By Warren Searles
Summary: Disinfection for the purpose of reagent grade water is an issue that faces many laboratory managers. As the following points out, there are many options and devices available to achieve the level of water desired. Yet, each alternative has its disadvantages. There are still positive steps to take while attempting proper disinfection and some of them are outlined here.
Water purified enough to provide reagent grade water is a major concern in the United States and throughout the world. Medical research, biotechnology, pharmaceutical research and general laboratory services of all sorts have proliferated in the last quarter of the 20th century and are increasing in the 21st century. As the research market grows, so will the need for microbial-free reagent grade water.
One of the first books given me to read when entering the water purification field was Martha Winstead’s “Reagent Grade Water: How, When and Why.”1 Chapter one discusses the makeup of source water, including a discussion on microbiological contamination and indicating a need for disinfection of the source water. To complicate the matter, it states (though undocumented) that there’s a very slight possibility that “prions”—infectious particles composed of simple protein2—could enter the water supply. We can rely on the municipal supply to be safe for human consumption because federal and state governing bodies like the U.S. Environmental Protection Agency (USEPA) regulate it. Table 1 summarizes3 the basic regulation of the public water supply’s microbiological contaminants. Still, there are disinfection concerns the laboratory manager needs to consider when setting up his or her reagent grade water treatment system.
Most laboratories are located in PWS (public water supplier) districts where chlorine is commonly used in more than 67 percent of all surface water treatment plants4 as a disinfectant in the source water. The Safe Drinking Water Act (SDWA) regulates the introduction of chlorine and its residual in the community water supply.
Selecting an option
The SDWA also permits other disinfectants to be considered5 by the PWS. They are:
- Ozone (O3);
- Chlorine dioxide (ClO2);
- Potassium permanganate (KMnO4);
- Chloramine (NH2Cl);
- Ozone/hydrogen peroxide combinations (O3/H2O2);
- Ultraviolet irradiation (UV); and
- Microfiltration/Ultrafiltration (MF/UF).
Water enters the laboratory and is thus assumed to be disinfected; however, there are a number of factors that can distort even a well regulated and monitored supply. These include: 1) distribution pressure—falling below 20 pounds per square inch gauge (psig) may require a boil notice; 2) seasonal upsets that may allow biological contamination; 3) catastrophic situations such as earthquakes, flooding and other events; 4) changes in supply sources, like using a new well or changing from ground to surface water supply; and 5) groundwater wells that are damaged, of poor construction or otherwise require disinfection because they’re under the influence of surface water.
Because of conditions independent to the immediate control of the PWS or the private supply, the laboratory manager shouldn’t automatically assume the supply is disinfected. In 1994, cities drawing water from Lake Michigan experienced an infestation of zebra mussel in the lake around their water supply intakes. Recent studies6 have shown that zebra mussels may mobilize toxic materials from the sediments into the food chain in two ways. First, when the mussels filter algae that has absorbed toxic materials, they either ingest the toxic materials—which accumulate and concentrate in the mussel’s fatty tissue and is then passed on to fish and ducks that prey on mussels. Or they release the toxins as waste, putting it back into the water column and thus the ecosystem of the lake. The PWS take drastic steps to protect the public; however, those steps will ripple through the supply to create potential havoc to downstream users who further purify the water for reagent grade uses (see http://www.reagents.com/products/reagents/grades.html for variations).
Similarly, users of Lake Ontario water reported7 that in the late summer or early fall, its water releases an earthy, musty smell and taste in your tap water. Natural, seasonal changes in Lake Ontario can cause this to happen. This occurrence is common to all cities and towns that draw their water from the lake. The water temperatures, which over the year average six to seven degrees Celsius at the intake pipes, can climb to as high as 25°C. These high temperatures result in increased growth of algae.
Certain types of algae produce compounds that cause a noticeable odor or taste even at extremely low levels. One of these is geosmin, which is usually measured in parts per trillion (ppt). Humans can detect its presence in concentrations as small as 10 ppt. These episodes can result in concentrations of more than 50 ppt, a level where the compound can be easily detected via the tap by most people. Several lake water customers have experienced biological problems as determined by taste and odor as an indirect result of Lake Michigan’s zebra mussel and algae infestation. Although the public agencies disinfect the water to a highly regulated standard, the treatment may not meet the standards for reagent grade water.
Hot times in the city
A disinfection issue peculiar to cities is pressure losses due to fire hydrants being opened to cool children playing in the summer heat. The result of lower pressure may cause groundwater to seep into the water supply if proper backflow prevention design isn’t employed or maintained. Disinfection of the plant and laboratory’s plumbing systems is common in facilities located in older neighborhoods.
