Treatment of Trichloroethylene in Aqueous Solution Using Nanoscale Zero-Valent Iron Emulsion
The objective of this research was to evaluate the treatment efficiency of a trichloroethylene(TCE)-contaminated aqueous solution and soil by combined technologies of the emulsified nanoscale zero-valent iron slurry (ENZVIS) and electrokinetic remediation process. Nanoiron was synthesized using the chemical reduction method by industrial grade chemicals. The synthesized nanoparticles contained elemental iron and iron oxide as determined by X-ray diffractmetry(XRD). Micrographs of FE-SEM have shown that a majority of nanoiron were in the size range of 30~50 nm.
The stability study of food-grade soybean oil emulsion was conducted using six non-ionic surfactants and soybean oil. The results have shown that the emulsion prepared by mixed surfactants (Span 80 and Tween 40) and soybean oil yielded a better emulsion stability. Based on the above finding, the nanoiron slurry, soybean oil and aforementioned, mixed surfactants were used to prepare ENZVIS.
Degradation of TCE by ENZVIS under various operating parameters was carried out in batch experiments. The experimental results have indicated that emulsified nanoiron outperformed nanoiron in TCE dechlorination rate. ENZVIS (0.75 g-Fe0/L) degradated TCE (initial conc.= 10 mg/L) down to 45 %. An increase of the oil dosage could improve the stability of the emulsion, but yielding a negative influence on degradation of TCE. Experimental results also showed that ENZVIS could remove TCE up to 94 % when pH=6. It was also formed that a higher TCE initial concentration would result in a higher TCE removal efficiency. In addition, using ENZVIS to degraded TCE-contaminated artificial groundwater has indicated that nitrate and carbonate of groundwater will suppress nanoiron reaction with TCE. Especially, a high concentration of carbonate in the reaction system might form a passive film or precipitates on nanoiron surface.
This study further evaluated the treatment efficiency of combining ENZVIS and electrokinetic technology in treating a TCE-contaminated soil. Experimental conditions were given as follows:(1) initial TCE concentration in the range of 98~118 mg/kg; (2) an electric potential gradient of 1 V/cm; (3) a daily addition of 20 mL ENZVIS; and (4) a reaction time of 10 days. Experimental results have shown that an addition of ENZVIS to the anode reservoir of strongly acidic and oxidative environment would cause nanoiron to corrode rapidly and decrease TCE removal efficiency. On the other hand, an addition of ENZVIS to the cathode reservoir would enhance the degradation of TCE therein. In summary, an addition of ENZVIS to the cathod reservoir would yield the best TCE removal efficiency.
Advisor:Gordon C. C. Yang; Kuei-jyum Yeh; Bing-hong Chen; Ruey-an Doong
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:emulsified nanoscale zero valent iron trichloroethylene electrokinetic contaminated soil surfactant
Date of Publication:08/27/2007