United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-114 Sept. 1984 ''i
Project Summary
Filtration of Giardia Cysts and
Other Substances
Volume 1: Diatomaceous Earth
Filtration
Kelly P. Lange, William D. Bellamy, and David W. Hendricks
How effective is filtering drinking
water through diatomaceous earth to
remove Giardia lamblia cysts, total
coliform bacteria, standard plate count
bacteria, turbidity, and particles? We
evaluated the process for a range of
operating conditions and simulated
ambient conditions. Hydraulic loading
rates imposed were 2.44, 4.88, and
9.76 m/hr (1,2. and 4gpm/ft2). Seven
grades of diatomaceous earth were
used. Temperatures were from 5° to
19°C; concentrations of Giardia cysts
ranged from 50 to 5000 cysts/L; and
bacteria densities were varied from 100
to 10,000/100 mL.
The results of this study showed that
diatomaceous earth filtration is an
effective process for water treatment.
Giardia cyst removals were greater than
99.9 percent for all grades of diatoma-
ceous earth tested, for hydraulic loading
rates of 2.44 to 9.76 m/hr, and for all
temperatures tested. Percent reduction
in total coliform bacteria, standard
plate count bacteria, and turbidity are
influenced strongly by the grade of dia-
tomaceous earth used. The coarsest
grades of diatomaceous earth
recommended for water treatment
(e.g., C-545®)* will remove greater
than 99.9 percent of Giardia cysts, 95
percent of cyst-sized particles, 20 to 35
percent of coliform bacteria, 40 to 70
percent of heterotrophic bacteria, and
12 to 16 percent of the turbidity from
Horsetooth Reservoir water. The use of
•Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
the finest grade of diatomaceous earth
(i.e., Filter-Cel®), or alum coating on the
coarse grades, will increase the
effectiveness of the process, resulting
in 99.9 percent removals of bacteria
and 98 percent removals of turbidity.
This Project Summary was developed
by EPA's Municipal Environmental
Research 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
This study was conducted at Colorado
State University under a cooperative
agreement with the U.S. Environmental
Protection Agency (EPA) to determine the
effectiveness of diatomaceous earth
filtration for removal of Giardia cysts. At
the same time, removals of turbidity, total
coliform bacteria, standard plate count
bacteria, and particles were determined.
Operating conditions examined included
the grade of diatomaceous earth,
hydraulic loading rates, influent
concentrations of bacteria and Giardia
cysts, head loss, run time, temperature,
and the use of alum-coated
diatomaceous earth.
Giardia lamblia is a protozoan
prevalent in the clear, cool waters
characteristic of the Rocky Mountain
region. This organism causes giardiasis,
a harmful but nonfatal intestinal disease.
Many communities use water from these
Rocky Mountain streams, which are
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considered pristine pure because they
look aesthetically pleasing and will meet
the 1-NTU turbidity water quality
standard. How to treat these waters has
become an important concern over the
last few years as outbreaks of giardiasis
have occurred. Economical and effective
filtration systems are needed to remove
Giardia cysts. Designs appropriate for
small water systems are particularly
needed.
Diatomaceous earth filtration was
introduced in 1942 as a technology for
water treatment. The process was
adopted by the U.S. Army for field use in
1944 after being shown effective for
removal of Endamoeba histolytica
cysts.The basic principles of the process
were outlined in the 1940's and 1950's,
and further studies were made in the
1960's.
The diatomaceous earth filtration pro-
cess consists of three basic operations:
(1) precoating, (2) filtering, and (3) clean-
ing. In precoating, an initial filter cake
consisting of a 3- to 5-mm layer of
powder-sized diatomaceous earth filter
medium is applied to a support
membrane called a septum. The cake is
applied by circulating flow from the
precoat tank through the filter, causing
the slurried diatomaceous earth to be
deposited on the filter septum. In
filtering.the second step of the process,
raw water combined with bodyfeed
passes through the filter cake. The
bodyfeed consists of a filter medium
slurry metered into the raw water stream
during filtration. The continuous addition
of bodyfeed maintains the filter cake
permeability. In the third operation,
cleaning, the filter cake is removed from
the septum and discarded.
