EPA-R2-73-281
July 1973 Environmental Protection Technology Series
Electrical Power Consumption For
Municipal Wastewater Treatment
National Environmental Research Center
Office Of Rearch And Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
U. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
-------
EPA-R2-73-281
July 1973
ELECTRICAL POWE.R CONSUMPTION FOR MUNICIPAL
WASTEWATER TREATMENT
By
Robert Smith
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
Program Element 1B2043
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE QF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.25
-------
ABSTRACT
Electrical power consumption by most conventional and advanced
processes for treating municipal wastewater has been estimated
on a unit process basis. Electrical power for complete plants
has been estimated by adding power consumption for individual
processes and plant utilities. Electrical power consumption
for wastewater treatment has been compared to other consumptive
uses of electrical power.
111
-------
TABLE OF CONTENTS
Page
INTRODUCTION 3
PRELIMINARY TREATMENT 7
INFLUENT PUMPING 9
SEDIMENTATION 11
TRICKLING FILTERS 14
ACTIVATED SLUDGE PROCESS 15
SLUDGE HANDLING AND DISPOSAL 17
CHLORINATION 35
LIGHTS AND MISCELLANEOUS POWER 37
PRODUCTION OF POWER BY UTILIZATION OF SLUDGE GAS 41
TOTAL ELECTRICAL POWER CONSUMPTION FOR CONVENTIONAL PLANTS 43
EXPENDITURE FOR ELECTRICAL POWER IN CONVENTIONAL PLANTS 51
ELECTRICAL POWER REQUIREMENTS FOR ADVANCED PROCESSES 61
ELECTRICAL POWER REQUIREMENTS FOR ADVANCED PROCESS TRAINS 71
COMPARISON WITH OTHER CONSUMPTIVE USES 77
APPENDIX 85
v
-------
FIGURES
Number Page
1. Sludge Handling Schemes 5
2. Installed Electrical Horsepower for Settlers
versus Length of Settler
12
3. Installed Electrical Horsepower for Settlers
versus Design Capacity 13
4. Number of Anaerobic Digesters per Installation
versus Total Volume of Di'gester Installation 22
5. Installed Horsepower for Anaerobic Sludge Digester
Heater and Heat Exchanger 24
6. Total Installed Electrical Horsepower for Vatcuum
Filters 29
7. Electrical Energy Requirements for Multiple ,
Hearth Furnaces 33
8. Estimated Floor Area for Wastewater Treatment
Plants 38
9. Electrical Energy Requirements for Lighting and
Miscellaneous Power 39
10. Electrical Energy Consumption by Municipal Wa'ste^
water Treatment Plants versus Plant Size 49
1]. Annual Expenditure for Electrical Power in
Conventional Plants versus Plant Size 57
12. Cost of Electrical Power versus Daily Usage 59
13. Electrical Energy Requirements for Microstireens 62
14. Electrical Energy Consumption for Tertiary Waste*
water Trains versus Plant Size 75
VI
-------
TABLES
Number Page
I Electrical Energy Requirments for Wastewater
Treatment Plants - Primary - Scheme I 44
II Electrical Energy Requirements for Wastewater
Treatment Plants - Primary - Scheme II 45
III Electrical Energy Requirements for Wastewater
Treatment Plants - Activated Sludge - Scheme II 46
IV Electrical Energy Requirements for Wastewater i
Treatment Plants - Activated Sludge - Scheme III 47
V Electrical Energy Requirements for Wastewater
Treatment Plants - High Rate Trickling Filter -
Scheme II , 48
VI Cost of Electrical Power - Primary - Scheme I 52
VII Cost of Electrical Power - Primary - Scheme II 53
VIII Cost of Electrical Power - Activated Sludge -
Scheme II 54
IX Cost of Electrical Power - Activated Sludge -
Scheme III ^5
X Cost, of Electrical Power i- Trickling Filter -
Scheme II 56
XI Estimated Electrical Power Corlsumption for
Alternative Tertiary Treatment Trains after
Secondary Treatment Plant Size 1 mgd 72
XII Estimated Electrical Power Consumption for
Alternative Tertiary Treatment Trains after
Secondary Treatment Plant Size 10 mgd 73
XIII Estimated Electrical Power Consumption fo'r
Alternative Tertiary Treatment Trains after
Secondary Treatment Plant Size 100 mgd 74
XIV Percentage Distribution of Mining and Manu-
facturing KWHRS by Major Groups of SIC for
Investor-Owned Electric Utilities in U.S. 78
XV Consumption of Electrical Energy Based on the
1968 Inventory of Municipal Waste Facilities 79
vii
-------
CONCLUSIONS
Electrical power consumed in municipal wastewater treatment is
about 1% of the average residential consumption of electrical
power when the distribution of treatment schemes given in the
1968 Inventory of Municipal Waste Facilities is used as a basis,
If all communities were served by activated sludge plants, the
electrical power used will be about twice this amount. This is
equivalent to about 15 watts per household. Thus, for complete
secondary treatment, the power consumed is about equivalent to
24 hour operation of one desk lamp per household. The power
consumed by tertiary treatment depends on the processes used,
but for the Lake Tahoe system of tertiary treatment, the power
consumed is about 40-50% greater than the power consumed in
conventional activated sludge treatment.
-------
INTRODUCTION
This report contains estimates of electrical power consumption
for most of the conventional and advanced processes used to treat
municipal wastewater. Much of the inforKbtion was taken from
literature available from equipment manufacturers and some in-
formation was available from reports on EPA-sponsored research
projects. The assistance of applications engineers representing
the equipment manufacturers has been invaluable in clarifying
important points and in the contribution of technical information
not available in the open literature. This report could not have
been completed without their generous contributions. The detailed
cost estimates reported from the South Lake Tahoe Public Utility
District in California have been most useful.
The first part of the report is devoted to detailed calculations
of electrical power consumption for individual conventional
processes. These estimates are then summed for primary, trickling
filter, activated sludge plants and the sludge handling schemes
selected are shown in Figure 1. Estimates of mechanical and
electrical energy available from the use of anaerobic digester
off-gas are made and these are compared to the energy expended
in operation of the plant. The cost of electrical power was taken
from the report "Typical Electric Bills 1970" by the Federal Power
2
Commission. A detailed rate schedule currently used by the Cincin-
nati Gas and Electric Company was used to convert the estimated
power consumption values to expenditure for electrical power.
The second part of the report presents detailed computations of
electrical power consumption for the advanced or tertiary processes
to be used downstream of secondary processes. Estimates of electrical
power usage made at Lake Tahoe were the principal source of this
information. Electrical power consumption estimates were then
summed for various alternative tertiary treatment trains.
-------
Finally, the electrical power used in treatment plants is related
to other consumptive uses such as the typical residental, use of
electrical power. In this way the use of electrical power in
treatment of wastewater is put into perspective with the national
scene.
-------
1
Primary
Settler:
<
i
2
4
Aerator
X"~X 3
/Final ^
Uet
<
tier/
> 5
I 6
Anaerobic Digester
Sludge Drying Beds
SLUDGE HANDLING SCHEME I
• _
Primary
Settler
<
•
4
Aerator
(FinaA „
\Sett ler/
<
Thickener '
> 5
i 6
Incinerator
Vacuum
Filter
Sludge
Holding
Tank
10
SLUDGE HANDLING SCHEME II
5
Anaerobic
Digester
Figure 1
-------
SLUDGE HANDLING SCHEME IH
Thickener
Air Flotation
Thickener
Sludge Holding Tank
Vacuum Filter
Incinerator
10
Figure 1 (Cont'd.
-------
PRELIMINARY TREATMENT
Preliminary treatment is a generic term which includes processes
such as bar screens, comminutors, grit removal, and flow measure-
ment. The electrical power consumption for these processes is
comparatively small.
Bar screens are recommended for installation upstream of the in-
fluent pumps to remove debris which would interfere with the oper-
ation of the pumps. An average of about 5 cu. ft. of debris per
million gallons is removed. The bar screen is cleaned of debris
by a rake which travels about 7.5 ft/sec and operates for a maximum
of about 6 minutes an hour. The channel which serves the bar screen
is sized for a velocity of about 2 ft/sec at average flow. Ac-
cording to manufacturer's literature the minimum size motor to
drive the rakes is \ horsepower and a bar screen with sufficient
capacity to serve a 15 mgd plant can be powered by either a 5§ or
3/4 horsepower electric motor. It will be assumed here that all
bar screens up to 15 mgd will be powered by a 3/4 hp motor and
for each additional 15 mgd increment an additional 3/4 hp motor
will be required.
The electrical efficiency of electrical motors will be taken as
0.877 as recommended by one of the principal suppliers of elec-
trical motors. The electrical power in kilowatts is then ex-
pressed as follows;
Kilowatts = 0.85 x Horsepower (1)
Bar screen power consumption for all plants up to 15 mgd is,
therefore 1.53 kwh/day. This estimate will apply to the 1 and
10 mgd plants. The corresponding power consumption for the 100
mgd plant will be 10.7 kwh/day,
3
Manufacturers' literature for comminutors which are used to grind
and shred floating debris gives the size of the installed motor
-------
on each size comminutor. Several typical sizes are shown below: ' ;
Average Flow Range
.25 - 1.82 mgd 0.75 horsepower motor
.97 - 5.10 mgd 1.50 horsepower motor
1.0 - 9.40 mgd 1.5 horsepower motor
1.30 - 20. mgd 2.0 horsepower motor
Thus, for the 1 mgd plant size the smallest size unit would be
sufficient. The electrical power consumption, since the communitor
will operate 24 hr/day, will be 15.3 kwh/day. At the 10 mgd size
a conservative estimate would be two of the 1.5 horsepower sizes
and the electrical power consumption would be 61 kwh/day. At the
100 mgd size five of the larger size should handle the flow and
the power consumed would be 204 kwh/day.
