Groundwater systems contamination mechanism

An important innovation in bioremediation technology has been the use of air sparging to oxygenate groundwater. A typical system is presented in Figure 14.6. Using this technique, the removal of contaminants is achieved using two simultaneous mechanisms ... 

In an air sparging system, the primary mechanism for contaminant removal is by the transfer of contaminants from the dissolved to the vapor phase. The extent to which this transfer can take place during air sparging depends on the Henry s law constant, which is an indication of the extent to which each will partition between the dissolved state and the vapor state under equilibrium conditions. A contaminant with a greater Henry s law constant is more readily stripped from groundwater by air sparging than one with a lower Henry s law constant. 

Constructed wetlands are engineered systems designed to mimic the physical, chemical, and biological mechanisms of a natural wetland. Wetlands may be constructed above ground to resemble natural wetlands such as swamps, bogs, and marshes or they may treat contaminated water below the surface. Constructed wetlands have been used for the ex situ treatment of groundwater contaminated with explosives. 

The lET barrier system is a patented, commercially available in situ technology for the diversion and collection of contaminated groundwater or the confinement of contaminated soil. The lET barrier can be constructed as a boom around a portion of the contaminated area or as a bottomless tank. Barriers consist of a high-density polyethylene (HDPE) liner or thick steel sheet pile with a patented locking mechanism. Collection reservoirs are installed adjacent to the barrier and can be used to treat contaminants in place or to pump contaminated groundwater to the surface for treatment. 

As a contaminant moves through soil and groundwater, chemical processes will affect both contaminant concentration and overall hydrogeochemistry (Schoonen, 1998) of the system. Different adsorption mechanisms cause pollutants to adsorb onto the soil, volatilize, precipitate, and be part of the oxidation-reduction processes. Adsorption is loosely described as a process in which chemicals partition from a solution phase into or onto the surfaces of solid-phase materials. Adsorption at particle surfaces tends to retard contaminant movement in soil and groundwater. 

There have been several modified systems since the invention of liquid membranes, including a facilitated transport mechanism. One of them is to disperse the receiving solution in an organic membrane phase on one side of a porous hollow fiber.Two plants to treat contaminated groundwater were built and operated based on this revised liquid membrane system. More discussion about this application is given below in the application section. 

Adsorption/Desorption While some contaminants move freely down the flow path at a velocity close to that of the groundwater itself, some tend to enter into complex adsorptioti/desorpfion reactions on the surfaces of soil and rock minerals. This often greatly retards their transport and increases their persistence into the aquifer system. Many organic compounds and heavy metals are prone to adsorpfion/desorpfion mechanisms. 

---