Activated Charcoal

Activated Charcoal

Definition
Activated charcoal is a fine, black, odorless, and tasteless powder. It is made from wood or other materials that have been exposed to very high temperatures in an airless environment. Once the volatile chemicals have been cooked off oxygen is introduced to burn millions of tiny pores between the carbon atoms. The highly porous charcoals produced have surface areas of 300-2,000 square meters per gram making them highly adsorbent.
The word adsorb is important here. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped.
Activated charcoal is good at trapping other carbon-based impurities ("organic" chemicals), as well as things like chlorine. Many other chemicals are not attracted to carbon at all -- sodium, nitrates, etc. -- so they pass right through. This means that an activated charcoal filter will remove certain impurities while ignoring others. It also means that, once all of the bonding sites are filled, an activated charcoal filter stops working. At that point you must replace the filter.

What Contaminants Does Activated Carbon Filters Remove From Water?
Activated carbon (AC) filtration is most effective in removing organic contaminants from water. Organic substances are composed of two basic elements, carbon and hydrogen. Because organic chemicals are often responsible for taste, odor, and color problems, AC filtration can generally be used to improve aesthetically objectionable water. AC filtration will also remove chlorine. AC filtration is recognized by the Water Quality Association as an acceptable method to maintain certain drinking water contaminants within the limits of the EPA National Drinking Water Standards

AC filtration does remove some organic chemicals that can be harmful if present in quantities above the EPA Health Advisory Level (HAL). Included in this category are trihalomethanes (THM), pesticides, industrial solvents (halogenated hydrocarbons), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs).
THMs are a byproduct of the chlorination process that most public drinking water systems use for disinfection. Chloroform is the primary THM of concern. EPA does not allow public systems to have more than 100 parts per billion (ppb) of THMs in their treated water. Some municipal systems have had difficulty in meeting this standard.
The Safe Drinking Water Act mandates EPA to strictly regulate contaminants in community drinking water systems. As a result, organic chemical contamination of municipal drinking water is not likely to be a health problem. Contamination is more likely to go undetected and untreated in unregulated private water systems. AC filtration is a viable alternative to protect private drinking water systems from organic chemical contamination.
Radon gas can also be removed from water by AC filtration, but actual removal rates of radon for different types of AC filtration equipment have not been established.
Water Contaminants Not Removed by AC Filtration
Similar to other types of water treatment, AC filtration is effective for some contaminants and not effective for others. AC filtration does not remove microbes, sodium, nitrates, fluoride, and hardness. Lead and other heavy metals are removed only by a very specific type of AC filter. Unless the manufacturer states that its product will remove heavy metals, the consumer should assume that the AC filter is not effective in removing them. Refer to the other circulars in the Treatment Systems for Household Water Supplies series for information on systems that do remove the contaminants listed above.

Water Testing
Regular water testing is recommended to reduce the risk of consuming contaminated water. Many contaminants are not detected by the senses. Even if contamination can be detected by color, smell, or taste, only a laboratory test can tell you the quantity of contaminant actually present. Testing should always be done by a reputable or state certified laboratory. Prior to sending in your water sample, determine what you want your water tested for. Contact the laboratory to find out how to take a proper water sample. Remember, there are thousands of substances that can contaminate your water, and they all have slightly different chemical behavior. Proper sampling and handling for one type of contaminant may cause erroneous results for other types of contaminants.
Once you have the laboratory results in hand, make sure you understand the numbers. If you don't fully understand the results, don't assume anything. The testing laboratory will be able to answer any questions you may have regarding your test results. Understanding the laboratory results will help you select the best and most economical water treatment system. Sometimes just a single piece of equipment, such as an AC filter, is all that is necessary to treat the problem. Other times you may need completely different equipment or possibly a combination of equipment. It all depends on the type and amount of contaminants present in your water.

The adsorption process depends on the following factors: 1) physical properties of the AC, such as pore size distribution and surface area; 2) the chemical nature of the carbon source, or the amount of oxygen and hydrogen associated with it; 3) chemical composition and concentration of the contaminant; 4) the temperature and pH of the water; and 5) the flow rate or time exposure of water to AC.

