Currently, 42 million people in the United States obtain their water
from private well water or surface water systems. Research is needed to
find improved treatment technologies which include point of use/point
of entry (POU/POE) treatment devices for individual homes, buildings,
and structures and transportable or modular treatment systems. These
could be employed for the duration of time when water supplies are
contaminated or treatment systems are inoperable.
Intec has the research team and capabilities in place to offer a solution to this problem.
Recently, there have been some advances in alternative disinfection
methods and technologies (Ozonation, Chloramines, Ionization and
Ultraviolet radiation, etc.). At the same time, there is a growing
concern of the potential long term affect of the Disinfectant
Byproducts (DBPs). Due to the ability of many forms of disease causing
organisms to become resistant to currently utilized disinfection
methods, a dual approach method or rotation of disinfection methods
have become of more interest.
Chlorine and its various forms (chlorine gas, chloramine, chlorine
dioxide, calcium hypochlorite, sodium hypochlorite, etc.) have been
utilized as disinfectants in public water supplies for about a century.
However, recent studies have shown that chlorine may directly or
indirectly be the principal cause of many forms of cancer.
The EPA adopted a trihalomethane regulation in 1979 to limit the
allowable level of carcinogenic disinfection byproducts in drinking
water. Although chlorine is a good disinfectant, it also can form trace
amounts of a DBP called trihalomethane (THM)[i]. THMs are chemicals
that are formed when organic materials (e.g., decaying trees and leaves
as well as urban farm run-off) combine with free chlorine. This has
caused concern about using chlorine, in recent years, and water
companies have searched for ways of reducing these byproducts.
Chloramines are actually used as DBP inhibitors in 30% of the nation's
surface water supplies and are expected to grow to 65% within 10
years[ii]. Chloramines are formed by the mixture of chlorine and
ammonia in water. However, chloramines have their drawbacks as well.
According to the California Professional Association of Specialty
Contractors, chloramines contribute to pitting, pinholes, and potential
failure of copper pipe[iii]. It is believed that this reaction only
occurs when there is aluminum present in the water[iv]. Chlorine
dioxide can also be utilized as a DBP inhibitor. When added to
chlorine, a reduction in total trihalomethane (TTHM) has been
observed[v]. At the same time, chlorine dioxide is known of producing
chlorites that are identified as causing hemolytic anemia[vi].
Currently, the maximum contaminant level for total THMs is 0.1mg/L in
drinking water.
Ozone has also received a lot of attention recently. It is highly
effective for all groups of organisms, particularly viruses and
bacteria and it can treat high volumes of water. Ozone may be the
strongest and most capable disinfectant against cryptosporidium.
However, it does have its disadvantages as well. Ozone can produce
excessive bromates (which is a potential carcinogen) if the water
contains bromide[vii]. It also possesses a reduced efficacy in cold
water. Ozone also does not provide a persistent residual disinfection
capability, may require high capital investments, and has relatively
high operating and maintenance costs[viii].
In the United States and abroad, ionization is utilized as an
alternative for chlorine disinfection in many applications. It has
proven to be very effective against Legionella in hot water systems and
had great residual disinfection capabilities.
Ultraviolet (UV) disinfection is becoming more popular and economical
than ever before. UV light is a point-of-contact disinfection system
that is highly effective in the inactivation of protozoa (viruses
remain most resistant) and does not require the addition of any
chemicals, requires short contact times, and posses no known DBPs. It
does this without altering the chemistry, taste, and quality of water.
Turbidity, however, does affect the quality of disinfection because of
what is known as the shadowing effect. Also, as in the case of ozone,
UV has no residual disinfection capacity.
To date, no single disinfection method is capable of producing the
results that are necessary in keeping our drinking water safe 100% of
the time. Many water treatment facilities are now using multi-barrier
approaches to disinfection. Most are still utilizing chlorine as their
primary disinfectant and then using additives to reduce DBPs. The
industry focus does not need to be on the reduction of DBPs such as
TTHM, but on eliminating it altogether.