Equipment for grit removal, according to one manufacturer , comes
in sizes capable of handling 5 mgd. The installed electric motor
is % horsepower. Thus, one horsepower per 10 mgd will be assumed.
The grit is removed usually during the high flow period in the
morning hours between 8-12 a.m. Therefore, at the 1 mgd size
electrical power consumption is estimated as 1.7 kwh/day.
At the 10 mgd size the power consumption can be estimated as 3.4
kwh/day and at the 100 mgd size as 34 kwh/day.
Flow measurement is accomplished by a Parshall flume in the smaller
plants and by a Venturi or magnetic flow meter in the larger sizes.
The power consumption for these flow sensing devices is negligible.
-------
INFLUENT PUMPING
A major part of the electrical power consumption at a waste-
water treatment plant is attributable to pumping the main stream
from one level to a higher level. The total pumping head to bring
the wastewater from the interceptor to the plant level varies some-
what with the plant, but about 30 ft. is commonly observed. The
horsepower consumed in pumping water is given by the following
relationship:
Pumping Horsepower = ^D * X° X H (2)
^ 1440 x 3960 x e^ v '
h
M3D = volume of water pumped, millions of gallons per day
H = total dynamic head, ft. of water
e, - hydraulic efficiency
This relationship can be simplified as follows:
Pumping Horsepower = MGD x 0.1754 x H/e (3)
The hydraulic efficiency of water pumps depends on the volume of
water pumped as well as the total dynamic head delivered. Since
most water pumps are driven by induction motors, the speed of the
pump is almost fixed. If the duty cycle for a pump is known, the
hydraulic efficiency can be accurately determined from the pump
map. For estimates of the kind made here, this is not possible.
Therefore, rough averages for hydraulic efficiency will be used.
One principal supplier of water pumps recommended the following
values which will be used in this report:
up to 1000 gpm 70% hydraulic efficiency
1000 - 7000 gpm 74% hydraulic efficiency
over 7000 gpm 83% hydraulic efficiency
Assuming a total dynamic head of 30 ft. for influent pumping, the
power consumption at the 1 mgd plant is computed as 133 ;ewh/day.
For the 10 mgd the corresponding value is 1451 kwh/day. For the
100 mgd size the value is 12,933 kwh/day.
-------
In this report, other pumping requirements such as recirculation
pumping for activated sludge process or trickling filters or
pumping of the main stream through such processes as carbon ad-
sorption, filtration, reverse osmosis, etc. will be handled in
a similar way.
10
-------
SEDIMENTATION
Settlers for removal of suspended solids from raw wastewater and
secondary settlers, used with the activated sludge process, can
be constructed in either a circular or a rectangular shape. In
this report only rectangular settlers will be considered. Rec-
tangular settlers are normally constructed with common walls and
the number of individual settlers needed, assuming an overflow
rate of 800 gpd/sq ft, as a function of plant size is given below;
MGD Number of Individual Settlers Length, feet
13 37
24 50
35 56
46 60
56 74
10 8 106
20 11 149
30 14 172
40 16 198
5O 17 232
6O 19 248
70 20 274
80 22 283
90 23 304
1OO 24 323
3
According to manufacturer's literature , the installed electrical
horsepower to drive the flights depends primarily on the length
of the settler as shown in Figure 2. The installed horsepower,
as a function of average flow, can, therefore be determined as
shown in Figure 3. Since settlers normally operate 24 hr/day,
we can compute the power consumption at !:he 1 mgd size as 30.6 kwh/day.
The corresponding values for 10 mgd and 100 mgd sizes are 122 kwh/day
and 734 kwh/day.
11
-------
--H- INSTALLED ELECTRICAL HORSEPOWER FOR SETTLERS
versus
LENGTH OF SETTLER
Length of Settler, ft.
FIGURE 2
-------
FPr
rr 11 j 111111
\ r TTTI
±r
TI !
rfl
-flfl
i!
:hr!:
INSTALLED ELECTRICAL HORSEPOWER FOR SETTLERS
versus
DESIGN CAPACITY
4 5 6789 10
10
Design Capacity, mgd
FIGURE 3
13
-------
TRICKLING FILTERS
Trickling filters can be designed in many configurations and the
pumping power consumed will depend on the configuration. The
loading in mgd/acre roughly divides filters into standard and
high rate. Filters with loadings in the range of 1.1-4.4 mgd/
acre are called standard filters while filters with loadings in
the range 8.7-44 mgd/acre are known as high rate. Recycle of the
main stream is commonly employed with high rate filters while
standard rate filters usually have no provision for recycle.
The depth of rock media in all filters is about 6 feet. The dis-
tributor is normally about 1 foot above the top of the rock media
and a head loss of about 2 feet occurs in the underdrains. The
head loss across the distributor is about 3 feet. Thus, the head
loss through a one stage trickling filter is about 12 feet. The
electrical power consumed in driving the main stream through the
filters is therefore, 61 kwh/day for the 1 mgd size, 580 kwh/day
for the 10 mgd size, and 5173 kwh/day for the 100 mgd size.
The recirculation ratio (volume of recycled stream/volume of main
stream) varies from 0.5 to 3 in most cases. A recycle ratio of
2.0 will be assumed here. When recycle is used, the power con-
sumption can be estimated by multiplying the estimates given above
by the recirculation ratio plus one.
For trickling filters without recycle, the power consumption is
only about one-tenth that required for supplying air to the acti-
vated sludge process.
Sludge production in high-rate trickling filters has been found
to be 35-50% of the BOD plus suspended solids load entering the
filter. If the primary settler removes 50% of the suspended solids
and 35% of the BOD, the sludge production is about 700-900 Ib/mg,
which is approximately the same as the conventional activated sludge
process.
15
-------
ACTIVATED SLUDGE PROCESS
Supplying oxygen to the activated sludge process is one of the
principal needs for electrical energy- The diffused air system
is most commonly used and the amount of air needed depends on the
strength of the primary effluent, the detention time in the aerator,
the concentration of mixed liquor suspended solids used, and whether
or not nitrification occurs. For normal conditions, such as 130
mg/1 5-day BOD into the aerator and a mixed liquor suspended solids
concentration of 2000 mg/1, the oxygen requirement is about 728
Ib. 0 per million gallons treated. If we take the aeration ef-
£
ficiency (oxygen dissolved/oxygen supplied) as a nominal 5%, the
amount of air required is about 0.92 scf/gal. To supply this air,
positive displacement or centrifugal compressors can be used. The
pressure to be supplied by the compressor is about 8.1 psig. The
power needed to compress the air, assuming isentropic compression,
is given by the following relationship:
(4)
Work of Compression, BTU/lb = c T (P /P ) n _
p J. 21
c = specific heat of air at constant pressure =
P .24 BTU/lb/°F
T = temperature of inlet air = 70° F = 530°R
P = outlet pressure, psia
P = inlet pressure, psia
n = ratio of specific heats = 1.40
Substituting into equation 4, the work required to compress atmos-
pheric air to 8.1 psig is 17 BTU/lb. Using the assumed value of
1 scf/gal and an air density of 0.075, 3125 Ib. of air per hour
must be delivered at the 1 mgd plant site. Since 2545 BTU/hr
is equivalent to one horsepower, the adiabatic horsepower associated
17
-------
with the air delivered is 20.87 at the 1 mgd plant size. If we
take the adiabatic efficiency of the blower as O.8, the horse-
power needed to drive the blower is 26.1 horsepower for the 1
mgd size. Since the blower operates 24 hr/day, the power consump-
tion at the 1 mgd size will be 532 kwh/day.
Literature from suppliers of mechanical aerators quote a transfer
efficiency of 3.5 Ib. 0 per bhp-hr in clean water and ideal con-
ditions. After the various correction factors are applied, the
effective transfer efficiency is about 2.17 Ib. C>2/bhp-hr. Since
we had assumed 1 scf/gallon for the diffused air system which is
equivalent to about 791 Ib. 0 /mg, the amount of power needed to
transfer this amount of oxygen, using mechanical aerators, is 365
bhp-hr/mg or 15.2 HP at the 1 mgd size.
Thus, based on this analysis, it would appear that mechanical
aeration is significantly less expensive than diffused air. The
five percent efficiency assumed for diffused air is conservative
and in tests made at the Milwaukee Wastewater Treatment Plant}
efficiencies as high as 15-17% have been observed for the ridge
and furrow type of diffused air system.
Recirculation of activated sludge requires electrical power. The
installed pump capacity recommended is 100% of the main stream,
but on the average, only about 50% of the main stream is returned.
From discussions with consulting engineers and pump manufacturers,
the pumping head for recirculation was estimated to be 15-20 ft. of
water. Thus, the electrical power consumption is 45 kwh/day at the
1 mgd size, 423 kwh/day at the 10 mgd size and 3131 kwh/day for the
100 mgd size.
Power requirements for final sedimentation will be taken as equal
to those already estimated for primary sedimentation.
The Linde Division of Union Carbide Corporation4 has estimated the
power requirements for generation of pure oxygen and dissolving it
in the aerator water at 25 hp for the 1 mgd size, 142 hp for the
6 mgd size, 700 hp for the 30 mgd size and 1960 hp for the 1OO mgd
size. An aerator with 2 hours detention time was assumed in making
these estimates.
