Non-Thermal Plasma for Chemical-Free Water Treatment

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Before water reaches the tap, it must go through a range of treatment steps to make it wholesome and fit for human consumption. This involves the usage of large amounts of chemicals to remove dissolved and suspended contaminants and disinfection of the water. One of the important characteristics of water that has significant effect on the effectiveness of the treatment process is pH (a measure of the acidity of water). This parameter is so important to the point that if it is not properly controlled within a certain range, the treatment process fails. pH control is required for example during water clarification and disinfection and also during removal of phosphorus or heavy metals in wastewater. The requirement for pH control during water and wastewater processing is wide and touches almost all steps in the treatment process. However, accurate control of pH requires the use of a significant amount of chemicals such as lime, caustic soda, hydrochloric acid, and sulphuric acid. Until now, addition of chemicals to control the pH is the "norm" and this practice has not been challenged or disrupted. With increasing pressure on natural resources and stringent environmental and safety legislations, there is a need for new sustainable processes to reduce the use of chemicals and the associated carbon footprint with their transportation. With this in mind, radical thinking in this ignored area is required. A new sustainable and innovative approach for pH control is the subject of this proposal. The basic concept of the new idea is that when water is exposed to plasma, its pH changes to either acidic or alkaline values. This project will use this concept to develop a new sustainable method for the control of pH in water and wastewater treatment processes and this technique is expected to lead to a chemical-free treatment method with a range of additional benefits. Plasma plays an important role in a wide variety of industrial applications such as material processing and semiconductor manufacturing. More recently, interest has increased significantly in liquid plasma discharge as an alternative to conventional water treatment techniques. Out of the types of plasmas, non-thermal plasma (NTP) is of interest since the power used is mainly to generate the plasma without heating the bulk volume. NTP is produced by a high voltage discharge between two electrodes where a large amount of high energetic electrons, various reactive molecular and radical species, ions and photons are generated (e.g. OH-radicals, ozone, hydrogen peroxide, UV, shock waves). When water is exposed to this highly reactive environment, a range of useful chemistries for the oxidation of contaminants and disinfection of water resulting from the synergetic effects of these take place. Removal of contaminants in water has been the main focus of research carried out on plasma application in water treatment so far. However, when applied to water, NTP does not only produce oxidants and disinfectants, but also it has potential to change the pH of the water hence it can be used as a method to control pH in water. The primary focus of this research is to determine the optimal conditions for controlling pH in water under conditions similar to those expected in a real treatment process. This will involve the design and fabrication of three plasma prototypes with different electrode configurations, then determine the most effective NTP operating conditions that enables production of water at a given alkaline and acidic pH set values. The system will then be tested using real drinking waters and real wastewaters. The project will also provide an appreciation of the additional benefits that the system is expected to offer such as removal of pesticides, metals and endocrine disrupting chemicals and based on the outcomes of this study, the key issues that will determine the commercial potential of NTP for pH control will be defined.