PLASMA WATER

Dr.S S Verma, Department of Physics, S.L.I.E.T., Longowal, Distt.-Sangrur (Punjab)

Water: The living water of lakes and rivers water possesses a certain supply of such elementary particles, or plasma structures that allows water to purify itself. Thanks to these structures, the purification of water takes place. That’s why before human interference, the water was not infected with bacteria or with microorganisms and toxins because it constantly cleansed itself. Water is essential for all life forms. Be it for personal use such as drinking and bathing or industrial processes such as cooling towers, the importance of water cannot be understated. The scarcity of fresh water makes the situation especially complicated. Freshwater scarcity derived

from seasonal weather variations, climate change, population explosion, and over-development has led to serious consideration towards water issue.  Advanced water treatment technologies will be required to process the water to the point that it can be reused in a meaningful way. Additionally, there is growing concern regarding micro-pollutants, such as pharmaceuticals and personal care products, which have been detected in finished drinking water not removed by conventional means. The removal of these contaminants by water treatment plants will also require advanced technology. One new and emerging technology that could potentially address the removal of micro pollutants in both finished drinking water as well as wastewater slated for reuse is plasma-based water purification.

Plasma: At a very high temperature gas becomes plasma which is described as a fourth state of matter (the others being solid, liquid and gas). It is best described as an electrically – charged gas. In an ordinary gas each atom contains an equal number of positive and negative charges. A gas becomes plasma when the addition of heat or other energy causes the negatively charged electrons in the gas atoms to completely split off from the positively charged atomic nuceli (or ions). Those atoms and the resulting electrically charged gas are said to be “ionized.” When enough atoms are ionized to significantly affect the electrical characteristics of the gas, it is plasma.

Plasma water: Lightning is one of Nature’s ways of making plasma, and scientists can replicate it in the lab by running electricity through a pair of electrodes; the strong electrical field ionizes air molecules and turns them into plasma. Scientists have been experimenting with creating plasmas since the late 19th century; sometime in the mid-20th century they discovered that when they exposed water to plasma, the water picked up molecules such as nitrogen oxide and hydrogen peroxide from the air that made it more acidic and capable of fending off microbes. The science around Plasma Activated Water (PAW) is still developing, but researchers are busy dreaming up potential applications for it. A gas discharge (plasma) is initiated via a plasma power supply in an oxygen and nitrogen containing gas flow. This ionizes the gas flow, creating ions, radicals and reactive species. This discharge will provide a number of key chemical processes:

• The plasma chemical production of NO and NOx.
• The plasma chemical production of ozone.
• The plasma chemical production of reactive species

Cold plasma is an emerging non-thermal disinfection and surface modification technology which is chemical free, and eco-friendly. Plasma treatment of water, termed as plasma activated water (PAW), creates an acidic environment which results in changes of the redox potential, conductivity and in the formation of reactive oxygen (ROS) and nitrogen species (RNS). As a result, PAW has different chemical composition than water and can serve as an alternative method for microbial disinfection. Plasma in contact with liquid water generates a host of reactive species that attack and ultimately mineralized contaminants in solution. This interaction takes place in the boundary layer or interaction zone centered at the plasma-liquid water interface. An understanding of the physical processes taking place at the interface, though poorly understood, is key to the optimization of plasma-based water purifiers. High electric field conditions, large density gradients, plasma-driven chemistries, and fluid dynamic effects prevail in this multiphase region. The region is also the source function for longer-lived reactive species that ultimately treat the water.

 Advantages of PAW:  It was experimentally established that water plasmas contain a lot of chemically active species such as OH radical, O radical, H radical which have strongly oxidized agents. Therefore, Plasma water treatment is starting to be applied in Advanced Oxidation Processes (AOP). Farmers dream of using PAW to spray their crops, to enhance growth (containing ammonia, it can be a natural fertilizer) and cut down on harmful microbes in the soil. Large-scale usages still a long way off because current machines only produce less amount of PAW.