18
-------
SLUDGE HANDLING AND DISPOSAL
Energy for pumping sludges from the primary settler and the acti-
vated sludge process is difficult to estimate, but the head to be
pumped against will be at least the 25-35 ft. required to pump the
sludge into the digester. Under average conditions, the sludge
volume in the primary plant will be about 0.00125 mgd/mgd of in-
fluent wastewater. For the activated sludge process, this ratio is
0.0052 mgd/mgd of plant influent. If we take the total head to be
100 ft., the power consumed in the 1 mgd primary plant is only
0.64 kwh/day. The power consumed for the 10 mgd and 100 mgd pri-
mary plants would be multiples of this value. For the 1 mgd acti-
vated sludge plant the power consumed for sludge pumping would be
2.66 kwh/day and for 10 mgd and 100 mgd the values would be 26.6
and 266 kwh/day-
The electrical power for operating gravity thickeners is based on
the drag forces on the sludge scraper. These are in the range of
8-12 Ib/ft of radius. The torque on the scraper and pickets, if
they are provided, equals the load in pounds per foot times the
radius in feet squared. The tip speed of the scraper is set at
1 ft. per minute. Horsepower is computed as torque (ft-lb) times
2 71 times the turning speed in rpm divided by 33,000. This relation-
ship can be reduced to the loading in Ib/ft times the radius in feet
divided by 33,000. This is clearly a negligible amount of power.
Since it is policy to install at least % horsepower motors, the
power can be estimated as \ horsepower per gravity thickener.
Primary plants are sometimes not equipped with gravity sludge thick-
eners. However, if a thickener is used, the normal loading rate is
16 Ib/day/sq ft. Since a 1 mgd primary plant will produce about
833 Ib/day of organic sludge, one 8 ft. dia. thickener should be
sufficient. At the 10 mgd size, two 18 ft. dia. thickeners should
be adequate. At the 100 mgd size, three 48 ft. dia. thickeners are
needed. Thus, the power consumed can be estimated as 10.2 kwh/day
at 1 mgd, 20.4 kwh/day at 10 mgd and 30.6 kwh/day at 100 mgd.
19
-------
The recommended loading rate for activated sludge plants is 8
Ib/day/sq ft. Since the activated sludge plant produces about
1726 Ib. of combined primary and waste activated sludge per million
gallons, the area needed at the 1 mgd size is 216 sq. ft. Thus,
one 18 ft. dia. thickener will be sufficient for the 1 mgd size.
For the 10 mgd size, two 38 ft. dia. thickeners will be adequate.
At the 100 mgd size, four 82 ft. dia. thickeners will be sufficient.
The installed horsepower is, therefore, 0.5 at the 1 mgd size, 1.0
at the 10 mgd size and 2.0 at the 100 mgd size. This is equivalent
to 10.2 kwh/day for 1 mgd, 20.4 kwh/day at 10 mgd and 40.8 kwh/day
at the 100 mgd size.
Installed horsepower for flotation thickening of waste activated
sludge is a log-log function of the surface area of the thickener.
For example, at 100 sq. ft. the installed horsepower is 14.5, at
1000 sq. ft. the installed horsepower is 115 and at 6000 sq. ft.
the installed horsepower is 570. The recommended loading rate
with chemical addition is 2 Ib/hr/sq ft. The loading rate, when
no chemicals are used, is about 0.5 Ib/hr/sq ft. The amount of
waste activated sludge produced is about 900 Ib/mg. Thus, at a
1 mgd plant where the flotation thickener is operated 40 hr/week
and chemicals are used, about 80 sq. ft. of surface area would be
required. The next largest standard size is 100 sq. ft. This
unit requires about 14.5 horsepower. The consumption of electrical
power will be 70 kwh/day. Similarly, at the 10 mgd size (assumed
to operate 100 hr/wk) the unit selected would be 400 sq. ft. and
the installed horsepower is 50 horsepower. Operating an average
of 14.3 hr/day the power consumption will be 608 kwh/day. At the
100 mgd size which operates 24 hr/day, the size of installation
will be two 1000 sq. ft. units having 115 horsepower each for a
total of 230 hp. The power consumption will be 4692 kwh/day. If
no chemicals are used the power consumption at 1 mgd will be 242
kwh/day, at 10 mgd 1800 kwh/day, and at 100 mgd 18,800 kwh/day.
The use of flotation thickeners for thickening of activated sludge
can be expensive in terms of electrical power consumption.
20
-------
Electrical energy is consumed in the anaerobic digestion process
for two principal reasons; first, for mixing the contents of the
primary digester (gas recirculation) and second, for heating the
incoming sludge and holding the contents of the digester at the
optimum temperature, usually about 95°F.
Anaerobic digesters range in size from 25 ft. in diameter to a
maximum of about 110 ft. The depth is generally about 20 ft. at
the 25 ft. size and about 35 ft. at the maximum size. The points
on Figure 4 show the number of anaerobic digesters in installations
with various total volumes.
The solid lines on the right and left of the data points represent
limits corresponding to 25 ft. diameter and 20 ft. deep digesters
on the left bound and 110 ft. diameter and 35 ft. deep on the
right bound.
An interesting and important problem is to find the number of
digesters which will minimize the cost of the installation when
one extra digester is provided (over and above the minimum re-
quirements) for cleaning and maintenance. This problem can be
solved in a crude way by assuming that the cost of the digester
is directly proportional to the volume of concrete involved.
Clearly, if no duplication of digesters were needed, the minimum
cost would be represented by building one large digester in every
case up to the maximum size of 110 feet. Thus, the optimum sizes
would be represented by a horizontal line at N = 1 terminating in
the right hand bound and then following the right hand bound.
Clearly, this principal is not always followed.
The results of the simplified analysis of optimum number of digesters
to provide one extra is shown by the squared points. The dashed
stepped line is only an approximation because the number of digesters
must be an integer. It appears from this analysis that at the larger
sizes, say about 500,000 cu. ft., practice is not significantly
different from the optimum number of digesters. At the smaller sizes,
21
-------
21- -
_LO.Q_.
T3 -:-
Vl
0)
0) -"•
•H
Q
•O
•H
- >
•H
T3
_ C
M-l
0 .
NUMBER OF ANAEROBIC DIGESTERS PER INSTALLATION
versus
TOTAL VOLUME OF DIGESTER INSTALLATION
-. -.I-:.
J+LL
±
~rr;
Jl"
in
^
itt
-ffft
tlfl
£S
±TE
I
a-
-, - -,._:-_i_
Li- I
iH-t
3 4 5678
! 10
100
3 4 5678910
1000
3 4 & 6789 10
Total Digester Volume, thousands of cubic feet
FIGURE 4
22
-------
however, there seems to be a tendency to not provide for dupli-
cation of digester facilities. Where duplication is shown, it
appears that three digesters might have been more cost-effective
than two digesters.
Electrical power is consumed in heating incoming sludge and over-
coming the heat loss to the environment. The usual practice is to
operate a hot water boiler and pump the sludge from the digester
through the hot water heat exchanger to maintain the temperature
in the digester at the 95°F level. The installed electrical horse-
power for units with heating capacities in BTU/hr is shown in
Figure 5. These motors do not all operate continuously, but the
manufacturer estimates that power consumption would, on the average,
be equivalent.to operation of all motors 75% of the day. By es-
timating the number and size of digesters for primary and activated
sludge plants of various sizes, the heat requirements can be found
and from this the consumption of electrical power.
Primary plants produce about 833 Ib/mg and activated sludge plants
about 1726 Ib/mg. In terms of volatile solids, these estimates
are 650 Ib/mg for the primary plant and 1275 Ib/mg for the activated
sludge plant.
For completely mixed digesters the recommended loading is 1000 cu.
ft. of digester volume for each 8O Ib. volatile solids per day-
Thus, a primary completely mixed digester for a primary plant would
be sized on 8,125 cu ft/mg. Similarly, for the activated sludge
plant the sizing parameter would be 15,400 cu ft/mg.
If we take conventional practice as a guide, (see figure 4 ) we can
assume that up to about 60,000 cu. ft. a single digester will be
provided. Two digesters might be provided up to a volume of about
400,000 cu. ft. Three digesters might be provided up to about
850,000 cu. ft. Four digesters will be provided up to 1,350,000
cu. ft. and above this the maximum size digester with 338,000 cu.
ft. might be used.
23
-------
_l _l.
r
41-r-
•ITr
4-
'0
9
INSTALLED HORSEPOWER FOR ANAEROBIC SLUDGE'—,.
DIGESTER HEATER AND HEAT EXCHANGER
10
1,000
.-pac.'-xv - tfion/sands of BTU/hr
•' 6 6 7 8 9 10
10,000
ICURE 5
-------
The number and volume of primary digesters in primary and acti-
vated sludge plants can, therefore, be estimated as follows:
Primary Plants Plant Size Activated Sludge Plants
1 digester @ 8,125 cu ft 1 mgd 1 digester @ 15,400 cu ft
2 digesters @ 40,625 cu ft 10 mgd 2 digesters @ 77,OOO cu ft
3 digesters @ 270,833 cu ft 100 mgd 5 digesters @ 308,000 cu ft
For primary plants, the heat load in BTU/hr can be computed as
9000 times the design population in thousands. The factor for
activated sludge plants is 15,OOO. Loss of heat through the walls
of the digester can also be estimated in an approximate way. For
digesters with gas recirculation and exposed outside walls, the
heat load can be approximated by multiplying the digester capacity
in thousands of cubic feet times a factor. This factor is 4800
for a moderate climate such as that for Cincinnati, Ohio. Heat
requirements for primary and activated sludge digesters can be
computed as follows :
Primary Plants :
BTU/hr = 90,000 x mgd + 4800 x I^ster volume cu. ft.
