Water Purity Systems in laboratories, utilize a number of different technologies to remove contaminants from feed water; each technology has different benefits and limitations. For critical applications requiring ultra-pure water, labs may develop multi-stage purification systems combining several filtration or absorption technologies.
MOST COMMON CONTAMINANTS IN LABORATORY WATER
The main categories of common water borne contaminants are microbes, enzymes, inorganic charged ions, colloids, gases, and organics.
Common contaminants within tap water include enzymes, gases, organics, microbes, colloids, and inorganic ions. Water purity systems are designed to filter specific classes of contaminants endemic to certain applications; other primary differences between systems include tank capacity, production rate, grade of water produced, scalability, level of maintenance, and remote dispensing.
METHODS OF LABORATORY WATER PURIFICATION
Distillation – The simplest form of water purification, involves boiling water in a flask connected to a cooling coil. The cooling coil condenses the water vapor back into liquid form and the water is eluted into a separate beaker or storage tank. This removes a wide variety of contaminants, but the process is time-consuming and laborious.
ION Exchange – This a gravimetric process whereby water percolates down a vertical column filled with ion exchange, bead-based resins. The round, semi porous beads exchange ions with the feed water, such as hydrogen ions for cations, like sodium ions. This low-cost, low-capacity purification method effectively removes inorganic charged ions from feed water but does not remove organics or microbes. Ion exchange is commonly used as a pretreatment step before further water filtration.
Ultrafiltration – A purification technology involving water passing through a semipermeable membrane. Suspended and high molecular weight solids are retained by the membrane filter, while low molecular weight solutes pass through the membrane into the permeate. Ultrafiltration effectively removes most microorganisms and particles from feed water, but organic molecules and inorganic ions are not filtered away.
Reverse Osmosis – This is a purification technology that uses an applied force to overcome osmotic pressure caused by chemical potential differences in the solvent. Although reverse osmosis removes all types of contaminants, the flow rate remains low; causing most labs to run RO systems overnight to ensure sufficient water is available each workday.
Activated charcoal - A filtration process designed to remove organics molecules from feed water. As water passes through the carbon filter, organic molecules bind to the pore walls through van der Waals forces. Charcoal filters last longer than other filtration media, but carbon filters do not remove inorganic ions, particulates, or colloids from water.
Ultraviolet (UV) germicidal radiation - Employs short-wavelength UV light to inactivate microorganisms. Beyond destroying a wide variety of microbes, UV light (emitted at 254 nm) oxidizes organic compounds to produce water with TOC levels below 5 ppb (parts per billion). However, UV light does not remove colloids, particles, or inorganic ions from water.
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