The White Tanks Regional Water Treatment Facility (White Tanks) is located in Surprise, Arizona, and treats surface water from the Colorado River that is delivered by a 336-mile (540-kilometer) man-made canal. Using surface water for a new water supply required that White Tanks comply with the United States Environmental Protection Agency’s (USEPA) Long Term 2 Enhanced Surface Water Treatment Rule (LT2 Rule).
The LT2 Rule was introduced in 2006 to address the risk of current water treatment practices not fully protecting the public from harmful protozoa including Cryptosporidium. This protozoan parasite can be present in surface water that is used as a drinking water source and can cause severe illness when ingested. Cryptosporidium’s small size (4-5 microns) can allow it to pass through filters and it is highly resistant to standard disinfectants like chlorine and chloramines.
The LT2 Rule is in place to protect against Cryptosporidium (and other disease-causing microorganisms such as Giardia). It requires high-risk and unfiltered drinking water treatment plants to install an additional treatment step providing a multi-barrier strategy.
Drinking water facilities can evaluate various USEPA-recommended technologies for meeting the LT2 Rule such as ultraviolet disinfection (UV), membrane filtration and ozone.
The TrojanUV Solution
After an evaluation of available technologies and suppliers, White Tanks chose TrojanUV disinfection to meet the LT2 Rule and to satisfy their site-specific needs. Two TrojanUVSwift™ units were installed in August of 2009.
UV is highly effective against Cryptosporidium and Giardia, easily inactivating them at low doses, making it a cost-effective solution. The USEPA Office of Water cost report determined that UV is less than 1/5th the cost of ozone disinfection and 1/10th the cost of membrane filtration (Figure 1).
UV, LT2 and Third Party Validation
UV systems used to comply with the LT2 Rule must undergo independent third party validation testing. The TrojanUVSwift went through full-scale testing to inactivate a test microorganism called MS2-phage. This nonpathogenic challenge microorganism was used to simulate the reactor’s performance in treating Cryptosporidium and demonstrate that the TrojanUVSwift could meet White Tank’s disinfection requirement.
“Our site-specific criteria for a solution was a small installation footprint and technology that was environmentally friendly”, says Joseph Cornejo, operator of the facility.
A UV system has a small footprint because of the short contact time needed to inactivate microorganisms. Microorganisms are inactivated virtually instantaneously within the reactor, compared to a requirement of several minutes for chemical disinfectants.
The footprint and resulting construction costs of UV systems are much smaller than chlorine and its required contact tanks.
UV disinfection is a physical process that adds nothing to the water but light. Disinfection byproducts (DBPs) are not created, making it an environmentally friendly technology.
As such, UV also becomes an ideal option for those facilities complying with USEPA’s Stage 2 Disinfectants and Disinfection Byproducts Rule (DBP Rule) promulgated simultaneously with the LT2 Rule. The DBP Rule’s purpose is to reduce the potential health risks of DBPs. Chemical disinfectants, such as chlorine, react with naturally-occurring materials in water to form these byproducts, which may pose health risks to both humans and aquatic life.
System Design Parameters
|Average Flow Capacity||13-14 MGD|
|Peak Flow Disinfection||40 MGD|
|Disinfection Requirement||3-log inactivation of Cryptosporidium
The TrojanUVSwift units have been working effectively and efficiently since their installation. Daily Cryptosporidium monitoring has revealed zero violations.
White Tanks operator, Joseph Cornejo, likes the equipment’s ease of operation, system automation and its accessibility for repair and calibration. He notes that, “The SCADA communication system is set to send an alarm to the control center automatically in the event that the combination of plant flow, UVT (UV Transmittance), and reactor power (level) results in operation outside the validation limits for the equipment (also referred to as off-spec water).”
Joseph also explains that the “facility output is currently 13-14 MGD with each of the two units capable of treating 20 MGD. This allows for facility volume expansion while still being able to achieve 3-log inactivation of Cryptosporidium and Giardia”. The TrojanUVSwift units will be working for White Tanks long into the future.
What You Should Know About Crypto
Cryptosporidiosis, the illness caused by Cryptosporidium can be severe or even fatal for infants, the elderly and other people with weakened immune systems. This gastrointestinal illness causes diarrhea, dehydration, stomach cramps, and/or fever symptoms that typically last from several days to two weeks.
Cryptosporidium has caused a number of waterborne disease outbreaks in the United States. One of the most damaging was in 1993 in Milwaukee, WI where 400,000 people became ill and 100 people died. Cryptosporidium contamination can come from agriculture, wastewater treatment plant discharges, wild life, and other sources of fecal matter.