Working Around the Clock

Preventive measures, such as operation diligence, emergency response plans and effective technology safeguard against contamination

The safety of the nation's water is protected by a cooperative relationship between governments at every level and water producers and purveyors. The U.S. Congress makes national water policy and has authorized the U.S. Environmental Protection Agency (EPA) to implement this policy by means of the Safe Drinking Water Act of 1974, as it is periodically re-authorized and amended. This act provided for a partnership between EPA and the states to protect drinking water supplies and sources. EPA establishes national drinking water standards to protect public health and provides technical and financial support to states and drinking water systems. The states implement and enforce these standards to ensure the delivery of safe water to the tap.

PWS Maintenance and Protection
There are approximately 170,000 public water systems in the United States. A Public Water System (PWS) is for the provision to the public of water for human consumption through pipes or other constructed conveyances, if such a system has at least 15 service connections or regularly serves at least 25 individuals for at least 60 days a year. The three types of public water systems are Community Water Systems (CWS), which supply water to the same population year-round; Non-Transient Non-Community Water Systems (NTNCWS), which supply water to at least 25 of the same people at least six months per year; and Transient Non-Community Water Systems (TNCWS), which supply water to places where people do not remain for long periods of time, such as a gas station or campground. These three types of public water systems currently serve a total of approximately 284 million people in the United States.

National water policy relies upon a multi-barrier approach to protect drinking water safety from the source to the tap. These barriers include source water protection, treatment, distribution system integrity and public information.

Water Treatment Plant Operation
Simply described, a water treatment plant operator's responsibility is to produce safe, pleasant and adequate supplies of potable water. Raw water is monitored as it enters the plant and flows through various treatment processes prior to distribution for consumption. Some of the typical duties performed by water treatment plant operators include:

  • Periodic operating checks of plant equipment, such as pumping systems, chemical feeders, auxiliary equipment (compressors), and measuring and control systems.
  • Maintain plant records, including operating logs, daily diaries and chemical inventories.
  • Monitor the status of treatment plant parameter guidelines, such as flows, pressures, and chemical feeds and water quality indicators by reference to measuring systems.
  • Collects representative water samples and performs laboratory tests on samples for turbidity, color, odor, coliforms, chlorine residual and other tests as required.

EPA has established minimum standards for the certification of water system operators.

Water Treatment Plant Safety
Drinking water facilities under the jurisdiction of a state must develop emergency response plans for natural and human-made disasters. In the event of an emergency, the drinking water utility would activate its emergency response plan in conjunction with local law enforcement and state emergency officials. This plan provides for shutting down the system, notifying the public of possible emergency steps and providing alternate sources of potable water, if needed. Coupled with performing their daily activities, water treatment operators are required to be up-to-date with their plant?s emergency response plan at all times. During an emergency, EPA will assist in the response if called upon by the state.

The September 2001 terrorist attack on the World Trade Center in New York City has emphasized the need to enhance current emergency response systems. Fortunately, this issue began to be seriously addressed in 1998 with the publishing of Presidential Decision Directive 63, which established the National Infrastructure Protection Center (NIPC). Within this framework, EPA was given the responsibility for critical infrastructure protection issues for water supply systems. EPA and the American Water Works Association?s (AWWA) Research Foundation are currently developing a vulnerability assessment methodology for use by water systems as a first step in assessing protection needs. This methodology is currently being tested in the largest water systems.

The Association of Metropolitan Water Agencies created the Critical Infrastructure Protection Advisory Group (CIPAG), which has brought together such groups as EPA, the Federal Bureau of Investigation (FBI), the U.S. Department of Energy (DOE), and water industry representatives. CIPAG established the Information Sharing and Assistance Center (ISAC), which when fully implemented, will allow the secure transmission of threat information and other sensitive data between government agencies and the water supply community. In the interim, an emergency contact network established by AWWA on September 11, 2001, is providing registered water systems with FBI threat warnings. CIPAG is also developing guidance documents for water system use in protecting, responding and mitigating the consequences of an attack. For the past two years, a web extension of the Information Sharing and Analysis Center has been under development (www.amwa.net/isac/index.html). Once operational, it will allow secured access to relevant information addressing water supply security.

While it is true that a lot of contaminants would be needed to contaminate a large reservoir, there is nonetheless a danger to water systems. AWWA has recognized that there "are many unprotected avenues of access to every water system which could be taken advantage of by a knowledgeable sociopath to inflict serious damage to a water supply system without detection in most communities."

