United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/027 Sept. 1985
Project Summary
r/l
Filtration of Giardia
Cysts and Other Substances:
Volume 3. Rapid-Rate Filtration
Mohammed AI-Ani, John M. McElroy,
Charles P. Hibler, and David W. Hendricks
Rapid-rate filtration was evaluated
for a range of operating conditions
using waters having turbidity levels of
less than 1 NTU and temperatures rang-
ing from 0° to 17°C. The object was to
determine its effectiveness as a process
in drinking water treatment for removal
of Giardia lamblia cysts, total coliform
bacteria, standard plate count bacteria,
turbidity, and particles from low-
turbidity, low-temperature water.
Results showed that when the filter is
operated as a strainer (i.e., when no
chemical coagulation is used); remo-
vals ranged from 0 to 50 percent.
Improvement was not significant when
ineffective coagulants or improper dos-
ages were used. Effective coagulation
(that adequate to reduce turbidity from
about 0.5 NTU to about 0.1 NTU) was
capable of removing 95 to 99.9 percent
of Giardia cysts and 95 to 99.9 percent
of total coliform bacteria. Two coagu-
lant aids were found in this research
that provided effective coagulation.
The filtration efficiency was unaf-
fected by mode of filtration. The in-line
mode was as efficient as the direct fil-
tration mode. Testing at 3° and at 17°C
showed no discernible differences in
percent removals. Increasing the
hydraulic loading rate from 8 to 41
cm/mm (2 to 10 gpm/ft2) showed no
discernible effect until the latter rate
was reached. The work showed that
efficient filtration of Giardia cysts and
other substances present in low-
turbidity waters requires careful selec-
tion of coagulants and the use of proper
dosages. Turbidity reduction can be
used as a measure of efficiency. Rou-
tine use of pilot plants, operated side-
by-side with full-scale plants, is
advocated for this purpose. The pilot
plant can be spiked with bacteria as
another means to evaluate the effec-
tiveness of coagulation.
This report is the third (last) describ-
ing the research conducted under EPA-
CSU Cooperative Agreement No.
CR808650-02. The first was entitled
"Filtration of Giardia Cysts and Other
Substances. Volume 1: Diatomaceous
Earth Filtration." EPA/600/S2-
84/114, September 1984, and the
second was entitled "Filtration of Giar-
dia Cysts and Other Substances.
Volume 2: Slow Sand Filtration,"
EPA/600/S2-85/026, April 1985.
This Project Summary was devel-
oped by EPA's Water Engineering
Research Laboratory, Cincinnati. OH.
to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Background
Giardiasis is an intestinal disease
caused by ingestion of cysts of the proto-
zoan Giardia lamblia. In recent years,
reports of waterborne outbreaks of giar-
diasis in the United States have become
increasingly frequent. Some 53 water-
borne outbreaks and 20,039 cases were
reported during the period 1965 through
1981. Most outbreaks have been
-------
reported in small mountain communities
in the western and northeastern United
States, but during the period 1983-84,
cases were reported in Pennsylvania as
well.
In the western United States, the cyst
is known to occur in ambient waters with
turbidity levels of less than 1 NTU.
Though there is no reason to believe that
cysts are not found pervasively in all
kinds of waters, it is important to point
out that they do occur in low-turbidity
waters and that many outbreaks have
been associated with these clear waters.
The conventional wisdom is that such
waters are likely to be benign, since even
without treatment, they may nearly con-
form to well-established standards—the
1-NTU turbidity standard and the coli-
form standard, for example. Yet public
systems using low-turbidity raw waters
may meet all of these standards and still
the source of a giardiasis outbreak.
A major process problem for treatment
plants using low-turbidity waters is that it
is common practice not to use chemical
pretreatment, though polymers are
sometimes used as filter aids. These
waters may already meet the 1 NTU tur-
bidity standard, and coliform counts are
often very low, e.g. 10 organisms/100
ml. Thus, they are not as easily used mea-
sures of process efficiency as they are in
other surface waters, such as those
found at lower elevations. Also, the low
turbidity waters are more difficult to
treat. Without chemical treatment, how-
ever, the rapid-rate filtration process is
simply a method of straining and its use
deviates from one of the basic tenets of
rapid-rate filtration-that chemical pre-
treatment be integral to the process.