• PAW is easy to apply replacing the traditional sanitizing solutions.
• Synergistic effect of acidification of water and reactive species is evident in PAW.
• Nitrate of PAW absorbed through the roots act as plant growth enhancers.
• Active species of PAW contribute to seed germination enhancement.
• PAW has the ability to inhibit the hormones responsible for seed dormancy.

Growing applications: Plasma activated water has been widely considered an effective agent for surface decontamination and is increasingly used for disinfection of medical equipment. The project will explore the generation of Plasma Activated Water for food security related applications. Recently it has been discovered that the treatment of water with cold gas plasma introduces exciting new properties that are beneficial for a range of high impact applications – from the direct treatment of food to improve shelf-life, to decontamination of food processing equipment and even the improved germination of seeds. Plasma-activated water is receiving much attention in biomedical applications because of its reported potent bactericidal properties. Reactive oxygen and nitrogen species (RONS) that are generated in water upon plasma exposure are thought to be the key components in PAW that destroy bacterial and cancer cells. In addition to developing applications for PAW, it is also necessary to better understand the RONS chemistry in PAW in order to tailor PAW to achieve a specific biological response.

A researcher’s team recently reported that soaking button mushrooms in plasma-activated water reduced counts of bacteria and fungus and helped keep the mushrooms fresher. A team has been designing tests that would establish PAW’s suitability for sterilization in medical settings. Another team showing that PAW promoted germination and root growth in zinnia flowers. Meanwhile, it is also found that a 15-minute exposure to PAW killed more E. coli bacteria suspended in the water than did a three-hour exposure. Because non-thermal plasma (NTP) is such a powerful catalyst, it can be applied to water to achieve valuable reactions and results.  For example, plasma can be used to sterilize and disinfect dirty water and make it safe for drinking. In addition to this usage, the pH of water can be both increased and decreased with plasma. Arguably one of the most exciting water applications of plasma is its potential to create an organic and nitrogen rich fertilizer for agriculture purposes. Plasma Water has been shown to:

• Increase rooting speed
• Reduce water consumption
• Enhance seed germination
• Stimulate plant growth
• Prevent pests

Water applications of plasma:

• Breakdown of organics/hydrocarbons
• Color treatment
• Deodorization
• Breakdown of chemicals in water (i.e. pharmaceuticals)
• Breakdown of algae and unwanted bacteria
• Increase/decrease of pH
• Bleach alternative
• Increase the nitrogen in water for agriculture (creating fertilizer)
• Removal of scale build up in inner wall of pipes
• Sterilization/disinfection
• Increase the moisture sensitivity of surfaces

Other uses

Plasma can be used in the entire life cycle of fresh produce, from soil to fork:

• Sterilize seeds while in storage
• Enhance seed germination
• Air cleaning, sterilization, and removal of volatile organic compounds in greenhouse facilities
• Treatment, sterilization, and cleaning of water used for produce washing after harvest
• Disinfection of produce before packaging
• Air cleaning, sterilization, and removal of volatile organic compounds in the packaged produce storage facility and transportation vehicles
• Control of pests and pathogens at the in-store display case and in-store storage
• Removal of ethylene from air to reduce rate of aging
• Sterilization of cutting boards, knives, and other food processing equipment both at home and in food processing facilities or grocery stores
• Plasma-assisted destruction of hazardous waste and/or waste-to-energy conversion of the nonhazardous food wastes

 Generation of plasma water: Different plasma sources employed for PAW generation, its physico-chemical properties and potential areas of PAW applications. More specifically, the physical and chemical properties of PAW are outlined in relation to the acidity, conductivity, redox potential, and concentration of ROS, RNS in the treated water. Finally, the role of PAW in improving the agricultural practices, for example, microbial disinfection promoting seed germination and plant growth, is gaining interest. Precision are currently evaluating a novel cold plasma system for the prevention of postharvest spoilage and shelf life enhancement in minimally processed fruit and vegetables with the objective of eradicating all microorganisms; bacterial, fungal and viral particles in fruit and vegetables. The project aims to investigate a non-destructive low thermal plasma system with the capability of eradicating all microorganisms; bacterial, fungal and viral particles in fruit and vegetables