^
Activated Sludge Plants :
/, , ^ ~~~ •, *r>^^ Digester volume cu. ft.
BTU/hr = 150,000 x mgd + 4800 x - —
1000
The capacity of sludge heating units for each size of plant can
now be computed as follows;
Primary Plants Plant Size Activated Sludge Plants
1 @ 129,000 BTU/hr 1 mgd 1 @ 223,920 BTU/hr
2 @ 645,000 BTU/hr 10 mgd 2 @ 1,119,600 BTU/hr
3 @ 4,300,000 BTU/hr 100 mgd 5 @ 4,478,400 BTU/hr
25
-------
The installed horsepower can be taken from Figure 5 to give the
following estimates:
Primary Plant Plant Size Activated Sludge Plant
1 unit @ 1.1 hp 1 mgd 1 unit @ 1.15 hp
2 units @ 3.1 hp = 6.2 hp 10 mgd 2 units (§ 4 hp = 8 hp
3 units @ 10.3 hp = 30.9 hp 100 mgd 5 units @ 10.3 hp = 51.5 hp
Assuming that these installed electric motors operate about 75%
of the time, the following estimates for electrical power con-
sumption can be computed:
Primary Plant Plant Size Activated Sludge Plant
16.8 kwh/day 1 mgd 17.6 kwh/day
95. kwh/day 10 mgd 122.4 kwh/day
473. kwh/day 100 mgd 788 kwh/day
These are the electrical energy requirements for the primary digester
which is always heated. If the secondary digester is to be heated
these values should be multiplied by two. Secondary digesters are
usually not heated.
Electric motors are also used to drive the gas recirculation equip-
ment for mixing the contents of the primary digester.
From specifications of manufacturers' of gas recirculation systems
for mixing of anaerobic digesters, the following operating horse-
powers are shown as a function of the diameter of the digester;
25-30 ft. dia. 4.09 HP
31-40 ft. dia. 5.20 HP
41-50 ft. dia. 5.20 HP
51-80 ft. dia. 8.18 HP
81-110 ft. dia. 11.0 HP
Since the mixers normally operate 24 hr/day, the electrical power
consumption can be estimated directly from the installed horsepower
shown above.
26
-------
Since the depth of sludge in the digester is known to vary from
20 ft. at the 25 ft. dia. size to 35 ft. at the 110 ft. dia. size,
the diameter of the digesters required can be computed as follows:
Primary Plants Plant Size Activated Sludge Plants
1 @ 23 ft. dia. 1 mgd 1 @ 31 ft. dia.
2 @ 47 ft. dia. 10 mgd 2 @ 62 ft. dia.
3 @ 102 ft. dia. 100 mgd 5 @ 108 ft. dia.
The installed electrical horsepower for mixing is given below:
Primary Plants Plant Size Activated Sludge Plants
1 @ 4.09 hp 1 mgd 1 @ 5.2 hp
2 <§ 5.2 hp = 10.4 hp 10 mgd 2 @ 8.18 hp = 16.36 hp
3 @ 11 hp = 33 hp 100 mgd 5 @ 11 hp = 55 hp
Power consumption in kwh/day are given below;
Primary Plants Plant Size. Activated Sludge Plants
84 kwh/day 1 mgd 106 kwh/day
212 kwh/day 10 mgd 334 kwh/day
673 kwh/day 100 mgd 1122 kwh/day
Aerobic digestion is sometimes used to destroy suspended solids in
waste activated sludge and to improve the dewatering characteristics
of the remaining solids. The aerobic digester is similar to an
aerator used in the activated sludge process except that settling
and recycle of thickened sludge is not provided. The digester is
supplied with diffused air, except during the periods when the con-
tents of the digester are allowed to settle in order to draw off
the thickened digested sludge. The detention time needed, when
waste activated sludge alone is digested, is in the range 15-20 days
Since the volume of the waste activated sludge stream is about
0.018 mg/mg, a 1 mgd plant would produce about 18,000 gallons of
waste activated sludge per day, requiring about 36,000 cu. ft. of
digester capacity. About 25-30 cfm per 1000 cu. ft. of digester
capacity is recommended to keep the sludge in suspension and supply
27
-------
the oxygen demand of the microorganisms. Since about 90O scf is
needed in diffused air system, the air requirements for the 1 mgd
aerobic digestion process exceeds the requirements for the con-
ventional activated sludge process by a factor of 1.3. Thus,
aerobic digestion increases the electrical power consumption of
activated sludge plants significantly-
The installed electrical horsepower for vacuum filters is shown
in Figure 6 . The estimated amounts of sludge to be vacuum fil-
tered, using sludge handling scheme II for primary plants and
sludge handling schemes II and III for activated sludge plants.
is shown below together with the size of filter likely to be in-
stalled and the operating times:
PRIMARY PLANTS
SCHEME II
1 mgd
10 mgd
100 mgd
508 Ib/day
5,080 Ib/day
50,800 Ib/day
60 sq. ft.
125 sq. ft.
250 sq. ft.
0.94 hr/day
5. hr/day
24. hr/day
ACTIVATED SLUDGE PLANTS
1 mgd
10 rngd
100 mgd
1,046 Ib/day
10,886 Ib/day
108,860 Ib/day
SCHEME II
60 sq. ft.
575 sq. ft.
2 x 575 = 1150 sq. ft.
4.36 hr/day
5. h r/day
24. hr/day
ACTIVATED SLUDGE PLANTS SCHEME III
1 mgd
10 mgd
100 mgd
1,661 Ib/day
17,261 Ib/day
172,610 Ib/day
60 sq. ft.
575 sq. ft.
3 x 430 = 1290 sq. ft.
4.6 hr/day
5. h r/day
24. hr/day
Using these estimates and the installed electrical horsepower
shown in Figure 6, the following electrical power requirements
can be calculated;
PRIMARY PLANTS SCHEME II
1 mgd 10.4 kw-hr/day
10 mgd 108 kwh/day
100 mgd 847 kwh/day
ACTIVATED SLUDGE PLANTS SCHEME II
1 mgd
10 mgd
100 mgd
57 kwh/day
346 kwh/day
3325 kwh/day
28
-------
TOTAL INSTALLED ELECTRICAL HORSEPOWER FOR VACUUM FILTERS
Vacuum Filter Area, sq. it.
-------
ACTIVATED SLUDGE PLANTS SCHEME III
1 mgd 60 kwh/day
10 mgd 346 kwh/day
100 mgd 3947 kwh/day
Electrical power consumption by centrifuges used for dewatering
digested organic sludge can be estimated accurately by the manu-
facturers of the equipment, but the computations are complex and
depend on the specific application intended. The type of centri-
fuge considered here is the solid bowl centrifuge for dewatering
digested organic sludge. Estimates of power consumed are shown
below for four different centrifuge sizes:
1. 0.73 - 1.6 horsepower/gpm
2. 0.8 - 1.48 horsepower/gpm
3. 0.43 - 0.81 horsepower/gpm
4. 0.41 - 0.74 horsepower/gpm
The limits of power consumption shown above correspond to 1000 g's
and 20OO g' s. The lower value is typical of operation where the
sludge is to be disposed of by land spreading. The higher value
is characteristic of a dryer sludge which might be incinerated.
The range of volume handled per centrifuge is 10 gpm for the
smaller size and 140 gpm for the larger size. When waste sludge
is to be incinerated, it is common practice to provide a gravity
thickener upstream of the centrifuge. The concentration of the
thickened sludge would be about 5% solids. If we take the amounts
of sludge given in the discussion on vacuum filters and convert
these amounts to gpm, assuming a solids concentration of 5%, the
volume of the stream to the centrifuge in the primary plants is
0.85 gpm at 1 mgd, 84.7 gpm at 10 mgd and 847. gpm at the 100 mgd
size if the centrifuge is operated 24 hr/day. Thus, the power
consumed in the primary plants would be 28 kwh/day at 1 mgd, 256
kwh/day at 10 mgd and 1400 kwh/day at 100 mgd. For activated
sludge plants using sludge handling scheme II, the power consumed
at 1 mgd would be 57 kwh/day, at 10 mgd 368 kwh/day and at 100 mgd
31
-------
2740 kwh/day. For activated sludge plants using sludge handling
scheme III, the corresponding values would be 90 kwh/day at 1 mgd,
435 kwh/day at 10 mgd and 4348 kwh/day at 100 mgd. Thus, the
electrical power consumption for centrifugation of digested sludge
is somewhat higher than that required for vacuum filters.
The amounts of sludge to be incinerated will equal the amounts
7
vacuum filtered. Figure 7 shows the electrical power consumption
as a function of hearth area in terms of kwh per ton of sludge in-
cinerated. The recommended loading is 2 Ib. of sludge per hour
per sq. ft. of hearth area. The size of incinerator likely to be
used is shown below together with the electrical power consumption:
PRIMARY PLANTS
1 mgd
10 mgd
100 mgd
SCHEME II
85 sq. ft.
510 sq. ft.
2 x 575 = 1150 sq. ft.
28.4 kwh/day
152.4 kwh/day
1148. kwh/day
ACTIVATED SLUDGE PLANTS SCHEME II
1 mgd
10 mgd
100 mgd
112 sq. ft.
1,117 sq. ft.
2,275 sq. ft.
ACTIVATED SLUDGE PLANTS
SCHEME III
1 mgd 166 sq. ft.