Without such chemical treatment, sub-
stances in the raw water such as Giardia
cysts and bacteria can and do pass
through the filter. Though such waters
have ocassionally been treated success-
fully, chemical pretreatment knowledge
is not adequate to effect rapid-rate filtra-
tion of low-turbidity, low-temperature
waters containing Giardia cysts.
Objectives
The purpose of the research was to
determine how to remove Giardia lamblia
cysts from water supplies by rapid rate
filtration when raw waters have turbidity
levels of less than 1 NTU. The main objec-
tives were (1) to determine a chemical
pretreatment for low-turbidity water that
results in efficient rapid-rate filtration.
and (2) to determine the respective roles
of process variables on removal efficien-
cies of Giardia cysts, turbidity, and bacte-
ria. Process variables included chemical
pretreatment (coagulant selection and
dosages), filtration mode (conventional,
direct, or in-line), media, hydraulic load-
ing rate, and temperature. A third objec-
tive was to determine whether a
surrogate indicator was feasible to
assess the treatment efficiencies for
removal of Giardia cysts.
Methods
Pilot Plants
The research was based on two physi-
cal models—laboratory-scale and field-
scale, rapid-rate filtration pilot plants.
The laboratory-scale pilot plant was a
dual-train, conventional, rapid-rate filtra-
tion plant built to be operated under pres-
sure. The raw water to be processed was
from the Cache La Poudre River when
water with less than 1 NTU turbidity
could be obtained. When this was not
possible, and artificial low-turbidity
water was prepared by treating water
from the Horsetooth Reservoir with dia-
tomaceous earth filtration to remove
turbidity-causing particles without
changing chemical quality. The raw
water was stored in a 1400-L,
temperature-controlled milk cooler and
then pumped by a positive displacement
pump (with dampenertocontrol pressure
surges) to three rapid-mix basins in ser-
ies.-Each basin was a 12.7-cm cube
(inside dimensions). The stirring paddles
had four rectangular blades 1.25 cm
wide, 1.25 cm high, and 2.54 cm from the
center of stirring shaft to outer edge of
blade. The maximum rotational speed of
the shaft was 600 rpm, yielding a calcu-
lated G value of 400 sec' at 20°C. The
rotational speed could be varied by
means of a rheostat control I ing the motor
speed. Chemicals were metered by posi-
tive displacement pumps capable of
metering flows as low as 0.2 ml/min.
Flows were measured volumetrically
using 50-ml graduated burettes, which
served also for chemical storage.
Four filter columns 183 cm long were
installed from a manifold that permitted
one to four filters to be operated in any
combination. Two of the filters were 5 cm
in diameter, and two were 10 cm. Copper
coils were installed in the top of the filters
for temperature control. Tailwater eleva-
tion was controlled by overflow cups,
which were maintained above the media.
Headloss across the media was mea-
sured by a mercury manometer. Air
scrubbing and backwash were provided.
The experiments used both a single sand
medium (76 cm deep) and dual media of
anthracite and sand (45 cm and 30 cm
deep, respectively).
The field-scale pilot plant was a 1.3-
L/sec (20-gpm) trailer-mounted package
water treatment plant. During periods of
low-turbidity water, this unit was located
adjacent to the Cache La Poudre River at
Fort Collins Water Treatment Plant No. 1.
Both the laboratory-scale and the field-
scale pilot plants could be operated in
three modes of filtration: conventional
(rapid mix, flocculation, sedimentation,
filtration), direct (rapid mix, flocculation,
filtration), and in-line (rapid mix, filtra-
tion). The in-line mode was used for the
research, except for the beginning
exploratory work to ascertain the effect of
the filtration mode.
