Drinking Water Treatment - Aeration

Drinking Water and Human Health December 06, 2010 Print Friendly and PDF

EFFECTIVE AGAINST: Aeration water treatment is effective for management of dissolved gases such as radon, carbon dioxide, some taste and odor problems such as methane, and hydrogen sulfide, as well as volatile organic compounds, like MTBE or industrial solvents. It is also effective in precipitating dissolved iron and manganese. Aeration raises the pH of water.

NOT EFFECTIVE AGAINST: Aeration is not effective for removal of heavy metals, or pathogenic (disease-causing) organisms like bacteria and viruses.

Contents

Uses of aeration

Aeration is an in-line point-of-entry process that reduces the concentration of volatile organic compounds. Aeration also removes dissolved gases such as hydrogen sulfide, methane, and radon.

Aeration oxidizes dissolved iron, although the resulting iron particles can foul the packing material in some aeration devices.

How aeration works

Aeration treatment consists of passing large amounts of air through water and then venting the air outside. The air causes the dissolved gases or volatile compounds to release from the water. The air and the contaminants released from the water are vented. In the case of iron and manganese, the air causes these minerals to move from their dissolved state to a solid state and precipitate out of solution. The water can then move through a filter to trap the iron and manganese particles.

Aeration devices range from a simple, open holding tank that allows dissolved gases to diffuse into the atmosphere to a more complex aeration system that has a column or tower filled with packing material. As water passes through the packing material, the gases are released.

Adjusting the water pressure is usually necessary following treatment. This involves installing a pump after the treatment device to distribute the water throughout the home.

Types of aeration devices

The three types of aeration devices in home usage are packed tower aerators, multi-stage diffused bubble aerators, and spray aerators.

Packed tower aerator

This system has a tower that may be as tall as 10 feet, filled with packing material. This packing material can range from ¼ inch to 3 inches in size and may be pieces of ceramic or plastic. There is no strong evidence indicating that one type of packing material is better than another. In general, however, the smaller the individual pieces of a particular type, the greater the removal efficiency but the higher the energy costs for air pumping.

In this system, water falls from the top of the tower by gravity while air is blown from the bottom of the unit in a direction opposite to the water flow. Volatile contaminants are transferred to the air by rising to the top of the tower and venting to the outside.

Diffused-bubble aerator

A diffused-bubble aerator has several chambers and a diffuser through which air blows. The diffuser produces fine bubbles that rise through the water as it flows from chamber to chamber. These bubbles carry the volatile chemicals through a vent system to the outside air. The more chambers the system has, the greater the air-to-water contact. Some diffused bubble aerators have a high-float switch that triggers an alarm when the chambers are in danger of flooding.

Spray aerator

Spray aeration removes low levels of volatile contaminants, especially radon. In a spray aeration system, water enters through the top of the unit and emerges through spray heads in a fine mist. Treated water collects in a vented tank below the spray heads. Radon and other volatile contaminants are released and vented to the outside.

Air intakes for the aerator can be positioned either outside or inside the home. Avoid areas that have moisture, mold, odors or airborne particles. For locations inside the home, the intake should be at least a foot above the floor and preferably near the ceiling. If the home is “air-tight” construction, an interior intake location may result in a vacuum being created within the home. This will prevent proper venting of the heating system combustion gases unless a fresh air source is provided. If the intake is outside the home, the intake should be high enough to avoid contaminant discharges from such devices as power lawn mowers, leaf blowers, automobiles, boiler exhausts, as well as splash from roof runoff and garden hoses. The intake also needs to be positioned away from the waste air discharge location on the aeration treatment system. An air filter can be installed at the air intake to ensure clean air. Steps should be taken to prevent entry of animals and insects into the intake air.

Waste air from the aerator needs to be disposed of outside the home. Waste air is moist and has a higher concentration of the contaminant that was removed from the water. The waste air discharge point should be above the eave of the roof. Place the vent away from windows and on the downwind side of the prevailing wind direction. The waste air line should include a manufactured vent cap that prevents the entry of dust, bird droppings, small animals, and other bacterial hazards. Mist will carry over from the aerator into the waste air vent line and condensation may also occur. Both the intake and waste air line need to be sloped to allow drainage for moisture. The waste air line connections need to be air tight within the home to prevent leakage of hazardous gas.

Maintenance of aeration systems

Regardless of the quality of the equipment purchased, it will not perform satisfactorily unless maintained in accordance with the manufacturer’s recommendations for maintenance, cleaning, and part replacement. Packed tower and diffused bubble aerators must have the blowers maintained by periodically lubricating the motor and changing the air filters. Keep a log book to record water test results, equipment maintenance, and repairs. Proper, adequate ventilation is a must when operating an aeration system. The tanks and trays need occasional cleaning as precipitated sulfur, iron sulfide, rust, and algae collect. A valve controlled drain line to the ground surface makes flushing the storage tank once or twice each year easier.

Other considerations for aeration systems

Ensure the system is installed and operated according to the manufacturer’s instructions. After installation, retest both the raw water (prior to treatment) and the treated water at a state certified laboratory to ensure the system is working properly and removing the contaminants. Continue to test the quality of both the raw and treated water annually or more frequently (quarterly or semi-annually) if high levels of contaminants are present in the raw water. Frequent testing will help determine how well the treatment system is working and whether maintenance or replacement of components may be necessary.

If there are elevated levels of dissolved iron or manganese in the water, the aeration process can cause rust and other solids to form, staining plumbing fixtures and clothing unless a post treatment filter is installed to trap the solid forms of iron and manganese. On the other hand, if the raw water coming into the house contains elevated levels of iron and manganese in its solid, precipitate form, a filter may need to be installed before the water enters the aeration system.

Bacterial slime may grow in aerators, requiring continuous or periodic chlorination. Chlorination may oxidize iron and cause it to precipitate out, requiring the need for a filter to remove the iron particles. The advantage of aeration is that there is no disposal or regeneration of treatment media necessary. This is especially important when the contaminant being treated would constitute a hazardous waste disposal problem, such as radon.

Re-pressurizing the treated water is usually necessary. This involves installing a pump after the treatment device to distribute the water throughout the home.

Aeration systems are generally more expensive than other water treatment systems. They are most often used in situations where the levels of volatile compounds are extremely high. If the volatile compound concentration is below 1 milligram per liter or if radon levels are below 5,000 picocuries per liter, activated carbon may be a more economical treatment method.

Another consideration is the length of time the treatment is required. If the water source is only temporarily contaminated, aeration may be a more complex system than is necessary and activated carbon may be more appropriate.

Questions to ask before you buy

Before purchasing a water treatment device, have your water tested at a state certified laboratory to determine the contaminants present. This will help determine if aeration is an effective treatment method for the situation. See Questions to Ask Before You Buy A Water Treatment System for more information.


Adapted from: Wagenet,L., K. Mancl, and M. Sailus. (1995). Home Water Treatment. Northeast Regional Agricultural Engineering Service, Cooperative Extension. NRAES-48. Ithaca, NY.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.