Operating parameters for diatoma-
ceous earth filtration include the grade of
diatomaceous earth (a commercial
designation of particle size), hydraulic
loading rate, precoat thickness, bodyfeed
concentration, terminal headloss, and
run time. Chemical coating of the
diatomaceous earth may be used under
some circumstances to improve removal
effectiveness.
The protozoan Giardia lamblia is of
interest because itcausesgiardiasis. This
organism has been identified as a
pathogen only recently. Giardiasis is
considered a serious problem in
mountainous and forested regions of the
United States where the organism is
endemic; the Giardia cysts shed by dogs,
humans, and animals, such as the
beaver, are believed to be of the Giardia
lamblia species.
The Giardia lamblia trophozoite (Figure
1 a) can reside in the intestine of a variety
of warm-blooded animals. The cyst
(Figure 1b) is the form shed and
transmitted. An infected person may
shed up to 900 million cysts per day. The
cyst form of the organism is hardy and
may remain viable for a long period (2
months, for example), particularly in cold
water. Infection is caused by ingestion;
an infective dose may be from 1 to 10
cysts and the incubation period is 1 to 2
weeks. A surface water supply source is a
vehicle for cyst transmission.
Materials and Methods
Design of Tests
The objective of the experimental pro-
gram was to evaluate the removal
effectiveness of diatomaceous earth
filtration for the dependent variables
(Giardia cysts, total coliform bacteria,
standard plate count bacteria, turbidity,
particle counts, and headloss) as a
function of the independent variables
(grade of diatomaceous earth, run time,
headloss, hydraulic loading rate, temper-
ature, influent coliform concentration,
and alum coating). This was achieved by
changing a given independent variable
over a range of magnitudes and observing
the effect on the filtration performance
(i.e., the dependent variables).
Tests were terminated either at the
predetermined head loss across the
septum of 40 psi, or after a given period of
operating time. The precoat application
was established at 1 kg/m2(0.2lb/ft2)for
all tests. The bodyfeed concentration was
established by using successive
concentrations until a linear headloss
versus time relationship was found.
5-15 fjrn
9-21
Flagella
The pilot plant was used mostly in the m
laboratory, but final confirming tests ~
were conducted in the field. The filter, the
main element of the system (Figure 2),
consisted of a 1 -ft2 septum enclosed in a
pressure housing. The septum used in
this work was stainless steel wire mesh
of 110 x 24 wires per in.2. The operations
were controlled by the ancillary pumps,
valves, and gauges.
Experimental Procedures
Giardia testing began with the process-
ing of Giardia cysts from dog fecal
samples. The processing consisted of
adding the infected feces to distilled
water, straining the feces and then
making a count of cysts in the fecal
concentrate.
A known concentration of the Giardia
concentrate was then added to a 1400-L
filter feed tank. This tank was a modified
milk cooler that could be maintained at 2
to 15 *1°C. The filter feedtank wasfilled
with Horsetooth Reservoir water and
cooled before the addition of the cysts.
Primary settled sewage was added also to
increase the concentration of total
coliform bacteria.
Preparation for a test run began with
the precoat step. After precoating, 10 ^
mg/L chlorine was added for dismfec- ^
tion, and the recycle of precoat water was
continued for 10 min The chlorine was
purged by operating in the filtering mode
for 30 min Sampling was started after
the 30-min washout period.
Samples were obtained from the filter
feed tank and from the effluent side of the
filter for measurements of turbidity,
particle counts, total coliform bacteria,
standard plate count bacteria, and
Nuclei
Claw-like
Median Bodies
8-12
Figure 1 .