Safe Water
Water system personnel can undertake additional safeguards including limiting access within and throughout the utility treatment and storage facilities, meeting shipments at their gates, conducting additional testing and monitoring of chemicals agents delivered to the plant before they are introduced into the treatment system, reassessing procedures and systems that are in place to detect security incursions and providing additional training to their personnel to be alert to the signs of a potential threat.

The goal of any security system should be to "detect, delay and respond." Basically, some terrorists will be deterred if they think their actions might be detected; others will be deterred if they are delayed for a significant period of time before reaching their end goal, because they fear detection. If sabotage does occur, be it contamination of the water or physical destruction of the system facilities, then utility staff must detect that an event has occurred and respond quickly and appropriately to keep the consequences to a minimum.

New technologies, such as DNA chips, show promise in detecting whether any biological contamination of water has occurred. Similarly, bioluminescence test systems have proven reliable in detecting general chemical contamination. A system available for environmental and water services monitoring and protection is the Rapid Response Water Testing System. This portable system can indicate the quality of a water sample in only minutes. In theory, the system works on the principles of the luminometer and the chemiluminescence process. The chemiluminescence process is a chemical reaction that occurs in a water sample when specific reagents are added. A byproduct of this reaction is light that is measured by the luminometer. When a toxic material or a contaminant exists in the water, light production is inhibited. By establishing a baseline or normal reading at a plant or water source, subsequent samples can be measured and compared to this baseline, helping to rapidly determine if there has been any significant change in the chemical profile.

In conjunction with safety procedures and the systems designed to facilitate them, the normal water treatment process will, in many cases, remove any immediate threat to the public from introduced contaminants. The vigorous multiple barrier treatment process includes various forms of filtration and disinfection technologies. Some of these technologies include chlorination, on-site sodium hypochlorite generation, ultraviolet disinfection and reverse osmosis. Both ultraviolet disinfection and filtration via reverse osmosis are being used increasingly to enhance the treatment of potable water. As these technologies emerge in this market, it is important for treatment plant operators to understand the fundamentals of operation respective to these technologies.

Ultraviolet Disinfection
Ultraviolet (UV) disinfection is the process where microorganisms are exposed to UV light at a specified intensity for a specific period of time. This process renders the microorganism "microbiologically dead." UV light penetrates the cell wall of the microorganism affecting the DNA by fusing the Thyamine bond within the DNA strand, which prevents the DNA strand from replicating during the reproduction process. This fusing of the Thyamine bond is known as forming a dimerase of the Thyamine bond. If the microorganism is unable to reproduce/replicate then it is considered to be "microbiologically dead."

The wavelength of light that has been determined to be most efficient for absorption within the cell is approximately 260 nano meters (nm). Currently, most lamp technologies, low pressure-standard intensity and low pressure-high output, generate UV light at 253.7nm, which is 90 percent efficient at producing germicidal UV light. The amount of UV light intensity, generated by a specific lamp is a function of power applied to the lamp and the arc length of the lamp. Medium pressure and UV Pulse systems generate a polychromatic output, of which a maximum of 25 percent is within the germicidal range.

UV dose is measured as microwatt seconds per square centimeter (ws/cm2). This measurement is a function of UV intensity over a known time frame given a specific flow rate and a known sized UV reactor. Most UV systems in use today for disinfection are sized to provide a minimum dosage of 30,000 ws/cm2. In 1969, the U.S. Department of Health, Education and Welfare Public Health Service, Division of Environmental Engineering and Food Protection issued a guideline that UV systems should provide a minimum dose of 16,000 ws/cm2. This value is still used today in sizing some residential UV systems.

Organism

99.99% Inactivation

DOSE, millijoule per squared centimeter (mJ/cm2)

90% Inactivation

DOSE, mJ/cm2

Cryptosporidium parvum oocysts

7.90

3.0

Giardia lamblia cysts

<10

N/A

Legionella pneumophila

N/A

1.2

Escherichia coli

5.6

1.5

Pseudomonas aeruginosa

22.00

5.50

Mycobacterum tuberculosis

24.00

6.00

Dose Requirement Table: (Section of Organism Dose Table)

While providing a 99.99 percent inactivation of bacterium and viruses, UV will have no effect on water chemistry. Therefore, the use of corrosion inhibitors or pH control will still be necessary.