Physical Properties
Forces of physical attraction or adsorption of contaminants to the pore walls is the most important AC filtration process. The amount and distribution of pores play key roles in determining how well contaminants are filtered. The best filtration occurs when pores are barely large enough to admit the contaminant molecule (Figure 1). Because contaminants come in all different sizes, they are attracted differently depending on pore size of the filter. In general AC filters are most effective in removing contaminants that have relatively large molecules (most organic chemicals). Type of raw carbon material and its method of activation will affect types of contaminants that are adsorbed. This is largely due to the influence that raw material and activation have on pore size and distribution.

Chemical Properties
Processes other than physical attraction also affect AC filtration. The filter surface may actually interact chemically with organic molecules. Also electrical forces between the AC surface and some contaminants may result in adsorption or ion exchange. Adsorption, then, is also affected by the chemical nature of the adsorbing surface. The chemical properties of the adsorbing surface are determined to a large extent by the activation process. AC materials formed from different activation processes will have chemical properties that make them more or less attractive to various contaminants. For example chloroform is adsorbed best by AC that has the least amount of oxygen associated with the pore surfaces. The consumer can't possibly determine the chemical nature of an AC filter. However, this does point out the fact that different types of AC filters will have varying levels of effectiveness in treating different chemicals. The manufacturer should be consulted to determine if their filter will adequately treat the consumer's specific water problem.

Contaminant Properties
Large organic molecules are most effectively adsorbed by AC. A general rule of thumb is that similar materials tend to associate. Organic molecules and activated carbon are similar materials; therefore there is a stronger tendency for most organic chemicals to associate with the activated carbon in the filter rather than staying dissolved in a dissimilar material like water. Generally, the least soluble organic molecules are most strongly adsorbed. Often the smaller organic molecules are held the tightest, because they fit into the smaller pores.
Concentration of organic contaminants can affect the adsorption process. A given AC filter may be more effective than another type of AC filter at low contaminant concentrations, but may be less effective than the other filter at high concentrations. This type of behavior has been observed with chloroform removal. The filter manufacturer should be consulted to determine how the filter will perform for specific chemicals at different levels of contamination.

Water Temperature and pH
Adsorption usually increases as pH and temperature decrease. Chemical reactions and forms of chemicals are closely related to pH and temperature. When pH and temperature are lowered many organic chemicals are in a more adsorbable form.

Exposure Time
The process of adsorption is also influenced by the length of time that the AC is in contact with the contaminant in the water. Increasing contact time allows greater amounts of contaminant to be removed from the water. Contact is improved by increasing the amount of AC in the filter and reducing the flow rate of water through the filter.

Activated Carbon Filtration Equipment
AC filters can be placed in the three following categories: 1) pour-through; 2) faucet-mounted; and 3) high-volume
Pour-through AC filters are the simplest. They work like a drip coffee maker. Water is poured in the top and filters by gravity through the filter to the bottom. They are quite slow and handle only small volumes of water.
Faucet-mounted AC filters are small units attached on the end of a standard kitchen faucet. They are convenient to use, but because of their size require frequent change. Some units have bypass valves, so that just water for cooking and drinking is filtered.
High-volume AC filters contain much more AC than either the pour-through or faucet-mounted models. High-volume units are designed to be installed in-line, generally under the sink. They are installed on the cold water line, and some units are installed with a bypass to separate cooking and drinking water from other uses. Under exceptional circumstances all water may need to be treated by AC filtration. A high-volume unit may be installed at the point of entry to the house if all water needs to be treated.
Results of Activated Carbon Filter Testing
In recent years several independent laboratories have tested AC filtration equipment for effectiveness in contaminant removal. Organizations involved in AC testing are the Gulf South Research Institute, National Sanitation Foundation, Canadian Bureau of Health, Consumer Reports and Rodale Press Product Testing Department.
Based on the testing results of these organizations, general recommendations can be made regarding AC filtration. High-volume AC units should be used if removal of health threatening contaminants is your concern. Pour-through and faucet-mounted units do not provide the contact time for significant removal of contaminants. If you are only concerned with taste, odor, or color, pour-through and faucet-mounted units will probably do the job. However, they will still require changing much more often than high-volume AC filters.
Efficiency of contaminant removal and equipment operation vary even among the high volume AC units. The most efficient unit is not always the most expensive one.
Eventually the AC filter loses its ability to remove contaminants, because it becomes clogged with material. In the case of taste and odor, the time to change the filter is easy to detect. However, in the case of other contaminants, it is more difficult to determine when the filter is no longer performing at an adequate level. Most manufacturers recommend a filter change after a certain volume of water has passed through the filter. Some AC units actually meter the water and automatically shut down after a specific quantity of water has passed through the filter. A general rule of thumb for high-volume AC filters is to change the filter after six months of use or 1000 gallons of filtered water. Tests done by Rodale Press Product Testing Department indicated that filtering performance was reduced dramatically after 75 percent of the manufacturer's recommended life time. These results suggest that filters should be changed more often than suggested by the manufacturer. Some AC filters are claimed to last for five years, because they are rechargeable with hot water (145 degrees F). The heat is supposed to release adsorbed organic chemicals. Little information is available on the prolonged effectiveness of rechargeable AC units. General recommendations are somewhat useful guidelines, but there is no guarantee that they apply to any specific situation. Remember, the only certain way of knowing whether contaminant levels are acceptable or not is by having your water tested.

