ENVIROi
OFFICE OF ENFORCEMENT
EPA-330/1-74-001
and
Type Automatic Sampling Techniques
on an
NATIONAL FIELD INVESTIGATIONS CENTER-DENVER
DENVER, COLORADO
SEPTEMBER 1974
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ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
COMPARISON OF MANUAL (GRAB) AND VACUUM
TYPE AUTOMATIC SAMPLING TECHNIQUES
ON AN INDIVIDUAL AND COMPOSITE SAMPLE BASIS
NATIONAL FIELD INVESTIGATIONS CENTER - DENVER
DENVER, COLORADO
SEPTEMBER 1974
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DISCLAIMER
Mention of brand name of equipment does not constitute endorse-
ment or recommendation of product by the Environmental Protection
Agency. The information and findings presented in this paper are
not to be construed as representing official equipment design or
modification specifications.
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TABLE OF CONTENTS
Disclaimer
Glossary
I. Introduction
II. Summary and Conclusions
III. SERCO Automatic Sampler
IV. Field Study Procedure
V. Statistical Approach
VI. Statistical Analysis of Data
VII. Additional Data Evaluation
VIII. Discussion
Appendix
1. SERCO Automatic Sampler Technical Report
2. SERCO Automatic Sampler Specifications
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GLOSSARY
Composite Sample - Individual grab samples of fixed volume collected
on a regular time basis and combined on the
basis of the corresponding volume of flow at
the time of collection.
Individual Grab Sample - One sample of fixed volume collected either
or Grab Sample manually or by automatic sampler and analyzed
independently.
TS - Total Solids
TSS - Total Suspended Solids
VSS - Volatile Suspended Solids
Statistical Parameters
u = Population mean
0 = Population standard deviation
°J = Standard error of the population mean
X" = Sample mean
S = Sample standard deviation
S = Standard error of the sample mean
A
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I. INTRODUCTION
The National Field Investigations Center-Denver (NFIC-D) has been
engaged in water quality and waste source evaluation studies since its
inception. Due to the magnitude of the surveys, NFIC-D often has relied
upon automatic samplers, particularly the SERCO, to collect samples of
the wastewater streams. These samplers are used to collect water
samples over specified periods for subsequent compositing; individual
grab samples are collected manually.
With the advent of compliance monitoring, the use of automatic
samplers is expected to increase. Data provided by the manufacturer
show that the automatic and manual sampling methods are equivalent
(Appendix). To confirm that the sampling methods are equivalent,
NFIC-D conducted studies at a local wastewater treatment plant (WWTP)
and statistically evaluated the results. This paper presents the results
of these studies.
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II. SUMMARY AND CONCLUSIONS
The SERCO automatic sampler was compared with the manual sampling
method on a composite sample and individual grab.sample basis on
July 16-21, July 22-27, and August 15-22, 1974. Samples were collected
from a local wastewater treatment plant and analyzed for total solids,
total suspended solids and volatile suspended solids July 16-27, and
for total suspended solids August 15-22; composite samples were combined
on a flow weighted basis.
The statistical approach used to evaluate the data was the two-tailed
"t" test at a risk level of 5% (95% confidence level). The pooled .-
sum of squares method was used to calculate the statistical parameters.
The hypothesis, tested statistically, was formulated: the mean of the
samples collected by one sampling technique is equal to the mean of the
samples collected by either a similar sampling technique or different
sampling method. If the value of "t" calculated from the data was
less than the tabular value of "t", the hypothesis was accepted.
The automatic sampler data were also compared with one another to
determine if there was a significant difference in the samples when the
probe inlets faced upstream downstream, or lateral to the direction
of flow.
Although the samples were collected in locations where the waste-
water was thoroughly mixed, the possibility existed that the solids
could vary with depth. Since the automatic sampler collects samples
at depth, and manual collection includes surface sampling, a special sampler
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manually operated, was fabricated to collect samples at the same depth
as the automatic sampler. Results were compared with results from the
manual and automatic sampling methods.
The sampling frequency for a composite sample was evaluated also.
Samples were collected manually at 15 and 60 minute intervals for 6
hours and composited individually.
Based on the statistical evaluation, the following conclusions
were made:
EQUIVALENT ON A COMPOSITED SAMPLE BASIS
1. Automatic Sampler and Manual Sampling Method
2. Automatic Sampler and Special Sampler
3. Automatic Sampler and Automatic Sampler
4. Manual Sampling Method and Special Sampler
5. Manual 6-Hour Composite (15-minute interval) and Manual 6-Hour
Composite (60-minute interval).
6. Automatic Sampler and Manual 6-Hour Composite (15 and 60-minute
intervals).
EQUIVALENT ON AN INDIVIDUAL GRAB SAMPLE BASIS
1. Automatic Sampler and Automatic Sampler-'
2. Manual Sampling Method and Special Sampler
NOT EQUIVALENT ON AN INDIVIDUAL GRAB SAMPLE BASIS
1. Automatic Sampler and Manual Sampling Method
2. Automatic Sampler and Special Sampler
a/ The samples collected with the probes in the upstream and downstream
positions were not equivalent only for the VSS parameter for the
influent, July 16-21. Since the VSS parameter was considered unsatis-
factory for the statistical comparison, it was concluded that all
probe positions collected equivalent samples.
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In the above comparisons, the automatic sampling method, with the probes
facing in any position relative to the direction of flow, was equivalent
to the other sampling methods, except on the individual grab basis.
In the comparison of automatic sampler vs. automatic sampler, the position
of the probe was not significant as samples were equivalent on a composite
sample basis and grab sample basis.
The temperature of the first sample collected by the automatic
sampler was monitored for six and ten hour periods. About six hours
is required for the initial sample to cool from'21°C to 4°C. When the
bottles and automatic sampler were cooled prior to the sampling period
(i.e., overnight), the time required to cool the sample from 21°C to
4°C was only three hours. When the ambient air temperature is above
freezing, the rate of temperature drop may be further increased by
replacing the insulated metal box housing the sampler, with a non-
insulated metal housing, and packing ice between the metal housing and
an insulated outer box. This modification is currently being done by
NFIC-D.