Experimental Design
The purpose of the laboratory-scale
pilot plant was to ascertain the effect of
selected process variables on a group of
dependent variables. The purpose of the
field-scale pilot plant was to conduct con-
firming tests for several of these varia-
bles. The process variables examined
included the effects of temperature,
coagulant types and dosages, hydraulic
loading rate, and media on removals of
Giardia cysts, total coliform bacteria, and
turbidity, with some measurements of
removals of standard plate count bacteria
and particles. Field-scale tests were con-
ducted under low-turbidity low-
temperature river conditions to verify the
effects of no coagulation, nonoptimum
coagulation, and optimum coagulation
on removals of turbidity, total coliform
bacteria, and Giardia cysts.
Giardia Cyst Sampling and
Analysis
Giardia cysts in the filter effluents
were concentrated by polycarbonate
membrane filters with 5: m pore sizes.
The entire flow from the laboratory-scale,
rapid-rate filter column was passed
through a 142-mm-diameter membrane
filter. To sample the field-scale pilot
plant, a portion of the effluent was
passed through a 293-mm-diameter
membrane filter. The total volume of
water passed through the membrane fil-
ter was limited by the pressure increase
across the filter. Sampling was termi-
nated when the pressure became about 5
psi. Usually about 20 L was passed
through the 142-mm membrane filter,
but 140 L was passed in one test. When
the sampling was ended, the membrane
filter holder was removed from the filter
effluent line, and the membrane was
-------
removed and washed to remove cysts and
anything else that had collected on the
membrane. The sample was then sent to
a laboratory, where the cysts were
counted using a micropipette technique.
To determine removals of Giardia cysts
under a given set of filtration conditions,
the milk cooler (used as a reservoir for the
laboratory-scale pilot plant) was spiked
with several million cysts (determined to
be Giardia lamblia) obtained from the
feces of infected dogs. To spike the field-
scale pilot plant, a cyst concentrate was
metered into the influent pipe where it
was mixed as the result of the turbulent
flow through four elbows.
To determine the concentration of
cysts in the milk cooler, a sample stream
was pumped through the 5-yum, 142-mm
polycarbonate filter. For the field-scale
pilot plant, the influent cyst concentra-
tion was sampled by pumping a portion of
the flow (after the four mixing elbows)
through the 293-mm membrane filter.
Sampling and Analysis of
Turbidity, Bacteria, and Particles
Sampling for turbidity, bacteria, and
particles was done with grab samples.
For the laboratory-scale pilot plant, these
samples were taken from water in the
milk cooler, after spiking, and from the
filter effluent stream after 30 min, 60
min, and (for some tests) 2 hr of opera-
tion. Cuvettes were used for the turbidity
samples, and sterile 250-mL plastic bot-
tles were used for bacteria sampling. For
particle sampling, 500-mL bottles were
used. They were cleaned and rinsed with
distilled water passed through 0.2-fjm
filters. For the field-scale pilot plant, sam-
ples were taken after the mixing elbows
for the influent stream and from the dis-
charge line for the filtered water.
Results
Removals
Table 1 summarizes the removals of
turbidity, standard plate count bacteria,
total coliform bacteria, particles, and
Giardia cysts for low-turbidity water at
low temperatures (2° to 4°C). Results of
21 test runs are shown for three catego-
ries of chemical pretreatment: (1) none,
in which no chemicals were used, (2)
nonoptimum, in which a nonoptimum
chemical dose was used as determined
by turbidity removal, and (3) optimum, in
which an optimum chemical dose was
used as measured by turbidity removal.
Raw water turbidity levels were0.4to 0.7
NTU for water hauled from the Cache La
Poudre River for the pilot plant tests, and
0.2 to 0.6 NTU for the water obtained by
diatomaceous earth filtration of Horse-
tooth Reservoir water (referred to in this
report as artificial low turbidity water).
The effects of chemical pretreatment
can be seen in Table 1. For the eight tests
with no coagulant dosage, removals of all
parameters except particles were uni-
formly low. No explanation exists for the
higher percent removals of particles. For
the nonoptimum chemical dose, the per-
cent removals were generally higher but
not uniformly high. For the optimum
chemical dosage, percent removals of all
parameters were uniformly high, ranging
from about 80 to greater than 99.9. The
exception. Run 106, was for a polymer
used commonly as a filter aid for low-
turbidity waters. The result is added to
the table to illustrate that high removals
cannot be expected for some polymers.
