By Gary Battenberg
The ancient Egyptians used charcoal to smelt ores to make bronze, adsorb unpleasant odors, cure intestinal ailments and for use in the preservation of the dead as far back as 3750 B.C. Phoenicians were credited for charring barrels to hold drinking water on long sea voyages around 400 B.C. and this practice was adopted by many other seafarers throughout history until the 1800s. The charring of oak barrels also removed those pesky volatile organic chemicals to give whiskey its delicious personality. Hippocrates is among the most historical figures of medicine and by 50 A.D., started using charcoal for numerous medical purposes, including treatment for epilepsy, chlorosis, vertigo and other ailments. By 2 A.D., Claudius Galen had written nearly 500 papers on the use of charcoal in medicine.
In 1776, the year the Declaration of Independence was written and the US became a nation, experiments with carbon proved that color was removed from liquid phase solutions. From that time on, applications for various forms of carbon quickly grew, including decoloring of sugar to produce a whiter, more appealing sweetener. In 1881, Heinrich Kayser coined the term adsorption, which described charcoal’s affinity to uptake gasses. That term is used in our industry vocabulary today when describing application for many other contaminants that carbon has proven to be effective.
Relative effectiveness of GAC
Granular activated carbon (GAC) has been widely used in water conditioning since the early 1960s and is generally accepted as the best available adsorbent for chlorine removal. Under proper operating conditions one cubic foot of GAC will remove one part per million (ppm) of chlorine from one million gallons (3,785,000 liters) of water. There are many other applications for GAC and when properly applied has a very high affinity for and capability to remove color, taste and odor, tannins, phenols, pesticides, detergents, trihalomethanes (THMs), organics and toxic organic compounds. As great a workhorse as GAC is, however, there are also conditions where GAC is not applicable and others where GAC is a poor choice and not recommended. Let us look at the viability of GAC and rate the use on a scale of zero to five, with zero being the worst and five being an excellent, proven application.
Zero: not applicable
Contaminants remaining in water after passing through GAC include carbon dioxide, hardness (calcium and magnesium), lime, nitrates and phosphates. These are among many inorganic constituents in water for which GAC has no affinity. There are few exceptions where contaminants that are organically complexed may be reduced using GAC. Examples of these are arsenic, chromium and mercury, which may be bound by oxidized iron. It has long been a standard practice to effectively remove/reduce arsenic from water where iron is present by using an oxidizer, such as chlorine or hydrogen peroxide. Other treatment includes manganese greensand filter regenerated with potassium permanganate, which has been used for many years in municipal water treatment plants very effectively for the removal of iron and arsenic.
One: poor, not recommended
Other contaminants that are virtually unaffected after passing through GAC include ammonia, boron, fertilizers, inorganic acids, metal salts and seawater. Here again, inorganic makeup of these constituents is unchanged or only slightly changed in the effluent stream from GAC. There is a renewed interest in dioxin removal from municipal water sources. Dioxin is a byproduct of the cooling of flue gasses in various incineration combustion processes of municipal or industrial waste and is responsible for toxic contamination of the environment. GAC is not a recommended choice for dioxin removal because of the very slow adsorption process of GAC. Powder activated carbon (PAC) injection, however, has shown exceptional adsorption capacity. Due to its very small particle size, PAC is injected into wet or dry flue-gas emission streams and has proven to be a very effective, economical and flexible technology to remediate the problem.
Two: fair/limited application
Here we see some reduction of contaminants but it must be understood that performance expectations are not a primary function of GAC, regarding the inorganic makeup of emulsions consisting of two or more liquids that are unmixable and/or tend to have very limited mutual solubility. Other inorganic constituents include fluorides, formaldehyde, suspended oil, precipitated iron, precipitated sulfur, sediment, soluble iron, suspended matter (silt) and urine.
Three: good results
Now we can see where application of GAC will generally yield good results when properly applied. Contaminant removal/reduction include acetic acid (a component of vinegar), amines (ammonia derivative), detergents, heavy metals (copper, particulate lead, selenium, zinc), hydrogen sulfide, nitric acid, plating wastes, soap and vinegar. Note that particulate lead (Pb) is mentioned herein. Soluble (dissolved) lead is removed at a higher percentage using carbon-block filters specially formulated for lead removal/reduction. Performance expectations using GAC are best where service flowrates do not exceed six gpm per square foot of surface area. Example: a 10-inch diameter tank has a square foot area of 0.54. Multiply 0.54 by six and the maximum service flowrate should not exceed 3.24 gpm.