The results confirm that the vacuum type automatic sampler evaluated
in this study may be used to collect representative wastewater samples
on a composite basis. Modifications to the sampler are necessary to
provide adequate sample preservation.
The findings also raise serious doubts as to the viability of
accepted manual grab sampling methods, particularly with respect to
high and variable solids collection. Therefore NFIC-D has initiated an
ancillary testing program to develop reliable grab sampling equipment
and techniques.
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III. SERCO AUTOMATIC SAMPLER
The SERCO automatic grab sampler, Model NW-8, works on a vacuum
principle. Twenty-four, 500 ml bottles are evacuated to approximately
25 inches of mercury by means of an AC operated vacuum pump. Each bottle
is connected by an individual tygon tube or similar tubing to an intake
probe which is immersed in the wastewater stream. Samples are collected
when the mechanical triggers are activated sequentially using a clock
and distributor arm assembly-'. As each trigger is activated, the
vacuum on the respective sample bottle is released and a wastewater
sample is drawn into the bottle.
The amount of the sample collected depends on the atmospheric pressure,
the degree of evacuation, and the lift. After collection, the samples
are hand composited on an equal volume or flow weighted basis. The
sampler is readied for the next compositing period by back-flushing the
collection lines with tap water and inserting clean bottles.
The sampler is housed in a metal case. The 24 bottles encircle
two plastic ice containers used to preserve samples. NFIC-D has
modified the unit for summer and winter application. The entire unit
is placed in a foam insulated plywood box. For warm weather use,
additional ice is packed between the metal case and plywood box to
increase the rate of temperature decrease and to help maintain low
sample temperatures. During cold weather conditions, a heat source
(light bulb), which is controlled by a thermostat, is placed inside the
plywood box to prevent the clock, mechanical parts, and samples from
freezing. The heat source operates with either AC or DC power.
a/ Triggers can be activated at various intervals, usually 5, 15
or 60 minute, depending upon the clock used.
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The sampler has proved mechanically reliable under extensive use by
NFIC-D field personnel. Operational difficulties are minimal and only
routine maintenance is required.
A more detailed description of the SERCO automatic sampler is
presented in the appendix.
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IV. FIELD STUDY PROCEDURE
A local wastewater treatment plant was selected for the study due
to its proximity to the NFIC-D laboratories and reliable flow measuring
equipment. The study was conducted over three periods, July 16-21,
July 22-27, and August 15-22, 1974.
A. Parameters Evaluated
Total solids (TS), total suspended solids (TSS), and volatile
suspended solids (VSS) were evaluated for the July studies. The only
parameter used in the August study was TSS since most NPDES permits
limit suspended solids rather than TS and VSS. Analyses were done
according to Methods for Chemical Analysis of Water and Wastes, EPA,
NERC-AQC Laboratory, Cincinnati, Ohio, July 1971, as specified in the
October 16, 1973 issue of the Federal Register, "Guidelines Establishing
Test Procedures for Analysis of Pollutants".
Field measurements of pH and temperature were made as samples
were collected. Flows were determined from a Parshall flume and
recording device. During the July study a thermocouple probe was
placed inside an automatic sampler bottle containing the first sample
collected and the rate of temperature decrease was monitored.
B. Sampling Methods
To minimize the variations in the data during the evaluation of
manual and automatic sampling methods, samples were collected simultaneously.
The trigger mechanisms on the automatic samplers were tripped by hand
at the same time that manual samples were collected. All composite
samples were manually combined on a flow weighted basis at the end of
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the sampling period. Dye was added periodically at the influent to the
grit chamber to insure that the wastestrearn was mixed thoroughly at the
sampling location downstream from the grit chamber. Dye was also
added periodically in the final clarifier overflow to the wet-well to
determine that adequate mixing occurred at this sampling location. All
samples were preserved under ice and analyzed within two hours at the
laboratory.
Automatic samplers were compared with the manual sampling method
on an individual grab sample basis and a composite basis.
July 16-21 (Influent)
Three automatic samplers were placed at the plant influent, each
with a sampling probe inlet facing in a different position, e.g.,
upstream, downstream, and lateral (perpendicular), to the direction of
flow. Samples were collected hourly for 12 hours with the automatic
samplers and by the manual sampling method and composited at the end of
each 6-hour period, yielding 2 sets of composite samples per sampling
technique daily. In addition, two 6-hour composites, composed of
24 manually collected samples (15-minute intervals) were collected
sequentially over the 12-hour period to determine if a significant
difference existed as a result of the sample collection frequency at
random intervals.
Six individual grab samples were collected by each sampling technique
during the 12-hour period.
July 22-27 (Influent and Effluent)
The automatic sampler probes were placed in the influent and effluent
in the lateral position only, since under many field conditions, this
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is the only position available due to the limitations of the probe length
and the configuration of the sampling location. Samples were collected
hourly using automatic and manual sampling techniques. These samples
were composited at the end of 24 hours.
Six individual grab samples, each from the influent and effluent,
were collected randomly over 24 hours using both sampling techniques.
August 15-22 (Effluent)
Four automatic samplers were placed at the effluent wet-well. Two
sampling probes were placed with the intakes facing upstream and two
probes were placed in a lateral position. All probes were positioned
at the same depth. Samples were collected for 12 hours at 1-hour
intervals and composited at the end of each 6-hour interval, providing
8 composite samples daily. In addition, four random grab samples were
collected daily with each automatic sampler.
Grab samples were collected manually at the same time that the
automatic samplers collected samples and composited in the same manner.
Manual grab samples were also collected for individual analysis at the
same times as the automatically collected samples.
Although the samples were collected at locations where the waste-
water was thoroughly mixed, the possibility existed that the solids
could vary with depth. Because the automatic sampler probe is immersed
in the wastewater stream and manual sampling normally includes surface
flow as well as the flow at depth, a special sampler was built to obtain
a grab sample at the same depth as the automatic sampler probe.
