By Paula I. Rice

Summary: It’s clear not all carbons are alike in terms of contaminant reduction performance when it comes to drinking water filtration. Rigorous product development, quality control and experimentation have shown compressed carbon block products to be far more efficient at removing contaminants of aesthetic and health concern.

Drinking water pollution comes from many sources. Surface water becomes contaminated from agricultural runoff, community landfills, polluted runoff (the nation’s leading cause of water pollution), and hazardous wastes produced as byproducts of manufacturing. Groundwater is contaminated by leaks of pollutants such as gasoline and MTBE from leaking underground storage tanks and injection of hazardous waste into deep wells—which is being phased out. The drinking water treatment industry is experiencing significant growth due to consumer demand for products protecting them from these potentially harmful contaminants found in drinking water supplies as well as aesthetic improvements.

Highly regarded
The effectiveness of any drinking water treatment device is measured by the performance of its filter. A close review of NSF certification listings shows that solid carbon block filters are the most effective for reducing a wide range of contaminants including those that may be found in groundwater. Certain drinking water treatment units (DWTU) that use solid carbon block filters have been tested and certified to reduce as many as 65 contaminants (see Table 1).

In the early 1970s, solid carbon block filter technology was developed for the purpose of treating contaminants for health reasons as well as aesthetically improving water quality. The technology combines mechanical filtration, chemical reaction and physical adsorption into a single device to reduce a broad spectrum of harmful contaminants.

Importance of raw materials
Activated carbon is the primary raw material used in solid carbon block filters. Once a customer’s objectives are identified, the manufacturer can then determine the characterization of activated carbons and specialized media to use for their specific filters. Carbons specified are especially effective in reducing inorganics such as lead and mercury as well as organic compounds—disinfection by-products (DBPs), volatile organic compounds (VOCs), PCBs, MTBE, etc. By using specialized media along with the carbon, filters can be produced for specific applications and/or to achieve greater capacity ratings for certain contaminants, such as lead.

Many carbons are selected with a high surface area and high retentivity characteristics. Years of research, development and manufacturing experience have helped some companies develop specifications for carbon and other media that give their compacted carbon block filters distinctive performance advantages over other treatment alternatives. Quality assurance procedures are carefully developed and maintained to assure that raw materials meet carbon block filter manufacturers’ high standards.

Technological advantages
As evidenced by the NSF certification of solid carbon block filters, companies have been successful in developing the technology to produce filters that provide greater chemical adsorption and mechanical filtration. Materials are formed into a carbon block, which is densely compacted. Compression enhances the kinetics of the filter and provides performance that cannot be achieved with extruded or granular activated carbon (GAC) filters.

Compacted solid carbon block filters have a large surface area for chemical/physical adsorption to take place. With a solid carbon block, the water contact time is longer and provides for greater adsorption of many different chemicals, pesticides, herbicides and certain heavy metals. A close review of NSF listings confirms that only compacted carbon block filters have been certified to reduce PCBs—a difficult contaminant to treat—and only a handful of products have been tested and certified to reduce a wide range of contaminants that are more difficult to reduce (see Table 2).

In addition, the densely compacted carbon block mechanically filters particles down to 0.5 micron (µm), including oocysts and cysts (Giardia and Cryptosporidium), asbestos, turbidity and particulates. Most filter designs incorporate an outer prefiltration medium to remove large particles and prevent premature clogging of the filter.Compacted filters are exceptionally uniform and don’t channel or allow bypass. Some companies are able to offer a diverse product line because their solid carbon block filters are molded and compacted individually.

Filter capacity
Filter capacity varies depending on the density and size of the filter. The characterization of activated carbons and/or specialized media will also determine the capacity of the filter. Capacity ratings apply to the chemical adsorption capabilities of the carbon and specialized media—carbons with a high surface area allow for long life and high adsorption capacity. Capacity ratings for solid carbon block filters range from 35 gallons to more than 1,000 gallons.

Claims of capacity aren’t applicable to contaminants reduced by mechanical filtration because of broad variations in the quality and quantity of physical matter in the drinking water. The solid carbon block filter is engineered so that contaminants removed by mechanical filtration will cause the flow rate to decrease and the filter to clog, thus offering protection to the consumer from Giardia, Cryptosporidium and other contaminants with a specific physical size. Premature clogging can be prevented with use of a prefiltration medium, which will remove large particles.

Solid carbon block filters are used in point-of-use drinking water treatment devices designed for end-of-tap, pour-through, countertop, undersink and inline applications. In addition, carbon block filters may also be used as pre-filters and/or post-filters with other technologies such as reverse osmosis, ultraviolet and ceramic filters, allowing distributors of those devices to expand health claims for their products and extend their useful life before servicing or replacement.

Solid carbon block filters effectively treat the age-old contaminants of yesteryear, such as lead, TCE, chlorine, benzene and “new” contaminants found in the nation’s drinking water supplies today like MTBE, chloramines and PCBs. They’ll also likely be proven capable of significantly reducing contaminants that may be found in drinking water supplies in the future such as antibiotics and other pharmaceutical drugs. The effectiveness of solid carbon block filters in treating a broad spectrum of contaminants of aesthetic as well as health concern makes it the technology of choice by original equipment manufacturers, dealers, distributors and—more importantly—consumers.

About the author
Paula I. Rice is vice president of administration at Las Vegas-based Multi-Pure Corp.—a contract manufacturer of solid carbon block filters with production facilities in Chatsworth, Calif., and Las Vegas. Applying technological experience from its 30-year history, Multi-Pure successfully develops innovative solutions to new contamination problems. Its filters were the first to be NSF tested and/or certified for reduction of PCBs, MTBE and chloramines. Before joining Multi-Pure, Rice served as associate vice president of business affairs at the University of Southern California. A member of the Water Quality Association, she serves on WQA and NSF committees. For more information, she can be contacted at (702) 360-8880, email: or website:


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