Home Water Treatment Using Activated Carbon

COOPERATIVE EXTENSION SERVICE MICHIGAN STATE UNIVERSITY JANUARY 1990 (NEW) EXTENSION BULLETIN WQ23

HOME WATER TREATMENT USING USING ACTIVATED CARBON A carbon (AC) filters have been used in home ACTIVATED CARBON water purification systems primarily to remove taste and odor. Taste and odor, although AC IS A BLACK, solid substance resembling undesirable, are generally not granular or powdered charcoal. It is extremely considered unhealthy. In recent years, porous with a very large surface area. One ounce however, AC filters have been used to remove of AC has an estimated 30,000 square yards of some of the contaminants that have been surface area. Certain contaminants accumulate discovered in water supplies. on the surface of the AC in a process called adsorption. AC is most effective at removing organic compounds such as volatile organic The two main reasons that chemicals adsorb compounds, pesticides and benzene. It can also onto AC are a "dislike" of the water, and remove some metals, chlorine and radon. As attraction to the AC. Adsorption of most with any treatment system, it cannot remove contaminants results from a combination of all possible drinking water contaminants. these reasons. Many organic compounds, such as chlorinated and non-chlorinated solvents, Because AC systems are limited in the types of gasoline, pesticides and trihalomethanes can be compounds they can effectively remove, it is adsorbed by AC. AC is effective in removing essential that the homeowner determine which chlorine and moderately effective in removing water contaminants are present before some heavy metals. AC will also remove metals purchasing such a system. Anyone who that are bound to organic molecules. Fluoride, suspects they have a water quality problem chloride, nitrate, hardness (calcium and should first have their water analyzed by their magnesium) and most metal ions are not local health department or a reputable removed by AC to any significant degree. laboratory. These analyses are costly, but worth the expense since they are necessary to It is important to note that carbon is not determine the appropriate home treatment necessarily the same as AC. AC removes vastly system and how best to operate such a system. more contaminants from water than does A state or local health official can interpret ordinary carbon. Fig. 1 shows how contaminants water analysis result. Some laboratories may adsorb on an activated carbon filter. also provide this service. AC FILTERS Note that home water treatment is considered only a temporary solution. The best solutions Home AC treatment systems are quite simple. to a contaminated drinking water problem are The AC is normally packaged in filter cartridges to either end the practices causing the that are inserted into the purification device. contamination or change water sources. Water needing treatment passes through the cartridge, adsorption rates. contacting the AC on its way to the faucet. AC filters eventually Rust, scale, sand or other sediments can become fouled with contaminants clog any AC filter. A solution to this and lose their ability to adsorb problem is to place foam or cotton filters pollutants. At this time, they (often called sediment or fiber filters) need to be replaced. between the cartridge and incoming water. When sediment filters become AC treatment systems are clogged, they need to be replaced or they typically point-of-use (POU) - will cause water pressure to drop. installed where they typically treat water used for drinking and cooking only. An AC filter must be deep enough so that the AC filters can be placed on the end of the pollutants will adsorb to the AC in the time it faucet, on the countertop, or under the sink. takes the water to move through the filter The POU systems often have a bypass so that water appropriate filter depth depends on the flow rate for purposes other than drinking and cooking of water through the filter. The slower the flow can also be dispensed at the tap without being rate, the better the removal. The poor treated. This increases the life of the AC, performance of some end-of-faucet devices is reducing the time between filter replacements. probably due to improper filter depth.

A POINT-OF-ENTRY (POE) system is more Physical and chemical characteristics of the appropriate if a contaminant is present that water will also affect performance. The acidity poses a health threat from general use as well and temperature can be important. Greater as from consumption. Volatile organic acidity and lower water temperatures tend to compounds and radon are examples of this type improve the performance of AC filters. of contaminant. These contaminants may get into the indoor air when water is used for OPERATION, MAINTENANCE AND COST showering and washing. In this case, it is more AC FILTERS have a limited lifetime. economical to have a large POE system that Eventually, the surface of the AC will be treats water as it enters the home than to have saturated with adsorbed pollutants, and no POU systems at each tap. further purification will occur. This is called breakthrough - the pollutants have broken AC filters used for home water treatment through the filter to emerge in the treated water contain either granular activated carbon When this occurs, it is possible that the (GAC) or powdered block carbon. Although contaminant concentrations in the treated both are effective, one study comparing GAC water win be even higher than those in the with block AC filters showed that the block AC untreated water. At this time, the cartridge filters were more effective in removing needs to be replaced. Knowing when chlorine, taste and halogenated organic breakthrough will occur and thus when to compounds. replace the cartridge is a major problem with AC treatment. The amount of AC in a filter is one of the most important characteristics affecting the amount Unfortunately, no alarms accompany and rate of pollutant removal. More carbon in a breakthrough. Unless the pollutants are cartridge means more capacity for chemical smelled or tasted they can be unknowingly removal, resulting in longer cartridge lifetime. consumed. In most cases, breakthrough can be This means fewer cartridge changes and less positively verified only by costly chemical chance of drinking contaminated water. testing. Frequent chemical testing is Particle size will also affect the rate of removal; impractical smaller AC particles generally show higher Public health officials consider AC home of devices may not protect you. treatment a temporary solution to be used only until the source of contamination can be SINCE PREDICTING when breakthrough will eliminated. occur is not always easy or accurate, it may be beneficial to replace the cartridge more often and expensive. However, occasional sampling than the manufacturer recommends. In some may be useful in helping to predict when cases cartridge replacement should be breakthrough will occur and alert the user to performed twice as often as recommended by the replace the filter before this happens. manufacturer. Reduction in water pressure, change in taste, or sediment in the water are SOME CARTRIDGES are sold with predictions indicators of filter malfunction When these about their longevity. These are generally only occur, the cartridge should be replaced. crude, estimates since they do not take into consideration factors that are characteristic to Unfortunately, AC filters can be excellent a specific water source, such as pollutant places for bacteria to grow. Conditions for concentration. The retailer you purchase the bacterial growth are best when the filter is treatment device from can make better saturated with organic contaminants, which estimates of the filter's useful lifetime based on supply the food source for the bacteria, and water usage (flow rate) and pollutant when the filter has not been used for a long concentrations shown in the chemical analysis. period of time. It is still unclear whether the Hence, to get the most accurate estimates, you bacteria growing on the carbon poses a health should learn what these amounts are before threat. Some manufacturers have placed silver purchasing the system. Note that if pollutant in the AC in order to prevent the growth of concentrations increase over tame and testing bacteria. The effectiveness of this procedure is not performed to reveal this change, such has, not been independently verified. In estimates may turn out to be not very practical addition, silver may contaminate the drinking or useful. water.

