EFFECTIVE AGAINST: Fluoride, arsenic, selenium, and chromium.
- 1 Uses of activated alumina
- 2 How activated alumina works
- 3 Capacity of an activated alumina device
- 4 Maintenance of an activated alumina device
- 5 Special considerations
- 6 Questions to ask before you buy
Uses of activated alumina
Activated alumina can be used as a point-of-entry or point-of-use water treatment device. Activated alumina absorbs contaminants instead of filtering them. The effectiveness of activated alumina depends on the contaminant, characteristics of the alumina, the device design, and water quality.
Activated alumina can be an effective treatment method for source water with a high total dissolved solids level, or sulfate concentration. However, a serious drawback to using activated alumina is that regenerating it requires the use of strong acid and base solutions that are undesirable for home storage and handling.
How activated alumina works
Activated alumina devices contain a packed bed of activated alumina granules. As water passes through the device, certain contaminants are adsorbed to the activated alumina granules.
The effectiveness of activated alumina depends on the chemical form of the contaminant to be removed. For example, under certain circumstances chlorinating the water before activated alumina treatment will convert arsenic into the form most likely to be adsorbed by activated alumina.
The success of activated alumina treatment is pH dependent. In general, the water pH should be less than 8.5. For fluoride, a pH between 5 and 6 is optimum. For arsenic, a pH of 7 is recommended. Pretreatment to reduce pH may be necessary for activated alumina to be effective.
When the untreated water contains suspended solids, pretreatment with a 5-micron cartridge sediment filter is required to prevent clogging of the activated alumina bed. In addition, if iron and manganese are present, their concentrations should be below the EPA Secondary Drinking Water Standards of 0.3 mg/L for iron and 0.05 mg/L for manganese.
Capacity of an activated alumina device
Flow rate and contaminant removal capacity are the two factors in determining the total capacity of an activated alumina device. Flow rate is dependent on the surface area of flow, the pore size of the activated alumina granules, and the available water pressure. As flow area increases, the flow rate increases, assuming other factors are equal. Flow rate decreases as pore size decreases.
Household water pressure is usually sufficient for producing adequate amounts of treated water. Point-of-use activated alumina units with a separate faucet can generate approximately 1 gallon per minute of treated water at household pressures. Point-of-entry devices may produce as much as 7 to 10 gallons per minute. If additional flow capacity is needed and a larger device is not available, two devices can be used in parallel. The contaminant removal capacity depends mostly on the amount of alumina in the device.
Maintenance of an activated alumina device
Maintenance of an activated alumina device includes replacing the cartridge and monitoring treated water quality. Manufacturers may suggest guidelines for maintenance based on gallons of water treated or time the device is in operation. These recommendations give a rough estimate, but maintenance will vary depending on water quality and flow rate.
Water treatment dealers should backwash the activated alumina material immediately after installation and regularly as part of the regeneration service. Backwashing removes the finest activated alumina particles and dust from the filter material, which is necessary to prevent the activated alumina particles from cementing together. Cementing occurs when the device is unused for several days, and it reduces adsorption capacity.
Since most chemicals removed by activated alumina are tasteless and odorless, treated water must be tested once per month for the first few months after installation to determine the device’s contaminant removal capacity.
After the capacity of the device is determined, develop a maintenance schedule based on gallons of water treated or time in operation. However, monitoring based on gallons treated is preferred because water use can vary. The device has reached its removal capacity when the concentration of the contaminant in the treated water exceeds the safe level determined by the EPA drinking water standards. Be aware that the concentration of contaminants in groundwater may change, so occasional testing after the capacity is determined is still necessary to ensure that contaminant levels have remained constant.
Activated alumina cartridges should be sent to water treatment professionals for regeneration since the chemicals used are hazardous.
When activated alumina is used to remove a hazardous chemical, dispose of or regenerate the activated alumina carefully to avoid contaminating water supplies or landfills. Non-coliform bacteria can grow on the activated alumina medium, but coliform bacteria do not seem to grow in the filter.
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 and their concentrations. This will help you determine if activated alumina is an effective treatment method for your 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.