United States
                    Environmental Protection
                    Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
                    Research and Development
EPA/600/S2-85/092 Sept. 1985
&EHV         Project Summary

                    Ultraviolet  Disinfection  of
                    Water  for  Small  Water
                    Supplies
                    Dale A. Carlson, Robert W. Seabloom, Foppe B. DeWalle, Theodore F.
                    Wetzler, Jogeir Engeset, Richard Butler, Somboon Wangsuphachart, and
                    Sinclair Wang
                      Ultraviolet (UV) radiation was con-
                    sidered as an alternative means of dis-
                    infecting small drinking water supplies.
                    A major impetus for this study was the
                    U.S. increase in reported waterborne
                    disease outbreaks caused by  Giardia
                    lamblia, an organism that is highly re-
                    sistant to conventional chlorination.
                      Both field and laboratory studies
                    were used to evaluate the effectiveness
                    of UV radiation in reducing the viability
                    of Escharichia coli, Yersinia sp., and Gi-
                    ardia sp. UV sources included commer-
                    cial UV reactors and an excimer laser.
                      6. muris was used as a surrogate for
                    G. lamblia so that reliable excystation
                    and a consistent population of infective
                    organisms could be attained through-
                    out the seasons and through the proj-
                    ect study period.
                      G. muris cysts  were significantly
                    more resistant to UV than £. coli and
                    more resistant than Yersinia sp. The ef-
                    fectiveness of disinfection depended on
                    the amount of UV radiation reaching
                    the organisms and on any hydraulic
                    shortcircuiting. The presence of en-
                    trapped air in the commerical UV reac-
                    tors decreased the efficiency of the re-
                    actor.
                      Natural  or added color in the test
                    waters decreased the effectiveness of
                    UV disinfection on G. muris. For the
                    range and type of turbidity examined,
                    the shielding effect against bacterial
                    disinfection noted in other studies was
                    not observed.
                      Studies on G. muris cysts indicated
                    that storage time and temperature af-
fected the viability of the cysts and that
the rate of decrease in viability approxi-
mately doubled with each 10°C increase
in temperature above freezing. Below
freezing, however, cyst viability was
shortened to hours rather than to days
for above-freezing conditions.
  Physical stress produced by pressure
and alum addition in water treatment
processes appeared to damage and
even destroy cysts.
  This Project Summary was devel-
oped by EPA's Water Engineering Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).

Introduction
  The germicidal effects of sunlight
have long been known, but artificial ul-
traviolet (UV) radiation can obtain much
better microbiocidal action at a wave-
length of about 260 nm. A common
form of artificial UV radiation with  a
wavelength of 253.7 nm can be pro-
duced by low-pressure mercury vapor
lamps. The inactivation of microorgan-
isms by UV radiation is based on photo-
chemical reactions in the DNA that re-
sult in coding system errors.
  Early attempts to use UV radiation for
public water supply treatment began in
1910. They were not very successful and
were abandoned in favor of chlorina-
tion. However, two factors have re-
newed interest in UV radiation for pub-

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lie water supply disinfection: (1) the fact
that chlorination can produce byprod-
ucts that may be carcinogenic to hu-
mans and possibly toxic to aquatic life,
and (2) a large increase in giardiasis in
the United States, a waterborne disease
caused by the chlorine-resistant Giardia
lamblia cyst. The major impetus for this
study was the dramatic  increase
in waterborne disease, specifically
giardiasis, in the United States since the
mid-1960's.  The present investigation
uses both field and  laboratory studies
to evaluate the effectiveness of UV
radiation in reducing the viability  of
Escherichia coli, Yersinia sp.,  and
Giardia sp. UV sources included  com-
mercial UV reactors and  an excimer
laser.