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A 500 ml sample bottle was attached to a metal pole; a rubber stopper,
mounted on a tripping rod, sealed the bottle until it reached the desired
depth at which time the stopper was removed, the sample collected, and
the stopper was replaced. Composite and grab samples were collected
with the special sampler at the same times that the automatic and
manual samples were taken.
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V. STATISTICAL APPROACH
A. Parameters
Since the entire wastewater stream could not be examined to deter-
mine actual values of the statistical parameters, estimators were used
to evaluate a given parameter. For example, the sample mean I is an
estimator for the population mean u, and the estimator for o, the
standard deviation of the population distribution, is S. When making
inferences based on estimators, it is necessary to obtain estimates for
the variances of the estimators. In the case of the sample mean, the
2 2
variance is o_ = a /n where n is the sample size. To estimate the variance,
? 2
S-rr^ = S /n is substituted. The standard error of the mean o is estimated
X X
by S_.
X
B. "t" Test
The "t" distribution was used to test the hypothesis that the mean of
the samples collected by one method is equal to the mean of the samples
collected by another method, e.g., composite sample made up of individual
hand grab samples vs composite made from samples collected by an automatic
sampler.
The t-distributions are a one-parameter family of distributions.
The distributions vary with the size of the sample and the effect of
sample size is evaluated in terms of degrees of freedom. The distribution
is symmetric with the mean equal to zero, but for finite degrees of
freedom, it differs from the normal distribution in that there is more
area in the tails of the t-distribution and it is more peaked. As the
degrees of freedom increase (i.e., more samples), the more closely the
t-distribution resembles the normal distribution.
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If the sample size, n, is small (less than 30), the "t"-test is
used, even if the samples are from populations which depart "moderately"
from normal populations (1). The value of "t" is calculated from the
equation
t = |x'-p|'/T
s
Special tables list the value "t" may reach for given probability levels,
and the calculated "t" may be compared with the tabular value to determine
if the hypothesis is valid. If the absolute value of the calculated "t"
is less than the tabular value, the hypothesis is acceptable.
C. Two Sample Techniques
If two independent random samples, one from each of two populations
are collected, the pooled technique may be used to estimate the variance
in the "t" test. Since the two independent random samples came from
2
the same wastewater stream, the variance, a , and mean, \i, are assumed
to be the same for both populations and the best estimate is obtained by
pooling the information contained in both samples.
The "t" statistic is then calculated as follows:
- (p- -UP)
nl n2
where Sp is the pooled variance estimator and the degrees of freedom
equal to n + n - 2. Since v is equal to y,, t = ] >\ , ,
1 £ I * Sp/1 i
"] "2
The calculated value is compared with the tabular value to determine
if the hypothesis that the means are equal is true. For this study,
a risk level of 5% was selected (95% confidence level).
Wieks. S.S.. Elementary Statistical Analyses. Princeton University
Press. Princeton, New Jersey, 1958.
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VI. STATISTICAL ANALYSIS OF DATA
The statistical hypothesis, the mean of the samples collected by
one sampling technique is equal to the mean of the samples collected by
either a similar sampling technique or different sampling method, was
formulated and evaluated at the 95% confidence level. The hypothesis
was tested using the "t" distribution, and the pooled sum of squares method
was used for calculating the statistical estimators. If the value of "t"
calculated from the data was less than the tabular value for "t", the
hypothesis was accepted. A 2-tail test was used and the a/2 value was
0.025. The degrees of freedom were dependent on sample size.
A. Significance of the Automatic Sampler Probe Position
1. July 16-21 Sampling Period - The automatic sampler probes were
placed in the influent with the inlets facing upstream, downstream, and
laterally to the direction of flow. Samples were collected for evaluation
on an individual grab basis and a 6-hour composite basis for 6 days.
Thirty-six samples were collected for the grab basis evaluation and
twelve samples were collected for the composite basis evaluation (Table
VI-1).
Based on the 6-hour composite samples, the statistical analysis showed
that the automatic samplers collected equivalent samples for the three
probe positions for all three parameters.
The same results were obtained on the grab sample basis evaluation
for all probe positions for TS and TSS. However, for the VSS parameter,
the samples collected with the probes in the upstream and lateral positions
were not equivalent. The upstream vs downstream and downstream vs lateral
samples were statistically equal.
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TABLE VI-1
COMPARISON OF SAMPLING METHODS
WWTP INFLUENT
July 16-21, 1974
Grab Samples h£/=36 6-Hour Composite Samples N=12
Sampling
Technique
Automatic Sampler
Upstream^/
Downstream
Lateral
Manual Sample
60 minute-'
15 minute
TS (mq/1)
Range
533-741
554-742
548-774
525-730
-
Mean
641
650
660
620
- •
TSS (mq/1)
Range
26-240
24-292
12-324
10-224
-
Mean
126
133
155
108
-
VSS (mq/1)
Ranqe
22-108
18-278
8-314
6-210
-
Mean
110
116
139
94
-
TS (mq/1)
Ranqe
581-965
588-690
580-728
595-653
525-730
Mean
662
642
650
627
620
TSS (mg/1)
Range
92-182
92-180
80-230
86-156
56-174
Mean
118
125
136
112
121
VSS (.mg/11
Ranqe
72-146
70-170
74-212
82-144
34-150
Mean
100
111
123
101 *
103
a/N is the number of samples.
b/Indicates probe inlet position relative to the direction of flow.
c/Indicates the elapsed time between sample collection.
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2. August 15-22 Sampling Period - Four automatic samplers were
used to collect the effluent, two probes were placed with the inlet facing
in the upstream position (UP-1 and UP-2) and two with the inlet facing
laterally (LAT-1 and LAT-2) to the direction of flow. The sampling
duration was 12 hours per day over the 7-day period, however samples were
composited after the first six hours and after the second six hours for
a total of 14 samples per automatic sampler. Twenty-eight individual
grab samples were also collected at random with each sampler during the
7 days for a comparison on an individual grab sample basis.