For the optimum chemical dosage, fil-
tered water turbidity was generally about
0.05 NTU: the percent removals ranged
from 82 to 93.
The field-scale pilot plant runs (117
and 129) in Table 2 shows results
obtained for tests with no coagulant dos-
age in which Giardia cysts and coliform
bacteria were injected into low-turbidity,
low-temperature raw water. Without a
coagulant, coliform bacteria removals
were 20 and 15 percent, respectively.
The Giardia cyst removal of Run 117 was
only 30 percent. No Giardia removal data
are reported for Run 129 because the
cysts had questionable identities for
analysis. The effluent turbidity was
greater than the influent turbidity for
each of these runs without chemicals.
Runs 123 to 128 were classified as
nonoptimum. Results for removals of tur-
bidity, total coliform bacteria, and Giardia
cysts were not significantly different than
those for tests without coagulant dosage.
For example, in Runs 123 and 124, remo-
vals of Giardia cysts were 45 and 40 per-
cent, respectively; coliform removals
were 20 and 50 percent, and turbidity
removals were less than 1 percent. The
coagulant aid commonly used in the
Rocky Mountain Region was simply not
appropriate for the low-turbidity waters.
Run 138 was classified as optimum.
Removals in all three categories were
high (i.e., 95 percent for Giardia cysts, 98
percent for coliform bacteria, and 42 per-
cent for turbidity). Coagulant chemicals
used for Run 138 were 7.0 mg/L of alum
as AI2(SO4)314H20 and 2 mg/Lof Mag-
nifloc 572C®.* These coagulant
* Mention of trade names or commercial products
does not constitute endorsement or recommen-
dation for use.
dosages and chemicals were found to be
effective in bench-scale and laboratory-
scale testing. For this test, the raw water
turbidity was 0.7 NTU, the effluent tur-
bidity was 0.4 NTU, and the water
temperature was<1°C. Most important
was the selection of the polymer used as
a coagulant aid with alum.
The data in Tables 1 and 2 show that
with proper chemical pretreatment, rem-
ovals of turbidity, standard plate count
bacteria, total coliform bacteria, parti-
cles, and Giardia cysts were uniformly
high—generally greater than 80 percent
for turbidity and 98 percent for other
parameters. Run 138 in Table 2 for field-
scale testing showed a nominal deviation
from this general finding, having only 42
percent turbidity removal but 95 percent
removal of Giardia cysts and 98 percent
removal of total coliforms. For nonopti-
mum chemical dosages, results were
more variable, with both high and low
removals. With no chemical pretreat-
ment, removals were markedly lower for
all parameters except particles, which
ranges from 81 to 99 percent. Using an
effective polymer is important also, as
demonstrated by the results of Runs 127
and 128, which used some of the poly-
mers found to be inefficient in filtration.
These results show that with proper
chemical pretreatment, rapid-rate filtra-
tion will generally remove 95 to 99.9 per-
cent of Giardia cysts.
The data in Tables 1 and 2 show that
rapid-rate filtration will work only as a
simple strainer when no chemicals are
used and will pass appreciable percen-
tages of turbidity, bacteria, and Giardia
cysts. The critical importance of proper
chemical coagulation is demonstrated.
From these results, little doubt exists that
the rapid-rate filtration process can be
effective if the proper chemicals are
selected and if they are used at proper
dosages.
Effects of Process Variables
The process variables investigated
were chemical pretreatment (coagulant
selection, coagulant dosages, and mode
of filtration), comparison of single and
dual media, hydraulic loading rate, and
temperature. The effects of these varia-
bles on turbidity removal was the main
focus because it indicated removals of
both bacteria and Giardia cysts.
Coagulant Selection
Alum alone was not effective as a
chemical coagulant for low-turbidity
waters unless a high dosage was used
(e.g., 15to50mg/LasAI2(S04)314H20).