A sediment filter installed ahead of any AC filter will prolong the life of the AC unit. Sediment can easily clog the pores of an AC filter within a short period of time. A good sediment filter can be purchased for only a fraction of the price of most high volume AC filters.

The Bacteria Issue
AC filters can be a breeding ground for microorganisms. The organic chemicals that are adsorbed to the AC are a source of food for various types of bacteria. Pathogenic bacteria are those that cause human diseases such as typhoid, cholera, and dysentery. Public water systems must treat for disease causing bacteria; therefore, the likelihood of disease causing bacteria being introduced to an AC filter from public drinking water is remote. AC filtration should only be used on water that has been tested and found to be bacteria free or effectively treated for pathogenic bacteria.

Other types of non-pathogenic bacteria that do not cause diseases have been regularly found in AC filters. There are times when high amounts of bacteria (non-pathogenic) are found in water filtered through an AC unit. Research by R. L. Caldron and E. W. Mood (1987) shows little risk to healthy people that consume high amounts of non-pathogenic bacteria. We regularly take in millions of bacteria every day from other sources. However, there is some concern for certain segments of the population, such as the very young or old and people weakened by illness. Some types of non-pathogenic bacteria can cause illness in those whose natural defenses are weak. Flushing out bacteria that have built up in the filter can be accomplished by running water through an AC filter for about 30 seconds prior to use. Water filtered after the initial flushing will have much lower levels of bacteria and ingestion of a high concentration of bacteria will have been avoided. The flushing procedure is most important in the morning or any other time of the day when the filter has not been used for several hours.
Some compounds of silver have been used as disinfectants. Silver has been added to certain AC filters as a solution to the bacteria problem. Unfortunately, product testing has not shown silver impregnated AC to be much more effective in controlling bacteria than normal AC filters. Only in the first month of operation did there appear to be any advantage to using an AC filter that contained silver.
EPA requires registration of all types of water treatment equipment that contain an active ingredient for the purpose of inhibiting the growth of microorganisms. Registration does not guarantee that the product is effective. It only guarantees that the active ingredient will not leach from the filter at levels that would be a health hazard.
 

Home Water Treatment Using Activated Carbon

Introduction

Activated carbon (AC) filters have been employed in home water purification systems primarily for removal of taste and odor. Taste and odor, although undesirable, are generally not considered unhealthy. In recent years, however, AC filters have been used for the removal of some of the contaminants that have been discovered in water supplies.
This bulletin discusses the use of AC filters for home water treatment. AC is most effective at removing organic compounds, such as volatile organic compounds, pesticides and benzene. It can also remove some metals, chlorine and radon. As with all treatment systems, it cannot be used for removal of all possible drinking water contaminants.
Because AC systems are limited in the types of compounds they can effectively remove, it is essential that the water contaminants be determined prior to the purchase of such a system. Anyone with a suspected water quality problem should first obtain a water analysis from a reputable laboratory. These analyses are costly but worth the expense since they are necessary to determine the appropriate home treatment system and how best to operate such a system. A state or local health official can aid in the interpretation of the water analysis results.