10 mgd 1,752 sq. ft.
100 mgd 2 x 1849 = 3698 sq. ft
54
245
1905
75
328
3280
kwh/day
kwh/day
kwh/day
kwh/day
kwh/day
kwh/day
32
-------
ELECTRICAL ENERGY REQUIREMENTS FOR MULTIPLE HEARTH FURNACES
6 7 8 9 10
Hearth Area per MHF, sq. ft,
FIGURE 7
33
-------
CHLORINATION
The dose of chlorine for disinfection of primary effluent is
20-25 mg/1. For activated sludge effluents the corresponding
dose is 8 mg/1. Thus, the average useage of chlorine is 187
Ib/mg for primary plants and 67 Ib/mg for activated sludge plants.
The three standard sizes of chlorinators are 400 Ib/day, 2000
Ib/day and 8000 Ib/day. When the chlorine is removed from the
storage pressure vessel as a gas, the power requirements for these
chlorinators are negligible; 30 watts for the 400 and 2000 Ib/day
units and 75 watts for the 8000 Ib/day unit.
If a large amount of chlorine is used at a plant, it is often ad-
vantageous (reduced storage) to remove the chlorine as a liquid
and then evaporate the chlorine to a gas before use in the chlor-
inator. The kilowatt rating of a standard evaporator is 18 kilo-
watts. The manufacturer recommends the use of an evaporator if
chlorine useage exceeds 2000 Ib/day.
The actual dissipation of electrical energy can be computed from
the heat of vaporization of chlorine (123.7 BTU/lb) and the heat
required to raise the temperature of the gas to ambient temperature.
The specific heat of chlorine is 0.115 BTU/lb and since the boiling
point is -30 F, about 11.5 BTU/lb is needed to bring the gas to
room temperature. The total to evaporate chlorine is 135 BTU/lb.
One kilowatt-hr is equivalent to 3412 BTU.
The 2000 Ib/day point is equivalent to about 10 mgd for a primary
plant and 30 mgd for an activated sludge plant. The 1 mgd plait
would, therefore, consume only 30 watts or 0.72 kwh/day. The 10
mgd primary plant would consume 3C watts plus 135 BTU/lb or a total
of 82.4 kwh/day. The 10 mgd activated sludge plant would consume
only 3O watts. The 100 mgd primary plant would consuma 20,825 Ib
Cl per day. The chlorinators would corsume 225 watts and the heat
to vaporize the chlorinS would amount to 824 kwh/day for a total of
829 kwh/day. The corresponding value for the 100 mgd activatec
sludge plant is 226 kwh/day.
35
-------
LIGHTS AND MISCELLANEOUS POWER
Additional electrical power is used in plants for indoor and out-
door lighting, operation of hand tools and office equipment, and
other miscellaneous uses. The annual reports of the larger plants
often give an estimate of this consumptive use, but in the smaller
plants, an estimate must be made. The circled points in Figure 9
show values taken from the annual reports of ;four large plants.
Building electrical usage for lights and outlets is often estimated
as 2-4 watts per square foot of floor area. In estimating the
building power consumption for plants in the 1-10 mgd range, a
working day of 10 hours was assumed. The floor area assumed as
a function of plant size is shown in Figure 8 .
8
From a recent study made by Black and Veatch Consulting Engineers ,
the estimated number of outdoor lights was found to be four lights
at a 1 mgd plant, 8 lights at a 5 mgd plant and 12 lights at a
10 mgd plant. The average expenditure per outdoor light was
estimated as $25 per year. If we take the average cost of elec-
trical power as 2 cents/kwh, one light would consume 342 watts,
which is a good average between the conventional 400 watt street
light and the 250 watt pole light often used in plants around
aerators and settlers. If we assume that the outdoor lights are
turned on for an average of 10 hr/day, the curve shown in Figure 9
can be constructed.
37
-------
ESTIMATED FLOOR AREA FOR WASTEWAIER TREATMENT PLANTS
EEE
HI
±1-
1
=F-t
-FI-FF
-fi+4
-. H-
•I
-47.
:f
i-lt
±
-h-
+H
ffil
ffi
c±tti
-Li-J-l-
I
l+tr^fF^
—h~H- ^f\ ' ,e,
±t
TTi
s
I
t;±
+irt
if*
it
- -p
--S-I -"-
•ff
±fl±
ill
-FT-
3EE
1
itri
I
:Ef
:Tf
:±
rt
Q) '
=! n-
1
m
•ffi
I
turn
ttt
2 4 5678910
10
3 4 5 678910
100
Plant Size, mgd
38
FIGURE 8
-------
ELECTRICAL ENERGY REQUIREMENTS FOR LIGHTING AND MISCELLANEOUS POWER
3 4 567691
2 3 45678SI
3 4 567091
4 567891
4 567891
>>
-3
Thin-)
i
T"
•~:p::
f"T
i _.
Tffi-
1
O
i— I
•H
•H-i-i
Ite
1
-4-4.
__| .
i_
iti:
ii
tt
il
B
10
100
Plant Size, mgd
FIGURE 9
-------
PRODUCTION OF POWER BY UTILIZATION OF SLUDGE GAS
Gas produced as a result of anaerobic digestion of organic sludge
can be used to supply internal combustion engines. These 1C engines
can be direct coupled to air blowers or water pumps or can be used
to drive electric generators. Digester gas can also be used to
heat the digesters or to support combustion in the incinerator.
Digester gas is normally about 65-7O% methane by volume. The
volume of gas produced per pound of volatile solids destroyed is
reported as 17-18 scf/lb at the larger and better instrumented
plants. Smaller plants report lesser values, sometimes as low as
6 scf/lb VSS destroyed, but these lower values are probably due to
poor measurement techniques. The fuel value of methane is about
963 BTU/scf and since digester gas is about 67% methane, the fuel
value of digester gas is about 645 BTU/scf.
Average values for volatile solids fed to the digesters is 650
Ib/mg for primary plants and 1275 Ib/mg for activated sludge
plants. if we assume that about 50% of these volatile solids
will be destroyed in the digester and a yield of 17.5 scf/lb
destroyed, the amount of digester gas available will be 5688 scf/mg
for the primary plant and 11,156 scf/mg for the activated sludge
plant.
The BTU's available for power generation will be 3.669 x 10
fi
BTU/mg for the primary plant and 7.20 x 10 BTU/mg for the acti-
vated sludge plant. If we use this gas in an internal combustion
engine, the power produced, using 7000 BTU/bhp-hr, will be 524
bhp-hr/mg for the primary plant and 1029 bhp-hr/mg for the activated
sludge plant. Assuming 24 hr. operation of the blowers, a direct
coupled 1C engine would develop about 43 horsepower per million
gallons in the activated sludge plant. Thus, sufficient gas is
produced to drive the blowers.
At the Cincinnati Mill Creek Primary Plant where digester gas is used
41
-------
to generate electrical power, it has been reported that 17.5 scf
of digester gas is used to produce one kilowatt-hour. Therefore,
if all of the gas was utilized, about 325 kwh/mg could be produced
in the primary plant and 627 kwh/mg could be produced in the acti-
vated sludge plant. Since primary plants use about 235 kwh/mg, it
should be possible to supply all of the electrical energy require-
ments for primary plants by using an 1C engine to drive a generator.
This is, in fact, what is done at the Mill Creek Plant and a neg-
ligible amount of power is purchased. The activated sludge plants
consume an average of 942 kwh/mg; this exceeds the amount of power
which might be generated by utilization of digester gas. Even in
activated sludge plants a.maximum of 2/3 of the power needed could
be generated by using sludge gas.
Since sludge gas is not produced continuously, a storage sphere
is normally provided and some power is consumed in storing the gas
at about 40 psig. Sludge gas is also often used for heating the
digester or for operating the incinerator. Thus, the total amounts
estimated above might not be available for power generation.
42
-------
TOTAL ELECTRICAL POWER CONSUMPTION FOR CONVENTIONAL PLANTS
Since estimates of power consumption have been made for all of
the conventional processes shown in Figure 1, these can now be
summed to find the total power consumption for complete plants.
These totals are shown in Tables I and II for primary plants using
sludge handling schemes I and II. In Tables III and IV the totals
for activated sludge plants using sludge handling schemes II and
III are shown. Table V gives the totals for trickling filter
plants using sludge handling scheme II. Since no electrical power
is used by sand drying beds, the totals for activated sludge plants
using sludge handling scheme I can be found by subtracting the con-
sumption for vacuum filtration and incineration from totals for
sludge handling scheme II. These totals are 1004 kwh/day at 1 mgd,
8218 kwh/day for 10 mgd and 75,864 kwh/day for the 100 mgd size.
Similarly, the totals for trickling filter plants using drying
beds would be 610 kwh/day at 1 mgd, 4215 kwh/day at 10 mgd, and
35,052 kwh/day at 10O mgd.
Total electrical power consumption for plants taken from Tables
I-V are shown plotted versus plant size in Figure 10. Power con-
sumption for activated sludge plants is almost linear with plant
size because influent pumping and diffused air consumption are
the major uses and these are linear with the volume of the main
stream. The curves for primary and trickling filter plants show
significant economy of scale.