The following comparisons were made of the automatic samplers for
both composite and the individual grab samples collected over the 12 hour
daily sampling period (Table VI-2).
a) UP-1 vs UP-2 and LAT-1 vs LAT-2 to determine if two samplers
with probes placed in the same direction collected equivalent
samples, and
b) Upstream position vs lateral position to determine the effect
of probe position on sample collection.
The statistical analysis showed that the samplers were equivalent for all
comparisons.
The same comparisons, a) and b), were also made using the individual
6-hour composites collected during the first and second 6-hour intervals
over the 12-hour sampling period (Table VI-3). The statistical analysis
again showed that samplers were equivalent for all comparisons.
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TABLE VI-2
COMPARISON OF SAMPLING METHODS
TOTAL SUSPENDED SOLIDS
WWTP EFFLUENT
August 15-22, 1974
Grab Samples
= 28 6-Hour Composite Samples N=14
Sampling
Technique
Automatic Sampler
Upstream^l-
Upstream-2^/
Lateral-!
Lateral -2
Manual Sample
Special Sampler-
Range
(mq/1)
10-45
10-61
9-66
9-42
6-32
4-39
Mean
(mq/1)
25
26
29
26
21
21
Range
(mq/1
16-48
14-55
8-41
11-59
19-67
9-39
Mean
(mq/1)
28
30
26
30
30
23
a/N is the number of samples.
b/Indicates probe inlet position relative to the direction of flow.
c/Indicates either first or second sampler.
(I/Special sampler collected samples from the same depth as the automatic
samplers. Sampler was manually operated.
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TABLE VI-3
COMPARISON OF SAMPLING METHODS
INDIVIDUAL SIX-HOUR COMPOSITE SAMPLES
TWELVE HOUR STUDY PERIOD
TOTAL SUSPENDED SOLIDS (mg/1)
WWTP EFFLUENT
August 15-22, 1974
Upstream27-!"7 Upstream-227 Lateral-1 Lateral-2 Manual Sample
Ranqe Mean Ranae Mean Ranap Mpan Uanno Moan uanna u^,.
First Six 16-48 27 14-55 30 8-41 23 11-59 26 19-67 32
Hour Period
Second Six 21-39 29 16-50 30 21-37 30 22-40 33 20-37 28
Hour Period
Special Sampler"
Range Mean
9-37 21
15-39 26
a/ Indicates probe inlet position relative to the direction of flow.
b_/ Indicates either first or second sampler.
£/ Special sampler collected samples from same depth as the automatic samplers
Note: Number of samples collected by each method was 7.
Sampler was manually operated.
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B. Comparison of Automatic Sampler vs Manual Sample Method
1. July 16-21 Sampling Period - Manual samples were collected
according to established procedures. The discrete manual samples were
collected using a fixed volume dipper (stainless steel) attached to a
metal pole. The dipper was rinsed several times in the wastestream
before the sample was taken. The samples were placed in 500 ml bottles
and stored at 4°C.
The manual sampling technique was compared with the automatic sampling
technique with the probes placed in the three different positions (Table VI-1).
Based on the 6-hour composite samples, samples collected manually were
equal to the samples collected with the automatic samplers. On an
individual grab sample basis however, the manual sampling method was
not equivalent to the automatic sampling method for the lateral and
downstream probe positions, but was equivalent when the probe was in the
upstream position.
2. July 22-27 Sampling Period - Manual and automatic sampling
techniques were compared on the wastewater treatment plant influent and
effluent (Table VI-4). The automatic sampler probes were placed in the
lateral position only. Samples were composited over 24 hours.
On the 24-hour composite basis for the influent samples, the auto-
matic sampling and the manual sampling methods were equivalent only for
the total solids parameter. The two sampling techniques were statistically
equivalent for the effluent samples for TS, TSS, and VSS.
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TABLE VI-4
COMPARISON OF SAMPLING METHODS
WWTP INFLUENT AND EFFLUENT
July 22-27, 1974
Sampling
Technique
24-Hour Composite^/
Automatic Sample) —
Manual Sample
Grab Sample-
Automatic Sampler-
Manual Sample
TS (me /l)
Range
573-720
574-640
493-776
446-712
Mean
629
607
649
602
Influent
TSS (mq/1)
Range
106-178
81-120
25-350
7-328
Mean
143
93
138
88
VSS (mq/1)
Range
. 86-158
68-106
21-324
7-274
Mean
122
81
122
78
Effluent
TS (nig/
Range
481-510
442-514
459-539
456-537
1)
Mean
497
498
507
502
TSS (mq
Range N
/I) VSS
ean Ranae
(.man)
Mean
12-26 22 12-30 20
16-139 45 16-105 37
13-52 26 10-42 23
4-42 20 4-42 19
a/ Sample size = 6
b_/ Sampler probe inlet in the lateral position relative to the direction of flow.
£/ Sample size = 35 for the influent and 36 for the effluent.
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On an individual grab basis, the two methods were not equivalent for
total suspended and volatile suspended solids for'either the influent or
the effluent samples. For the total solids parameter, the sampling methods
were equivalent for the effluent, but not for the influent.
3. August 15-22 Sampling Period - Based on the 6-hour composite
samples, the sample collected with the automatic samplers with the probes
in the upstream and lateral positions were equal to the samples collected
manually (Table VI-3).
^v/^ On the individual grab sample basis, the automatic sampling and
/manual sampling methods were not equivalent.
^L-—
C. Comparison of Manual Sample Method and Special Sampler
Since the analysis of the data for the July studies showed that the
automatic samplers were not equivalent to the manual sampling method on
an individual grab sample basis, a special sampler was fabricated to
collect samples at the same depth as the automatic, sampler probes (Section IV).
The special sampler, operated manually, was used during August 15-22.
The samples collected by the manual method were statistically equal
to the samples collected by the special sampler for the individual grab
samples and the 6-hour composite samples (Table VI-2).