-------
Table 1. Effect of Chemical Pretreatment on Removal of Turbidity, Standard Plate Count Bacteria, Total Coliform Bacteria, Particles, and Giardia
Cysts from Water with Artificial Low-Turbidity, and Low-Temperature Cache La Poudre River Water. Subject to In-Line, Laboratory-
Scale Rapid-Rate Filtration*'^
Conditions
Filter Raw Water
Run
No..
46
47
49
48
119
120
121
122
69
82
114
50
51
52
53
70
81
104b
106
107b
118
V
Icm/minft
8.46
22.59
22.20
8.26
41.40
32.00
20.70
9.60
22.69
22.45
7.8
8.20
23.48
8.45
23.19
22.20
8.35
8.26
8.47
8.38
9.37
Media§
SandIL)
DuaKLI
Sand(L)
DuaKLi
DualfF)
Dual(F)
DuaKF)
DuaKF)
Dual(L)
Dual(L)
Dual(F)
SandIL)
DuaKU
DuallL)
SandIL)
DuallL)
DuallL)
DuaKF)
DuaKF)
DuaKF)
DuaKF)
Source"
HDE
HDE
HDE
HDE
CLP
CLP
CLP
CLP
HDE
HDE
CLP
HDE
HDE
HDE
HDE
HDE
HDE
CLP
CLP
CLP
CLP
Temp.
ret
3.0
3.0
2.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
4.0
3.0
4.0
4.0
3.0
3.0
3.5
3.5
3.0
3.0
Pretreatment
(Chemicals Used)
Dosage
Category^
None
None
None
None
None
None
None
None
Nonoptimum
Nonoptimum
Nonoptimum
Optimum
Optimum
Optimum
Optimum
Optimum
Optimum
Optimum
Optimum
Optimum
Optimum
Species
None
None
None
None
None
None
None
None
alum/573c
alum/572c
alum/572c
alum/572c
alum/572c
alum/572c
alum/572c
alum/573c
alum/572c
alum/572c
8102N
alum/572c
alum/572c
Dosage
99.9
83.0
>99.9
>99.9
99.5
99.9
79.8
>99.9
90.0
99.4
Particle
Count
86
99
99
94
90
86
82
82
-142.4
99.6
58.9
98.6
98.9
99.2
93.8
81.9
98.3
98.6
87.0
95.4
tt
Giardia
Cysts
7.6
96.3
>99.9
99.9
41.9
36.4
36.3
68.3
99.2
tt
95.3
97.8
99.1
99.7
99.5
99.4
tt
98.7
39.5
>99.9
97.6
"Artificial water was obtained by diatomaceous earth filtration of Horsetooth Reservoir water; filtered water turbidity ranged from 0.2 to 0.6 NTU.
f The term "in-line" filtration is the designation for treatment train comprising rapid mix and filtration (no flocculation or sedimentation).
$ The term "V" designates a hydraulic loading rate, which equals flow divided by area of filter.
§Sand /L) means the media was all sand and was obtained from Love/and Treatment Plant at Big Thompson Canyon. Bed depth was 76 cm. Dual (L) means the bed
comprised 30 cm sand from Loveland and 45 cm anthracite having the trade name Philterkal Special No. 1 (produced by Reading Anthracite Coal Company. Pottsville,
PA 17901). Dual (F) means that the bed contained 30 cm of sand obtained from Port Collins Treatment Plant No. 2 and 45 cm of Philterkal Special No. 1 (R) anthracite.
* * HDE is water obtained from Horsetooth Reservoir, filtered by diatomaceous earth to give low turbidity (0.2 to 0.6 N TU). CLP is low turbidity raw water obtained from the
Cache La Poudre River during the period September to April when raw water turbidity was generally 0.4 to 0.7 NTU.
ft "Optimum" and "none optimum" are designations of coagulant dosages producing turbidities of filtered water that are minimum and greater than minimum.
respectively.
tt No sample taken.