43
-------
TABLE I
ELECTRICAL ENERGY REQUIREMENTS FOR WASTEWATER TREATMENT PLANTS
TYPE OF PLANT Primary
SLUDGE HANDLING SCHEME I
Killowatt -hours/day
PLANT SIZE
PRELIMINARY TREAT mNT
Bar Screens
Comrainutors
Grit Removal
INFLUENT PUMPING (30 ft TDH)
PRIMARY SEDIMENTATION
(800 gpd/sq ft)
TRICKLING FILTERS
Recirculation Pumping
Final Sedimentation
ACTIVATED SLUDGE PROCESS
Diffused Air
Recirculation Pumping (50%,
17.5 ft)
Final Settlers (800 gpd/sq ft)
CHLORINATION
SLUDGE HANDLING AND DISPOSAL
Sludge Pumping
Gravity Thickeners
Air Flotation Thickeners
Anaerobic Digesters
Mixing
Heating
Vacuum Filtration
Multiple Hearth Incineration
LIGHTS AND MISCELLANEOUS POWER
TOTAL Kilowatt-hours/day
1 mgd
1.53
15.3
1.7
153
30.6
0.72
'0.64
10.2
84.
17.6
57.
372
10 mgd
1.53
61.
'3.4
1,451
122.
82.4
6.4
20.4
212.
122.4
210.
•2293
100 mgd
10.7
204.
34.
12,933
734.
829.
64.
30.6
673.
788.
2400.
18,700
44
-------
TABLE II
ELECTRICAL ENERGY REQUIREMENTS FOR WASTEWATER TREATMENT PLANTS
TYPE OF PLANT Primary
SLUDGE HANDLING SCHEME II
Killowatt -hours /day
PLANT SIZE
PRELIMINARY TREATMENT
Bar Screens
Comminutors
Grit Removal
INFLUENT PUMPING (30 ft TDH)
PRIMARY SEDIMENTATION
(300 gpd/sq ft)
TRICKLING FILTERS
Recirculation Pumping
Final Sedimentation
ACTIVATED SLUDGE PROCESS
Diffused Air
Recirculation Pumping (50%,
17.5 ft)
Final Settlers (800 gpd/sq ft)
CHLORINATION
SLUDGE HANDLING AND DISPOSAL
Sludge Pumping
Gravity Thickeners
Air Flotation Thickeners
Anaerobic Digesters
Mixing
Heating
Vacuum Filtration
Multiple Hearth Incineration
LIGHTS AND MISCELLANEOUS POWER
TOTAL Kilowatt-hours/day
1 mgd
1.53
15.3
1.7
153
30.6
0 . 72
.64
10.2
84.
17.6
10.4
28.4
57
411
10 mgd
1.53
61.
'3.4
1451.
122.
62.4
6.4
20.4
212.
122.4
108
152.4
210
2,343
100 mgd
1'''. 7
204.
-J4
12,,,,
7J4.
82-.
64.
30.6
673.
788.
847.
,'1448.
2 , 400
21,000
45
-------
TABLE III
ELECTRICAL ENERGY REQUIREMENTS FOR WASTEWATER TREATMENT PLANTS
TYPE OF PLANT Activated Sludge
SLUDGE HANDLING SCHEME II
Killowatt -hours/day
PLANT SIZE
PRELIMINARY TREAT NE NT
Bar Screens
Comminutors
Grit Removal
INFLUENT PUMPING (30 ft TDH)
PRIMARY SEDIMENTATION
(300 gpd/sq ft)
TRICKLING FILTERS
Recirculation Pumping
Final Sedimentation
ACTIVATED SLUDGE PROCESS
Diffused Air
Recirculation Pumping (50%,
17.5 ft)
Final Settlers (800 gpd/sq ft)
CHLORINATION
SLUDGE HANDLING AND DISPOSAL
Sludge Pumping
Gravity Thickeners
Air Flotation Thickeners
Anaerobic Digesters
Mixing
Heating
Vacuum Filtration
Multiple Hearth Incineration
LIGHTS AND MISCELLANEOUS POWER
TOTAL Kilowatt-hours/day
1 mgd
1.53
15.3
1.7
153
30.6
532
45
30.6
.72
'2.65
10.2
106.
17.6
57.
54.
57
1,115
10 mgd
1.53
61.
3.4
1 , 451
122.
5,320
423
122.
.72
26.6
20.4
334.
122.4
346.
245.
210
8,809
100 mgd
10.7
2O4.
34.
12,933
734.
53,200
3,131
734
266
266
40.8
1,122.
788.
3,325.
,'1,905.
2,400
81,094
46
-------
TABLE IV
ELECTRICAL ENERGY REQUIREMENTS FOR WASTEWATER TREATMENT PLANTS
TYPE OF PLANT Activated Sludge SLUDGE HANDLING SCHEME III
Killowatt -hours /day
PLANT SIZE
PRELIMINARY TREATMENT
Bar Screens
Comminutors
Grit Removal
INFLUENT PUMPING (30 ft TDK)
PRIMARY SEDIMENTATION
(800 gpd/sq ft)
TRICKLING FILTERS
Recirculation Pumping
Final Sedimentation
ACTIVATED SLUDGE PROCESS
Diffused Air
Recirculation Pumping (50%,
17.5 ft)
Final Settlers (800 gpd/sq ft)
CHLORINATION
SLUDGE HANDLING AND DISPOSAL
Sludge Pumping
Gravity Thickeners
Air Flotation Thickeners
Anaerobic Digesters
Mixing
Heating
Vacuum Filtration
Multiple Hearth Incineration
LIGHTS AND MISCELLANEOUS POWER
TOTAL Kilowatt-hours/day
1 mgd
1.53
15.3
1.7
153
30.6
532
45
30.6
.72
2.65
10.2
70.
60.
75.
57.
1,085
1O mgd
1.53
61.
'3.4
1,451
122.
5,320
423
122.
.72
26.6
20.4
608.
346.
328.
210.
9,044
100 myd
10.7
204.
34.
12,933
734.
53 , 200
3,131
734
266.
266.
30.6
4,692.
3,947.
3,280
2,400.
85,862
47
-------
TABLE V
ELECTRICAL ENERGY REQUIREMENTS FOR WASTEWATER TREATMENT PLANTS
High Rate
TYPE OF PLANT THrklinq Filter SLUDGE HANDLING SCHEME II
Killowatt -hours/day
PLANT SIZE
PRELIMINARY TREATMENT
Bar Screens
Comrainutors
Grit Removal
INFLUENT PUMPING (30 ft TDH)
PRIMARY SEDI1\ENTATION
(800 gpd/sq ft)
TRICKLING FILTERS
Recirculation Pumping
Final Sedimentation
ACTIVATED SLUDGE PROCESS
Diffused Air
Recirculation Pumping (50%,
17.5 ft)
Final Settlers (800 gpd/sq ft)
CHLORINATION
SLUDGE HANDLING AND DISPOSAL
Sludge Pumping
Gravity Thickeners
Air Flotation Thickeners
Anaerobic Digesters
Mixing
Heating
Vacuum Filtration
Multiple Hearth Incineration
LIGHTS AND MISCELLANEOUS POWER
TOTAL Kilowatt-hours/day
1 mgd
1.53
15.3
1.7
153
30.6
183
30.6
.72
'2.6t
10.2
106
17.6
57
54
57
721
10 mgd
1.53
61.
3.4
1,451
122.
1740
122
.72
26.6
20.4
344
122.4
346
245
210
4,806
100 mgd
10.7
204.
34.
12,933
734.
15,519
734
266.
266.
40.8
1,122
788
3,325
1,905
2,400
40,282
48
-------
ELECTRICAL ENERGY CONSUMPTION BY MUNICIPAL WASTEWATER TREATMENT PLANTS
versus
PLANT SIZE
100,000
fi)
100
3 4 5678910
10
3 4 5678910
Plant Design Capacity, mgd
49
100
FIGURE 10
-------
EXPENDITURE FOR ELECTRICAL POWER IN CONVENTIONAL PLANTS
The cost of electrical power depends on the peak demand for power
as well as the amount of kilowatt-hours used. A schedule of charges
for electrical power used by the Cincinnati Gas and Electric Co.
is shown in the Appendix. The average cost of power in the United
States is published yearly by the Federal Power Commission and the
latest available nationwide averages are shown in the Appendix.
The cost of power, based on the Cincinnati Gas and Electric schedule
for the power categories used by the Federal Power Commission, is
also shown in the Appendix. Notice that these exceed the 1970
national average in the 150 kw, 30,000 kwh/mo category by 8%, in
the 300 kw, 60,000 kwh/mo category by 9% and the 1000 kw, 2000,000
kwh/mo category by 14%. The Cincinnati Gas and Electric schedule
has been used to compute the monthly expenditure for electrical
power in the five plant types shown in Tables I-V. These dollar
amounts are given in Tables VI-X. These values have been con-
verted to dollars per year and plotted in Figure 11.
9
In a paper by R. L. Michel of EPA, published in the Water Pollution
Control Federation for November 1970, the electrical power con-
sumption in plants was reported in terms of annual dollar expen-
diture for electrical power. This data was gathered over the
1965-68 period. The relationships reported by Michel cover the
range 0.1-10 mgd and his data for primary, high rate trickling
filter, and activated sludge plants are shown as dashed lines in
Figure 11. A multiplier of 1.12 was applied to Michel's data to
make it consistent with the cost of electrical power, using the
CG&E schedule shown in the Appendix.