• In-package decontamination of foods using cold plasma has advanced this technology as a unit process for fresh foods decontamination and shelf-life extension.
• Chemical residues of agricultural pesticides of varying structure can be degraded to safe or less-toxic structures using cold plasma.
• Cold-plasma-mediated control of contaminants, along with the promotion of seed germination and plant growth, offers alternatives to current pesticides and fertilizers for agriculture.
• Controlling plasma reactive species formulations in dry and liquid delivery formats advances the potential for understanding and successful translation to multiple points along the agriculture and food sectors.
• Employing predictive microbiology, process optimization tools and a systems approach with controlled reactive species formulations may achieve risk- or problem-tailored solutions for whole food systems.

Plasma water techniques:

Plasma is created when a gas is “energized” to create free electrons. If introduced into bubbles in water, the plasma forms highly active species of free radicals, which then attack any impurities present in the water. Scientists have developed technology that uses plasma to eliminate organic contaminants from water, whether these contaminants are water-soluble or sub-micron in size. This cutting-edge technology requires no chemicals and no filters — only electricity. High-energy pulses lasting only a millionth of a second can remove harmful organic contaminants without increasing the temperature of the water. The system injects water into a reaction chamber, where it achieves plasma state through a high-intensity electrical field. The microbiological content of the

water is then eliminated by electroporation, oxidation, ionization, UV and IR radiation.  Given the considerable promise of the technology there’s an urgent need to develop a pilot scale PAW system that can be used to generate results with real industrial relevance. Plasma-activated water (PAW) was prepared by exposure to nonthermal plasma produced by a positive dc corona discharge in a transient spark regime. The activation of water was performed in atmosphere of various surrounding gases (air, nitrogen, carbon dioxide, and argon). This PAW retains its biological activity, measured on the mouse neuroblastoma cells culture, even after storage for more than one year. The highest hydrogen peroxide content was found for PAWs prepared in the atmospheres of argon or carbon dioxide, whereas the PAWs prepared in air and nitrogen exhibited lower hydrogen peroxide content. The acidity of PAWs mediated by nitric and nitrous acid formation displayed an opposite trend.

A method to generating plasma activated water (PAW) was based on a well-known electrolytic method consists of a constant electrical current between unlike electrodes submerged in treated water. In another method, PAW is generated by treatment with a helium plasma jet. UV–vis spectroscopy method: a major advantage of UV–vis is that it can take multiple measurements during plasma activation. Two devices are used to generate low temperature plasmas generated at atmospheric pressure. The first device generates a plasma jet through a glass tube crossed by helium gas flow at atmospheric pressure. This helium plasma jet launched in ambient air was used in both direct seed treatment and the water activation. The second device is a dielectric barrier discharge generated in ambient air without rare gases and uses the seeds as a floating electrode. The parameters of the pulsed power supply used to generate these two low temperature plasmas are 10 kV for the voltage, 9.7 kHz for the frequency and 1 μs for the pulse duration. In the case of the plasma jet, the helium (with 4.5 for purity) was injected at 3 L min through a glass tube (4 mm inner diameter). The distance between the tube outlet and the treated target (either seeds or water) was fixed at 2 cm. In the case of the floating electrode dielectric-barrier discharge setup, the plasma formation is substantially different from the helium plasma jet since the plasma is generated directly in ambient air without using rare gases. The cylindrical high-voltage electrode, 8 mm in diameter, is covered by a glass dielectric with practically 8 mm for the inner diameter. The generated plasma species (radicals, excited, charged particles and photons) with the associated space charge electric field necessarily leads to a better plasma energy and efficiency than the case of helium plasma jet setup. The world’s most powerful X-ray laser, which has now been used to boil water to 100,000° C (180,000° F) in 75 millionths of a billionth of a second – turning it into a new, plasma-like state of water in the process.