D. Comparison of Automatic Sampler and Special Sampler
Based on the 6-hour composite samples, the automatic sampler
and special sampler collected equivalent samples (Table VI-2). However,
the methods were not equivalent on the individual grab sample basis.
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E- Composite Sample Collection Frequency (July 16-21)
Manual samples were collected hourly and every 15 minutes for 6
hours and composited into two separate samples to determine if there was
a significant difference in sampling frequency (Table VI-1). The frequency
of sample collection was insignificant as the samples collected at
each time interval were equal.
The samples collected manually every 15 minutes and composited
after 6 hours were also compared with the automatic sampler 6-hour composited
samples which were collected hourly. The former samples were equal
to the automatic sampler composites for all three probe positions, upstream,
.downstream, and lateral.
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VII. ADDITIONAL DATA EVALUATION
A. Sampling Velocities of Automatic Samplers
The relative intake sampling velocities of the automatic samplers
were measured for the period July 16-21. The tubing lengths from the
probe inlet to the top of the automatic sampler were marked at exactly
8.0 feet; the elapsed time between the tripping of the mechanical trigger,
releasing the vacuum, and the sample reaching the 8 foot mark was 1.0
second. The vacuum in the bottles was approximately 21 inches of mercury.
The lift was 8 feet and the barometric pressures ranged from 24.69 to 24.99
inches of mercury.
All of the automatic samplers had relative velocities of 8 feet per
second for a total of 34 observations. Since a greater vacuum can be
exerted at lower elevations, the velocities may increase. An increase
in velocity or vacuum would result in an increase in the amount of sample
collected.
B. Temperature Control in the Automatic Sampler (July 16-27)
The temperature inside the sample bottle containing the first
sample collected was monitored to determine the rate of temperature
decrease. The ambient air temperatures ranged from 27°C to 34°C
(80°F to 93°F) during the study. The temperatures were monitored for
6 hours during the July 16-21 period when the 6-hour composites were
collected and monitored for 10 hours during the July 22-27 period when
the samples were composited over a 24-hour period (Figures VII-1 and VII-2).
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FIGURE VII-1
AVERAGE TEMPERATURE DECREASE
AUTOMATIC SAMPLER BOTTLE
WWTP INFLUENT
6 HOUR COMPOSITE
JULY 16-21, 1974
B--
Not Precooled
Precooled
CVJ
Preservation Temperature
I
I
2 3 4
ELAPSED TIME (HOURS)
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FIGURE VII-2
AVERAGE TEMPERATURE DECREASE
AUTOMATIC SAMPLER BOTTLES
WWTP INFLUENT
24 HOUR COMPOSITE
JULY 22-27, 1974
Preservation Temperature
I I
0
4.6 8
ELAPSED TIME (HOURS)
10
12
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After collection it required approximately 6 hours for the samples
to reach 4°C from 21°C when precooling of the sampler was not practiced.
Whe precooling was employed, i.e., the automatic samplers were left
overnight in their plywood boxes which were filled with ice, the
temperature inside the sample bottle containing the first sample collected
dropped from 21°C to 4°C in approximately 3 hours, or one-half the
time required without precooling.
Temperatures of the first 6 individual samples, collected hourly,
at the time of composition are listed in Table VII-1.
TABLE VII-1
TEMPERATURE OF INDIVIDUAL SAMPLES
AUTOMATIC SAMPLER
JULY 16-21, 1974
Bottle No.
1
2
3
4
5
6
Initial
Temp
°C
21
21
21
21
21
21
Time Elapsed
Since Collection
Hours
5
4
3
2
1
0
Temperature (°C)
When Removed
From Sampler
4.9
7.0
9.5
11.8
16.8
21
Temperature
Decrease, °C
16.1
14
11.5
9.2
4.2
0.0
-------
-26-
VIII. DISCUSSION
The analytical techniques of the NFIC-D laboratory were checked
on duplicate samples during the study. The reproducibility of the laboratory
was 98.9%. The means of the samples and standard deviations were as
follows.
Mean (mg/1) Standard Deviation (mg/1)
Total Solids 526 8.71
Total Suspended Solids 33 5.71
Volatile Suspended Solids 32 5.30
The analytical techniques were assumed insignificant in the statistical
analysis since the reproducibility was very high and the variations of the
solids were high. In addition, the samples used for comparison were analyzed
at the same time and the laboratory techniques would be equivalent.
The statistical analysis of the sampling techniques showed that the
automatic samplers were equivalent to the manual sampling method on a
composite sample basis, but not on an individual grab sample basis.
Although the July 22-27 study showed that the automatic and manual sampling
techniques were equivalent for only total solids on the raw waste based on
the 24-hour composite, the previous week's study showed that TS, TSS, and
VSS were equivalent in the 6-hour composite samples. Since more samples
were collected the first week, using three probe positions, and since
only the lateral position was evaluated the second week, it was concluded
that insufficent samples (6) were collected and that the July 16-21 sampling
period was more representative of the automatic sampler performance.
-------
-27-
Although the automatic sampler can be used to collect grab samples
by installing a clock which activates the trigger mechanism at desired
times, the practice at NFIC-D is to collect grab samples manually and use
the automatic sampler for composite samples.
The data show that the samples collected manually were lower in
concentration than the samples collected automatically (Tables VI-1, 2,
and 4) on an individual grab basis. However, it cannot be concluded
from this study that the automatic sampler does not collect a representative
sample. In order to determine whether the automatically collected sample
or the manually collected sample represents the true conditions of the
wastewater stream requires that the parameters of the wastewater stream be
known. This type of study necessitates a synthetic wastewater which can
be rigorously controlled.
Ideally both methods should be compared using "isokinetic" sampling
conditions. In field application, this is not practical or achievable
to date. Manual sampling collects samples without exerting a velocity on
the stream and the sampling velocity of the automatic sampler is dependent
on the vacuum, lift, and barometric pressure, not on the flow rate.
The automatic samplers collected equivalent samples for the three
positions on both the composite and grab sample basis, with one exception.
