Water naturally contains various dissolved gases, such as oxygen, nitrogen, and carbon dioxide, which are physically trapped within the liquid. Degassing water is the process of removing or reducing the concentration of these dissolved gases. This common practice is important for maintaining water quality and optimizing various applications, as dissolved gases can influence water properties like pH and conductivity.
Why Remove Dissolved Gases from Water?
Removing dissolved gases from water is often necessary to prevent undesirable effects across various applications. High levels of dissolved oxygen, for instance, can accelerate corrosion in industrial systems, particularly in boilers and piping networks. This can lead to increased maintenance and reduced equipment lifespan. In drinking water, dissolved gases like methane and hydrogen sulfide can impart an unpleasant taste or odor, making their removal beneficial for palatability.
In the food and beverage industry, degassing helps prevent oxidation, which negatively impacts product quality and shelf life. For aquariums and hydroponics, managing dissolved oxygen levels is important for the health of aquatic organisms and plant growth. In laboratory settings, dissolved gases can interfere with sensitive analytical techniques, such as High-Performance Liquid Chromatography (HPLC), leading to inaccurate results and bubble formation in detectors.
Effective Methods for Degassing Water
Several methods effectively remove dissolved gases from water, each operating on distinct principles. Boiling or heating water is a straightforward thermal method where increased temperature reduces gas solubility, causing gases to escape as the water approaches its boiling point. While simple, this method can be energy-intensive and may not achieve complete degassing, and the water must be cooled before use.
Vacuum degassing involves reducing the pressure above the water, which lowers the partial pressure of dissolved gases and encourages them to come out of solution. This technique often occurs in a sealed chamber where a vacuum pump extracts the liberated gases. Vacuum degassing can operate at lower temperatures, making it suitable for heat-sensitive applications. It is capable of reducing dissolved gas levels to parts-per-billion in some advanced systems.
Sparging, also known as gas stripping, uses an inert gas like nitrogen or helium bubbled through the water to displace the dissolved gases. This method relies on the principle that the inert gas creates a lower partial pressure for the unwanted gases, causing them to transfer from the liquid to the gas phase. Stirring the solution vigorously and bubbling for a longer duration can maximize efficiency.
Ultrasonic degassing uses high-frequency sound waves to create microscopic vacuum bubbles within the liquid. Dissolved gases migrate into these bubbles, causing them to grow and rise to the surface, where they release the gases. This method is effective for continuous-flow applications and can also help remove entrained gas bubbles. Ultrasonic cavitation plays a supportive role in initiating bubble formation and accelerating gas release.
Selecting a Degassing Method and Maximizing Efficiency
Choosing the appropriate degassing method depends on various factors, including the volume of water to be treated, the desired purity level, available equipment, cost considerations, and time constraints. For example, boiling is accessible for small volumes, while industrial applications might require vacuum systems. The initial concentration of dissolved gases in the water significantly influences the effort needed for degassing.
Water temperature during the process also plays a role, as warmer water generally holds less dissolved gas, which can enhance removal efficiency. Maximizing the surface area exposure of the water to the degassing mechanism, such as using packed towers in vacuum degassers or fine bubbles in sparging, can improve gas transfer. The duration of the degassing process and the specific type of gas being removed also impact effectiveness.
Safety Precautions and Important Considerations
When degassing water, it is important to observe safety measures. If using boiling, caution is necessary due to high temperatures and the risk of burns. When employing vacuum equipment, ensuring proper seals and understanding pump operation is important to prevent equipment damage or personal injury. If sparging with gases, adequate ventilation is necessary to prevent gas accumulation in the workspace.
After water has been degassed, proper storage is important to prevent re-absorption of gases from the atmosphere. Storing degassed water in sealed containers minimizes contact with air, helping to maintain its low gas content. For applications requiring precise gas levels, monitoring dissolved gas concentrations before and after treatment can confirm the effectiveness of the degassing process. Devices such as dissolved oxygen meters or total dissolved gas sensors can measure these levels.