Sand capping for controlling phosphorus release from lake sediments

In this research, the use of the sand capping technique for controlling phosphorus release from lake sediment was evaluated experimentally. Multiple acrylic columns were prepared to measure the dissolved oxygen, oxidation reduction potential, total phosphorus, and phosphate concentrations of the overlying water on the capping layer with thicknesses of 0, 40, and 80 mm. Sand capping effectively slowed down the reactions that depleted the dissolved oxygen, which as a result, controlled the total phosphorus release from the sediment. Oxidation reduction potential of overlying water was estimated by measuring dissolved oxygen in situ or vice versa by an empirical model proposed in this research. Sediment disturbance should be considered during field construction of the cap system. The experimental results showed that phosphorus existed in a more stable form with capping than without capping.

Nonequilibrium mass transfer of multi-component NAPL in a soil column venting

This study was conducted to investigate the mass transfer behavior for a multi-component system in the soil venting process. Soil venting experiments were conducted using gasoline-contaminated soil and models of local equilibrium assumption (LEA) and the first-order kinetic approach were used to descnbe the gasoline volatilization process. However, the focus was on the application of the kinetic model. In both models, thirteen major components of gasoline were selected for the model input and the rest of the gasoline was divided into 11 groups based on the retention times in the gas chromatography of gasoline. The LEA model had the tendency of underestimating the gas concentration at the initial phase and overestimating at the later phase due to the different volatilities of multi-components. n the kinetic model, the estimation of mass transfer coefficient values were carried out by adopting the relationship developed in the single-components system and choosing the appropriate modified Sherwood number. This method resulted in the good agreement with the simulation and the experimental results.

Rapid reductive destruction of hazardous organic compounds by nanoscale Fe0

Fe0-mediated reductive destruction of hazardous organic compounds such as chlorinated organic compounds (COCs) and nitroaromatic compounds (NACs) in the aqueous phase is one of the latest innovative technologies. In this paper, rapid reductive degradation of COCs and NACs by synthesized nanoscale Fe0 in anaerobic batch systems was presented. The nanoscale Fe0, characterized by high specific surface area and high reactivity, rapidly transformed trichloroethylene (TCE), chloroform (CF), nitrobenzene (NB), nitrotoluene (NT), dinitrobenzene (DNB) and dinitrotoluene (DNT) under ambient conditions, which results in complete disappearance of the parent compounds from the aqueous phase within a few minutes. GC analysis reported that the main products of the dechlorination of TCE and CF were ethane and methane as well as that most of the nitro groups in NACs were reductively transformed to amine groups. These results suggest that the rapid reductive destruction by nanoscale Fe0 is potentially a viable in situ or aboveground treatment of groundwater contaminated with hazardous organic compounds including COCs and NACs.

Kinetics of reductive denitrification by nanoscale zero-valent iron

Zero-valent iron powder (Fe0) has been determined to be potentially useful for the removal of nitrate in the water environment. This research is aimed at subjecting the kinetics of denitrification by nanoscale Fe0 to an analysis of factors affecting the chemical denitrification of nitrate. Nanoscale iron particles with a diameter in the range of 1-100 nm, which are characterized by the large BET specific surface area to mass ratio (31.4 m2/g), removed mostly 50, 100, 200, and 400 mg/l of nitrate within a period of 30 min with little intermediates. Compared with microscale (75-150 microm) Fe0, end product is not ammonia but N2 gas. Kinetics analysis from batch studies revealed that the denitrification reaction with nanoscale Fe0 appeared to be a pseudo first-order with respect to substrate and the observed reaction rate constant (k(obs)) varied with iron content at a relatively low degree of application. The effects of mixing intensity (rpm) on the denitrification rate suggest that the denitrification appears to be coupled with oxidative dissolution of iron through a largely mass transport-limited surface reaction (<40 rpm).