The upstream vs the lateral positions were not equivalent for the VSS para-
meter during July 16-21 on an individual grab sample basis. However, the
upstream position was statistically equal to the downstream position and the
downstream position was equal to the lateral position for VSS. In the
analysis for VSS, inorganic material will also be volatilized in the muffle
-------
-28-
furnace along with the organic matter. The VSS are also more variable
in the influent than in the effluent. Therefore it was concluded that
VSS is not a satisfactory parameter for the statistical comparison. The
possibility exists that the VSS for the upstream position may have been
equivalent to the lateral position and statistically rejected (value of
"t" calculated was 2.04 and the tabular value was 1.997), especially since
the upstream vs downstream and downstream vs lateral were equivalent.
The possibility also exists of accepting a hypothesis when it is false.
However, the level of significance is selected to minimize the latter
possibility. In this study, the level of significance, a, was 0.05, and
the probability is much higher that a true hypothesis will be rejected
than a false hypothesis accepted. Since the August 15-22 data showed that
the probe locations, upstream vs lateral, were equivalent, and due to the
other factors cited above, it was concluded that all probe locations
collected statistically equivalent samples.
Since all probe positions collect equivalent samples on both a composite
and grab sample basis, field application is not limited due to the configuration
of the sampling site or height of the lift. Also, the probe can be positioned
laterally or downstream position in the flow to prevent clogging or freezing
of the inlet.
Sample collection frequency, on a composite basis, over a 6-hour
period was not significant as the samples collected every 15 minutes
and composited were equivalent to samples collected hourly and composited.
The application of sampling more frequently is recommended when the
wastewater stream is highly variable in strength. However, the length
of sampling period would then be limited by the number of sample bottles.
-------
-29-
The monitoring of temperature in the sample bottles clearly shows
that the bottles should be precooled before sampling begins. NFIC-D
is presently modifying the metal sampler case. A non-insulated case
(thin walled, sheet metal) will be used when ambient air temperatures
are above freezing. This casing will be used in the plywood box and
ice packed between the metal and insulated plywood walls. It is
expected that the temperature inside the sample bottles will decrease
at a greater rate, thus enhancing sample preservation.
-------
APPENDICES
-------
SONFORD PRODUCTS CORPORATION
2 US HAND TOWK* MINNCAPOLI9 ». MINNESOTA
SERCO Automatic Sampler
Technical Report
The SERCO Automatic Sampler operates on the principle of Boyle's Gas Law.
The sample is collected in the sampling container by a driving force caused by
the difference in pressure in the evacuated container and the atmospheric
pressure.
The size of sample collected depends on the atmospheric pressure, the level
of evacuation, the lift, and the volume of the sampling container. The standard
SERCO Sampler, Model NW-3, has a 16 02. sampling container and three foot lift.
Sample Volume
The volume of sample to expect at various conditions is shown in Figure 1
and 2, as well as in the table in the brochure.
In general, the larger the volume of sample collected, the more representative
it will be. According to Standard Methods for the Examination of Water and Waste
Water, each individual waste water sample collected for compositing should be at
least 120 milliliters and the portions should be collected each hour—in some cases
each half hour or even every 5 minutes—and mixed at the end of the sampling period,
or combined in a single bottle as collected. This minimum is noted on the two
figures and is recommended as the minimum volume of waste water to collect.
Smaller volumes can be considered for special applications, however.
Larger sample volumes will be necessary for stream sampling because each
individual sample will be analyzed. It is expected that about one liter (1000
milliliters) would normally be desired.
The volume of sample needed for other automatic samplinq applications, such
as river sediment studies and chemical processing control would be dictated by the
specific needs of the applications.
-------
SONFORD PRODUCTS CORPORATION
2355 Rand Tower
Minneapolis, Minnesota 55402
SAMPLING DATA
The following laboratory and field tests represent comparative analytical
data of samples taken at the same time by the SERCO Automatic Sampler and manually
for several different types of waste water. The comparison of sampler data with
data for manually collected samples does not mean that it is assumed that manual
sampling is more accurate. In fact, the samples collected with the Sampler may
be more representative of conditions in the flowing stream. However, manual
collection of samples is common in the waste water field and these studies have
been made to demonstrate that the SERCO Automatic Sampler can collect at least
as representative a sample as would be"collected manually.
I. ACTIVATED SLUDGE
Several samples of activated sludge were collected directly from an aeration
tank to determine the effect of the air bubbles in the liquid on the sampler, as
well as its ability to collect the solids. The results of the analysis are as
follows:
Suspended Solids, mg/1
Trial No. SERCO Automatic Sampler Manual
1 2585 2585
2 2650 2735
3 2790 2880
4 2950 2835
Average 2744 2759
Results of tests on concentrated activated sludge is as follows:
Suspended Solids, mg/1
Trial No.
1
2
3
4
Average
ERCO AUTOMATIC Sampler
17,490
16,750
17,530
17,360
17,540
Manual
18,040
17,410
18,960
17,350
17,940
-2-
-------
SONFORD PRODUCTS CORPORATION
2355 Rand Tower
Minneapolis, Minnesota 55402
II. DOMESTIC WASTE
Laboratory Test
Fresh raw domestic waste was brought to the laboratory for this study. While
the waste was being thoroughly mixed, nine samples were collected from the waste
sample container with the SERCO Automatic Sampler and then were collected manually
with 250 ml french-square bottles. The samples were collected alternately; that
:s, a sample was collected with the Sampler, then a sample was collected manually,
and so on. The raw waste was thoroughly mixed using two plunger type manual mixers.
These samples were analyzed for suspended solids and the data is as follows:
Suspended Solids, mg/1
Trial No. SERCO Automatic Sampler Manual
1 * 270 ~286
2 264 270
3 268 270
4 260 244
5 262 262
6 252 248
7 254 274
8 238 228
9 258 240
238-270 228-286
Average 258.3 258.0
Field Studies .
