MONITORING OF THE EFFLUENT STREAM
FROM WASTEWATER TREATMENT PLANTS
by
Robert Smith
ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Monitoring
Advanced Waste Treatment Research Laboratory
Cincinnati, Ohio
December 1971
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MONITORING OF THE EFFLUENT STREAM FROM WASTEWATER TREATMENT PLANTS
To evaluate the quality of the effluent stream from a waste-
water treatment plant the number of measurements required will de-
pend on the degree' of precision required by the regulatory agency.
Both the volume flow and the concentration of contaminants will
vary diurnally and seasonally. In some instances 24 hour composite
samples will be sufficient, in other cases the diurnal variation
will be measured. Ideally, all measurements should be made on-line
24" hours per day and 365 days per year. Automatic instruments to
accomplish this task, however, are not available at this time. The
following list represents a minimum set of measurements to character-
ize the effluent with respect to its impact on the receiving stream:
I*
1. Volume Flow, mgd
2. Water Temperature
3. pH
4. Suspended Solids Concentration, rag/1
5. Total Organic Concentration; COD, TOC, TOD, TC
The stream analyst might wish to substitute a measurement of 5-day
BOD or an oxygen uptake measurement as an alternative or in addition
to the fifth measurement shown in the list.
The first three measurements listed above can be made contin-
uously, but periodic maintenance will be required. An instrument
which will measure suspended soli'ds concentration with good precision
does not exist at this time. Several instruments are available which
i
operate on the principle of adsorbed or reflected light similar to
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a turbidometer. Under ideal conditions, the turbidity measurement
•
can be related to suspended solids in the range of 0-100 mg/1. One
alternative is to write the effluent standards in terms of turbidity
instead of suspended solids. A typical price for this kind of in-
strument is $1580 for the instrument and about $300 for the recorder.
-* - j
In the laboratory, suspended 'solids determination is simple and easy
to perform. The turbidity type of instrument has the advantage of
continuous on-line performa'nce.
In the measurement of suspended solids, total organic carbon,
and biodegradable organic carbon, the instruments available either
require significant amounts of maintenance and calibration time or
the measurement made is not truly equivalent to the corresponding
wet chemistry method. The question, therefore, arises whether the
use of the automatic instruments offers any true advantages over
providing a laboratory and hiring a full time chemist to make the
wet chemistry measurements. This question will be examined later
in this report, after the cost of the automatic instruments and the
cost of the alternative wet chemistry method are presented.
The traditional 5-day BOD is time consuming to perform in the
laboratory and has the disadvantage of the 5 day delay which pre-
cludes the use of the .measurement for plant control. An oxygen up-
take measurement can be made with an instrument marketed by Badger
Meter Manufacturing Company which will measure the oxygen depletion
in the sample over a 15 minute time period. The cost of this instru-
ment is now quoted as $3800 and the installation cost is estimated at
$100O. This instrument can be used to measure the concentration of
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biodegradable organics, but an operator will be needed essentially
•
full time to service and attend the instrument.
If a measure of total organics species (TOC) is needed, instru-
ments manufactured by Beckman instruments, Inc. and Ionics, Inc.
can be used to measure total organic carbon. The Beckman instrument
is a laboratory instrument and a chemist is required to prepare the
sample and to service and attend the instrument. The Ionics in-
strument is partially automatic and can be used on-line with or
without a filter in the sample line. This instrument will also
require significant attention and service to assure reliable and
accurate measurements. The cost of the Beckman instrument is $6195
complete. The Ionics, Inc. total organic carbon analyzer which is
an on-line instrument takes a sample every three minutes. This in-
strument is fed by an 1/8 inch line and will accept particles less
than 1/16 inch in diameter. The total cost of the Ionics TOC analyzer
is $9775.
Ionics also markets a Total Oxygen Demand instrument which is
similar to 'the TOC instrument in that it will accept some particles.
The TOD measurement represents all organic species which can be com-
bined with oxygen. The cost of the TOD instrument is $8750. The
estimated installation cost for each Ionics instrument is $1000.
•
The TOC and the TOD measurements are similar to the COD wet
chemistry method in that they do not measure the biodegradable
fraction of the organics present. Some instruments also make a
measurement of carbon before the dissolved carbon dioxide is removed
and this measurement is commonly called total carbon (TC.) Some
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minimal savings in cost can be realized if this measurement can be
substituted for the TOC measurement. The COD measurement requires
laboratory space and some glassware. Up to 72 COD determinations
can be made by one chemist in an 8 hour period.
Probably the most reliable way to measure the effluent volume
flow is with a Parshall flume. The Parshall flume is essentially
a Venturi with the water surface open to the atmosphere. The flow
is a non-linear function of the pressure drop across the Venturi.
The Parshall flume requires a concrete structure to support the
fiber-glass Parshall flume housing. The estimated cost of the con-
crete structure, the connecting pipeline and the fiber-glass housing
is shown in Figure 1. The cost of the electronic transmitter which
also interprets the non-linear pressure differential in terms of
volume flow is approximately $600. The recorder which gives in-
stantaneous flow, as well as the daily totalized flow, costs approx-
imately $700. If the flow recorder is positioned in the adminis-
tration building, the length of electrical cable will be about 7O
ft. for a 1. mgd plant, about 220 ft. for a 1O mgd plant and about
680 ft. for a 100 mgd plant. The cost of two two-conductor wires
in conduit will be about $150 for a 1 mgd plant, $4OO for a 10 mgd
plant and about $1200 for a 100 mgd plant.
