Plant operators, maintenance engineers and mechanics, specifying engineers, installation technicians, and others involved in inorganic and organic contaminant removal are oftentimes called upon to choose and apply filtration solutions. To best make these decisions, it is helpful to review information and updated insight on basic filtration technologies, along with their advantages and disadvantages.
What are Inorganic and Organic Contaminants?
The basic definition of organic compound is a compound that contains carbon atoms. Therefore, any compound that does not contain carbon is an inorganic compound. This is a good general rule to use. However, like most rules, there are exceptions. Some notable exceptions are carbon dioxide and carbon monoxide gases along with minerals like calcium carbonate (calcite) which are inorganic compounds.
The vast majority of inorganic contaminant removal applications are sediment or particulate reduction. In this case, particles in the water or fluid will need to be removed before the fluid can be used for its intended purpose. The particles may be visible to the naked eye or they may require magnification. Most people cannot see particles smaller than 40 microns (1 micron is one one-thousandth of a millimeter or 1/1000 mm). For comparison purposes, the approximate size of common particles and substances are listed below:
- Dust is up to 1 micron
- Cement dust is 3 to 4 microns
- A human red blood cell is 5 microns
- Pollen is 7 to 10 microns
- Silt is 10 to 75 microns
- The diameter of a human hair is 100 microns
- Sand is 75 to 1000 microns
Standard sediment removal filters, both bags and cartridges, are very effective at removing most sediment and particles from fluids. There are many different filter options for removing sediment and particles and these applications will be covered later in this article.
Inorganic contaminants can also be present in water as a dissolved substance, usually a mineral. Since these contaminants are present in ionic form and are not particles, they will pass through most standard filters. A good analogy is salt water. If salt water is filtered with standard filters, the product is cleaner salt water (not purified water). Inorganic contaminants in ionic form can be removed using ion exchange systems and reverse osmosis systems.
Free chlorine in water is another type of inorganic contaminant. It is added to many municipal water supplies because of its disinfecting capabilities. However, it can be an undesirable substance due to its oxidative properties and the unpleasant taste and odor it can add to water. Free chlorine is comprised of dissolved chlorine gas (Cl2), hypochlorous acid (HOCI) and/or hypochlorite ion (OCT). Carbon filtration is effective at removing free chlorine.
There are two main categories of organic contaminants: Volatile Organic Compounds (VOCs) and Total Organic Carbon (TOCs). VOCs are contaminants like solvents, hydrocarbons, alcohols, and other industrial compounds. TOCs are all-organic carbon compounds including decaying plant and animal matter. High TOC levels may be found in some surface water supplies (streams, rivers, lakes, reservoirs, etc.) It is less of an issue in ground water supplies. Carbon filtration is effective at removing most organic contaminants.
Removal of Inorganic Particulate Contamination
There are seemingly endless choices of sediment removal filters, from bag filters to a variety of cartridge filters - each with advantages and drawbacks. The intended application should determine which filter to use and which to avoid.