A SERCO Automatic Sampler was taken to a municipal waste treatment plant and
24 individual samples of the raw sewage were collected using the Sampler and 24
samples were collected manually at the same time. These samples were collected
over a period of about 30 minutes. The two sets of 24 samples were composited
separately and analyzed. The laboratory results are as follows:
Analysis SERCO Automatic Sampler
Manual
5-day BOD, mg/1 72 72
Total solids, mg/1 2230 2270
Total volatile solids, mg/1 510 575
Suspended solids, mg/1 112 113
Suspended volatile solids, mg/1 103 104
P" 7.70 7.70
The above data demonstrates the ability of the SERCO Automatic Sampler to
collect a representative sample of raw domestic sewage.
-------
SONFORD PRODUCTS CORPORATION
2355 Rand Tower
Minneapolis, Minnesota 55402
III. MEAT PACKING WASTE
Composited samples of meat packing waste were collected using the SERCO
Automatic Sampler and by manual procedures over the same 24 hour period. A total
of 24 individual samples were collected at one hour intervals with the Sampler.
The manual samples were collected at 30 minute intervals. The Sampler samples
were collected from the influent channel, ahead of the Parshall flume. The manual
samples were collected after the flume, as the waste water discharges into the
wetwell. However, the same waste flow was collected at each location. The five
day BOD results of the composited samples are as follows:
Analysis
5-day BOD, mg/1
PH
SERCO Automatic Sampler
2095
7.10
Manual
2095
7.10
Waste water samples were collected with the Sampler and manually from a com-
bined domestic waste and meat packing waste. The meat packing waste constitutes
about 90% of the waste water volume. The samples were collected manually and with
the Sampler at exactly the same time from the influent channel to the primary
settling tank. The analysis of the related samples are as follows:
SAMPLER
MANUAL
Sample
No.
1
2
3
4
5
6
7
8
Average
5-day BOD
mg/1
3280
2790
•—
—
1900
—
2050
—
2505
Total Solids
mg/1
6170
5590
3590
3790
3950
3820
4370
4330
4450
5-day BOD
mg/1
3300
2670
Total Solids
mg/1
6330
5590
3740
3560
3730
3810
4370
4440
4446
Based on previous analytical data, the suspended solids concentration of the
above sample would be expected to be 1000-1500 mg/1. The BOD and solids data
indicates that the SERCO Automatic Sampler will collect representative samples of
meat packing waste with high concentrations of organic solids. The total solids
data showed almost identical analytical results and the BOD data was within the
limits of accuracy for the test. It should be noted also, that the BOD of the
manual samples were slightly lower.
-4-
-------
SONFORD PRODUCTS CORPORATION
2355 Rand Tower
Minneapolis, Minnesota 55402
IV. PAPER MILL WASTE
Samples of paper mill waste water were collected both manually and with the
SERCO Automatic Sampler at the same time. The analysis of samples of the screened
wood room effluent are as follows:
Analysis for Total Solids, mg/1
Trial No. SERCO Automatic Sampler Manual
1
2
3
Average
The analysis of waste water from the Kraft Mill process is as follows:
Analysis for Total Solids, mg/1
SERCO Automatic Sampler Manual
710 725
The suspended solids concentration for the screened wood room effluent was
about 2000 mg/1 and for the Kraft Mill waste was about 100 mg/1. The sampling
station used for the wood room effluent was located very close to the screens,
making it difficult to obtain a uniform sample, which accounts for the variations
in the solids concentration for both methods. The average concentration of solids
for the wood roof effluent was higher in the samples taken with the Sampler because
they were collected near the bottom of the channel, while the manual samples were
collected near mid-depth. It is difficult to say which of the sampling methods is
more representative of stream conditions. However, this test does clearly show that
the SERCO Automatic Sampler can collect satisfactory samples of paper mill waste
water with suspended solids concentrations of at least 2000 mg/1.
-5-
-------
400
300
tn
•o 200
o
3
J, 100
i
"i
c
0
CO
at
c
llection con
hospheric pr
/
E R C 0 ;
:ainer size
ssure - 30
/
--/- -
/
'
) 5 10 1
u t o m a t
Sample
Model h
• 16 cJz.
n. Hg.
/
/
/
/
'A
5 2
Gage Vacuum
i c San
Size
W-3
y
/
V
/
/
) 2
- inches He
pier
3 foo
/
*
8 foo
: lift (h)
: lift (h)
13 foo
/
- — 120 ml
5 3
rcury
: lift (h)
• recomnende
0
1 minimum sa
iple
-------
3000
3750 ml- (1
gallon)
SERCO AUTOMATIC
Sample Size
llection Co
SAMPLER
with Variou
itainer
Volu les
2500
3000 ml
2000
•0
t—
ID
2000
1500
NOTE: The
were
Atmo
Gage
Othe
ollowing as
made for ca
pheric pres
Vacuum--26
physical c
umptions
culation:
ure—30 in.
n. Hg.
inditions
Hg.
1000
for
odel NW-3
1000 ml
500
\
16 oz.
20 ml Rccomnended Minim :m Sample
Lift in Fe«
-------
SERCO AUTOMATIC SAMPLER
Assembly for Model NW-3
1. The SERCO Automatic Sampler {Fig. 1) is shipped ready for operation except for placing the bottles in
the trays. Be certain the numbers on the bottles correspond both to the tray numbers and the numbers
on e?ch switch.
2. Water may be visible in some of the bottles and tubes when the sampler is received. This is simply
residual water left in the sampler after being tested prior to shipment. The water used is City of
Minneapolis tap water.
3. To Remove Arbor Hub — See Figures 2 and 3
a. Loosen and remove Knurled Screw (left hand thread).
LJ. R.-rnove Tripper Arm.
c. L dusen alien head set screw (B) on side of Arbor Hub.
d. Turn alien head screw (A) located in,Arbor Hub below Knurled Screw. This will force hub off the
tapered clock arbor.
4. To Install Arbor Hub — See Figures 2 and 3
a. Unscrew alien head screws (A) and (B) a few turns.
b. Place hub on clock arbor and tap gently to set in place.
c. Turn alien head screw (A) into hub just until it is in contact with top of clock arbor.
d. Tighten alien head screw (B) at side of Arbor Hub.
