學生 : 陳雅貞 日期 :

Introduction Polycyclic aromatic hydrocarbons (PAHs) are pollutants of major concern in soils and sediments. Surfactant-enhanced remediation (SER) has been suggested as a promising technology for the removal of hydrophobic pollutants from soil and groundwater. surfactants are viewed as being potentially useful for aiding the bioremediation of PAH-contaminated sites.

Introduction In practical applications, mixtures of surfactants, rather than individual surfactants are often used. Anionic–nonionic surfactants reduced precipitation and sorption loss, and enhanced the flushing and washing efficiency for contaminated soils. The surfactants, TW80, TX100, Brij35 and SDS were selected because they have been extensively used in bioremediation trials and are likely to be degraded in the environment.

The objectives of the present study are (1) to quantify the extent of phenanthrene solubilization in mixed anionic– nonionic surfactants; (2) to evaluate the biodegradation of phenanthrene associated to the mixed micellar phase by phenanthrene-degrading microorganisms. Introduction

Phenanthrene (purity > 98%) Sodium dodecyl sulfate ； SDS(purity>98%) Brij35 TW80 TX100 HPLC-grade methanol Materials

Experimental section Measurement of surface tension and CMC 都諾表面張力測定儀 The CMC values were obtained through a conventional plot of the surface tension versus the logarithm value of the surfactant concentration.

Experimental section Solubilization test Prepared at the total concentration of 5.0 and 10.0 mM (Mmixed surfactant solutions) the molar ratios of SDS to nonionic surfactant were 1:0, 9:1, 7:3, 5:5, 3:7, 1:9 and 0:1. single/mixed surfactant solutions The phenanthrene was separately added to each tube in an amount slightly more than required to saturate the solution Separate the undissolved phenanthrene Phenanthrene in solutions was analyzed at 254nm 48h ， 25 ± 1 ℃ 1.0ml of methanol and surfactant– water Solution diluted to 10ml.

Experimental section Biodegradation test of phenanthrene The biodegradation experiments in the dark to avoid photooxidation of phenanthrene. Surfactant solution and fine phenanthrene in the sealed flasks were shaken and then filtered to separate he crystalline particles The filtrate was transferred into flask. microorganism solution mineral basal medium solution Diluted with methanol and filtered through 0.22 μ m syringe filter. Ultraviolet spectrophoto detector high-pressure liquid chromatography

Results and discussion The surface tensions at a given molar ratio decreased with increasing total surfactant concentration, and each surface tension curve had a breaking point that was taken as a mixed CMC. Fig. 1. Plots of surface tension versus the total concentrations of SDS-TX100. The mixed CMCs were intermediates between the CMCs of the individual SDS and TX100. For SDS-TW80 and SDS-Brij35 systems, similar tendency was observed, but slightly different from SDS-TX100.

Results and discussion When Xnon was 0.9, the mixed CMC of SDS-TW80 and SDS- Brij35 were somehow less than those of pure TW80 and Brij35, respectively. During the formation of mixed micelle, nonionic surfactant molecules insert into the micelle of anionic surfactant and decrease the repulsion force among the ionic heads.

Results and discussion Fig. 2. Solubilization of phenanthrene by single surfactants The solubilities of phenanthrene were enhanced by each of surfactant solutions, in which the solubilities increased with increasing surfactant concentrations. Solubililzation of phenanthrene

Results and discussion S PAH,cmc (M) is the apparent solubility of a PAH compound at the CMC. S PAH, cmc(M) is the total apparent solubility of the PAH compound in micellar solution at a particular surfactant concentration greater than the CMC. C surf is the surfactant concentration at which S PAH,mic was evaluated. surfactantTW80Brij35TX100SDS MSR ＞ ＞＞

Results and discussion Fig. 3. Synergistic solubilization of phenanthrene by mixed surfactants, (a) SDS-TW80 (b) SDS-TX100 (c) SDS-Brij35 The compositions of mixed systems, S mix is greater than S cal.

Snon is the apparent solubility of phenanthrene in sole nonionic surfactant solution. the apparent solubility in sole SDS solutions. the intrinsicsolubility of phenanthrene in water (1.18mgL -1 ， 25 ℃ ) Ideal additivity rule Results and discussion

The degree of phenanthrene solubility enhancements by mixed surfactants (S mix )followed the order of SDS-TW80 > SDS-Brij35 > SDS-TX100. Th evalues of R shows that SDS- Brij35 exhibits larger extent of synergistic solubilization, which may be attributed to the same alkyl chain in the molecular structures of Brij35 and SDS. The degree of synergistic solubilization is relative large when Xnon is small. Results and discussion

Fig. 4. Degradation of phenanthrene in single or mixed surfactants. (a)SDS Biodegradation of phenanthrene Surfactants may improve the mass transfer of solid hydrocarbons, there by increasing the availability to microorganisms. However, with high CMC and low solubilizing capacity, SDS would not enhance availability of contaminants significantly. Mixing nonionic surfactant with SDS  mixed micelle  CMC, as mentioned above, bioavailability of phenathrene.

Results and discussion Fig. 4. Degradation of phenanthrene in single or mixed surfactants. (b) TW80 and SDS-TW80. That 17.39mgl -1 of phenanthrene in 0.5mM (655mgl -1 ) of TW80 solution disappeared within 60h. The degrading rate of phenanthrene was slightly faster in 2.0–0.5mM of SDS-TW80 solution. A large amount of phenanthrene (26.80mgL -1 ) in 5.0–0.5mM of SDS-TW80 was degraded with 96h.

Results and discussion Fig. 4. Degradation of phenanthrene in single or mixed surfactants (c) TX100 and SDS-TX100. SDS-TX100 systems, the degradation rates of phenanthrene in 2.0–1.0 and 5.0–1.0mM of SDS- TX100 systems were at large the same as that in 1.0mM (625mgl -1 ) of TX100.

Results and discussion Fig. 4. Degradation of phenanthrene in single or mixed surfactants. (d) Brij35 and SDS- Brij35. Phenanthrene in 1.0mM of Brij35 solutions was depleted within 36h mgl -1 of phenanthrene in 2.0– 1.0mM of SDS-Brij35 solution disappeared at 48h. The microorganisms took up about 96h to consume 33.32mgl -1 of phenanthrene in 5.0–1.0mM of SDS-Brij35 solution.

Results and discussion When the concentration of SDS increased, phenanthrene degradation could slow down. The application of surfactants to soil environments contaminated with PAHs has become a possible means to increase the bioavailability of these hydrophobic compounds and to facilitate their biodegradation.

Conclusions The experiment showed that CMCs of mixed surfactants are much lower than that of individual SDS. The solubility of phenanthrene was proportional to the concentration of the single surfactants when above the CMC. On the basis of MSR, solubilization capacity for phenanthrene was in the order: TW80 > Brij35 > TX100 > SDS.

Given the molar fraction of nonionic surfactant and the total surfactant concentrations,SDS-TW80 enhanced the solubility of phenanthrene most significantly among three mixed systems, while SDS-Brij35 exhibited larger extent of synergistic solubilization. In view of the biodegradation experiments, phenanthrene in mixed surfactant solutions was readily degradable during the experiment. Conclusions

No inhibitory effects on the microorganism duo to the mixing of SDS with TW80, TX100 and Brij35 were found. These results suggest the mixed surfactant solution may improve the performance of SER by increasing the bioavailability and biodegradation of PAHs and reducing the level of remediation expanses. Conclusions