH+4-N fluctuated from 58.1% to 92.7% and 64.7% to 95.9%, respectively, and those for NO-3-N and TP of the seven media did not show distinct differences.