ACTIVATED CARBON
AC is a black, solid substance resembling granular or powdered charcoal. It is extremely porous with a very large surface area. One ounce of AC has an estimated 30,000 square yards of surface area. Certain contaminants accumulate on the surface of the AC. This is called adsorption. The two main reasons that chemicals adsorb onto AC is 1) a "dislike" of the water and 2) attraction to the AC. Adsorption of most contaminants results from a combination of 1 and 2. Many organic compounds, such as chlorinated and nonchlorinated solvents, gasoline, pesticides and trihalomethanes can be adsorbed by AC. AC is also effective for removal of chlorine and moderately effective for removal of some heavy metals. Metals that are bound to organic molecules will also be removed by AC.
Fluoride, chloride, nitrate, hardness (calcium and magnesium) and most metal ions are not removed by AC to any significant degree.
It is important to note that carbon is not necessarily the same as AC. AC removes vastly more contaminants from water than does ordinary carbon.

AC FILTERS

Home AC treatment sytems are quite simple. The AC is normally packaged in filter cartridges which are inserted into the purification device. Water needing treatment passes through the cartridge, contacting the AC on its way to the faucet. AC filters eventually become fouled with contaminants and lose their ability to adsorb pollutants.
At this time, they need to be replaced. AC treatment systems are typically point-of-use (POU). This means that they are installed near the point of use, where they typically treat water used for drinking and cooking only. AC filters can be placed on the end of the faucet, on the countertop, or under the sink. POU systems often have a by-pass so that water for purposes other than drinking and cooking can also be dispensed at the tap without being treated. This increases the life of the AC, reducing the time between filter replacements.
A point-of-entry (POE) system is more appropriate, if a contaminant is present which may pose a health threat from general use as well as from consumption. Volatile organic compounds and radon are examples of this type of contaminant. These contaminants may get into the indoor air when water is used for showering and washing. In this case, it is more economical to have a large POE system which treats water as it enters the home than POU systems at each tap.
AC filters used for home water treatment contain either granular activated carbon (GAC) or powdered block carbon. Although both are effective, one study comparing GAC with block AC filters showed that the block AC filters were more effective in removing chlorine, taste and halogenated organic compounds.
The amount of AC in a filter is one of the most important characteristics affecting the amount and rate of pollutant removal. More carbon in a cartridge means more capacity for chemical removal and, therefore, leads to longer cartridge lifetime. This means fewer cartridge changes and less chance of drinking contaminated water.
Particle size will also affect the rate of removal; smaller AC particles generally show higher adsorption rates. Clogging by rust, scale, sand or other sediments can be a problem with any AC filter. A solution to this problem is the placement of foam or cotton filters (often called sediment or fiber filters) between the cartridge and incoming water. When sediment filters become clogged, they need to be replaced or they can cause a drop in water pressure.
Design of any AC filter must ensure that the filter is deep enough so that the pollutants will adsorb to the AC in the time it takes the water to move through the filter. The appropriate filter depth is dependent on the flow rate of water through the filter. The slower the flow rate, the better the removal. The poor performance of some end-of- faucet devices is probably due to improper filter depth.
Physical and chemical characteristics of the water will also affect performance. The acidity and temperature can be important. Greater acidity and lower water temperatures tend to improve the performance of AC filters.

