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Activated Carbon Filter

 

Introduction
Principles of Activated Carbon Filtration
Types of Units
Filter Selection
Filter Maintenance
Filter Cost

Activated carbon filter (point of use) and activated carbon material (insert)

photo by: Janick Artiola

click to enlarge

Introduction
Activated carbon filtration may be selected to reduce unwanted tastes, odors, and organic chemicals (such as disinfection by-products, pesticides, and solvents) from drinking water. Activated carbon will also reduce radon gas and residual chlorine. Activated carbon filters will not remove or reduce major inorganic ions (such as sodium, calcium, chloride, nitrate, and fluoride). However, some can reduce lead, copper, and mercury. Activated carbon filters will not soften the water or disinfect it. If the water source is cloudy, this type of filter may be used after a particle filter to remove particles that may plug or reduce its efficiency.

Principles of Activated Carbon Filtration
Activated carbon filtration makes use of a specially manufactured charcoal material made up of porous carbon particles to which most organic contaminants are attracted and held (sorbed) on/in the porous surface. However, organic pollutants have large differences in affinity for activated carbon surfaces. Also, the characteristics of the carbon material (particle and pore size, surface area, surface chemistry, density, and particle hardness), the size of the filter, and the flow rate of the water through the filter have a considerable influence on the pollutant removal efficiency of these filters. Usually, smaller carbon particles and slower water flows improve contaminant removal.

Types of Units
Faucet-attached devices, or point-of-use (POU) devices, may be directly attached to the faucet, or the filter may be placed on the countertop and connected to the faucet with a hose. These units may be equipped with a by-pass feature to draw unfiltered water. Units that attach to the faucet are very small in size and offer short contact time, relatively short life, and limited contaminant removal. Despite these limitations, these devices improve water taste and reduce smells when used as directed.

Pour-through filters also generally are also small and portable. Some work merely with gravity filtration and tend to be slow; others contain a power-operated pump. These devices also improve water taste and reduce smells when used as directed.

Speciality filters are intended to treat water for appliances such as ice makers and water coolers. These also are small units, normally a combination particle and activated carbon filter, installed in the water supply pipe. When service is required, the entire unit is replaced.

Line by-pass and stationary filters are very similar. These are usually the largest units and they are connected directly into the house plumbing, requiring the services of a plumber.

Filter Selection
When purchasing an activated carbon filtration device, first consider the quality of the drinking water. An activated carbon unit that will get rid of simple taste and odor problems is quite different from one designed to reduce low or hazardous levels of contaminants below national standards. The best unit for a given situation depends on the amount and type of carbon material contained in the unit, what contaminants it is certified to reduce, initial and replacement cost of filters, frequency of filter change, and operating convenience. Two other important factors to consider are the potential drop in water pressure in the home system after installation of a unit and the daily quantity of treated water supplied by the device. The carbon cartridge should have rigid sides to maximize contact between the water and the carbon.

Filter Maintenance
Activated carbon filter units need to have the carbon changed periodically. For small speciality units, the entire unit is normally replaced. Cartridge filters are the easiest to change. The ease of opening the filter housing and the amount of space required to change the filter should be considered. Filters should be changed on schedule to avoid contamination breakthrough. The filter material or cartridge should be replaced if left unused for an extended period of time (two weeks or longer).

Usage tips:
-- Only cold, disinfected water should be used.
-- A newly installed device should be flushed with water, following the manufacturer’s instructions. For pour-through models, water should flow slowly through the unit to assure adequate contact with the carbon.
-- Hazardous levels of organic chemicals (above NPDWS) should be treated with properly sized, professionally tested, and properly maintained activated carbon filter devices.

Filter Cost
The devices commonly available for the home range in price from $30 for point-of-use (POU) devices and pour-through filters to over $800 for point-of-entry (POE) units (installation not included). Replacement cartridges range in price from $3 to $50 or more. The filter cartridge replacement interval will determine annual maintenance costs.

(Portions of this text have been adapted from Lemly, A., L. Wagenet, and B. Kneen, "Activated carbon treatment of drinking water," Ithaca, NY: Cornell Cooperative Extension, Fact Sheet 3, Dec. 1995, and from Plowman, F.T., "Activated carbon," Durham: University of New Hampshire Cooperative Extension, Water Quality Fact Sheet 20, 1989.)

Go to other treatment methods:
Particle and Microfiltration Filters
Reverse Osmosis
Distillation
Ion Exchange Water Softening
Disinfection of Drinking Water
Other Treatment Methods


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