Electrokinetics barriers

The basic purpose of electrokinetic barriers is to prevent the migration of contaminants from its current location. These barriers are similar to traditional passive... 

Electrokinetic biobarriers (also known as electrokinetic biofences) are modified electrokinetic barrier used to contain and biodegrade organic pollutants in ground-... 

Lynch RJ, Muntoni A, Ruggeri R, Winfield KC. (2007). Preliminary tests of an electrokinetic barrier to prevent heavy metal pollution of soils. Electrochimica Acta 52(10) 3432-3440. 

Here is a typical example of a relevant problem an ancient Sardinian hillside mine. The island of Sardinia has been mined for silver, zinc, copper, and lead since Phoenician and Roman times and, until the 1970s, was the largest source of heavy metals in Europe. It has left a legacy of pollution problems associated with mine drainage, carrying pollutants from hillside mines down to valleys below. This is a situation that could well be applicable to treatment by an electrokinetic barrier. The application is as shown in Figure 16.1. 

There are a number of situations (e.g. the one outhned above) in which clean uncontaminated land adjacent to a problem area is at risk of contamination. Drainage from hillside mines located above an agricultural land or leakage from old landfill sites is a potential problem. It is in such circumstances that a possible solution to preventing contamination is the use of an electrokinetic barrier (Fig. 16.2). This is different from remediation by electrokinetics in the following ways ... 

Figure 16.2. Pian view—contaminated groundwater is redirected due to the electrokinetic barrier.

The above inequality lists the major players in the action of an electrokinetic barrier. Whether diffusion is important will depend very much on the timescale (Fig. 16.3). For the movement of contaminants through sands, it may be that diffusion can be neglected initially. The movement of chemicals in a solution by diffusion can be quite slow compared with other processes. The distance moved is proportional to the square root of twice the diffusion coefficient times the time taken. For example, for a molecule with a free diffusion coefficient of 10 m /s, the distance moved in Is is about 40/rm in 1 day, about 1.3cm in 1 week, about 3.4cm and in 1 year, about 25 cm. So, for a first approximation, we can perhaps neglect diffusion. However, for long-term protection, for example, of a landfill, diffusion would of course have to be considered. Adsorption, biodegradation, and reduction-oxidation are also not included in this simple approach. 

The followmg summarizes the studies of electrokinetic barrier tests that have been done in the last 10 years or so. 

Figure 16.23 shows the nitrate-nitrogen concentration at a distance of 20% inside the column from the anode end, for both an electrokinetic barrier and no barrier, against a hydraulic gradient of 1.25. After 13 days, the barrier is stiU seen to be holding the nitrates back (Manokararajah and Sri Ranjan, 2005a). 

Narasimhan (1999) suggested that an electrokinetic barrier can work with the pump and treat technology to improve the cleanup in fine-grained soils. By arranging the... 

An interesting proposal is to combine an electrokinetic barrier with a PEREBAR. Figure 16.25 shows one possible configuration of electrodes and reactive barrier. The electrodes are placed upstream of the barrier. The electric field hinders some groundwater constituents from moving with the groundwater flow into the barrier. 

Organics, Combined Barrier Chung and Lee also tested zeolite and sand, and iron and sand mixtures, with an electrokinetic barrier, and reported that 300 ppm of ethylene glycol and 50 ppm of cadmium were effectively removed (Chung and Lee, 2007a). 

A further method of generating a rather special electrokinetic barrier is that proposed by Faulkner, Hopkinson, and Cundy (2005). Using sacrificial iron electrodes, a low permeability iron-rich layer can be built up between the electrodes. Hydraulic conductivities around 10 ni/s are reported. Further details are given in the reference. 

Lynch RJ, Muntoni A, Ruggeri R. (2003). An electrokinetic barrier against heavy metal contamination in fine-grained soils. In Remediation of Contaminated Sediments (eds. M PeUei, A Porta). Second International Conference on Remediation of Contaminated Sediments. September 30-October 3, Venice, Italy. Columbus, OH Battelle Press. 

Narasimhan B. (1999). Electrokinetic Barriers to Contaminant Transport Nnmerical Modelling and Laboratory Scale Experimentation. MScThesis, Department of Biosystems Engineering, University of Manitoba, Winnipeg, Canada. 

Narasimhan B, Sri Ranjan R. (2000). Electrokinetic barrier to prevent subsurface contaminant migration Theoretical model development and validation. Journal of Contaminant Hydrology 42(1) 1-17. 

Reeve J. (2007). A Solar Powered Electrokinetic Barrier. MEng Dissertation, University of Cambridge Engineering Department, Cambridge, UK. 

The traditional methods described above require the use of heavy machinery, which may be difficult to access in a built-up environment. Since time is of essence in arresting the spread of contaminants to minimize the cleanup cost, novel methods that can overcome these difficulties are needed. The creation of an electrokinetic barrier is one such method that can address these concerns. In this method, an electrical field generated within/outside the contaminated zone causes the formation of a counter-gradient that can control the flow of water and contaminants. The relative ease of implementing electrokinetic barriers has generated a lot of interest in this technique as a viable alternative to traditional methods. The principles governing the creation of electrokinetic barriers are described in the next section. 

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