OPERATION, MAINTENANCE AND COST

AC filters have a limited lifetime. The surface of the AC will eventually be saturated with adsorbed pollutants, and no further purification will occur. This is called breakthrough; the pollutants have broken through the filter to emerge in the treated water. When this occurs, it is possible that the contaminant concentrations in the "treated" water will be even higher than those in the untreated water. The cartridge, at this time, needs to be replaced. Knowing when breakthrough will occur and thus when to replace the cartridge is a major problem with AC treatment.
Unfortunately, no alarms accompany breakthrough. Unless the pollutants are smelled or tasted, they can be unknowingly consumed. In most cases, breakthrough can be positively verified only by chemical testing. Frequent chemical testing is impractical and expensive. However, occasional sampling may be useful in helping to predict when breakthrough will occur and alert the user to replace the filter before this happens. Some cartridges are sold with predictions about their longevity. These are generally only crude estimates since they do not take into consideration factors that are characteristic to a specific water source, such as pollutant concentration. The retailer of the treatment device can make better estimates of the filter's useful lifetime based on water usage (flow rate) and pollutant concentrations shown in the chemical analysis. These calculations should be done before purchasing the system. However, it should be remembered that this will not be successful if pollutant concentrations increase over time and testing is not performed to reveal this change.
The water flow rate through the filter can either be estimated or measured with a flow meter installed near the AC filter. The retailer can calculate the maximum allowable number of gallons that can pass through the filter before breakthrough occurs and the homeowner can replace the filter when this number is reached. Remember, any prediction for filter replacement must be based on the actual pollutant concentrations present in the water. This again emphasizes the necessity of an initial water analysis and periodic routine analyses.
Some systems are sold with claims that the device will alert the user when replacement of the cartridge is needed. This is based on a pressure drop across the filter, which may or may not result from saturation of the filter.
Saturation and breakthrough may occur long before a filter becomes sufficiently clogged to cause excess pressure drop.
Thus, these types of devices may not protect you. The uncertainty in predicting breakthrough suggests that there may be benefit in replacing the cartridge more often than the manufacturer recommends. It has been suggested that in some cases, cartridge replacement be performed twice as often as recommended by the manufacturer. In addition, reduction in water pressure, change in taste, or sediment in the water are indicators of filter malfunction. When these occur, the cartridge should be replaced.
Another problem with AC treatment is that AC can be an excellent place for bacteria to grow. Conditions for bacterial growth are best when the filter is saturated with organic contaminants, which supply the food source for the bacteria and when the filter has not been used for a long period of time. It is still unclear whether the bacteria growing on the carbon may pose a health threat, or whether they are harmless.
Some manufacturers have placed silver in the AC in order to prevent the growth of bacteria. The effectiveness of this procedure has not been independently verified. In addition, silver may contaminate the drinking water.
The above considerations have led public health officials to consider AC home treatment primarily a temporary solution to be used only until the source of contamination can be eliminated and the water supply is safe. Even with proper installation, maintenance and operation, malfunction of home water treatment systems can occur.
AC filters vary in cost as they do in effectiveness. Good under-the-sink models cost between $200 and $700, while POE devices can cost as much as $3,000. End-of-faucet devices can be purchased for as low as $10. Tests show that under-the-sink models generally have more carbon, superior performance and greater convenience than faucet or countertop models.

CERTIFICATION AND VALIDATION
POU and POE home systems are not regulated by federal, state or local laws. The one exception, is that the US EPA does require AC filters with silver or other chemicals that may kill bacteria, be registered. Registration does not imply that EPA has tested or endorses use of these filters.
The industry is self regulated. Performance, construction, advertising, and operation manual information are evaluated by the National Sanitation Foundation (NSF) and the Water Quality Association (WQA). The NSF program is generally considered a certification program and establishes many performance standards which must be met for endorsement. The WQA program has less stringent standards and may be considered a validation program.
Certification and validation are helpful in ensuring effectiveness but should not be regarded as the major
criterion for a choosing a particular AC treatment system.

SUMMARY

Home water purification using Activated Carbon is one option to be considered by people with a drinking water quality problem.
Activated Carbon is considered the best home method for treating certain organic compounds. However, it is not recommended for metals and other ions that can also be common contaminants of drinking water.
The selection of an Activated Carbon filter should be based upon water analysis and a thorough assessment of the individual homeowner’s situation. A well informed decision will be the best insurance for protecting health.