Sketches of aj trophozoite and b) cyst stages of Giardia lambda (Jakubowski and II
Hoff, 1979). ^
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Giardia cysts. Grab samples were
collected for all parameters except
Giardia cysts. Other measurements
included elapsed time from beginning of
run, headloss, hydraulic loading rate, and
water temperature.
The Giardia cyst sampling technique
used a 142-mm-diameter polycarbonate
membrane filter with a 5- (im pore size to
remove and concentrate the cysts from
the sampled water. After the sample was
concentrated, the membrane filter was
washed and the wash water was
analyzed for cysts by microscopic
counting. The influent water in the fitter
feed tank and the diatomaceous earth
effluent were both sampled for Giardia
cysts in this manner. The influent sample
volume ranged between 2 and 10 L, and
the effluent sample volume ranged
between 86 and 174/L
Field tests to verify laboratory findings
were conducted in April and May 1983.
The April test used raw water from the
Cache La Poudre River, and the May tests
used water from Straight Creek and
Laskey Creek at the Dillon, Colorado
water treatment plant.
Leak Testing
During the initial phases of experimen-
tation, the need to determine whether a
leak was present in the filter septum or its
manifold became apparent. Thus a
technique was developed to test for leaks.
First the filter was precoated with 2
kg/m2 of the finest grade of diatoma-
ceous earth, Filter Cel. This grade was
determined to be capable of removing
100 percent of the applied coliform bac-
teria. Then the filter was operated at 1
gpm/ft2 for 1 hr with a high influent
coliform concentration. If any coliforms
were detected in the effluent, the
equipment was assumed to have a
mechanical problem resulting in a leak,
and the problem was corrected. This
technique was used as a quality control
measure throughout all testing.
Results
The diatomaceous earth filtration pro-
cess was found to be effective for remov-
ing Giardia cysts under virtually all
operating conditions tested No cysts
were detected in the filter effluent when
normal water treatment practices were
simulated. Note, however, that removals
of bacteria, turbidity, and particles in the
6.35-A«m to 12.67-/ym size range were
functionally dependent on: (1) grade of
diatomaceous earth, (2) use of chemicals,
(3) hydraulic loading rate, and (4) influent
concentrations.
Overflow
Cup
Effluent
Overall Process Effectiveness
Giardia cyst removals were greater
than 99.9 percent, regardless of grade of
diatomaceous earth, filtration rate, tem-
perature, duration of test, or influent
concentration of Giardia cysts (when
cysts are fewer than 10,000/L). The
single breakthrough occurred at a high
influent concentration of 33,600cysts/L.
Figure 3 illustrates the uniformly high
removals of Giardia cysts. Testing was
done only for the water treatment grades,
since removals would have been at least
as much for the finer grades.
The grade of diatomaceous earth was
not a factor in removal of Giardia cysts,
even with grades C-545 and C-535.
These grades create a filter cake with
reported median pore sizes of 17 and 13
fjm, respectively, which are larger than
Giardia cysts. However, many pores were
apparently smaller than the cysts and
blocked their passage.
Removal of coliform bacteria, standard
plate count bacteria and turbidity
approached 100 percent for the smallest
grades of diatomaceous earth and fell
below 40 percent for the coarsest grades
(Figure 3). Removals of total coliforms
and standard plate count bacteria would
follow this trend regardless of the water
source. Turbidity removal, however,
Recycle
Manometer
Spray Jet
Nozzles
Septum ~
Drain
Filter
Flowmeter
, Jet
Flow
1 w
Filler
Unit
Sample
Tap
Membrane
Sample Filter
Bodyfeed
Flowmeter
• Bodyfeed
P } Pump
Pressure
Relief
Valve
Dampener
Figure 2. Layout of diatomaceous earth filtration pilot plant.
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would depend on the size of the particles
making up the turbidity; improved
removal would result if the turbidity
consisted of larger particles.
Effects of Operating Conditions
on Removals
Operating conditionsexammed include
grade of diatomaceous earth, hydraulic
loading rate, Giardia cyst concentration,
bacteria concentration, temperature,
duration of filtration run, and alum
coating of the diatomaceous earth. The
influence of each condition on removals
of turbidity, bacteria, Giardia cysts, and
particles is reported in the following
paragraphs.
