Water Conditioning & Purification Magazine

Microbiological Testing of Activated Carbon Materials

By George Nowicki and Barbara Sherman

In order to assure a safe supply of drinking waters, microbiological testing of the materials used to purify the raw water supply (such as activated carbon sorbents) needs to be regularly scheduled. Previously, no regular testing existed for microbial contaminants on incoming sorbent materials; presently, incoming unused activated carbon or reactivated activated carbon supplies are not microbiologically tested. The authors have developed these needed test methods and discuss them here, addressing sorbent microbiological testing to a preliminary stage. The sorbent industries have not added significant and relevant testing to delivered products for some time. There is a marked trend in the marketplace of rising concern for microbiological contamination: fungus, bacteria and virus. The Department of Homeland Security has shown concern for microbial contamination of drinking water supplies, but more needs to be done.

Microbes grow on activated carbon
It is well accepted that microbes grow on granular activated carbons (GAC) and other forms of activated carbon. This favorable relationship is due to several fundamentals GAC characteristics. It is one of the best-available materials to eliminate chlorine taste and odors. GAC is famous for eliminating trace chlorine, long the most-used disinfectant at water plants. It does this by a chemical reaction where chlorine is converted to the tasteless and odorless chloride ion (we cannot taste chloride ions at low concentration.)

GAC accumulates nutrients for microbes by adsorbing their food supply out of water or air and concentrating it in the media. It has an irregular and rough surface to anchor onto or hide in cracks and crevices to avoid the bulk turbulent flow of water going through the filter. GAC is a reducing agent (slightly less reductive than copper) and it can reduce ionic toxic metals to their non-ionic insoluble forms.

Sorbent microbial testing
Some microbiological testing methods for GAC and other sorbent materials have been developed. Coliforms and fecal coliforms appear to be loosely held by sorbents, as sonication* is not required to extract them and accomplish positive identifications.

Microbes are too large to penetrate deeply into activated carbon products. Although more testing methods need to be developed (ideally producing results in minutes instead of 24 hours) results so far indicate that more microbiological testing of drinking water sorbents can be done at low cost. Having a water extract containing the target microbial analytes allows standard practices to be applied to determine the presence of the analyte on the sorbent material.

(*The process of dispersing, disrupting, or inactivating biological materials, such as viruses, by use of sound-wave energy.)

An easy, quick, low-cost US EPA-approved technique for the drinking water industry is the Colilert test method. Colilert is used directly on the sorbent water extract. This method for coliforms and fecal coliforms detection can be performed with low-cost equipment and personnel with average skill levels. The analyst only needs to put the Colilert reagent powder into the 100-milliliters of sample and incubate for 24 hours at 35 oC. A coliform-positive test turns yellow and fluoresces an aquamarine green color if it is positive for fecal coliforms when ultraviolet (UV) light is shined on the incubated sample container. Since the Colilert test is a very sensitive pass or fail/present or absent, it eliminates decision making by the laboratory and data user. The test costs about $10 (US) to conduct.

This new microbiological test method has been shown to detect low levels of coliform and fecal coliform contaminants on GAC. Samples were prepared with low levels of spiked microbes and successfully demonstrated the test’s ability to detect them. Also, other sorbent materials used to eliminate arsenic in drinking water have been validated with the Colilert test method. Microbiologically spiked iron oxides, titananiums and alumina sorbents have subsequently shown that these spiked sorbents can be detected with easy, simple and low-cost testing.

Recommended standard sorbent testing
It is recommended that the regulators, water suppliers, sorbent manufacturers and users consider additional testing methods for the sorbents used in water and air supplies for product purification. Microbes have a good relationship with GAC and should be regularly monitored. Detected microbes can be shocked and eliminated with a dose of chlorine. After shock disinfection of the filter bed, it should be re-tested to verify the problem has been eliminated. Some firms have taken advantage of the GAC-microbial relationship and developed commercial bio-filters. Microbial monitoring of these carbon bio-filter materials is important to validate a viable microbial population is present as a function of time. The Colilert test may be useful for this application. Activated carbon can be engineered in a wide variety of shapes and sizes, making it an ideal transport vehicle for microbes.

Testing sorbents prior to commercial use is easy to do and should be done more frequently. “An ounce of prevention is worth a pound of cure” as Ben Franklin advised. Another mistake often demonstrated by sorbent consumers is immediate utilization of ALL purchased sorbent. It is recommended that sorbent users collect and store a representative installation sample for later testing as a control if process problems occur or estimated remaining service time in carbon beds is required. Estimated remaining service time is a comparison test between the initial and used GAC. Most often when a sample of initial GAC is requested to provide the estimated remaining service time, none of the initial material in use has been saved.

Many municipal drinking water suppliers do not provide the ideal water preparation for customers. Some pull a raw water source and put it into the customer supply line with inadequate safeguarding treatments or inaccurate chemical treatment chemical. Low-cost,easy testing methods for microbial detection applied by municipalities and isolated home owners is recommended. The technology to accomplish this needed testing is now available.

Conclusion
The municipal water treatment industry provides many options to improve drinking water supplies. We use technology in our home to improve mediocre municipal supply to high quality water with low-cost activated carbon treatment. Since water is so important for good human health, homeowners need to be proactive on this subject to maximize potential water benefits. Today it is possible to do low-cost testing and water conditioning and purification at the residential level.

About PACS testing, consulting, and training
PACS is in its third decade of providing analytical services for the activated carbon and related industries. PACS provides the activated carbon users and manufacturers: independent testing services, consulting, training courses and the International Activated Carbon Conference (IACC) and courses program every year. The next IACC is in Pittsburgh, PA this October 18-19, 2007. The future IACC-21 Madrid, Spain conference July 5-6, 2008 theme is, Activated Carbon is for the Whole World.” A world-class group of instructors with industry and product knowledge and the teaching skills to help individuals at varying levels from beginner to advanced make up the PACS teaching staff. The approximate combined 235 years of practical experiences held by the teaching staff has helped many. Activated carbon adsorption is not a subject learned by formal education; it is developed by way of personal continuing education efforts and your networking. IACC-20 and IACC-21 information is available at the firm’s website: www.pacslabs.com and the preliminary program will be posted on the site in July for IACC-20 in October. Important parts of each IACC are the Hall-of-Fame award and Leadership Speaker programs. PACS is accepting nomination letters for Hall-of-Fame award and Leadership Speaker for 2008 carbon conferences to foster the advancement of the activated carbon industry. Fixed laboratory and mobile lab services are available. Environmental inspections and management plans are provided. PACS conducts 57 short courses of from one-to-three days duration designed for scientists and engineers as well as focused conferences throughout the year.

About the authors
George Nowicki, B.S. is a laboratory technician at PACS Laboratories and develops new computer programs and services to grow the business.

Barbara Sherman, B.A./M.B.A. is operations manager and directs the PACS short courses and conferences educational program. Education is important for employee and employer successes. She can be reached by e-mail: Barbpacs@aol.com.

The authors can be reached by phone: 724. 457. 6576 or at www.pacslabs.com.

About the company

PACS: Testing, Consulting and Training Services is located in Pittsburgh Pa. And Orlando Fl. Routine ASTM, AWWA and US EPA testing methods are provided, as well as advanced test methods such as Gravimetric Rapid Pore Size Distribution and calculated trace capacity number, Instrumental analysis: AA, GFAA, ICP, GC-MS, BET Surface Areas, Ion chromatography, HPLC, GC, wet chemistry and bacteriological testing services are also provided.

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