Common Disinfection By-products
Disinfection byproducts form when disinfectants, added to drinking
water to kill germs, react with naturally-occurring organic matter in
water. Below is a recap of DBPs and their health affects:
Total Trihalomethanes - Some
people who drink water containing trihalomethanes in excess of EPA's
standard over many years may experience problems with their liver,
kidneys, or central nervous systems, and may have an increased risk of
getting cancer.
Haloacetic Acids - Some
people who drink water containing haloacetic acids in excess of EPA's
standard over many years may have an increased risk of getting cancer.
Caused from chlorination
Bromate - Some people
who drink water containing bromate in excess of EPA's standard over
many years may have an increased risk of getting cancer.
Chlorite - Some
infants and young children who drink water containing chlorite in
excess of EPA's standard could experience nervous system effects.
Similar effects may occur in fetuses of pregnant women who drink water
containing chlorite in excess of EPA's standard. Some people may
experience anemia.
The Surface Water Treatment
Rule (SWTR) was one of the first regulations to set standards for the
control of Giardia in water by requiring a 3-log (99.9%) cyst removal
or inactivation. The 3-log removal is accomplished by properly
operating treatment plants, which achieve 2-log removal by conventional
treatment and then requiring the disinfection process to achieve the
remaining removal[ix]. These stringent demands are intended to protect
our citizens from future outbreaks. Other characteristics need to also
be considered when evaluating a system.
UV Disinfection
Ultraviolet Radiation (UV) disinfection is a process where
microorganisms are exposed to UV light at a specified intensity for a
specific period of time. This process renders the microorganism to be
considered "microbiologically dead" UV light penetrates the cell
membrane of the microorganism and fuses the thyamine bonds within the
DNA strand, which prevents the DNA strand from replicating. This fusing
of the thyamine bond is known as forming a dimerase of the thymine
bond. If the microorganism is unable to reproduce/replicate then it is
considered "microbiologically dead" While providing 99.99 percent
inactivation of bacteria and viruses, UV light will have no effect on
water chemistry[x].
Relatively low dosages of UV radiation (1-9mJ/cm2) have shown to
inactivate 2-4 log10 (99 - 99.9%) of C. parvum oocysts and G. lamblia
cysts[xi], [xii]. Studies have shown that while the C. parvum oocysts
have the capability of repairing DNA damaged from the UV radiation
process, the oocysts were not capable of recovering their infectious
nature after the UV exposure[xiii], [xiv], [xv].
NSF is an independent accreditor of water treatment systems. The
protocol for validation of residential UV disinfectant systems is the
NSF Standard 55. This standard is broken down onto two parts:
Class A - Point-of-entry
and point-of-use (POU/POE) devices are designed to disinfect and/or
remove microorganisms, including bacteria and viruses, from
contaminated water to a safe level. They aren't intended for treatment
of water that has an obvious contamination source such as raw sewage;
nor are systems intended to convert wastewater to microbiologically
safe drinking water. Class A systems are capable of delivering a UV
dose, at a wavelength of 254 nanometers (nm), to at least 40
milliJoules per square centimeter (mJ/cm? at the alarm set point the
point where a manufacturer will set its UV sensor to activate the
system alarm.
Class B - Point-of-use
(POU) systems are designed for supplemental bactericidal treatment of
treated and disinfected public drinking water or other drinking water
tested and deemed acceptable for human consumption by the state or
local health agency having jurisdiction. Class B systems aren't
intended for disinfection of microbiologically unsafe water but are
designed to reduce normally occurring nonpathogenic or nuisance
microorganisms only. The systems are capable of delivering a UV dose,
at 254 nm, to at least 16 mJ/cm2 at 70 percent of the normal UV lamp
output or alarm set point.
For drinking water, we are
only interested in the Class A certification. Under this certification,
there is 99.99 percent inactivation of Rotavirus, Cryptosporidium, and
Giardia. A recent study has shown that a UV dose of 20 mJ/cm2 is the
equivalent to 2.4 mg/L of chlorine for one minute or 2.4mg/L of
chloramines for one hour[xvi]. The same study concluded that a low dose
of 1.4 mJ/cm2 would provide a 2 log10 inactivation of Giardia lamblia
cysts. Furthermore, Cryptosporidium parvum was damaged to a point where
it could not repair itself at dosages of 17 mJ/cm2. While the results
of UF disinfection are impressive, UV has absolutely no residual
effect, would not prevent recontamination, repair, and is not as
effective in turbid solutions.
