Direct current driven persulfate delivery and activation for heterogeneous porous media remediation: Coupling effects of electric-thermal-chemical-flow fields.

Direct current (DC) has promising potential for persulfate delivery and activation in heterogeneous site remediation, yet requires deeper understanding. Here, we investigated the efficiency of DC for persulfate delivery and activation and compared with alternating current (AC). While AC electric field only influenced persulfate fate by Joule heating effect, DC electric field induced electrokinetic migration of persulfate and contaminants, as well as promoted persulfate activation with Joule heating and electrochemical reactions.

Spatiotemporal dynamic temperature variation dominated by ion behaviors during groundwater remediation using direct current.

Direct current (DC) electric field has shown promising performance in contaminated site remediation, in which the Joule heating effect plays an important role but has been previously underappreciated. This study focuses on the spatiotemporal characteristics and mechanism of temperature change in heterogeneous porous media with applied DC. The heating process can be divided into four phases: preferential heating of the low permeability zone (LPZ), rapid heating in the middle region, temperature drop and hot zone shift, and reheating.

Simulating field-scale thermal conductive heating with the potential for the migration and condensation of vapors.

Thermal conductive heating (TCH) is an in-situ thermal treatment (ISTT) technology for treating non-aqueous phase liquid (NAPL) source zones. Numerical models can be useful tools for improving remedial performance, but traditional multiphase flow models are rarely used to simulate mass recovery during ISTT applications at the field scale due to their computational expense. This study developed a 3D model based on macroscopic invasion percolation to simulate the vaporization of NAPL, and the subsequent vapor migration and potential condensation at the field scale.

Modelling gas-phase recovery of volatile organic compounds during in situ thermal treatment.

In situ thermal treatment (ISTT) technologies can be used to remove mass from non-aqueous phase liquid (NAPL) source zones. Ensuring the vaporization of NAPL and the capture of vapors are crucial, and numerical models are useful for understanding the processes that affect performance to help improve design and operation. In this paper, a two-dimensional model that combines a continuum approach based on finite difference for heat transfer with a macroscopic invasion percolation (macro-IP) approach for gas migration was developed to simulate thermal conductive heating (TCH) applications at the field-scale.

A numerical model for estimating the removal of volatile organic compounds in laboratory-scale treatability tests for thermal treatment of NAPL-impacted soils.

Treatability tests can be carried out to assess the potential effectiveness of thermal treatment technologies under different site conditions and are important for specific technology selection and design. In order to reduce the costs for laboratory tests and expand the insights from previous treatability studies, a one-dimensional (1D) radial finite difference model was developed to simulate the removal of volatile organic compounds (VOCs) in laboratory thermal treatability tests. The processes considered in the model include heat conduction, co-boiling of single-component or multi-component NAPLs with water, and water boiling.

Arsenic concentration and speciation in five freshwater fish species from Back Bay near Yellowknife, NT, CANADA.

The concentration of total arsenic and five different arsenic species [As(III), As(V), monomethylarsonic acid (MMA), dimethylarsenic acid (DMA), and arsenobetaine (AsB)], were measured in the muscle, liver and gastrointestinal tract (GIT) of five different fish species [lake whitefish (Coregonus clupeaformis), walleye (Stizostedion vitreum), northern pike (Esox lucius), white sucker (Catostomus commersoni) and longnose sucker (Catostomus catostomus)] from Back Bay, Great Slave Lake, near the city of Yellowknife, NT, Canada. The total concentration (dry weight) of arsenic in muscle ranged from 0.57 to 1.

Effects of arsenic speciation and low dissolved oxygen condition on the toxicity of arsenic to a lotic mayfly.

The influence of site-specific conditions on contaminant bioavailability and toxicity to benthic invertebrates is a key consideration in the environmental risk assessment process. This is particularly relevant for contaminants with complex speciation chemistries, such as arsenic. The present study addressed uncertainties regarding arsenic toxicity to a mayfly (Baetis tricaudatus) under low dissolved oxygen (DO) conditions characteristic of many contaminated sites.

Quantifying uranium complexation by groundwater dissolved organic carbon using asymmetrical flow field-flow fractionation.

The long-term mobility of actinides in groundwaters is important for siting nuclear waste facilities and managing waste-rock piles at uranium mines. Dissolved organic carbon (DOC) may influence the mobility of uranium, but few field-based studies have been undertaken to examine this in typical groundwaters. In addition, few techniques are available to isolate DOC and directly quantify the metals complexed to it.