Water and wastewater are conventionally treated by many techniques including chemicals (e.g. chlorination), sedimentation, filtering, and biological treatment. Usually a combination of treatments is applied, according to the type and level of contamination, and requirements for either use or discharge into the environment. One new family of treatments, Advanced Oxidation Processes (AOP), oxidizes in particular organic contaminants, forming eventually safe compounds such as water and carbon dioxide.
Plasma treatment is a sub-family of AOP. Plasma is the 4th state of matter, in which some of the atom are ionized, i.e. one or more electrons are removed from the atom, forming a positively charged ion. The electrons and ions move in response to an electric field, formed for example by applying a voltage between two electrodes. The motion of the electrons produces collisions with the surrounding atoms. Some of these collisions ionize the atoms, which sustains the plasma. Other collision excite the atoms to energetic states, which are more apt to combine with other atoms to form compounds and radicals. A radical is an unstable, short-lived compound.
For water treatment, the plasma may be in a gas, and then directed to the water, or at the surface of the water, or in bubbles within the water. Clear Wave’s submerged technique is in this latter category. Most techniques in this category apply a high voltage pulse between two electrodes to “breakdown” the water, and form a plasma. However, this requires expensive high voltage electronics, and is not energy efficient.
Clear Wave initiates the plasma by momentarily bringing two electrodes connected to a low voltage pulse circuit into contact, and then separating them. Current flow starts upon contact, continues during separation through the last points of contact, and then forms a plasma bubble in the liquid as the electrodes separate. This plasma is formed primarily of water vapor and some metal from the electrodes. The process is efficient because the circuit voltage is matched to voltage required to maintain the current through the plasma. And by using low voltage circuits, the circuit cost can be minimized.
Electron collisions with the atoms and molecules in the plasma bubble form significant quantities of the hydroxyl radical, OH⋅. These radical are very strong oxidizers, and aggressively attack organic contaminants. Furthermore, ultraviolet (UV) radiation is produced in the plasma. The combination of UV attacking bacterial DNA and OH⋅ attack on bacterial membranes very effectively disinfects the water.