The Pulsating UV Light is an attractive design because of its ability
to penetrate opaque or turbid liquids. This devise pulses at a rate of
up to 10,000 times per second. A UV light similar to the one shown in
Figure 2 below will be utilized on this research effort.
The initial construction costs for a UV system are higher than those
for a chlorine system. However, operation and maintenance costs for the
UV system are significantly lower over a 20 year time period. Also, the
only chemical that is used in the UV disinfection process is a dilute
acid used for cleaning tubes. Table 1 shows the UV dose that is
required by UV light to deactivate a wide range of microorganisms.
The environmental impact associated with UV light is the disposal of
the light source once it has been utilized. Mercury, a toxin, is
utilized in the device and is a hazard if not disposed properly.
However, the microwave pulsating UV light shown above does not utilize
mercury in its bulb.
Transition Metal Ionization Disinfection
Ionization is becoming more widely accepted as a disinfection method,
especially in hospital hot water systems. The biocidal effect of copper
and silver stems from a combination of mechanisms. These positively
charged metallic ions attach to the negatively charged bacteria cell
membrane and cause cell lysis and death[xvii], [xviii], [xix]. The
copper ions disrupt the enzyme structures of the cell allowing the
silver ions to penetrate inside where they rapidly kill the cell's life
support system. This is because the positively charged silver and
copper ions have an affinity for electrons and when introduced into the
interior of a bacterial cell, they interfere with electron transport in
cellular respiration systems. Metal ions will bind to the sulfhydryl,
amino and carboxyl groups of amino acids, thereby denaturing the
proteins they compose. This renders enzymes and other proteins
ineffective, compromising the biochemical processes they control. Cell
surface proteins necessary for transport of materials across cell
membranes also are inactivated as they are denatured. When copper binds
with the phosphate groups that are part of the structural backbone of
DNA molecules, the result is the unraveling of the double helix and
consequent destruction of the molecule[xx]. Copper concentrations of
0.2 to 0.4 mg/liter and silver concentrations of 0.02 to 0.04 mg/liter
are recommended for sufficient disinfection levels according to in
vitro and field studies[xxi], [xxii], [xxiii].
Unlike chlorine, copper-silver ionization does not result in dangerous
halogenated organic by-products such as trihalomethanes, chloramines
and chloroform. Also these ions are stable, making it easier to
maintain an effective residual [xxiv]. Furthermore, the ions will
remain active until they are absorbed by a microorganism. However,
using soluble metal salts as a source of these ions and monitoring
their concentrations to maintain consistent effects is cumbersome at
best. Consequently, most modern copper-silver systems use electrolytic
ion generators to control the concentrations of the dissolved metals.
The electrolytic ion generator is the most cost effective approach.
The efficacy of copper-silver disinfection is dependant upon several
variables. The concentration of copper and silver ions in the water has
to be of sufficient levels and is determined by the water flow, the
volume of water in the system, the conductivity of the water, and the
present concentration of microorganisms. This is similar to chlorine in
the fact that active disinfection levels are decreasing as it comes
into contact with microorganisms.
Electrodes should be in good condition and be comprised of pure metals.
When the water is hard or fouling is present, there will be a decrease
in electrode release. Examination of the electrodes on occasion can
prevent these problems in the future. The more pure the metals utilized
on the electrode, the less the electrodes suffer from limestone
formation and fouling.
The pH of water needs to be considered when examining the effectiveness
of copper-silver ionization. When the pH values are high, copper ions
are less effective. When the pH value exceeds 6, insoluble copper
complexes will precipitate. When the pH value is 5, copper ions mainly
exist as Cu(HCO3)+; when the pH value is 7 as Cu(CO3) and when the pH
value is 9 as Cu(CO3)22-. Silver ions are not affected by the pH of the
water and neither metal is affected by the temperature.
