By Rodney E. Herrington, P.E.

Summary: Remote sites maintained by the U.S. Forest Service for campers and others present special requirements to assure quality water for drinking and other uses.This article discusses a mixed oxidant approach to offer a residual for continued disinfection.


The U.S. Forest Service (USFS), a branch of the U.S. Department of Agriculture (USDA), operates numerous facilities in remote locations throughout the country. Inability to provide potable water can either shut down a facility or result in loss of revenue. To provide safe drinking water, the USFS must comply with the requirements of the U.S. Environmental Protection Agency (USEPA), particularly the Surface Water Treatment Rule (SWTR).

In general, the SWTR provides the most stringent requirements for filtration and disinfection due to likely contaminants in surface water sources. Since many of the sites are far away from paved roads or towns, it would be cost prohibitive for the USFS to maintain a sufficient staff of certified operators to perform grab sampling. In recent years the USFS—in partnership with private industry—has been actively working to develop a small, portable package plant to meet SWTR performance and continuous monitoring requirements.

The resulting units can treat 24,000 gallons per day (gpd)—90.9 cubic meters per day (m3/day)—to USEPA and State of California drinking quality standards; are portable in a small truck; run on 12-volt DC (VDC) power for solar, batteries, or conventional 120-volt AC (VAC) power; are self-monitoring with safety shutdown features; operate for 30 days unattended, and can treat surface or groundwater. Recently, about 20 of the systems have been built and a beta testing program has been conducted at several campgrounds.

System components
The system, shown in Figure 1, includes a mixed-oxidant disinfection technology, which utilizes an electrolytic cell that produces a mixed-oxidant solution consisting primarily of hypochlorous acid and other chlor-oxygen species that exhibit many of the positive features of other strong disinfectants, but also imparts a chlorine residual required by the USEPA. The electrolytic cell contains no membranes, which could become fouled.

It also incorporates cartridge filters from Rosedale Corp., a Hach CL17 chlorine monitor and two Hach 1720D low-range turbidity monitors for influent and effluent turbidity. All components are mounted on a lightweight aluminum frame approximately 34-inches × 60-inches (0.87 × 1.54 meters). The system includes a logic-based control system with a Datalogger, or data collection unit. To comply with the SWTR, the control system automatically shuts down water flow if the treated water doesn’t meet specifications.

Other safety features include shutdown and system drain in the event of freezing temperatures, as well as on-board diagnostics for fault detection. The control system automatically adjusts mixed-oxidant dose rates to maintain chlorine residuals within prescribed limits in the storage tank. A variety of energy conservation techniques are employed in the design as well. Valves are motor operated rather than solenoid, chlorine and turbidity monitors and back-lit displays are powered down during standby operation, and turbidity monitors are custom converted to 12 VDC rather than 110 VAC.

An effective tool
Several studies have been conducted on the mixed-oxidant technology by recognized experts in the disinfection field. Dr. Linda Venczel of the University of North Carolina at Chapel Hill, in cooperation with the Centers for Disease Control and Prevention (CDC) in Atlanta, has demonstrated 3-to-4 log inactivation of the Cryptosporidium oocyst3, as compared to no inactivation whatsoever by sodium hypochlorite.

By-product formation resulting from chlorine molecules combining with organic material in water sources are regulated by the USEPA under the Disinfectants/Disinfection By-Products (D/DBP) Rule and is limited—under the new Stage 1 D/DBP Rule—to 80 micrograms per liter (mg/L). Depending on the source water quality, the mixed-oxidant solution usually forms about a third less of the DBPs than conventional chlorination, as shown in both the laboratory and in the field.

Another feature of the mixed-oxidant solution is the ability to produce a longer-lasting chlorine residual in treated water compared to conventional chlorination technologies. Typical doses of mixed-oxidant as free available chlorine are 30-to-40 percent lower. This is supported by reports from hundreds of operators who are using mixed-oxidant technology. While difficult to quantify, many operators also report dramatic improvements in taste and odor in the water.

Meeting the protocols
Cartridge filtration technology was selected for this application based on reliability and performance for turbidity reduction and microorganism removal. Housings are stainless steel and the cartridges are multi-layer polyethylene with o-ring seals. The nominal rating for Giardia and Cryptosporidium removal is 1 micron with 2-log efficiency. To verify filter performance and repeatability, the U.S. Forest Service developed a filter test facility at its San Dimas, Calif.-Test and Evaluation facility. Concurrently, a filter test protocol was developed through consultation with the California Department of Health Services. While several manufacturers’ filters were evaluated, the Rosedale filters performed very well, meeting the removal criteria repeatedly.