For an additional $300 the tptalizer can be used to control a
proportional sample of the effluent stream. This, of course, does
not include the cost of the sampler. The cost of the sampler will
be in the range $1000-2000.
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COST OF EFFLUENT VOLUME FLOW MEASUREMENT
with
PARSHALL FLUME
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Plant Design Capacity, mgd.
Figure 1
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For water temperature measurement, a resistance type ther-
mometer would be the best choice. The thermometer will cost about
$80. One electronic transmitter will cost about $20O with an ad-
ditional $131 for installation. The recorder will cost about $30O.
Electrical wiring will cost about $150 for a 1 mgd plant, $400 for
a 10 mgd plant and $1200 for a 1OO mgd plant.
The electrode cell for pH measurement sells for about $300.
The transmitter will cost about $600 with an additional $131 for
installation. The recorder will cost about $300. Electrical wiring
will cost about the same as the temperature probe.
An alternative to automatic instrumentation is ivet chemistry
r
which requires adequate laboratory space, analytical instruments
and glassware. Laboratory facilities are normally installed in
treatment plants, although in the smaller plants they are often not
adequate. The mimimum recommended laboratory space is about 20 ft.
by 23 ft. in floor area. A prefabricated building of this size can'
be constructed for about $21.25 per square foot, or a total of about
$10,200. A total of about $17,100 will be required to equip such
a laboratory. An itemized list of recommended equipment is shown
with a floor plan of the laboratory in Figure 2. For effluent mon-
itoring alone, one chemist should be adequate. The level of chemist
should be about equivalent to GS-.7 in the government service. The
yearly salary would be $10,298 plus 15% for payroll extras, making
a total of $11,843 per year.
A summary of construction cost estimates for effluent monitoring
is shown in Table I. A 9x12 foot building has been provided at the
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EQUIPMENT FOR ANALYTICAL LABORATORY
Approximate Costs of Analytical Hardware
Bench space
Desks and other furniture
Glassware
Analytical equipment
Dissolved Oxygen Probe
Analytical Balance
Spectrophotoraeter
pH Meter
Conductivity Meter
Kjeldahl Digestor and Dist'n App.
Hot plates, flasks, condensers and
titration equipment.
Drying Oven
Muffle Furnace
Water Still
Wall cabinets, pegboard and miscellaneous
SAMPLE LAB.
20'
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$ 6,5OO
500
1,OOO
50O
1,000
2,OOO
50O
300
1,000
450
500
60O
75O
1,500
$17,100
i. FUME HOOD .
2 . BENCH UNIT W/ SINK
a PEG BOARD.
3 . PENINSULA TYPE BENCH
W/ CENTER DRAIN,
SHELF a SINK .
4 . CHEMICAL STORAGE .
5. INSTRUMENT TABLE W/
REGULATED VOLTAGE .
6 . DESKS .
7 . FILE CABINET .
6 . BALANCE TABLE.
9. TITRATION TABLE .
Figure 2
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TABLE I
CONSTRUCTION COST FOR' EFFLUENT MONITORING FACILITIES
Flow Measurement (Pars ha 11 flume)
Water Temperature Measurement
pH Measurement
Subtotal No. 1
Turbidity - Suspended Solids
•
Total Organic Carbon
Oxygen Uptake
9 ft. x 12 ft. Building
at sampling point «
Subtotal No. 2
2O ft. x 24 ft. Analytical
Chemistry Building
Laboratory Equipment
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$ 48 5O
861
13 5O
$7061
188O
10775
4800
400O
$21455
10200
17100
Subtotal No. 3 S $27300
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$16700
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1600
$19411
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4800
4000
$21455
10200
17100
$27300
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$72811
1880
10775
4800
4000
$21455
10200
17100
$27300
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\
sampling point to house the automatic sampling equipment to minimize
the length of the sampling lines. Notice that subtotals 2 and 3 are
not significantly different. If we also consider the fact that most
wastewater treatment plants are normally equipped with laboratory
facilities, the cost advantage appears to be in favor of using wet
chemistry for suspended solids, COD and oxygen uptake or BOD. It
is estimated that one full time chemist will be needed to service,
operate and calibrate the automatic instruments and that one full
time chemist can also make sufficient measurements by the wet chem-
istry method.
Although the best strategy will depend on the number and kind
of measurements required, it would appear reasonable to measure flow,
water temperature and pH automatically and rely on the wet chemistry
laboratory to perform the COD, BOD, and suspended solids measurements.
The construction cost involved would be the sum of subtotals 1 and 3.
This amounts to $34,361 for the 1 mgd plant, $46,711 for the 10 mgd.
plant and $100,111 for the 100 mgd plant. Since the major part of the
cost is in the Parshall flume, we can amortize this cost over 25
years at 6%. In terms of cents/Kgal the cost would be 0.7 cents/Kgal
for 1 mgd, 0.1 cents/Kgal for 10 mgd and 0.02 cents/Kgal for 10O mgd.
The cost of one full time chemist would be 3.2 cents/Kgal for the
1 mgd plant, O.32 cents/Kgal for the 10 mgd plant and 0.032 cents/Kgal
for the 100 mgd plant. The total cost would be the sum of amortization
and one full time chemist. This amounts to 3.9 cents/Kgal for 1 mgd,
0.42 cents/Kgal for 10 mgd and 0.05 cents/Kgal for 1OO mgd
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