5. To Install Gear Head — See Figure 4
a. Remove Arbor Hub (See mstructions)
b. Place Gear-Head over arbor and rotate until ends of Gear Head are under the heads of the posts
provided in top or clock nousmg.
c. Install auxiliary strap to hold gear head in place.
Routine Operating Instructions for Model NW-3
See Figure 1 and 2
1. Be certain all bottles and tubing are clean.
2. Wind clock used to actuate switches. When using the clock in a room where the noise level is high and
where the tick of the clock may not be heard, the motion of the main spring may be observed through
the especially provided hole in the Switch Plate. This assures the user that the clock is running.
3. Set rubber stoppers securely in the 24 bottles.
4. Place Vacuum Head over Sampling Head and hold in place until it is vacuum sealed.
-------
SERCO AUTOMATIC SAMPLER
5. Evacuate the system through the hose connection on the Vacuum Head using a vacuum source (such as a
vacuum pump, vacuum system, or ejector). This can be done in the lab or in the field if a source of
vacuum or power is available. A vacuum is assured in each bottle if each of the rubber tubes is collapsed
(flattened.) The necessary vacuum to be maintained in the bottles in order to obtain a properly sized
sample will vary with the conditions under which the sampler is used. See Table 1 for variation of
sample size with sampling conditions.
6. Seal off each bottle by setting the switches on the Switch Plate.
7. Release the Vacuum Head and check to see if all bottles are evacuated and holding a vacuum. This may
be easily done by observing the rubber tubes to see that each remains collapsed. As a precaution, the
tubes to each bottle should be checked again at the installation site to be assured that bottles are still
evacuated.
8. Set Tripping Arm to desired starting position. Be certain that the hole in the Tripping Arm fits snugly
over the raised section at the top of the Arbor Hub and that the Knurled Screw is tightened securely. If
Tripping. Arm is not securely attached to Arbor Hub it will turn and not be capable of providing the
torque to operate switches.
Caution: Do not set tripping Arm until you want to start sampling since the clock continues to run
once it is started.
9. If you wish to cool the samples, place the ice containers in bottom of sampler by centering them in the
painted'square in sampler bottom.
10. Lower rack into outer case.
11. Transport the sampler to point of use. Hang Sampling Head in the flow, and be sure it is-low enough
to obtain-a-sample when the flow level is at the minimum elevation.
12. Record the bottle number of the first sample and the time sampling is started.
13. After sampling period, bottles may be removed and covered with caps and transported to a laboratory
for analysis. Samples may be composited according to flow records and any one sample may be run
individually. (Sample bottles may be left in sampler and entire unit transported to lab.)
14. Back flush each line with water (preferably hot, if available) from the rubber stopper end, and allow to
dry for future use. Back flushing is best done with a piece of pipe or plastic tubing approximately
1/2-inch in diameter. With one end of this tube connected to a hose from the faucet, the other end may
be pressed firmly against the rubber stopper to force water back through the' sampling line. Also, the
solids should be flushed from under Sampling Head Shroud.
-------
Lifting
Handle
Twenty-four clear
flexible vinyl sampling
lines — '/. inch I.D.
Twenty-four
rubber sampling
lines. '/• inch 1.0.
Spring-driven
timing motor
with tripper-arm
Double-Hinged
cover
Polystyrene
rigid insulation
Stucco aluminum
outer case
VIEW OF SAMPLER
IN POSITION
FOR USE
Stainless
steel sampling
head
R ubber stoppers
in twenty-four
16oz. French
square glass
sample bottles.
Bott les are
numbered.
VIEW OF SAMPLER
REMOVED FROM CASE: Model NW-3
Bottles have been
removed to show core
space used to hold
ice for cooling
samples.
Figure 1
Table 1
APPROXIMATE VARIATION OF SAMPLE SIZE
WITH CONDITIONS OF SAMPLING
SAMPLE VOLUME
Milliliters
VACUUM GAGE
READING
IN. OF MERCURY
LIFT
3 FT.
LIFT
8 FT.
LIFT
13 FT.
26
370
282
153
24
333
363
400
237
272
310
97
128
167
22
295
323
356
395
193
222
257
300
43
67
97
137
20
259
283
312
347
149
173
204
240
6
27
56
18
221
243
268
300
105
125
150
180
16
184
203
222
252
61
77
97
120
14
147
163
178
205
27
28
43
60
12
no
123
134
157
10
74
83
90
110
8
36
43
46
62
ATMOSPHERIC
PRESSURE
IN. OF
MERCURY
30
28
26
24
30
28
26
24
30
28
26
24
The size of the sample varies with the lift, the length
and size of the sampling tube, the size of the sample
bottle, the atmospheric pressure, and the vacuum held
in the bottle. The values in the above table have been
obtained with the equipment furnished with Serco Auto-
matic Sampler Model NW-3.
SAMPLE
TUBE
LIQUID
SURFACE
SAMPLE
BOTTLE
-------
DETAILS OF SWITCH R
PLATE FOR MODEL NW-3
Figure 2
Knurled screw
holding tripper
arm
Nut for
winding
clock
Switch with
sampling line
sealed
Aluminum plate
Spring-driven
timing motor
rotating
once each
24 hours
Switch with
sampling
line open
Hole to observe
timing motor
operation
PLAN VIEW OF SWITCH PLATE
(Shown With Tubes Cut Off)
Figure 4
TRIPPER ARM
Gear heads are
available to earily
change the interval
of sampling from
hourly to every 30
minutes or
whatever is
required.
ALLEN-HEAD
SCREW (A) FOR
USE !N REMOVAL
OF HUB (RIGHT-
HAND THREAD)
TAPERED
CLOCK ARBOR
PLAN VIEW OF GEAR HEAD
INSTALLED ON CLOCK
Figure 3
KNURLED SCREW
(LEFT-HAND THREAD)
ARBOR HUB
ALLEN-HEAD SCREW (B)
(RIGHT-HAND THREAD)
- CLOCK
------- |