Grade of Diatomaceous Earth
As mentioned earlier, removals of
Giardia cysts are greater than 99.9
percent for all earth tested, but removals
of turbidity, standard plate count bacteria,
and total cohform bacteria are strongly
influenced by grade Removals of
particles in the 6.35- to 12.67-//m size
range were uniformly high (87 to 94
percent) for the water treatment grades of
diatomaceous earth, thus indicating no
correlation of particle removal to grade.
Hydraulic Loading Rate
Some scatter occurs in the data on the
effects of hydraulic loading on removals
of particles, standard plate count
bacteria, coliform bacteria, and turbidity;
but the trends are toward declining
removals with increasing hydraulic
loading rate. Percent removals of total
coliform bacteria were affected the most,
standard plate count bacteria declined
nominally, and particles and turbidity
were affected only moderately. The fine
clays constituting most of the raw water
turbidity passed readily through the C-
503 and C-545 diatomaceous earth
grades at all hydraulic loading rates.
Hydraulic loading rate had no detectable
influence on removal of Giardia cysts,
since all but one test resulted in complete
removal of the influent cysts. Because
the cysts are larger than some of the
pores in the filter cake (which vary
statistically), they will be blocked by some
pore as they are convected by the flow
within the cake.
Giardia Cyst Concentrations
No discernible relationship existed
between the Giardia cyst influent con-
centration and cyst removal. Influent
Giardia cyst concentrations ranged from
500 to 10,000 cysts/L, with one excep-
O
I
6
•Q
«J
to
10
CO
13
10
•6
-5
700
90
80
70
60
50
40
30
20
10
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grades. This phenomenon is reasonable,
since the finer grades can completely
strain coliform bacteria.
Turbidity did not vary enough in the
waters tested to determine whether a
relationship existed between influent
levels of bacteria and their removal. For
the laboratory tests with Horsetooth
Reservoir water, the influent turbidity
levels ranged only between 4.5 and 5.4
NTU.
Most turbidity in Horsetooth water was
caused by particles smaller than 1 //m.
Consequently, a 1-NTU turbidity standard
could be attained only with the finest
grade of diatomaceous earth or by using
alum-coated diatomaceous earth. Remov-
als of coliform bacteria were therefore
higher, since they were larger than much
of the turbidity. The small turbidity parti-
cles found in Horsetooth Reservoir are
not necessarily characteristic of all
waters, since many sources have been
treated to meet a 1-NTU standard with
water treatment grades of diatomaceous
earth and without chemicals.
Temperature
Water temperature did not appear to
affect any of the parameters measured.
Because the removal process in
diatomaceous earth filtration is physical,
slightly poorer removals might be
expected at lower temperatures because
shear forces are higher. This possible
effect was not noticeable, however, since
it was masked by the significant changes
in removal caused by variations in
influent concentration and flow rate.
Alum Coating
Alum-coated diatomaceous earth
removed significantly more total coliform
bacteria, standard plate count bacteria,
and turbidity than did the uncoated
diatomaceous earth. Coarse grades of
diatomaceous earth were used (e.g., C-
545 and C-503), and both the precoat and
bodyfeed were coated while in slurry
form. Removals of total coliform bacteria
ranged from 96 to 99.9 percent compared
with 30 to 70 percent without alum
coating. Removals of standard plate
count bacteria ranged from 79 to 99.5
percent compared with 38 to 56 percent
without alum coating. Turbidity removals
ranged from 66 to 99 percent compared
with 11 to 17 percent without alum
coating. These results demonstrate a
marked improvement in treatment with
alum coating and illustrate how
diatomaceous earth filtration can be
applied in otherwise marginal situations.
Note, however, that not all water
sources can be treated to a 1-NTU
standard with the normal water
treatment grades of diatomaceous earth.
