Water filters accept liquids of poor or unknown purity and discharge a clear, clean output.

Operation

Water filters remove impurities through finely porous physical barriers and/or chemical and biological processes. Presented in the context of the food industry, this lecture illustrates.

Video credit: Layne Christensen Company

Types

• Granular water filters use sand, anthracite, garnet, or other media to remove impurities down to about 1 micron in size. Activated carbon (adsorption) and ion exchange (softening and deionization) techniques address chemicals/gases and dissolved inorganics respectively.
• Membrane filters capture smaller than 1 micron particles through microfiltration, ultrafiltration, and nanofiltration. Reverse osmosis filters are slow, but can be 90-99% effective. Three general types of membranes are,
  • Depth which use absorption or entrapment
  • Screens use a set pore size to sort particulates
  • Surface membranes are made from multiple layers of media. When fluid passes through the filter, particles larger than the spaces within the filter matrix are retained.
• Distillation and ultraviolet radiation are filtration forms particularly effective against organics. Magnetic filters remove ferrous particles.

Gravity or pressure is used to push the water through the system.

Specifications

• The filtration grade (micron rating) indicates smallest particle size separated (e.g., 5, 75, 300, 600 µm).
• Maximum liquid flow ranges (e.g., 0.5 to 150 GPM).
• Filters operate at a maximum pressure (e.g., 60 to 300 psi).
• Maximum temperatures are set (e.g., 175 to 268 F).

Features

• Duplex transfer valves permit continuous filtration during change-outs.
• Integral bypass valves keep water flowing if the filter gets clogged.
• Spin-on (canister) filters prohibit a system from running without an element in place.
• High delta P indication notifies when the element needs to be replaced.
• Filters and their elements can be portable, reusable/cleanable and/or FDA compliant.
• Tank-mounted filters are attached to reservoirs. In-line filters interrupt a pipeline or hose.

Applications

Water filters are used in residences, municipality treatment plants, and industries such as electronics, biopharmaceutical, food and beverage, medical, pool and spa, and power generation.

References

EPA Science & Technology: Water

Different Water Filtration Methods Explained

How Water Filters Work

Water Filter Media

Image credit:

The Hilliard Corp.