Germicidal Characteristics of
UV Radiation

  Ultraviolet (UV) radiation is defined
as electromagnetic radiation occupying
a small portion of the electromagnetic
spectrum lying beyond visible light. The
wave lengths of UV radiation range
from about 4 to 400 nm, with the narrow
band  between 200 and 310 nm having
the greatest injurious and lethal effects
on microorganisms. The maximum mi-
crobiocidal action occurs at about 260
nm for practically all microorganisms
and is essentially congruent with the UV
absorption and photochemical sensitiv-
ity of deoxyribonucleic acid (DMA). The
inactivation  of microorganisms is then
essentially based on photochemical re-
actions in the DNA that result in errors
and  faults being introduced into the
coding systems. Nature has developed
various means of molecular-biological
error correction for the protection of the
vital DNA, and the selectivity of the re-
actions may be influenced by changes
in the organisms in different phases of
their  life cycle. Thus photo repair sys-
tems may resuscitate a seemingly dead
organism by either  longer wavelength
photo irradiation or dark incubation. In
addition, spores have been found to be
very resistant to radiation.
  The germicidal action of UV radiation
results from its exposure to or direct
contact with the organisms, and  it can
only  be effective if it is absorbed. The
lethal effect of UV radiation results from
a photochemical reaction initiated  by
absorption of a photon by the molecular
structure rather than by formation of a
toxic substance in the medium.
  The inactivation of microorganisms
resulting from UV exposure is propor-
tional to the intensity (mW/cm2) multi-
plied by the time of exposure (sec). The
product of the irradiation intensity per
area and the time is called the UV dose
(mW-sec/cm2). Note that the only ad-
verse effect of an excessive dose of UV
radiation is additional cost.

Sources of UV Radiation
  The sources of UV  radiation are of
two classes—natural and artificial. The
sun  is the  most important  natural
source of UV light. The oxidizing and
germ-killing  effects of sunlight con-
tribute considerably to the conservation
of our environment by natural photo-
chemical processes in the atmosphere
and by natural ultraviolet purification of
surface water. UV light can also be gen-
erated artificially by a wide  variety of
arcs and incandescent lamps. One com-
mon form of artificial UV radiation can
be generated from special  low-
pressure, mercury-vapor  lamps that
produce UV radiation as a  result  of an
electron flow between the electrodes
through ionized mercury vapor. These
artificial UV  radiation sources can sup-
ply energy in such relatively high doses
that in fractions of a second they can
accomplish a higher degree  of irradia-
tion than the sun can in several hours.
  Since the maximum UV sensitivity of
microorganisms and the UV emission
of the low-pressure  mercury vapor
lamp are well matched, the nearly
monochromatic low-pressure mercury
lamp has prevailed as the dominant ra-
diation source in research and practical
applications.

Early Experience with UV Dis-
infection
  The first recorded attempt  to use UV
radiation for public water supply treat-
ment was made in 1910 in France. Sub-
sequently, UV treatment was tried in the
United States with limited success, but
most systems were abandoned before
1930. The main reasons given for aban-
doning the  UV method of  treatment
were relatively high operating costs, op-
erating and maintenance problems, and
the advent of chlorination, which was
found to be  more efficient and reliable.

Procedures
  The UV equipment consisted of two
commercially available UV water disin-
fection units, a laboratory batch UV unit,
and an excimer laser UV unit to provide
coherent UV light at  several  discrete
wavelengths.
  The early stage of this study used
only G. lamblia cysts supplied mainly by
hospitals and pathology laboratories
across the State of Washington. How-
ever, the supply of G. lamblia cysts was
closely  related to the  outdoor recre-
ational activities in the area and was
hence very seasonal. In addition,  the
cysts proved  difficult to excyst consis-
tently,  which  severely limited the
amount of information that could be
gathered. Thus we decided to use
G. mur/s cysts, which were indicated by
current information to be at least as
resistant as G.  lamblia cysts. G. muris
cysts provided a relatively higher excy-
stability and less fluctuation  of  the
results. Until we develop a reliable
method to determine the viability of G.
lamblia, the use of G. muris cysts as a
surrogate  is warranted. Female Swiss
Webster mice were used for cyst prop-
agation.
  Strains of fully virulent Yersinia enter-
ocolitica were derived from human pa-
tients suffering from chronic gas-
trointestinal disease manifested  largely
by recurrent and sporadic diarrhea or by
acute episodes of ileitis. Three separate
media were studied  for isolating and
enumerating  Y. enterocolitica because
of the  lack of an acceptable standard-
ized method.  The first two  media,
MacTween* and mYE, required mem-
brane filtration  of the sample, and the
third medium, Tergitol-7 was inoculated
by surface spreading.
  Two different strains of E. coli were
evaluated in  the  batch UV studies: a
nalidixic-acid-resistant (NAR) strain and
a non-NAR strain.
  Three different media were used to
isolate and enumerate the two different
strains of £. coli. The first two  media,
eosin methylene blue (EMB) and m-
Endo, are commonly used media for
enumerating coliforms from water sam-
ples. Both media were substrates for
membrane filters. The third medium,
Tergitol-7 TTC, was used to differentiate
between E.  co//-NAR and background
coliforms. Water samples were surface-
spread on Tergitol-7 TTC agar.
  During the course of this investiga-
tion, efforts were made to obtain a UV
disinfection unit with  a self-contained
dosimeter so that the actual UV dosage
could  be read directly. These  efforts
were fruitless, and it was necessary to
rely on actinometry  to gauge the out-

*Mention of trade names or commercial  products
 does not constitute endorsement or recommenda-
 tion for use.