The agreement between Michel's data and the estimates produced in
this report is good for conventional primary plants. The agree-
ment for activated sludge plants is not as good and this could
be due to the use of sludge gas or natural gas in 1C engines to
power the blowers. The agreement between Michel's data on high
51
-------
TABLE VI
COST OF ELECTRICAL POWER - PRIMARY - SCHEME I
TYPE OF PLANT: Primary
SLUDGE HANDLING SCHEME: I
KW Demand
k'.vh/day
kv,'b/.T;o
Tirst 6000 kwh
60 x KW Demand x 1 . 42^/kwh
120 x KW Demand x 1.14^/kwh
120 x KW Demand x 0.82^/kwh
Additional kwh x 0.7 Iff /kwh
KW Demand minus 15
First 35 KW x $2 = $70
-Second 50 KW x $1.95 = $97.50
Third 900 KW x $1.50 = $1350
Additional KW Demand x $1.35
t
Total Monthly Bill, dollars
Cents /kwh
; -
i
Cents/1000 gallons treated
1 mgd
kwh
31
372
11,160
5,160
3,300
0
16
$/mo
157. 60
26.41
32.
216.01
1.936
.72
10 ngd
kwh
153
2,293
68,790
62,790
53,610
35,250
16,890
138
103
53
$/mo
157.60
130.36
100 mgd
kwh
1,013
18,700
561,000
555,000
494,220
209.30 !372'66°
150.55
11 Q . 97
70.
97.50
79.50
1,015.08
1.476
.338
251,100
998
963
913
13
$/mo
157.60
863. O8
1,385.78
996.79
1,782.81
70.
97.50
1,350.
17.55
|6,721.11
1.198
1 .224
-------
TABLE VII
COST OF ELECTRICAL POWER - PRIMARY - SCHEME II
TYPE OF PLANT; Primary
SLUDGE HANDLING SCHEME: II
KW Demand
kwh/day
kwh /mo
first 6000 kwh
60 x KW Demand x 1.42^/kwh
120 x KW Demand x 1.14pf/kwh
120 x KW Demand x 0,82(zf/kwh
Additional kwh x 0.71^/kwh
KW Demand minus 15
First 35 KW x $2 = $70
Second 50 KW x $1.95 = $97.50
Third 900 KW x $1.50 = $1350
Additional KW Demand x $1.35
1
Total Monthly Bill, dollars
Cents /kwh
Cents/1000 gallons treated
1 n
kwh
34
411
12.330
6,330
4,290
210
19
gd
$/mo
157.60
28.97
2.39
38.
226.96
1.84
.756
10
kwh
156
2,343
70 .,290
64,290
54,930
36,210
17,490
141
106
56
mgd
$/mo
157.60
132.91
213.41
153.50
124.18
70.
97.50
84.00
1 , 033 . 10
1.47
.344
100
kwh
1,138
21,000
630,000
624,000
555,720
419.160
282,600
1,123
1,088
1.038
138
'
i
i
mgd
$/mo
157.60 :
969.58
Ie 556,78
1,119.79
2 , 006 . 46
70.
97.50
1,350.
186.30
!
7,514.01 !
1.193
.250 1
-------
TABLE VIII
COST OF ELECTRICAL POWER - ACTIVATED SLUDGE - SCHEME II
TYPE OF PLANT: Activated Sludge
SLUDGE HANDLING SCHEME: II
KW Demand
kwh/aay
ku-h/mo
first 6000 kwh
60 x KW Demand x 1 . 42jZ?/kwh
120 x KW Demand x 1.14^/kwh
120 x KW Demand x 0.82^/kwh
1
Additional kwh x 0.71^/kwh
KW Demand minus 15
First 35 KW x $2 = $70
Second 50 KW x $1.95 = $97.50
Third 900 KW x $1.50 = $1350
Additional KW Demand x $1.35
Total Monthly Bill, dollars
Cents /kwh
Cents/1000 gallons treated
1 mgd
kwh
95.4
1,145
34,350
28,350
22,626
11,178
80.4
45.4
$/mo
157.60
81.28
130.51
91.67
70.
88.53
619.59
1.80
2.07
10 mgd
kwh
612
9,179
275,370
269,370
232,650
159,210
85,770
596
562
512
$/mo
157.60
521.42
837.22
602.21
608.97
70.
97.5
768.
3,662.92
. 1.33
1.22
100 mgd
kwh
4,566
84,288
2,528,640
2,522,640
2,248,680
1,700,760
1,152,840
4,551
4,516
4,466
3.566
$/mo
157.60
3,890.23
6,246.29
4,492.94
8,185.16
I
70.
97.50
1,350.
4,814.10
29, 303 . 82 i
~i
1.16
.977
-------
TABLE IX
COST OF ELECTRICAL POWER - ACTIVATED SLUDGE - SCHEME III
TYPE OF PLANT: Activated Sludge
SLUDGE HANDLING SCHEME: m
KW Demand
kwh/day
ku'h/mo
first 6000 kwh
60 x KW Demand x 1.42^/kwh
120 x KW Demand x 1.14^/kwh
120 x KW Demand x 0.32c?/kwh
Additional kwh x 0.71^/kwh
KW Demand minus 15
First 35 KW x $2 = $70
-Second 50 KW x $1.95 = $97.50
Third 900 KW x $1.50 = $1350
Additional KW Demand x $1.35
Total Monthly Bill, dollars
Cents/kwh
Cents/1000 gallons treated
1 m
kwh
93
1,115
33,450
27,450
21,870
10,710
78
43
gd
$/mo
157.60
79.24
127.22
87,82
70.
83.85
605.73
1.81
2.01
10
kwh
628
9,414
282,420
276,420
238,740
163,380
88,020
613
578
528
!
1
mgd
$/mo
157.60
535.06
859.10
617.95
624.94
70.
97.50
792.
3,754.15
1.33
1.25
100 mgd
kwh 1 $/mo
1 !
4824 1 [
89,056
2,671,680
2,665,680 157.60
2,376,240 4,110.05
1,797,360 6,599.23
1,218,480 4,746.82
8,651.21
4809
4774 70.
I
4724 j 97.50
3824 |l,350.
i
15, 162.40
,'30, 944.81
i
i 1.15
* 1 . 03
-------
TABLE X
COST OF ELECTRICAL POWER - TRICKLING FILTER - SCHEME II
TYPE OF PLANT: Trickling Filter
SLUDGE HANDLING SCHEME: II
KW Demand
kv,'h/day
kwh /mo
first 6000 kvvh
60 x KW Demand x 1 . 42^/kwh
120 x KW Demand x 1.14^/kwh
120 x KW Demand x 0.82<^/kwh
Additional kwh x 0.71ef/kwh
KW Demand minus 15
First 35 KW x $2 = $70
Second 50 KW x $1.95 = $97. 5O
Third 900 KW x $1.5O = $135O
Additional KW Demand x $1.35
Total Monthly Bill, dollars
Cents /kwh
Cents/lOOO gallons treated
1 mgd
kwh
6O
721
21,630
15,630
12,030
4,830
45
1O
$/mo
157.60
51.12
82. 08
39.61
70.
19.50
419.91
1.94
1.40
10 mgd
kwh
320
4,806
144,180
138,180
118,980
SO, 580
42 , ISO
3O5
270
220
$/mo
157.60
272.64
100 mgd
kvjh
2,182
$/mo
i
4O,282
1,208,460
1,202,460
1.071.540
809,700
314.88
547,860
299.48
7O.
97.50
330.
1,979.86
1 _^7
.66
2,167
2,132
2,O82
1.182
157.60
1.859.O6
2,984.98
2,147.09
3,889.81
70.
97.50
1,35O.
1,595.70
;
14^151.74 \
1.17
1
| .472
-------
H
O
-0
O
Cu
r-l
rf
O
•H
M
•p
O
0)
0
-------
rate trickling filters and the estimates made here is not good.
Michel's estimates for trickling filters is only slightly above
his estimates for conventional primary. The explanation for
this discrepancy is not known at this time. The cost of elec-
trical power versus the amount of power used, taken from Tables
is shown plotted in Figure 12.
58
-------
COST OF ELECTRICAL POWER
5 678910
1O,000
Daily Power Usage, kilowatt-hours/day
59
5 6 7 8 9 10
100,000
FIGURE 12
-------
ELECTRICAL POWER REQUIREMENTS FOR ADVANCED PROCESSES
The first process which might be considered for use downstream
of the activated sludge process is microscreening to remove sus-
pended solids which escape over the weirs of the final clarifier.
Installed electrical horsepower and average electrical power con-
sumption for microscreening equipment is shown in Figure 13. The
principal source of this information is a paper presented at the
41st Annual Meeting of the Ohio Water Pollution Control Conference
by E. W. J. Diaper of Glenfield and Kenned;- Inc. The triangular
points are from a recent EPA report 17090 EEM 12/71. Thus, the
power actually consumed is about 115 kwh/day for 1 mgd, 375 kwh/day
at 10 mgd and 1200 kwh/day at 100 mgd. The economy of scale is
apparently very significant.
Liquid alum can be added to the aerator to remove phosphorus with
the waste activated sludge. The usual dose of aluminum is 1.5
moles of aluminum per mole of phosphorus in the main stream. If
we take the influent phosphorus concentration as 10 mg/1, the
aluminum dose would be 13.05 mg/1 or 144 mg/1 of dry alum. Since
one gallon of liquid alum contains 5.4 Ib. of dry alum, the amount
of liquid alum used would be 222 gallons/mg treated. This is
equivalent to 9.25 gph/mgd. It is customary to install a one-third
horsepower motor on all feeders up to 60 gph. A second pump might
be needed to deliver the liquid alum to a head tank and a one-third
horsepower motor would also be adequate for this purpose. The ac-
tual horsepower consumed in raising the liquid 50 ft. would only be
0.3 horsepower at the 100 mgd size. The total power consumption
for feeding liquid alum will, therefore, be taken as 10 kwh/day
at the 1 mgd size, 15 kwh/day at the 10 mgd size, and 110 kwh/day
at the 100 mgd size.