Concerning PWS or private wells, cracked and damaged well casings have drawn iron bacteria from the groundwater supply into a laboratory of a dairy in Western Illinois. Another case in Wisconsin had groundwater contaminated by a flooding Mississippi River requiring shock chlorination of the municipal supply after the leak was found.
To ensure acceptable results, the lab manager needs to provide point-of-use (POU) or point of entry (POE) disinfection. Figure 1 describes a typical treatment system with the addition of a disinfection device.
Pros and cons
The disinfection device may be one of the following:
- Ozone (O3)
- Ultraviolet irradiation (UV)
- Microfiltration/Ultrafiltration (MF/UF), and/or
- Reverse osmosis (RO) system.*
* NOTE: ASTM standards require a double-pass RO (DPRO) for water for injection.
Ozone is a highly active oxidant and disinfectant, though typically not considered for POE due to cost and maintenance. Several companies offer quality products designed for small stream disinfection. The drawbacks are there can be a bromate compound by-product of the process, an independent source of dry air or oxygen is typically required for efficient production of ozone, and ozone is aggressive, requiring ozone destruction in tandem in many cases.
Distillation is a well-accepted, long-standing disinfection technology. Distillation has been used since the late 1800s to create water for hospital laboratories and processes. It has the dual advantage of disinfection and solids removal. The disadvantages are the equipment cost, operating and electric power costs—and equipment maintenance, though simple, must be done regularly.
UV will retard biological growth by destroying a cell’s ability to reproduce. If it’s on, pretreatment incorporated to avoid shadowing by larger particles, the system is properly sized for the flow and the bulb is fresh, the UV process will work very well as a disinfectant. Disadvantages are the typical 254-nm light won’t destroy pyrogens nor eliminate bacteria (only neuter it), maintenance of the bulb (cleaning or changing is critical), and selecting the correct downstream treatment to remove the neutered biological matter.
MF/UF is a new tool gaining acceptance. The USEPA is considering MF/UF for virus reduction as well as its current role of a turbidity (and bacteria associated with that turbidity) remediation device for surface water. The disadvantages are the maintenance requirements associated with a membrane system and the cost of the UF equipment; however, several companies are making POE MF/UF modules that reduce maintenance and cleaning requirements of the system.
RO systems—double- or single-pass—will disinfect water and remove solids. The disadvantages are equipment costs, maintenance costs, and proper application as dictated by the supply source. There are some innovations in the design of the RO that will provide disinfected water with a total dissolved solids (TDS) quality surpassing a single mixed-bed resin system.8
When setting up a laboratory water system or retrofitting an existing system, the laboratory manager has several tools to select from to ensure the water produced by his purification system meets the reagent grade water standards required by his customers. Supply water disinfection is critical to the success of that water purification system. Developing a good relationship with the local PWS or private supplier will greatly assist the manager. The PWS has a general idea when upsets occurs and what steps should be taken to ensure disinfection when those upsets occur. Bringing them into the “team” ensures the effectiveness of the POE disinfection system.
- Winstead, Martha, “Reagent Grade Water: How, When and Why?” The American Society of Medical Technologists, Library of Congress, CC#67-30132, 1967.
- Reynolds, K.A., “On Tap: Waterborne Prion Disease Transmission—Assessing the Risk,” WC&P, Vol. 43, No. 4, pp. 84-87, 2001.
- EPA Guidance Manual Alternative Disinfectants and Oxidants, Table 1-2, page 6, April 1999.
- EPA Guidance Manual Alternative Disinfectants and Oxidants, paragraph 1.3, April 1999.
- EPA Guidance Manual Alternative Disinfectants and Oxidants, April 1999.
- “Are Zebra Mussels in Iowa?” from the State of Iowa’s Department of Natural Resources, March 1998: http://www.state.ia.us/fish/news/exotics/zebra.htm
- “Why does my water taste and smell funny?” from the City of Toronto’s website: http://www.city.toronto.on.ca/water/smelly.htm
- HydroTec Systems Co. Inc., “Will treat potable water (WHO standard) to produce 5 million ohm permeate with a pH from 6.8 to 7.1 or the minimum of ASTM Type II laboratory grade water,” from http://www.purehts.com/Reagent.htm, revised April 30, 2001.
About the author
Warren Searles is president of HydroTec Systems Co. Inc., Rockton, Ill., an OEM of membrane separation products and other water purification systems. His background includes product manager of seawater desalting and applications engineer for Culligan International as well as Illinois Water Treatment Co. (absorbed by USFilter). Searles has a bachelor’s degree in physical sciences from Columbia College and an MBA from Lake Forest Graduate School of Management, both Chicago area institutions. He can be reached at (815) 624-6644 or email: [email protected].