To obtain a 1 -NTU effluent for these spe-
cial cases, the advantages of alum
coating must be weighed against using a
finer grade of diatomaceous earth. Both
techniques will reach the desired goal,
but only pilot plant studies and economic
considerations will determine which
approach should be taken.
Field Testing
Field tests were conducted to confirm
the laboratory results. Water was
obtained from the Cache La Poudre River
and from the raw water intake at the
Dillon water treatment plant. Turbidity
conditions were about 4 NTU for tests
conducted April 17,1983, at the Cache La
Poudre River, and about 0.6 NTU for the
May 1983 tests at Dillon. Despite the use
of these different water sources, no
Giardia cysts were detected in any
filtered water samples. Removals of
turbidity, total coliform bacteria, and total
plate count bacteria were all consistent
with laboratory results.
Conclusions
1. Diatomaceous earth filtration is
virtually 100 percent effective in
Giardia cyst removal for all grades of
diatomaceous earth over a wide
range of conditions.
2. Grade of diatomaceous earth is the
most important factor in the removal
of bacteria and turbidity. Removals
effected by coarse and fine grades
were, respectively, 17 and 98
percent for turbidity, 28 and 99.9
percent for coliform bacteria, and 38
and 99.8 percent for standard plate
count bacteria.
3. Increasing the hydraulic loading
rate causes a decrease in removals
of bacteria and turbidity for the
water treatment grades of
diatomaceous earth. The effect was
strongest for coliform bacteria and
weakest for turbidity. Hydraulic
loading rate showed no effect on the
removal of Giardia cysts.
4. Water temperature did not influ-
ence the effectiveness of diatoma-
ceous earth filtration, as demon-
strated by testing over the range of
3.5° to 15°C. The results are not,
however, conclusive.
5. Bacteria removal decreased with
increased influent concentrations of
bacteria, especially for the coarser
grades of diatomaceous earth. A
three-log increase in influent coli-
forms reduced removals from 77 to
39 percent for C-545; but for C-512,
a two-log increase in conforms
reduced removals only from 96 to 92
percent.
6. Bacteria removals decreased slight-
ly with increasing filtration time--
fro m 87 to 79 percent in 5.5 hr for C-
503 and from >99.98 to 99.92
percent for Standard Super-Cel.
7. Alum-coated diatomaceous earth
filtration removed significantly
more turbidity and bacteria than
diatomaceous earth filtration with
no alum. The use of alum coating
increased removals from 17 to 99
percent for turbidity, from 30 to 96
percent for total coliform bacteria,
and from 56 to 99.5 percent for
standard plate count bacteria.
8. Increased removals of turbidity and
bacteria can be accomplished either
by chemically coating the diatoma-
ceous earth or by using a smaller
grade.
9. Field testing with two different raw
waters yielded the same results as
laboratory tests.
10. Pilot-plant testing should be done
before implementing any full-scale
application of diatomaceous earth
filtration. Applicability, design
criteria, and operating conditions
cannot be determined without pilot
tests.
11. Periodically, a diatomaceous earth
filtration system should be checked
for leaks by applying Filter-Cel and
then filtering a coliform-contamin-
ated water. In production of potable
water, this should be done only as a
part of a routine performance
evaluation program in which careful
controls are set up to ensure that a
cross connection is not possible.
The full report was submitted in
fulfillment of Cooperative Agreement No.
CR808650-02 by Colorado State
University under the sponsorship of the
U.S. Environmental Protection Agency.
*USGPO: 1984-759-102-10668
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Kelly P. Lange. William D. Bellamy, and Davis W. Hendricks are with Colorado
State University, Fort Collins, CO 80523.
Gary S. Logsdon is the EPA Project Officer (see below).
The complete report, entitled "Filtration of Giardia Cysts and Other Substances:
Volume 1: Diatomaceous Earth Filtration," (Order No. PB 84-212 703; Cost:
$19.00, 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:
Municipal Environmental 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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