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 put of the UV unit. Since the geometry
 of the unit, the flow patterns at various
 Reynolds numbers, the degree and in-
 tensity of reflection,  the  average dis-
 tance between lamps, the penetration
 depth, the cleanliness of the liquid and
 of the UV lamp, the  degree of  short-
 circuiting, and the degree of light scat-
 tering all have potential effects on the
 dosages applied, photo  actinometry
 was used to access the UV  light inten-
 sity of exposure.
  Giardia cysts, Yersinia, and E. coli or-
 ganisms were spiked  into  the UV treat-
 ment unit influent stream  through a
 manifold and then mixed by a static
 mixer. The organisms then passed
 through the UV contactor with various
 detention times and hence different ra-
 diation doses. Color and turbidity were
 added to determine their influence on
 cyst and organism survival. The effect
 of storage time on 6. muris cysts at var-
 ious  temperatures was also investi-
 gated, as well as their settling character-
 istics in quiescent conditions. Finally,
 zeta  potentials were determined  for
 G.  lamblia  over a wide  range  of pH
 values.

 Results and Discussion
  With relatively long exposure times of
 about 20 min, a 99-percent kill of cysts
 was obtained by the Pen Ray Batch Re-
 actor (Figure 1). Figure 2 compares data
 on  Giardia cyst survival versus UV
 dosage from another study (Rice, E. W.
 and J. C. Hoff. 1982. Inactivation of
 Giardia lamblia Cysts by Ultraviolet Irra-
 diation. Appl. Environ.  Microbiol.
 42:546-547)  with data obtained in this
 study using a commercially available
 reactor. Note that the  relatively low de-
 struction rate of Giardia cysts shown in
 the data from Rice and Hoff in Figure 2
 was due to the low UV exposure dose,
 and that commercial UV disinfection
 units  used in this study can achieve dis-
 infection of the cysts. For all experimen-
 tal conditions in which color was added
 to the water (regardless of the source),
 an increase in absorbance at 254 nm re-
 sulted in an increase in the percentage
 of cyst survival (Figure 3). On the other
 hand, when turbidity was added, the de-
 gree  of cyst inactivation  was not af-
 fected with the retention time held con-
 stant  (Figure 4).
  Though the laser-generated UV radia-
 tion has a considerably greater intensity
 than the mercury-vapor UV lamps, the
 detention time for the laser pulse is on
the order of 10 nano-seconds.  Thus
equivalent dose ranges can be obtained
from both sources. Data from this study
suggest that the commerical UV units
are much more effective than the ex-
cimer laser unit in inactivation of Giar-
dia cysts.
  Comparison of UV inactivation curves
for Y.  enterocolitica, E. coli, and  G.
muris  cysts  graphically exhibits the
tremendous resistance cysts have to UV
inactivation. The fact that both Yersinia
and Giardia cysts  are more resistant to
UV than E. coli has important implica-
tions where the total coliform proce-
dure is used to monitor disinfection effi-
ciency and indicate microbiological
water quality. Outbreaks of giardiasis in
water supply systems that reported sat-
isfactory total coliform concentrations
are indicative  of the problems as-
sociated with using coliforms as indica-
tor organisms  for adequate UV
disinfection.
  A study was conducted on the effects
of storage time on G. muris cysts at var-
ious temperatures. The  1°C,  5°C, 10°C,
and 20°C experiments showed differ-
ences  in die-off rates. No excystable
cysts were observed at  1"C,  5°C, 10°C,
and 20°C after storage periods of 120,
95, 63, and 26 days, respectively.
  The settling characteristics were mea-
sured  for G. muris cysts in distilled
water under quiescent conditions. They
                                        demonstrated, for example, that after
                                        2 days, approximately 50 percent of the
                                        cysts were removed from the water
                                        column.
                                        Conclusions
                                         1. The excystation procedure for Giar-
                                           dia cyst viability was unreliable for
                                           G. lamblia cysts and could not be
                                           used to provide significant data.
                                         2. To determine cyst viability, G.
                                           muris cysts were used as a surro-
                                           gate for G. lamblia because of their
                                           relatively  higher percentage of ex-
                                           cystability and more consistent re-
                                           producibility under laboratory con-
                                           ditions.
                                         3. Unlike chlorine and ozone, UV radi-
                                           ation has  no problems with mixing
                                           <(mass transfer) in  the contactor; it
                                           also produces no residual. How-
                                           ever, like  chlorine  and ozone con-
                                           tactors, flow dispersion has a signif-
                                           icant impact on UV's biocidal effect.
                                         4. As the UV reactors approached
                                           plug flow, greater degrees of disin-
                                           fection were obtained.
                                         5. Direct measurement of the actual
                                           UV dosage in the two commercially
                                           available  UV contactors  was not
                                           possible.  Instead, it was necessary
                                           to rely on  actinometry and inactiva-
I
  too