Furthermore, the polymers tested were
not effective when used alone. Thus
attention was focused on selection of a
polymer that could be an effective coagu-
lant aid when used with alum. To screen
polymers and determine dosages, turbid-
ity reduction was used as the measure of
effectiveness. Turbidity should be
reduced from about 0.5 NTU in raw water
to 0.1 or 0.05 NTU in filtered water. The
search for an effective coagulant aid was
wholly trial and error. The idea was to test
different polymers as coagulant aids and
then to stop when an effective one was
found. Nine polymers were tested using
the laboratory-scale pilot plant. Two of
these, Magnifloc 572C® and Magnifloc
573C®, were determined to be effective
as measured by turbidity removal. Some
recommended polymers found effective
elsewhere by others were not effective
for the low-turbidity raw waters. All
chemicals were added to mixing basins
except 8102®, which was injected into
the pipeline ahead of the filter. This
procedure simulated the practice of using
the polymer as a filter aid. The effect of no
chemical addition (i.e., using the filter as
a strainer) should be noted. Without the
use of coagulant chemicals, or with the
use of unsuitable coagulant chemicals,
removals of turbidity are erratic.
The data showed that a combination of
alum and 572C® or 573C® will remove
85 percent or more of the Giardia cysts.
Many of the data show removals greater
than 99.9 percent. Without chemicals,
removals are likely to be in the 0 to 50
percent range, which corroborates the
turbidity removal results for runs with no
chemicals.
Dosages of Coagulants
Data obtained showing filtered water
turbidity as a function of alum and 572C®
dosages showed that when alum is used
with Magnifloc 572C® as a coagulant aid,
filtered water turbidity levels can be
reduced to 0.05 NTU nominally (as com-
pared with nominal raw water turbidity of
about 0.5 NTU). The response surface
does not seem to be strongly sensitive to
either alum or polymer dosage, but it
does show that either alum alone or poly-
mer alone is not effective. The polymer
dosage used most often in the research
was 1 to 2 mg/L, with alum dosages of 3
to 7 mg/L as AI2(SO4)3 14 HjO. When
the dose of an effective type of polymer
exceeded 1 mg/L and the alum dose
ranged between 3 and 15 mg/L, Giardia
removals were generally high.
Mode of Filtration
Coagulation and flocculation of the
low-turbidity waters did not produce any
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Table 2. Turbidity, Giardia. and Coliform Results of Using Low-Turbidity Raw Water* for Field-Scale. Rapid-Rate Filtration Pilot Plant
Coagulants Used
Turbidity
Giardia Cysf+V
Run
Ho.
117
129
123
124
125
126
127
128
138
Coagulant
Dosage
Category
None
None
Nonoptimum
Nonoptimum
Nonoptimum
Nonoptimum
Nonoptimum
Nonoptimum
Optimum
Chemical
Species!
None
None
8102
8102
Alum
Alum
Alum/8102
Alum/8102
Alum/572-C
Chemical
Dose
0
0
0.1
0.4
0.4
5.0
3.0/0.2
3.0/0.4
7.0/2.0
Water
Temp.
2
1
1
1
1
1
1
1
<1
Influent" l
(NTU)
0.4
0.6
0.6
0.6
0.55
0.55
0.9
0.9
0.7
•ffluent*
ITU)
0.6
0.7
1.1
0.85
1.0
1.0
1.1
0.9
0.4
^ Percent Influent®
Removal cysts/L
<1 260
<1 Q"*
<1 325
<1 325
98
* Cache La Poudre River water having raw water turbidities less than 1 NTU.
+ Nalco 8102, Magnifloc S72-C.
J Alum doses are mg/L as AI2 (S04)3 14H, O.
" Influent turbidity before contaminant injection.
++ Effluent turbidity after 1 hr of filtration.
§§ Detected cyst concentrations, sampling influent stream after mixing by four elbows and before injection of coagulants. Membrane filters used were Nucleopore
polycarbonate 5-micrometer pore size, 293-mm diameter. Samples were analyzed by micropipette technique.
*** Procedures were the same as used for influent sampling and analysis.
+++Q indicates cysts were of questionable viability; ND indicates no data, missed dilution range.
visible floe unless high alum dosages
were used. Therefore conventional filtra-
tion using sedimentation was not used.