The water flow rate through the filter can The above considerations have led public health either be estimated or measured with a flow officials to consider AC home treatment a meter installed near the AC filter The retailer temporary solution to be used only until the can calculate the maximum allowable number source of contamination can be eliminated and of gallons that can pass through the filter the water supply is safe. Even with proper before breakthrough occurs and the installation,, maintenance and operation, homeowner can replace the filter when this malfunction of home water treatment systems number is reached. Remember, any prediction can occur. for filter replacement must be based on the actual pollutant concentrations present in the AC filters vary in cost as in effectiveness. Good water. This makes the necessity of an initial under the-sink models cost between $200 and water analysis and periodic routine analyses $700, while POE devices can cost as much as all the more important. $3,000. End-of-faucet devices can be purchased for as low as $10. Tests show that Some systems are sold with claims that the under-the-sink models generally have more device win alert the user when replacement of carbon, and provide superior performance and the cartridge is needed. This is based on a greater convenience than faucet or countertop pressure drop across the filter, which may or models. may not result from saturation of the filter. (NOTE. Dollar values are provided as a rough guide to compare Saturation and breakthrough may occur long costs of different systems. Current prices are likely to be higher before a filter becomes sufficiently clogged to than those quoted.) cause excess pressure drop. Thus, these types AC FILTER GUIDELINES SUMMARY 1. Make sure the filter contains AC. 2. Know the quantity of AC in the filter since this will HOME WATER purification using AC is one determine the amount and rate of pollutant removal. option that is often used by people with a 3. Use pre-filters to add life to AC filters. 4. Replace pre-filters and AC filters regularly. drinking water quality problem. AC is 5. Determine appropriate intervals for replacement of AC considered the best home method, for treating filters based on contaminant concentration, water certain organic compounds. However, it is not characteristics, water flow rate, depth of filter, type and recommended for metals and other ions that can amount of AC and pre-filter. Retailers can help in this analysis. also be common drinking water contaminants.

The selection of an AC filter should be based CERTIFICATION AND VALIDATION upon., water analysis and a thorough assessment of the individual homeowner's CERTIFICATION of treatment products is situation. Being well informed before making a available from independent testing laboratories, decision is a homeowner's best insurance for such as the National Sanitation Foundation protecting health. (NSF). Results from NSF tests provide good measures of the effectiveness of devices This material is based upon work supported by the U.S. Department of Agriculture, Extension Service, under project designed to treat water for both esthetic and number 89-EWQI-1-9144. The publication was developed by health reasons. The Water Quality Association the Community Assistance Program in Environmental (WQA) a self-governing body of manufacturers Toxicology, a program in Michigan State University's Center for and distributors, offers voluntary validation- Environmental Toxicology and Department of Resource Development that is supported in part with a grant from the programs to its members. Validation is less Charles Stewart Mott Foundation stringent than certification Note that certification or validation will not ensure effective treatment; all systems must be designed for each particular situation and maintained properly.

For general water quality information For questions about water testing, test For further information on water and and referrals, contact. interpretation and treatment systems, home water treatment, consult the contact. following publications, available from Your county Cooperative your county Extension office: ExtensionService office (listed Your local health department under “County Government” in the (listed under city or county in the phone E-2016, “Testing for Contaminants: A white pages of your phone book). book). Guide for the Home and Farm"

Center for Environmental Michigan Department of Public WQ 02, "Guidelines for Testing of Toxicology Health Private Wells" Michigan State University Division of Water Supply 3423 North East Lansing, Michigan 48824 Logan Street P.O. Box 30195 Lansing, WQ 19, “Nitrate- A Drinking Water (517)353-6469 Michigan 48909 (517) 335-9216 Concern”

Institute of Water Research WQ 21, "A Guide to Home Water Michigan State University Treatment" East Lansing, Michigan 48824. (517)353-3742 WQ 22, "Distillation for Home Water Treatment"

WQ 24, "Reverse Osmosis for Home Treatment of Drinking Water" New:1:90 5M-KDP-HP Price 30 cents FILE: 28.362 (Water & Water Quality)

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