Copper-silver ionization affectivity is also determined by the presence
of chlorine which causes silverchlorine complex formation. When this
occurs, silver ions are no longer available for disinfection. However,
copper ions are still active and when combined with low levels of free
chlorine, prove to be an effective method of killing a wide range of
pathogenic bacteria under controlled test conditions [xxv]. To combat
the potential of bacteria having the ability to develop a resistance to
most treatment of disinfection and even heavy metals, a program of
periodic chlorination or ozination can be implemented. As mentioned
earlier, it is very effective for pathogen control and will prevent the
ability to develop a resistance.
The ionization systems have several advantages that include:
Advantages
Installation and maintenance is easy
Efficacy is not effected by water temperatures
Very good residual disinfection protection
Recolonization is delayed because copper-silver ions kill rather than suppress
Effective on even on Legionella
Disadvantages
Some bacteria are believed to have developed resistance to copper-silver ionization
High pH levels reduce the disinfection of copper (levels < pH 8.5).
No oxidation affect
Legionella bacteria are very susceptible to copper-silver ionization
and will even take care of the bio film it produces. The copper ions
remain within the bio film, causing a residual effect. When copper and
silver ions are added to water constantly, the concentration of
Legionella bacteria remains low. The deactivation rate of copper-silver
ionization is lower than that of ozone or UV. A benefit of
copper-silver ionization is that ions remain in the water for a long
period of time causing long-term disinfection and protection from
recontamination. Copper and silver ions remain in the water until they
precipitate are absorbed by bacteria or algae, or removed from water by
filtration.
Microorganisms Deactivated by Copper Ionization
Bacteria
Cu ppm
Bacteria
Cu ppm
Cladophora
0.5
Microspora
0.40
Closterium
0.17
Palmella
2.00
Coelastrum
0.05 - 0.33
Pandorina
10.00
Conferva
0.25
Raphidiiun
1.00
Desmidium
2.00
Scenedesmus
1.00
Draparnaldia
0.33
Spirogyra
0.12
Escherichia coli
0.20
Starastrom
1.50
Entomgplprn
0.50
Ulothrix
0.20
Eudorins
10.00
Volvox
0.25
Hydrodictyon
0.10
Zygnema
0.60
Protozoa
Cu ppm
Protozoa
Cu ppm
Ceratium
0.33
Mallomonas
0.50
Chlamydomonos
0.50
Nematodes
0.70 - 1.0
Cryptomonas
0.50
Peridinium
0.50 - 2.00
Dinobryan
0.18
Synura
0.12 - 0.25
Euglena
0.50
Uroglena
0.05 - 0.20
Glenodinium
0.50
Fungus
Cu ppm
Fungus
Cu ppm
Leptornitus
0.40
Sappolagnia
0.18
Diatoms
Cu ppm
Diatoms
Cu ppm
Asterionella
0.12 - 0.20
Nitzchia
0.50
Fragilaria
0.25
Synedra
0.36 - 0.50
Melosira
0.20
Stepbanodiwus
0.33
Navicitia
0.07
Tabellaiia
0.12 - 0.50
Miscellaneous
Cu ppm
Miscellaneous
Cu ppm
Chara
0.10 - 0.50
Potamogeton
0.30 - 0.80
Nitella, flexilis
0.10 - 0.18
The health benefits of copper and zinc are well documented. The trace
mineral copper helps prevent anemia, bone and skeletal defects, a
degeneration of the nervous system, defects in the color and structure
of hair, reproductive problems, and abnormal cardiovascular
problems[xxvi]. Also, copper is as important as calcium and zinc for
bone formation, red blood cell integrity, skin and immune functions,
nervous system functions, and the conversion of beta carotene into
vitamin C[xxvii].
Currently, Intec utilizes only copper in its disinfection process for
drinking water. Other metals are being researched and funding has been
applied for through both the EPA for small public drinking water
systems and the USDA for poultry water disinfection. The information
above is part of one of our research efforts.
