To reduce the conductivity in water, the number of total dissolved solids (TDS) need to be removed either by an ion exchanger like flocculation, reverse osmosis (RO), or distillation.
Electrical conductivity (EC) measures the ability of a material to transmit an electrical current over a certain distance, usually measured in Siemens (S) per distance. The power to conduct water comes from the ion concentration within the water, which comes from dissolved solids and inorganic materials like carbonate compounds, chlorides, and sulfides.
As dissolved solids and inorganic chemicals conduct an electrical current, conductivity increases in water as salinity increases. Conductivity is also directly affected by water temperature: as water temperature increases, the conductivity also increases.
Why Is Conductivity Important To Measure?
Conductivity is a general measure of water quality. Drastic changes in conductivity are often indicators of water pollution from discharge or another pollutant.
Measuring the conductivity of water tells us how many dissolved substances, chemicals, and minerals are in the water. Even small amounts of these and total dissolved solids (TDS) can increase the conductivity of water.
When the conductivity of the water is too high, these TDS remain in the water altering the water quality, therefore it must be reduced. Water with high conductivity also has higher corrosive and encrusting effects. For example, high conductivity water clogs sensitive devices and degrades water system products.
But, before we look at how to reduce the conductivity of water, it is essential to know what affects conductivity.
What Affects The Conductivity Of Water?
Many factors can affect the electrical conductivity of water, these can be split into natural impacts and human impacts.
Natural impacts include:
Human impacts include:
The good news is that conductivity can be changed by understanding what elements can change electrical currents in the water.
Reducing The Conductivity Of Water
High conductivity levels are related to high TDS concentrations (the number of dissolved mineral salts) in water. First, a conductivity meter is used to measure the amount of TDS in the water to give the conductivity reading. The conductivity value should range between 0.005 to 0.05 S/m in drinking water.
You need to reduce the TDS to reduce the conductivity in water because conductivity is proportional to the TDS. A simple and economical way to remove TDS in water is by flocculation.
Flocculation involves adding a chemical coagulant (iron chloride (FeCl2/Fecl3) or iron nitrate (Feno33)) to the water. Adding chemical coagulants facilitates bonding between the particles in the water, creating larger aggregates, and making it easier to separate them during the sieving or settling process after flocculation.
Flocculation is widely used to reduce the conductivity in water treatment plants and sample processing for monitoring applications.
Reverse osmosis (RO) is also effective, but it is expensive. An RO system is a form of water purification where unwanted molecules, ions, and large particles are separated by force from the water via a partially permeable membrane. In industrial demineralization, RO is commonly used because it removes around 99% of all minerals in the water. Reverse osmosis also achieves conductivity of around 10-20 μS/cm.
If a lower conductivity is required, an ion exchange demineralization cartridge is added after the RO process to reduce the conductivity to less than 1 μS/cm.
Another process to reduce the conductivity of water is distillation. During distillation, the water becomes free from minerals. Water distillation boils water until it evaporates and condenses, leaving behind impurities, and producing clean, pure water.
The effectiveness of water distillation depends on the contaminants in the water. As some organic compounds have lower boiling points than water, contaminants can re-enter the water. Therefore, most water distillers use a filter media (usually containing activated carbon) to trap contaminants left over.
Reverse osmosis is the preferred method to reduce the conductivity of water over water distillation, as RO passes water through multiple filters, stripping off all the minerals, followed by adding healthy minerals into the water, improving the water quality. While distillation purifies water, it doesn’t add healthy minerals to the water.
Water distillation is also not a fast process: distillation takes between four and six hours to produce one gallon of purified water. However, this can be accelerated using a large distiller, producing up to three gallons of purified water per hour.
Conductivity sensors emit an electrical charge via a conductivity probe, which is dipped into the water being tested. An increase or decrease in the number of dissolved ions results in an increase or decrease in the electrical charge. The conductivity meter measures this charge and provides the solution’s conductance.
When the probe is inserted into the water, an electrical current flows between the two electrons inside the probe, which are separated at a specific distance. The ion concentration in the water determines if the conductance is high or low.
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