   90


   80


   70


 5 60

   50


   40


   30


   20


   10


    0
Pen Ray UV Bench-Scale Study
1-Liter, 4-Inch Diameter Vessel
Giardia muris Cyst Concentration. 350/ml
in Distilled Water (Temp. 22.7°C-24.5°C)


O--O  1st Run 10/2/83)
A---A  2nd Run (9/27/83)
O-O  3rd Run (10/4/83)
      Average Survival Rate
                                    The intensity of the Pen Ray UV Unit used
                                    in this experiment was 0.0914 mW/cm"
                                                                 35
     0        5       10       15      20       25

                                 Exposure Time, min

     0      27.4     54.8      82.3      109.7    137.1     164.5    191.9

                              UV Dosage, mW-sec/cm*

Figure 1.    Giardia muris cyst survival versus UV exposure time with a Pen Ray UV lamp.

                                       3

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                                           Flow-Through
                                          Disinfection Unit
                                                             A  Giardia lamblia Study (Rice and Hoi'f. 19811

                                                             A  Giardia muris Study of Pure Water Systems
                                                                 1-30 Disinfection Unit using Cedar River
                                                                 Water or Seattle City Water

                                                             •  Giardia lamblia Study of Pure Water Systems
                                                                 1-30 Disinfection Unit using Recirculation
                                                                 of Distilled Water

                                                             •  Giardia muris Study of Batch UV Pen Ray Unit
                                                          	Reduction in unit efficiency due to
                                                                short-circuiting at low flowrates when
                                                                theoretical detention time exceeded
                                                                50 seconds in the flow-through disinfection
                                                                unit.



                                                                            f
                                                                                                 T
                              t
                                                           I
                                                               I
                                                                                                               j	I
Figure 2.
                   J     °    '   10-            J     °   '   10*

                                              UV Dosage, mW-sec/cm*

           Survival of Giardia sp. cysts versus UV dosage.
                                                                                            104
                                               10s
   100
    80
    60
                                                  Color Measured as Absorbance
                                                          @ 254 nm (Nominal)
 CO
    40
    20
                                                            0.100cm'1

                                                            0.050 cm"1

                                                            0.0/0 cm'1
                                                  Pure Water Systems 1-30 UV unit
                                                  Cedar River Water Spiked with
                                                 Cedar River Color Concentrate
                                                                t (0.1161
                                                                . (0.060)
                                                                1(0.007)  i
                                                      I
                         10        15       20       25

                            Theoretical Detention Time, sec
                                                               30
35
Figure 3.
            Effect of Cedar River color on G iardia muris cyst survival under UV light at various
            detention times for Pure Water Systems unit.
   tion of B. subtil is spores to indicate
   the dosage.
6. The low destruction rate for Giardia
   cysts reported by previous investi-
   gators was primarily due to low UV
   exposure dose relative to the actual
   dose required.
7. Giardia cyst inactivation is a func-
   tion  of UV  energy absorption and
   thus depends on the amount of UV
   light that reaches the cyst and the
   time of exposure. Where  commer-
   cial UV unit design permits short-
   circuiting, the time for 100 percent
   inactivation can be  expected to be
   protracted.
8. The  commercial UV disinfection
   units tested can achieve  disinfec-
   tion of Giardia sp. The design of the
   units is important in the detention
   time required  for exposure to UV
   light. For the Pure Water Systems

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  100
   80
g? 60
I 4°
   20
                                    Pure Water Systems, 1-30
                                    Cedar River Water Spiked With
                                    Turbidity from the White River
                                    Plus Natural Turbidity
                                    Theoretical Detention Time

                                      • 10 sec
                                      A 75 sec
                                      • 30 sec
                                 456