After the initial system installation in August 1995, at the Lime Kiln campground on Highway 1 in California, the system operated reliably over a range of operating conditions and flow rates. From manual readings, chlorine residual at all locations in the system was always maintained above 0.2 milligrams per liter (mg/L). In January 1997, a portable package plant (P3) system was installed in a suburb of Cordoba, Mexico, as a part of the USTIES program sponsored by the USEPA and the USDA. Other units were phased into operation over a period of several months. Initial unit installations are listed in Table 1. While each of the 10 P3 systems is identical, they’re installed at sites with varying conditions. Typical variations include water pressure, power sources, solar exposure and ambient temperature extremes. Significant flexibility has been designed into the P3 control system to allow interface with site-specific pumps, solenoids, relays and other devices.

On-site performance
Many of the sites where the P3 systems are installed are seasonal campgrounds. The beta program also had the benefit of winter shutdown and restart of the system in spring. In general, the systems have performed very well after the initial startup problems were resolved. As a result of the beta test program, and lessons learned, several minor changes have been made to the P3 system to mitigate future problems. Subsequent system installations and startups have gone much more smoothly (see Figures 2&3).

Operational cost issues vary with each site depending, for the most part, on source water quality. Typically, treated water can be produced for less than $0.50 per thousand gallons, which includes all consumables. These systems have been meeting the SWTR requirements and have been doing so without excessive operator interface. In many cases, these systems have reduced the work load requirements from previous systems, and in most cases have significantly reduced the safety hazards associated with water disinfection at these sites.

Typical output from the P3 system is a graphical presentation of the turbidity and chlorine residual values. Figure 5 offers such a presentation of the data taken from the system at Bridge Campground. From July 15 to 21, the water system was down for other maintenance.

Conclusion
Responding to the latest requirements of USEPA drinking water standards, the U.S. Forest Service can now offer the public quality drinking water from most ground and surface water sources. This is being achieved with an automated package plant that has undergone extensive development utilizing safe, state-of-the-art disinfection technology and a cost-effective, reliable filtration system. The system also meets the goals of portability, extended run times with minimal operator and maintenance requirements and assurance that the public it serves are happy campers.

Acknowledgment
Development of this system was primarily driven by the requirements of the USDA Forest Service, which was coordinated by Dave Erlenbach and Brenda Land at the Forest Service Technology and Development Center in San Dimas, Calif. Both have been instrumental in the success of this program.

References

  1. Bradford, W.L., and Amos Coleman, “Disinfection By-Product Produced in Raw Water
    Treated with Mixed-Oxidants,” Los Alamos Technical Associates, Los Alamos, N.M., and U.S. Army Belvoir Research, Development and Engineering Center, Fort Belvoir, Va., 1993
  2. Land, Brenda, “Alternative Technology Demonstration Test for 3M Model 723A Cartridge
    Filter Suitable for Small Surface Water Treatment Package Plant,” San Dimas Technology and Development Center, San Dimas, Calif., March 27, 1998.
  3. Venczel, L.V., M. Arrowhead, M. Hurd, and M.D. Sobsey, “Inactivation of
    Cryptosporidium parvum Oocysts and Clostridium perfringens Spores by a Mixed-Oxidant Disinfectant and by Free Chlorine,” The University of North Carolina, CB# 7400 Chapel Hill, N.C., 27599 (1995); Centers for Disease Control (CDC), Applied and Environmental Microbiology, CDC Division of Parasitic Diseases, Atlanta, Ga., April 1997, p. 1598-1601.
  4. Venczel, L.V., “Evaluation and Application of a Mixed-Oxidant Disinfection System for
    Waterborne Disease Prevention,” University of North Carolina at Chapel Hill, School of Public Health, 1997.

About the author
Rodney Herrington is vice president of engineering and research and development for the MIOX Corporation in Albuquerque, N.M. He’s involved in the development of a full range of products that include a small disinfection “pen” for individual water treatment up to commercial systems that produce several hundred pounds per day of chlorine equivalent. He has been with the MIOX since its inception in 1994 and holds a master’s degree in mechanical engineering from Texas A&M University. He can be reached at (505) 343-0090, email: rodneyh@miox.com or website: http://www.miox.com

Share.

Comments are closed.