The experimental work began by using
direct filtration (rapid mix, flocculation,
and filtration). Shortly thereafter, the in-
line filtration mode, which included rapid
mix followed by filtration, was also tried.
Two comparisons of in-line and direct fil-
tration, with all conditions the same for
each, resulted in filtered water turbidity
levels of about 0.1 NTU for each. Based
on these data, all further test runs were
performed using the in-line mode of
filtration.
Media
Three test runs were conducted to
compare filtered water turbidity levels for
the same conditions with single medium
(76 cm sand) and dual media (30 cm sand
and 45 cm anthracite). The first compari-
son was for runs with no chemical pre-
treatment. With raw water turbidities of
0.5 NTU, filtered water turbidities were
0.4 NTU for both the single and dual
media. Headloss was 92 cm of water for
the single media and 54 cm of water for
the dual media after 50 min of operation.
Water temperatures were 2° to 4°C. The
second comparison was conducted using
alum and 573C® chemical pretreatment
at optimum dosages with respect to tur-
bidity removal. Effluent turbidities were
0.04 NTU for both, and again, headless
was higher for the single media. Based
on these results, the dual media was pre-
ferred because of lower headloss.
Hydraulic Loading Rate
Tests conducted to determine the
effect of hydraulic loading rate on remo-
vals of turbidity, standard plate count
bacteria, total coliform bacteria, and
Giardia cysts at optimum chemical dos-
ages showed little influence on removals
of total coliform bacteria. Even at 25
m/hr (10 gpm/ft2), the removal is 99 per-
cent. Similar influences are seen for re-
movals of standard plate count bacteria
and Giardia cysts. The influence is
stronger, however, for removals of tur-
bidity. Another series of tests was con-
ducted under nearly the same conditions,
except the sand in the dual media was
obtained from the Loveland, Colorado,
Water Treatment Plant. The trends were
virtually the same. These results indicate
that the hydraulic loading rate has little
influence on percent removals of Giardia
cysts and bacteria in the range of 4.9 to
19 m/hr (2 to 8 gpm/ft2). An influence
begins to become discernible, however,
at 25 m/hr (10 gpm/ft2). Pilot testing
should be conducted to ascertain the
influence of hydraulic loading rate for the
conditions at hand in a particular
situation.
Temperature
The removals of turbidity, standard
plate count bacteria, and total coliform
bacteria measured at operating tempera-
tures of 5° and 18°C, for four conditions
of chemical pretreatment showed either
no difference for the two temperatures or
conflicting trends. If there is an influence,
it does not seem to be great. The data
showed no conclusive trends.
Surrogate Indicators for Giardia
Cyst Removal
Sampling of raw or filtered water to
recover Giardia cysts requires passing a
large volume of water through a mem-
brane filter or through a fiberwound filter
with a pore size small enough to strain
the cysts. Whatever cysts were in the
sample will be retained by the filter if its
pores are smaller than the cysts. Once
the sample is obtained, measurement of
Giardia cyst concentration requires
skilled technique to process, identify, and
count the cysts. Routine measurement of
Giardia cysts is not likely to be incorpo-
rated into water treatment practice. Thus
a surrogate indicator for removals of
Giardia cysts is desirable. Several were
investigated, including turbidity, parti-
cles, standard plate count bacteria, and
total coliform bacteria. Histogram plots
were developed to relate removals of
Giardia cysts with removals of turbidity
and also removals of Giardia cysts with
removals of total coliform bacteria. Sim-
ilar histograms could have been deve-
loped using particles or standard plate
count bacteria, but for the sake of brevity,
this was not done. Also the use of particle
counting was not continued throughout
the project since considerable effort was
required. Considering the effort and qual-
ity of the relationships obtained, turbidity
and total coliform bacteria were the most
useful surrogate parameters.
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For example, one of the histograms
showed that if turbidity removal is high,
removal of Giardia cysts wilJ be high also.
Specifically, the plot showed 44 observa-
tions when turbidity removal was greater
than 70 percent for low turbidity raw
water. Of these 44 observations, 37
show removals of Giardia cysts exceed-
ing 99 percent. In other words, if turbidity
removal exceeds 70 percent and if fil-
tered water turbidity is lower than 0.10
NTU, the probability is 0.85 (37/44) that
removals of Giardia cysts would equal or
exceed 99 percent.
