| Surfactants and cyclodextrins are good solubilizers to organic contaminants.Great advantages, which include high contaminant removal ratio and shortremediation period, have been observed when they are used in remediation oflow-polarity organic compounds contaminated soil and aquifer. In this paper, thesolubilization abilities of β-cyclodextrin, carboxymethyl-β-cyclodextrin, andsurfactants to low-polarity organic contaminants has been investigatedsystematically. Effects on the solubilization of these solubilizers are discussed indetail. The solubilization power of different cyclodextrins and surfactants hasbeen compared. Laboratory and in situ remediation study for the contaminatedsoil in the original site of Changzhou Dye Chemical Plant have been carried out.A useful method for the remediation of similar contaminated site has beenproposed. The acute toxicity of β-cyclodextrin and carboxymethyl-β-cyclodextrinto Daphnia magna and photobacteria is reported, in order to estimate thepotential environmental biological effects of cyclodextrins.The major achievements in the paper include the following aspects:1. A simple synthetic method for the synthesis of β-cyclodextrin derivativecarboxymethyl-β-cyclodextrin is reported. The solubilization ofβ-cyclodextrin and carboxymethyl-β-cyclodextrin to polycyclic aromatichydrocarbon and aromatic halides have been investigated systematically.Effects on the solubilization of these solubilizers are discussed in detail.(1) β-Cyclodextrin and carboxymethyl-β-cyclodextrin has great solubilizationpower to low polarity organic compounds. The apparent solubility of PAHand aromatic halides in cyclodextrin solution increased linearly with theincreasing of cyclodextrin concentration. The solubilization effect is causeby the formation of inclusion complexes between cyclodextrin and organiccompounds.(2) Because cyclodextrins have fixed cavity size, the fitness of moleculestructure with the cyclodextrin cavity has predominant effect on thesolubilization efficiency. The better the fitness of the molecule, the morestable of inclusion complex formed, the greater the solubilization power.(3) The solubilization effect is also related to the octanol-water partitioncoefficient logKow. For the aromatic halides investigated, which have asimilar molecular size, the solubilization efficiency is linearly parallel tothe logKow of the compounds.(4) The solubilization power of carboxymethyl-β-cyclodextrin is lower thanthat of β-cyclodextrin for the same compound. This phenomenon isinterpreted by the difference in polarity and size of carboxymethyl groupand hydroxyl group. The bigger molecular size and higher polarity ofcarboxymethyl group may impede the partition of low polaritycompounds from water to the cyclodextrin cavity.2. The solubilization power of different types of surfactants to trichlorobenzenehas been compared with sodium laurylsulfate (SDS), cetyltrimethylaminiumbromide (CTAB), and alkyl polyethoxy ether (LAE) as representatives. Theco-effect of three types of surfactants and carboxymethyl-β-cyclodextrin wasinvestigated.(1) The solubilization power of non-ionic surfactant LAE to trichlorobenzeneis greater than ionic surfactants SDS and CTAB. The main reason for thisdifference is due to the difference in micellar structure and solubilizationbehavior of trichlorobenzene in the micelle.(2) The solubilization of surfactants to trichlorobenzene is not only observedabove micellar concentration (CMC) of surfactants, but also appearedbelow CMC. Present of surfactant multiplier in the solution at lowconcentration and the decrease of solution polarity in the presence ofsurfactant monomer may be contributed to the effect.(3) The presence of different surfactants in the carboxymethyl-β-cyclodextrin(CMCD) solution has different effect on the solubilization behavior oftrichlorobenzene in the system. The apparent solubility oftrichlorobenzene in CMCD solution in the presence of surfactants is notincreased linearly with the increase of CMCD concentration. Comparedwith the solubility in absence of surfactants, the solubility oftrichlorobenzene is decreased in some degree at the presence of surfactantsin CMCD solution. But, at low CMCD concentration, the addition of SDScould result in a significant increase of trichlorobenzene solubility. Thisphenomenon may be caused by formation of mixed micelle of surfactantswith CMCD, and the mixed micelle has better solubilization power ofsurfactant.(4) Cyclodextrins have great inclusion power to surfactants. Addition ofCMCD to surfactant solution could completely depress the solubilizationeffect of surfactants to trichlorobenzene.3. Removal of aromatic contaminants from polluted soil by flushing withsurfactant solution has been investigated. Laboratory and in situ remediationstudy for the contaminated soil in the original site of Changzhou DyeChemical Plant has been carried out. Aromatic contaminants in soil canremove effectively by Surfactant solution. The removal efficiency for phenol,and nitrobenzene are 93.97%, 78.74% respectively by flushing with 1.0g/Lsodium dodecylbenzosulfate solution. The elution ratio of major contaminantsfrom the in situ soil sample is also higher than 90%.4. Studies for the solubilization and removal of naphthalene from soil withCMCD and non-ionic surfactant indicates that the two solubilizers have goodsolubilization power to naphthalene in aqueous solution. Although hesolubilization power of non-ionic surfactant LAE to naphthalene is about 4 to5 times higher than that of CMCD, 10g/L LAE has little effect on removal ofnaphthalene from soil, compared to the high efficiency (53.9% removal) ofCMCD at the same concentration. Sorption of surfactant on soil has greatlydecreased the solubilization power of non-ionic surfactant to contaminant.5. The acute toxicity of β-cyclodextrin and carboxymethyl-β-cyclodextrin isdetermined with Daphnia magna and photobacteria. The EC50 value showsthat β-cyclodextrin has no toxicity to photobacteria, while toxic to Daphniamagna at high concentration (EC50=1.27g/L). Compare to β-cyclodextrin,carboxymethyl-β-cyclodextrin is quite toxic to photobacteria (EC50=0.28g/L),and has similar toxicity to Daphnia magna.
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