Assessment of the Use of Partitioning and Interfacial Tracers To Determine the Content and Mass Removal Rates of Nonaqueous Phase Liquids

Abstract

It was assessed whether partitioning and interfacial tracers can be used to determine the content and mass removal rate of nonaqueous phase liquid (NAPL) in porous media. Retardation factors for these tracers were determined for five different model matrices contaminated with hexadecane as NAPL. The retardation of the partitioning tracer 2,4-dimethyl-3-pentanol was correlated with the degree of NAPL saturation for four of the five matrices (r 2 = 0.93, n = 8). The observed retardation factors matched the retardation factors predicted with the independently determined hexadecane−water partitioning constant and the degree of NAPL saturation, indicating that this tracer may be used to estimate the degree of NAPL saturation of porous media. The mass removal rates of NAPL from columns packed with different matrices were determined by measuring the amount of hexadecane in the column effluent during elution with electrolyte solution. These removal rates differed over 3 orders of magnitude, dependent on the matrix used. The retardation of the interfacial tracer alkylbenzenesulfonate was higher for matrices with higher NAPL mass removal rates but was not correlated to the degree of NAPL saturation. This indicates that the retardation factors of alkylbenzenesulfonates in NAPL-contaminated media contain information related to the NAPL mass removal rates.

The enhancement by surfactants of hexadecane degradation by Pseudomonas aeruginosa varies with substrate availability

“…Column studies with hexadecane-contaminated matrices were performed as described previously (Noordman et al, 2000b). Stainless steel preparative HPLC columns (length 7.0 cm, i.d.…”

“…After saturation of the columns by elution with 100 ml min − 1 electrolyte solution using a flow rate of 0.1 ml min − 1 , the concentration of the hexadecane was determined by GC analysis of five 7 ml effluent fractions. Subsequently, tracer experiments were done which lasted for up to 20 pore volumes (Noordman et al, 2000b). The breakthrough profiles of the conservative tracer potassium bromide indicated that the columns were packed homogeneously and that physical non-equilibrium effects were absent.…”

“…Rhamnolipid was analyzed by HPLC using evaporative light scattering detection (ELSD) (Noordman et al, 2000a). SDBS was analyzed by HPLC using UV detection at 228 nm (Noordman et al, 2000b). The nonionic surfactants Brij 30 (polyoxyethylene(4)dodecyl ether), Brij 35(polyoxyethylene(23)dodecyl ether), and polyoxyethylene(10)dodecyl ether were analyzed using HPLC-ELSD with gradient elution.…”

“…Since the amount of hexadecane in the column effluent exceeded its aqueous solubility (3.6×10 − 3 mg l − 1 (Schwarzenbach et al, 1993)) for columns packed with CPG-10-3000, sea sand, and silica 60, hexadecane was eluted from these columns partly in solubilized or emulsified state (Table 1). Flow interruption experiments have shown that hexadecane elution from the columns packed with contaminated silica 60 was limited by mass transfer rates of hexadecane from the matrix to the aqueous phase (Noordman et al, 2000b). Furthermore, since the residual amounts of hexadecane in the matrix samples taken after the experiment from the top, bottom, and from the mixed column content of columns packed with silica 60 and sea sand were equal, hexadecane was removed from the column material to the same extent in all positions (Noordman et al, 2000b).…”

“…Flow interruption experiments have shown that hexadecane elution from the columns packed with contaminated silica 60 was limited by mass transfer rates of hexadecane from the matrix to the aqueous phase (Noordman et al, 2000b). Furthermore, since the residual amounts of hexadecane in the matrix samples taken after the experiment from the top, bottom, and from the mixed column content of columns packed with silica 60 and sea sand were equal, hexadecane was removed from the column material to the same extent in all positions (Noordman et al, 2000b). This implies that the rate with which hexadecane was removed from the columns was dependent on the mass transfer rate of hexadecane from the matrix to the mobile phase and not on its subsequent transport velocity.…”