A current trend within the United States is to evaluate the use of UV for disinfection of waters, both surface and subsurface, being used for potable water systems. About one percent of the 40 billion gallons of drinking water provided daily by public water utilities in the United States is currently utilizing UV disinfection. There are a number of installations and pilot treatment systems being evaluated today and EPA is currently developing regulatory standards for the application of UV for potable water systems. The current regulatory trend appears to be establishing a minimum dose of 40,000 ws/cm2 as acceptable for potable water supplies when utilizing UV technology. Other requirements will include the use of UV intensity meters and their associated alarm connections, third party certification of UV systems, performance monitoring and minimum dose requirements.

Prior to this trend, UV disinfection has been used as a polishing effect on the post side of filtration in the water treatment process. The "polishing effect" refers to the use of UV to inactivate any bacteriological breakthrough that formed inside a filtration system.

Reverse Osmosis
Reverse osmosis (RO) filtration uses a semi-permeable membrane that enables the water being purified to pass through while contaminants remain behind. Traditionally, osmosis refers to the attempt to reach equilibrium by dissimilar liquid systems trying to reach the same concentration of materials on both sides of a semi-permeable membrane. Reversing the osmotic process is accomplished by applying pressure to stop the natural osmosis process, creating reverse osmosis.

Most reverse osmosis technology utilizes the crossflow process, allowing the membrane to continuously clean itself. This process facilitates long term performance of the membrane by reducing fouling. In essence, water passes through the membrane while a separate flow ensures that precipitated salts and other impurities are rejected from the membrane surface.

Reverse osmosis removes virtually all organic compounds, 90 to 99.6 percent of all ions and rejects 99.9+ percent of viruses, bacteria and pyrogens. Pressure, on the order of 200 to 1,200 psig (13.8 to 68.9 bar) is the driving force of the rejection process. The required pressure is highly a function of the salt concentration of the water. Also, the higher the pressure, the larger the driving force and the greater the amount of purified water produced. The membrane usually accounts for 15 to 40 percent of the price of a RO system. Since it must be replaced periodically, significant importance is placed on the selection process. Many types of membranes exist with unique characteristics and selection criteria should include chemical tolerance, mechanical suitability, cleanability, separation, flow performance and membrane life. Today's membranes are constantly being improved, thus making RO an even more economical process.

The continued success and efficiency of an RO system makes it a popular choice for the potable water treatment process. An RO system can be manufactured to specification for use in almost any water treatment plant. The relatively simple operation and diagnostic and safety features, such as Programmable Logic Control (PLC) screens, product and brine flow meters, built-in membrane cleaning systems and analogue total dissolved solids (TDS) readout meters have contributed to the success of RO systems in the potable water treatment market.

On Alert
The constant responsibility of a public water system to undertake measures that protect the interest of public health is undeniable. Coordinated efforts at local, state and federal levels have lead to the development of strict regulatory measures that address appropriate procedures, dealing from everyday operation to emergency response plans. At an operational level, a treatment plant operator must recognize the important public health role afforded by their position. In addition, the emergence of technologies that help facilitate and ensure the safety of the treatment process, such as ultraviolet disinfection and reverse osmosis filtration must be examined and implemented where possible.

References

  • American Water Works Association -- www.awwa.org
  • U.S. Department of Health, Education and Welfare Public Health Service, Division of Environmental Engineering and Food Protection: "Policy Statement on Use of the Ultraviolet Process for Disinfection of Water."
  • "Service Systems International Expects New Regulations for the Disinfection of Drinking Water to Increase Ultraviolet Use" Business Wire (July 2001) 278.
  • Henley, M. "Biocontrol-Microbial Control is Important Water Treatment Market," Ultrapure Water Journal, 18.1 (January 2001) 11-16.
  • Reeves, P., Carmody J., Martyak, J. "Ultraviolet (UV) Light for Chlorine Removal in a High-Purity Water System," Ultrapure Water Journal, 18.1 (January 2001) 38-41.
  • Paulson, J. David. "Membranes, the Finest Filtration," Filtration News, July 01, 1995.
  • U.S Environmental Protection Agency, Office of Drinking Water. "Water Treatment Plant Operation, a Field Study Training Guide" Volume 1.

This article originally appeared in the 05/01/2002 issue of Environmental Protection.

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