An interesting review report on “A critical review of the application of electromagnetic fields for scaling control in water systems: mechanisms, characterization, and operation” was reported by Lu Lin, Wenbin Jiang, Xuesong Xu and Pei Xu published in Nature Partner Journals Clean Water published on June 2020 [1].
Water is the precious matter in the world. source
U.S. General Services Administration has interested on non-chemical water treatment technologies. It has mentioned following important points: non-chemical technology promises to increase the period between required blow-down cycles, thus reducing water consumption, minimizes associated issues of chemical storage, handling, and disposal, and may permit on-site re-use of cooling-tower “blow-down” water as “grey water”, it promises to be life cycle cost effective based solely on the reduction in chemical costs, this technology may reduce or eliminate chemical costs, it may not reduce other contractor costs, and the technology is applicable to all condenser water systems”.
A research team from the Department of Civil Engineering, New Mexico State University, USA has revealed that the conventional chemical treatments for scale control are expensive which may cause health concerns and ecological implications. The non-chemical water treatment technologies such as electromagnetic field (EMF) have attractive options, so that the use of scale inhibitors, antiscalants, or other chemical involved processes can be avoided or minimized.
Figure 1. Typical EMF devices with different configurations [1].
EMF device configurations are important for this water treatment process. Generally, there are two configurations for an EMF device used in water systems: permanent magnets and solenoid coil (Figure 1). Permanent magnets have been prepared from ferromagnets of iron-based, nickel-based, cobalt-based or rare earth element based compounds [2]. The EMF generated by permanent magnets depends on the arrangement and the number of permanent magnets. Some are arranged with alternating poles of magnets, others are arranged without alternations.
Alabi et al., have mentioned that conventional methods of preventing scale formation which includes ion exchange, pre-precipitation of the sparingly soluble salts, and addition of chemicals and scale inhibitors. These methods are expensive and may change the solution chemistry, causing health concerns for human or aquatic life [3]. Besides, the scale inhibitors are primarily phosphate compounds, which may be harmful to the environment bringing about undesired effects such as eutrophication and algal blooms.
Different non-chemical water treatment systems:
There are four non-chemical water treatment systems which include electromagnetic field (EMF), ultrasonic, catalytic materials, and alloys.
1. Ultrasonic waves can bring significant mechanical and thermal effects, generate powerful shock wave and micro-streaming to prevent scaling [1].
2. The trace amount of catalytic materials like Zn can slow down the nucleation rate of calcium carbonate and also promote its crystallization in the aragonite rather than calcite form [1].
3. EMF as a scale control device has been employed for over a century. The use of EMF as non-chemical water treatment devices for scale control was initially proposed by Porter [4].
Figure 2. Sketch of the set-up of the magnetic treatment of circulating water: (a) apparatus and (b) permanent magnet disposition [5].
Lin et al., has summarized the scaling prevention mechanisms into two fundamentally different approaches: (i) hydration effects, and (ii) magneto hydrodynamic phenomena under continuous flow condition. Both of the mechanisms were the results of Lorentz forces—forces acting on a moving charged particle in an EMF. The schematic diagram of EMF treatment of circulating water and permanent disposition is shown in Figure 2, which was reported by F. Alimi in Water Science & Technology.
For future applications, EMF with high intensity and the less homogeneous waveform is recommended as a pretreatment forwater system. Longer exposure time and higher flow rate can enhance bulk precipitation. To reduce adherent scaling on the reactor surface, smooth surface and low leachate pipe materials such as glass and metal are recommended. Besides, moderate water recovery (<80%) for RO operation can avoid the block of the concentrate flow channel. Conventional RO spacer is a obstruct for the success of EMF, a new open channel spacer will be advantageous to wash out bulk precipitates and enhance EMF efficiency.
--- Pei Xu, Professor, NMSU, USA
Lu Lin has concluded that some additional reproducible studies are required to explore and elucidate the fundamental scientific basis for scaling prevention effects of EMF technologies. To better understand antiscaling mechanisms, real-time monitoring techniques are needed to apply into EMF treatment systems.
References
1. L. Lin, W. Jiang, X. Xu, P. Xu, npj Clean Water (2020) 25.
2. R. D. Ambashta, M. J. Sillanpaa, Hazard. Mater. 180, 38–49 (2010).
3. A. Alabi, M. Chiesa, C. Garlisi, G. Palmisano, Environ. Sci.: Water Res. Technol. 1, 408–425 (2015).
4. A. F. Porter, U.S. Patent 50,774 (1865).
5. F. Alimi, A. Boubakri, M. M. Tlili and M. B. Amor, Water Science & Technology (2014), doi: 10.2166/wst.2014, 377.
Blog Written By
Dr. A. S. GANESHRAJA
National College, Thiruchirappalli
Tamilnadu, India
Blog Editors
Dr. S. Chandrasekar
Dr. K. Rajkumar
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Dr. Y. Sasikumar
Dr. K. Vaithinathan
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