Effects of soil fines and surfactant sorption on contaminant reduction of coarse fractions during soil washing.

The reduction of contaminants sorbed on the coarse fraction of soils to the level below clean-up requirements is essential for an effective soil washing process. This study investigated the effects of soil texture and surfactant sorption on the reduction of total petroleum hydrocarbons (TPH) in coarse fraction during soil washing. Batch TPH sorption experiments were conducted on soil slurry with various soil fine/coarse ratios and surfactants Octylpheny polyoxyethylene (TX-100) and Dodecylpyridinium chloride (DPC) at the dosage below their saturation levels of sorption. In a sandy loam soil of low silt and clay contents, increasing the fine/coarse ratio from 0.4 to 1.2 without adding surfactants resulted in a reduction of TPH levels in the coarse fraction by 30%. Increasing the fine/coarse ratio along with sorbed surfactant (3000 mg TX-100 or 10,000 mg DPC per kg soil) further reduced TPH concentrations in the coarse fraction. For a silty loam soil already containing a high percentage of fine particles, increasing the fine/coarse ratio from 5.9 to 18.8 without surfactant addition yielded no further TPH reduction in the coarse fraction. On the other hand, surfactant sorption at the fine/coarse ratio of 5.9 improved the washing efficiency of the coarse fraction. These experimental results suggested the importance of high contents of soil fines and surfactant sorption in achieving low contaminant concentrations of coarse fractions during soil washing.

Sorption and desorption kinetics of surfactants TX-100 and DPC on different fractions of soils.

Surfactant-based technologies are promising remediation alternatives. The information on sorption and desorption kinetics of surfactants on soils is important in the successful application of surfactant-based technologies. In this study, the sorption and desorption rates of nonionic surfactant TX-100 and cationic DPC were correlated to the surfactant concentration, soil organic matters (SOM), and soil cation exchange capacity (CEC). The results indicated that at higher initial surfactant concentrations, sorption rates of surfactants increased linearly with SOM and soil CEC for TX-100 and DPC, respectively. The sorption rates and initial surfactant concentrations followed the first order relation for TX-100 and second order for DPC. A linear relationship between the sorption rates of surfactants and soil characteristics was developed. The desorption rates of TX-100 and DPC increased linearly with the increased surfactant levels sorbed on soils but were irrelevant to soil characteristics and the contact time of surfactant sorption. The rate of surfactant desorption was similar as the amount of surfactants sorbed on soils was in the same range. The cationic DPC sorbed and desorbed at two orders of magnitude faster than the nonionic TX-100, suggesting that both sorption and desorption have to be considered in the remediation process.

Chemical oxidation of chlorinated non-aqueous phase liquid by hydrogen peroxide in natural sand systems.

This study explored the Fenton-like oxidation of trichloroethylene (TCE) existing as dense non-aqueous phase liquid (DNAPL) in natural silica sand (iron=0.04 g/kg) and the sand from an aquifer (iron=2.01 g/kg). Glass bead containing no iron mineral was used as the control. Batch oxidation experiments were conducted to assess interactions between oxidant and TCE DNAPL. Column experiments were performed to evaluate dynamics of TCE and H(2)O(2) during oxidation. The pH was not altered. In the batch system, a single application of 3% H(2)O(2) to the aquifer sand oxidized 40% of the added TCE DNAPL in 1 h, which was four times of that by dissolution with the gas purge procedure. This demonstrated the ability of mineral-catalyzed Fenton-like reaction to directly oxidize TCE in non-aqueous liquid. In the column experiments, after passing 7 pore volumes (PVs) of 1.5 and 3% H(2)O(2) solution, the residual TCE in aquifer sand column was 12.0 and 2.6% of the initial added, respectively. On the other hand, 28.4% of the added TCE still remained in the silica sand column by 7 PVs of 3% H(2)O(2). The distribution of TCE in column and effluent indicated the occurring of direct oxidation of TCE DNAPL and the increased solubilization, which probably due to size reduction of DNAPL droplets, followed by water-phased TCE oxidation.

Co-surfactant of ethoxylated sorbitan ester and sorbitan monooleate for enhanced flushing of tetrachloroethylene.

This work evaluated the flushing efficiency of tetrachloroethylene (PCE) using the co-surfactant of non-ionic ethoxylated sorbitan ester (Tween) and oilphilic sorbitan monooleate (Span 80), which formed more hydrophobic micelles than Tween alone. The flushing efficiency was evaluated with laboratory columns filled with silica and aquifer sand. Results from column flushing were also compared to those of batch solubility experiments to study the removal mechanism by the co-surfactant solution. Compared to Tween 80 alone, the molar solubilization ratio and the affinity between the micelles and PCE increased 84% and 90%, respectively, by the co-surfactant solution of Tween 80 and Span 80 mixed at a 4:1 ratio. Flushing with 1% Tween 80 solution yielded a steady PCE recovery of 7% for both silica and aquifer sand in each pore volume (PV). Flushing with co-surfactant of 1% Tween 80 + Span 80 (4:1) further increased PCE recovery to 10% for silica sand and 13% for aquifer sand per PV. A comparison of results from column flushing and batch solubility tests indicated that the primary flushing mechanism of PCE using the co-surfactant solution of Tween 80 + Span 80 (4:1) was micellar solubilization.

Oxidation of chlorophenols in soil at natural pH by catalyzed hydrogen peroxide: the effect of soil organic matter.

This investigation reports on the effects of soil organic matter (SOM) during the oxidation of chlorophenols with Fe2+-catalyzed H2O2 (Fenton oxidation) system. The soil pH was 7.1 and was not altered. Sorption experiments of soil pre-treated under various oxidation conditions were performed. Concentrations of organic matter in the liquid phase and soil before and after oxidation were analyzed. The results were correlated to the observation in batch Fenton oxidation tests. They showed that the oxidation of chlorophenols at natural soil pH depended on the dose of H2O2 and Fe2+. The soil organic content did not vary significantly after various Fenton treatments, while the sorption of chlorophenols was 10-25% less by the oxidation. The concentration of chlorophenols in the liquid phase exhibited a "decrease and rebound" phenomenon in the batch Fenton oxidation tests. It appeared that the oxidation of SOM resulted in the release of sorbed chlorophenols which were then oxidized by the excess H2O2. An "oxidation-desorption-oxidation" scheme was proposed to describe one of the interaction mechanisms among the oxidant, SOM, and chlorophenols during oxidation.