Four: very good
GAC yields good results when properly applied to contaminants such as acetone, alcohols, antifreeze, chloramine, chlorophyll, citric acid, lactic acid, mercaptans (odorant in natural gas), methyl acetate, methyl alcohol, methyl chloride, organic acids, ozone, potassium permanganate, solvents, sulfonated oils, tannins, taste and odor, and taste from organics. Performance expectations using GAC are best where service flowrates do not exceed 1- 1.25 gpm per square foot of surface area. The service flowrates drop considerably when organic chemicals are the target for removal. Here is where empty-bed contact time figures into the interpretation of the water analysis and the total of contaminants competing for adsorption sites on the carbon bed. Routine testing of the effluent water is required and prompt replacement of the media is essential to ensure consistent contaminant-free water.
GAC is a proven application with a very high affinity for toxic organics removal from water when properly applied. There are many organic chemicals and toxic organic compounds that make up the US EPA primary (health-related) drinking water regulations. Because many of these contaminants are highly complexed, the recommended service flowrate should not exceed 0.7-0.9 gpm per square foot of surface area. Again, empty-bed contact time must be calculated to ensure optimal removal of the target contaminants. A partial list of contaminants include benzene, butyl alcohol, butyl acetate, calcium hypochlorite, chloramine, chlorine, chlorobenzene, chlorophenol, diesel fuel, dyes, gasoline, glycols, herbicides, hydrogen peroxide, hypochlorous acid, insecticides, isopropyl alcohol, ketones, methyl ethyl ketone (MEK), naphtha (dry cleaning), odors (general) dissolved oil, organic esters, oxygen, PCBs, pesticides, phenol, plastic taste, rubber hose taste, sodium hypochlorite, THMs, toluene (dry cleaning), trichloroethylene, turpentine and xylene (dry cleaning).
When specifying GAC for contaminant removal, there are correction factors that must be considered when calculating the removal efficiency relative to the target contaminants. These factors include pH values between five and 10; temperature from 50°F to 100°F; efficiency factors from 90 to 99.9 percent and finally, the mesh size of the carbon, including 8 x 30, 12 x 40 and 20 x 50. The mesh size of the GAC will determine the backwash rate required for lift and reclassification where backwash is required. When the mesh size and type of carbon are selected, the volume of GAC is multiplied by the factors of pH, temperature and efficiency, relative to the target contaminants. An accurate water analysis is essential to assure effective removal of the target contaminant(s).
Dealers participating in markets where water sources contain known contaminants for which GAC exhibits high affinity are no doubt selling and servicing RO drinking-water appliances or specialized carbon filter products to remove unwanted contaminants from customers’ drinking water at a point of use. POE products that treat all the service plumbing of the home or business are becoming more prevalent, given the high profile of contamination issues in the 24-hour news cycle.
For commercial, industrial and institutional applications where performance specifications are very tight, it is best to consult a carbon supplier that has application specialists to assist with analysis interpretation, adsorption isotherm calculations, pilot-scale products and testing to confirm efficacy before the actual scaled project is approved. A note of caution is needed here relative to atmospheric conditions when working with wetted carbon. Wet activated carbon depletes oxygen from air. Whenever workers enter a vessel containing [wet] carbon, all precautions must be taken since dangerously low levels of oxygen may be encountered. Atmosphere sampling and work procedures for potentially low oxygen areas should be followed. Facilities with large installations that require ingress into large vessels typically have safety stewards on staff with safety gear and personnel onsite during service to GAC filters.
As we have seen, carbon has been in use in various forms for many types of applications for many years. While GAC covers a lot of ground regarding water treatment, there are some water constituents that remain unchanged after being exposed to carbon. If you are not sure if carbon is an acceptable media to use for a certain application, do not guess and compromise your customer or prospective customer. Be diligent and do obtain accurate water testing and counsel from a supplier with the expertise to support you in service to your community. Your business reputation is on the line, so scrupulous attention to detail is where problem-water issues require very accurate analysis interpretation before specification, installation, start-up and commissioning of critical applications.
About the author
Gary Battenberg, an industry veteran of 38 years, is Technical Manager Water Treatment Department, at Dan Wood Co. His primary focus is training personnel in water testing, application, installation and startup, service/diagnostics and maintenance for the department. Battenberg will be responsible for water system specification for commercial and problem water applications. Previously, he was a Technical Support and Systems Design Specialist with the Fluid System Connectors Division of Parker Hannifin Corporation. Battenberg’s expertise includes the fields of domestic, commercial, industrial, high-purity/sterile water treatment processes. He has worked in the areas of sales, service, design, installation and manufacturing of water treatment systems and processes utilizing filtration, ion exchange, UV sterilization, reverse osmosis and ozone technologies. Battenberg can be reached by phone at (269) 329-0050 or by email, email@example.com.
About the company
Dan Wood Quality Home Services Company of Portage, MI is a state-licensed contractor for plumbing, heating, air conditioning, boiler service and installation, well pump service and installation, and water conditioning dealership. The company was founded in 1908 by Dan’s Grandfather in Detroit, MI. Today, the company is in its fouth generation, carrying on the family tradition of quality home services with a service vehicle fleet of 35 trucks. The company maintains an A+ consumer rating and provides 24/7/365 service to the local community.