AC FILTER GUIDELINES

1. Make sure the filter contains Activated Carbon.
2. Know the quantity of Activated Carbon in the filter since this will determine the amount and rate of pollutant removal.
3. Use prefilters to add life to Activated Carbon filters.
4. Replace both prefilters and Activated Carbon filters regularly.
5. Determine appropriate intervals for replacement of Activated Carbon filters based on contaminant concentration, water characteristics, water flow rate, depth of filter, type and amount of Activated Carbon and prefilter. Retailers can help in this analysis.
Other useful feature over time and testing is not performed to reveal this change.
The water flow rate through the filter can either be estimated or measured with a flow meter installed near the Activated Carbon filter. The retailer can calculate the maximum allowable number of gallons that can pass through the filter before breakthrough occurs and the homeowner can replace the filter when this number is reached. Remember, any prediction for filter replacement must be based on the actual pollutant concentrations present in the water. This again emphasizes the necessity of an initial water analysis and periodic routine analyses.
Some systems are sold with claims that the device will alert the user when replacement of the cartridge is needed.
This is based on a pressure drop across the filter, which may or may not result from saturation of the filter.
Saturation and breakthrough may occur long before a filter becomes sufficiently clogged to cause excess pressure drop.
Thus, these types of devices may not protect you.
The uncertainty in predicting breakthrough suggests that there may be benefit in replacing the cartridge more often than the manufacturer recommends. It has been suggested that in some cases, cartridge replacement be performed twice as often as recommended by the manufacturer. In addition, reduction in water pressure, change in taste, or sediment in the water are indicators of filter malfunction. When these occur, the cartridge should be replaced.
Another problem with Activated Carbon treatment is that Activated Carbon can be an excellent place for bacteria to grow. Conditions for bacterial growth are best when the filter is saturated with organic contaminants, which supply the food source for the bacteria and when the filter has not been used for a long period of time. It is still unclear whether the bacteria growing on the carbon may pose a health threat, or whether they are harmless.
Some manufacturers have placed silver in the AC in order to prevent the growth of bacteria. The effectiveness of this procedure has not been independently verified. In addition, silver may contaminate the drinking water.
The above considerations have led public health officials to consider Activated Carbon home treatment primarily a temporary solution to be used only until the source of contamination can be eliminated and the water supply is safe. Even with proper installation, maintenance and operation malfunction of home water treatment systems can occur.
AC filters vary in cost as they do in effectiveness.
Good under-the-sink models cost between $200 and $700, while POE devices can cost as much as $3,000. End-of-faucet devices can be purchased for as low as $10. Tests show that under-the-sink models generally have more carbon, superior performance and greater convenience than faucet or countertop models.

CERTIFICATION AND VALIDATION

POU and POE home systems are not regulated by federal, state or local laws. The one exception, is that the US EPA does require AC filters with silver or other chemicals that may kill bacteria, be registered. Registration does not imply that EPA has tested or endorses use of these filters.
The industry is self regulated. Performance, construction, advertising, and operation manual information are evaluated by the National Sanitation Foundation (NSF) and the Water Quality Association (WQA). The NSF program is generally considered a certification program and establishes many performance standards which must be met for endorsement. The WQA program has less stringent standards and may be considered a validation program.
Certification and validation are helpful in ensuring effectiveness but should not be regarded as the major criterion for a choosing a particular AC treatment system.

SUMMARY
Home water purification using AC is one option to be considered by people with a drinking water quality problem.
AC is considered the best home method for treating certain organic compounds. However, it is not recommended for metals and other ions that can also be common contaminants of drinking water.
The selection of an AC filter should be based upon water analysis and a thorough assessment of the individual homeowners situation. A well informed decision will be the best insurance for protecting health.

AC FILTER GUIDELINES
1. Make sure the filter contains AC.
2. Know the quantity of AC in the filter since this will determine the amount and rate of pollutant removal.
3. Use prefilters to add life to AC filters.
4. Replace both prefilters and AC filters regularly.
5. Determine appropriate intervals for replacement of AC filters based on contaminant concentration, water characteristics, water flow rate, depth of filter, type and amount of AC and prefilter. Retailers can help in this analysis.

The undesirable elements are: Lots of water, which cools fire. It might take a year of outdoor drying to dry the wood naturally. Volatile compounds, like methane and hydrogen, also are sent packing. And tars, which is a generic name for big, smoky, sticky molecules that form liquids when they're cool, are sent away in reeking, yellow clouds. The tars, in particular, can contain carcinogenic compounds, like benzo-A-pyrene, and, according to Hurt's calculations, "a zillion" other bad actors.
Anyway, with the volatile component baked "away," you're left with a heap of black stuff that's just 20- to 25-percent of the original volume of the wood. It's chiefly carbon, with traces of volatile chemicals and ash. And when it burns, it won't belch smoke, and it will burn long, hot and steady. So, charcoal is just wood with the messy and dangerous parts baked off. (Charcoal briquettes are a little more than that -- they often have additives: borax to bind the charcoal; nitrate to ignite it; and lime to whiten the ash so you know to begin cooking.)

Once the gasses are gone, the oxygen in the air around the coals is able to come in and steadily pick off carbon atoms. These freshly-built molecules fly away as carbon dioxide or, in trace amounts, carbon monoxide.

And activated charcoal? The stuff in aquarium filters and drinking-water filters and air filters? If you let oxygen eat at charcoal a bit before extinguishing the flame, it bores countless tiny holes into the surface. These holes are marvelous at trapping molecules of filth from the water or air passing through. Activated charcoal is just burned charcoal, overcooked by amateur combustors who ignored that white ash on their briquettes.