A similar histogram was constructed
using coliform bacteria as the surrogate.
The histogram showed that if high remo-
vals of total coliform bacteria occur by the
filtration process, then high removals of
Giardia cysts can also be expected.
Though the histogram indicated that
removals of total coliform bacteria would
be a good indicator for removals of Giar-
dia cysts, this use may not be practical for
water treatment plants using mountain
streams as a source of supply. In such
streams, concentrations of total coliform
bacteria are usually less than 100 organ-
isms/100 ml. To evaluate filtration per-
formance, a pilot filter should be operated
alongside the full-scale filter and spiked
with raw sewage. Turbidity, on the other
hand, is easy to measure.
To summarize, removals of turbidity
could be used to monitor plant perfor-
mance routinely. Periodic evaluations
could be done by spiking a pilot column
with coliform bacteria. Both are recom-
mended when filtering low-turbidity
waters.
Conclusions
This research shows that proper chem-
ical pretreatment is imperative if the
rapid-rate filtration process is to be effec-
tive when using low-turbidity waters.
Most important is selection of proper
coagulant polymers to use with the pri-
mary coagulant, such as alum. The range
of dosages must also be proper to achieve
high reductions of turbidity. With proper
chemical pretreatment, removal of all
parameters can be expected to exceed 70
percent for turbidity, 99 percent for bac-
teria, and 95 percent for Giardia cysts.
With no chemical pretreatment, removal
of Giardia cysts, bacteria, and turbidity
can be expected to range from 0 to 50
percent. The turbidity rule of thumb of 70
percent removal pertains to low turbidity
waters, nominally about 0.5 NTU for the
raw water. If raw water turbidity levels
are greater than 10 NTU, the rule does
not apply since the turbidity reductions
should be sufficient to meet standards. If
the raw water turbidity is about 0.1 NTU,
it would be very difficult to use this rule of
thumb as the turbidity reduction may not
be easily detectable.
The roles of other process variables
were not as important as chemical pre-
treatment. In-line filtration was as effec-
tive as direct filtration. Singlemedium
(sand) and dual media (anthracite and
sand) both have the same efficiencies in
reducing turbidity and bacteria. Hydraulic
loading rate has very little effect on remo-
vals when it ranges between 5 and 19
m/hr (2 and 8 gpm/ft2). At 25 m/hr (10
gpm/ft2), a moderate effect is indicated.
Investigation of temperature influence
showed no trend in removals of turbidity,
bacteria, and Giardia cysts at 5°C com-
pared with removals at 18°C. Further
work is recommended in this area.
Analysis of data by means of histo-
grams showed that both removals of tur-
bidity and total coliform bacteria could
serve as surrogate indicators of removals
of Giardia cysts. If percent removal of tur-
bidity is 70 or greater, for example, reduc-
ing turbidity from say 0.5 NTU to 0.15
NTU, the probability is 0.85 that removal
of Giardia cysts will exceed 99 percent.
Pilot filter columns spiked with coliform
bacteria are recommended for use along-
side the full-scale filters to evaluate prop-
erly filtration of low-turbidity waters.
The full report was submitted in fulfill-
ment of EPA Cooperative Agreement No.
CR808650-02 by Colorado State Univer-
sity under sponsorship of the U.S. Envi-
ronmental Protection Agency.
U. S. GOVERNMENT PRINTING OFFICE:1985/559-l 11/20685
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Mohammed A I-A ni is with the Water Board of the Scientific Research Council,
Bagdad. Iraq; John M. McElroy is with CH2M-HHI Consulting Engineers,
Bellevue, WA 98009-2050; David W. Hendricks and Charles P. Hibler 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 3. Rapid-Rate Filtration," (Order No. PB85-194 645/A S; Cost: $25.00,
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:
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
Official Business
Penalty for Private Use $300
EPA/600/S2-85/027
0000329 PS
AGENCy
60604
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