                                   Turbidity, NTU
                                                              10
Figure 4.
Effect of turbidity from White River on UV disinfection of G. muris cysts at various
theoretical detention times for the Pure Water Systems unit (with trapped gasi.
    unit, 1 percent survival was attained
    at detention times longer than  60
    sec. In contrast,  detention times
    longer than about 22 sec were  re-
    quired to reach survival  levels of
    less than 1 percent in the Ultraviolet
    Technology, Inc., unit.
 9.  Short-circuiting and collecting of air
    bubbles in commercial UV disinfec-
    tion units can seriously impair the
    disinfection capability of the unit.
10.  Commercial UV disinfection units
    could be modified to make more ef-
    ficient use of the generated UV light
    and hence increase the feasibility of
    UV disinfection.
11.  The information presented here in-
    dicates that the coherent UV light of
    the  excimer laser is  no more effi-
    cient  in  removing Giardia cyst  vi-
    ability than is the UV light from
    mercury-vapor tubes in terms of the
    energy output.
12.  Laser  equipment  available during
    the experimental period was unreli-
    able and too difficult to operate to
    be considered for use in field  or
    commercial disinfection systems.
13.  For  all experimental conditions,
    color with an absorbance at 254 nm
    was found to increase cyst survival.
    For  example, color caused a de-
    crease in UV disinfection  effective-
    ness.
14.  The presence of relatively small
    inorganic or organic particulates
    (5-fim diameter or less) had no dis-
    cernible effect on the UV disinfec-
    tion of cysts.
                            15. Turbidity in the form of larger sus-
                                pended particulates (>5 nm) may
                                provide shielding and protection to
                                the organisms.
                            16. Virulent Yersinia were less resistant
                                to UV inactivation than  Giardia.
                                Hence if Giardia are removed by
                                UV, Yersinia can  be expected to
                                have been destroyed as well.
                            17. Virulent Yersinia that contained a
                                plasmid demonstrated significantly
                                greater resistance to inactivation by
                                UV than its nonplasmid  counter-
                                part.
                            18. UV killed E. co//very effectively.
                            19. The fact that both Yersinia and Giar-
                                dia cysts were more resistant to UV
                                than E. coli has important implica-
                                tions where the total coliform test js
                                used to monitor  microbiological
                                water quality.
                            20. Size and morphological characteris-
                                tics of organisms and particles  ap-
                                peared to be very important factors
                                in shielding them  from UV radia-
                                tion.
                            21. Storage time and  temperature  af-
                                fect cyst viability. The decrease in
                                viability approximately  doubles
                                with each 10°C increase in tempera-
                                ture above freezing. At  freezing
                                temperatures, however, cyst viabil-
                                ity  is drastically shortened from
                                months and days to hours.
                            22. Zeta potentials for  6. lamblia cysts
                                were time dependent, indicating a
                                change in cyst  characteristics with
                                storage.
23. The physical  stress produced by
    pressure and alum addition  ap-
    peared to damage or even destroy
    cysts.

Recommendations
1.  The effect of turbidity on disinfection
   of Giardia sp. needs more study. The
   particle size and form and its interfer-
   ence with UV disinfection particu-
   larly need to be investigated.
2.  A more practical method of measur-
   ing  and recording the actual deliv-
   ered UV dose in the contactor is des-
   perately needed.
3.  Further work is needed to improve
   the accuracy and precision of  the
   G. lamblia excystation procedure.
4.  Further studies should  be done to
   determine the  effects  of storage,
   temperature,  and sedimentation on
   Giardia sp. in the water environment.
   These factors may significantly influ-
   ence the operational mode for treat-
   ment of surface water supplies.
5.  Pressure  and coagulant addition
   may also have drastic influences on
   the survival of Giardia cysts and thus
   need to be investigated.
6.  The design of UV contactors  must
   eliminate  or minimize short circuit-
   ing  and air entrainment,  and opti-
   mize reflected radiation to improve
   biocidal effect.
  The full report was submitted in fulfill-
ment of Cooperative Agreement No.
809321  by the University of Washing-
ton, Seattle, WA, under the sponsorship
of the U.S.  Environmental Protection
Agency.
                                                                             
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      Dale A. Carlson, Robert W. Seabloom, Foppe B. DeWalle, Theodore F. Wetzler,
        JogeirEngeset, Richard Butler, Somboon Wangsuphachart, and Sinclair Wang
        are with University of Washington, Seattle, WA 98195.
      Donald J. Reasoner is the EPA Project Officer (see below).
      The complete report, entitled "Ultraviolet Disinfection of Water for Small Water
        Supplies, "(Order No. PB 85-239 960/AS; Cost: $ 14.50, subject to change) will
        be available only from:
             National Technical Information Service
             5285 Port Royal Road
             Springfield, VA 22161
             Telephone: 703-487-4650
      The EPA Project Officer can be contacted at:
             Water Engineering Research Laboratory
             U.S. Environmental Protection Agency
             Cincinnati,  OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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