The addition of alum to the aerator will result in extra sludge
production and extra electrical power consumption. Addition of
61
-------
EL-RCTRICAL ENERGY REQUIREMENTS FOR MICROSCREENS
3 4 567891
2 3 4567691
3 4 557891
2 3 4567891
3 4 567891
1000
100
0.1
10
.01
10
100
1000
Design Capacity, mgd
FIGURE 13
-------
alum to the aerator will result in an increase of about 40% in
sludge production. The increased power consumption for mixing
and heating of anaerobic digesters will be about 25 kwh/day at
1 mgd, 90 kwh/day at 1O mgd, and 400 kwh/day at the 100 mgd level.
Increased power for vacuum filtration will be 42 kwh/day at 1 mgd,
87 kwh/day at 10 mgd, and 964 kwh/day at 100 mgd. Additional power
for incineration of the extra sludge will amount to 24 kwh/day at
1 mgd, 141 kwh/day at 10 mgd, and 1044 kwh/day at 100 mgd. Thus,
if we select sludge handling scheme II for use with alum addition
to the aerator, the total additional power consumption will be
101 kwh/day at 1 mgd, 333 kwh/day at 10 mgd, and 2518 kwh/day at
100 mgd.
For lime clarification, Lake Tahoe estimates power consumption as
431 kwh/day for clarification, 637 kwh/day for dewatering of lime
mud, and 55O kwh/day for recalcining of lime sludge for a total of
1618 kwh/day at the 7.5 mgd size. Lake Tahoe uses two stage lime
clarification with the ammonia stripping tower built over the
second clarifier. The EPA report on lime clarification, TWRC-14 ,
gives the installed horsepower per densator as 14/11 times the flow in
mgd for sizes of 11 mgd and less and 14 + 0.06 (mgd - 11) for sizes
greater than 11 mgd. Thus, the installed horsepower for a two stage
lime clarification at the 7.5 mgd size would be estimated as 10
horsepower per clarifier which would consume an average of 408
kwh/day which is close to the Lake Tahoe value. Using the estimates
from TWRC-14 we can estimate the power consumption for lime clari-
fication at the 1 mgd size as 52 kwh/day, at the 10 mgd as 611
kwh/day and at the 100 mgd size as 2958 kwh/day. The largest
densator will handle 20 mgd so the power requirements for this size
was multiplied by five to find the estimated power requirements for
the 100 mgd size.
At the Lake Tahoe plant, the lime sludge with a solids concentration
of about 1% solids is first gravity thickened to about 4.9% solids
and then dewatered with centrifuges before disposal. The estimated
-------
lime sludge produced by the 7.5 mgd plants is 17 tons per day of
dry solids. A fraction of this must be wasted to prevent build-
up of phosphates in the system. The estimated amount to be re-
calcined is 9 tons per day at the 7.5 mgd plant. Thus, roughly
one-half of the lime sludge would be combined with the organic
sludges and disposed of by incineration or land fill.
The underflow stream from the lime sludge thickener at Lake Tahoe'
was estimated as 36 gpm with a solids concentration of 4.9%. The
amount of electrical power used in the dewatering process was given
as 637 kwh/day at the 7.5 mgd size and this would correspond to
31.2 horsepower for 24 hr/day or 0.324 hp/gpm. Estimates from
the manufacturer for the 24" x 60" centrifuge, used at Lake Tahoe,
was 0.43 - 0.81 hp/gpm. These values were for digested primary
sludges and, therefore, the 0.324 hp/gpm value seems reasonable.
Therefore, for lime sludge dewatering, the estimates are 84.9 kwh/
day at the 1 mgd size, 849 kwh/day for the 10 mgd size and 8490
kwh/day for the 100 mgd size.
In the Lake Tahoe estimate for recalcination, only the cost of the
recalcined sludge was included and the cost of burning the waste
lime sludge with the organic waste sludge was included in the cost
of the conventional processes. The policy used here will be to
charge the cost of burning the waste lime sludge to the lime recal-
cination process. A loading rate of 2 Ib/hr/sq. ft. will be assumed
for the waste lime sludge. Since about 8 tons/day of waste lime
sludge are burned at the 7.5 mgd size, the estimate of power con-
sumption will be 100 kwh/day at 1 mgd, 450 kwh/day at 10 mgd, and
3500 kwh/day at 100 mgd for burning of the waste lime sludge.
The 14.25 ft. diameter, 6 hearth recalcination furnace used at
Lake Tahoe has a hearth area of 575 sq. ft. The maximum capacity
of this furnace is given as 20 tons/day or about 3 Ib/hr/sq. ft.
It was found at Lake Tahoe that the optimum feed rate was 1.13
Ib/hr/sq. ft. to maximize the activity of the recalcined lime.
This value will be used here. Using a recalcination rate of 1.29
64
-------
tons/day/mgd, the size of the recalcination furnace at the I mgd
size should be 457 sq. ft. if the furnace is operated an average
of 5 hours per day.
From the electrical power consumption estimates shown in Figure 7
for incineration of organic sludge and the fact that the loading
rate is 2 Ib/hr/sq. ft., we can derive the following relationship
for power consumption in terms of kilowatts/sq. ft.
kilowatts/sq. ft. = 0.636 (hearth area, sq. ft.)~°'37712
Using this relationship, we find the power consumption for the re-
calcination furnace used at Lake Tahoe to be 33.3 kw. The 550 kwh/
day estimated at Lake Tahoe would correspond to a loading of about
1.3 Ib/hr/sq. ft.
Using the optimized loading of 1.13 Ib/hr/sq. ft., the 10 mgd plant
would require a hearth area of 951 sq. ft., if operation is 24 hr/day.
The next standard size furnace is 988 sq. ft. The power consumption
would be 46.7 kw or 1120 kwh/day. At the 100 mgd size, a hearth
area of 9513 would be required. Three recalcination furnaces with
hearth area of 3120 sq. ft. would be sufficient. The power consump-
tion would be 95.5 kw per furnace or 6874 kwh/day total. Electrical
power consumption for the 1 mgd plant would be 30.8 kw or 154 kwh/day,
Thus, the total power consumption, including burning of waste lime
sludge, would be 254 kwh/day at 1 mgd, 1570 kwh/day at 10 mgd, and
10,374 kwh/day at 100 mgd.
For recarbonation, Lake Tahoe estimates 702 kwh/day. It will be
assumed here that power for recarbonation is proportional to flow.
Therefore, the power consumption at 1 mgd would be 93.6 kwh/day,
for 10 mgd, 936 kwh/day, and for the 100 mgd size, 9355 kwh/day.
Ammonia stripping requires a significant amount of power because
the water must be pumped to the top of the tower and the volume
of air required to strip the ammonia from the water is large. At
Lake Tahoe the estimate was 672 kwh/day/mgd for each day the ammonia
65
-------
stripping tower is in operation. In the colder climates, the
ammonia stripping tower is likely to freeze in the winter months
and provision must be made for this if a yearly average is com-
puted. At Lake Tahoe it was estimated that the tower could operate
about 65% of the year.
The principal consumptive use of electrical power, associated with
multi-media filtration, is the energy required to pump the main
stream through the filters. Additional power is required for back-
washing, surface spray, and feeding of chemicals. The estimates
for electrical power from Lake Tahoe are not generally applicable
because of the filters and the carbon adsorption vessels are in
series, and because of the peculiarities of the site. For example,
•«
the total dynamic head for the filters was given as 1OO ft. of
water. Actually, the filters which were sized for 5 gpm/sq. ft.
were backwashed when the head across the two filters in series
reached 16 ft. of water. Horsepower for pumping the main stream
is given by the following relationship:
Horsepower = mgd x 0.17546 x TDH/eff
mgd = millions of gallons per day
TDH = total dynamic head, ft.
eff = hydraulic efficiency
Backwash pumps must deliver about 5% of the main stream against a
head of about 75 ft. Surface wash pumps operate for about 15
minutes per day and are sized for about 1.42 gpm/sq. ft. at a head
of about 300 ft. If we use a hydraulic efficiency of 70% for the
1 mgd size and an average pumping head of 15 ft., the power consumed
by the main stream would be 77 kwh/day. For backwashing, the power
consumption would be 19.2 kwh/day. For surface spray, the power
consumption would be 3.3 kwh/day and the total would be 99.5 kwh/day.
Since the power consumption will be proportional to flow, except for
the hydraulic efficiency, the estimate for 10 mgd would be 953 kwh/
day and 8743 kwh/day at the 100 mgd size.
66
-------
The pressure drop through a column of granular carbon varies with
the application rate and with the length of the column. When the
design contact time and the hydraulic surface loading is known,
the length of the column can be computed with the following re-
lationship :
Column Length, ft. = gpm/sg. ft. x contact time, min.
7.48
If we assume a design contact time of 40 minutes and a hydraulic
surface loading of 7 gpm/sq. ft., the length of the column re-
quired is 38 ft. The pressure drop through 38 ft. of clean granular
carbon will be about 8.23 psig or 19 ft. of water. It is common
practice to design the pressure contactors for a maximum working
pressure of 50 psi or 116 ft. of water. The average of these two
is about 68 ft. of water. Therefore, the electrical power used in
pumping the main stream through the granular carbon will be about
348 kwh/day at the 1 mgd size. If variable speed pumping is used
rather than a flow equalization tank, this value might be increased
by about 25%. The corresponding values for 10 mgd and 100 mgd are
3287 kwh/day and 29,308 kwh/day. About 5% of the main stream will
be used for backwash and the pumping head will be about 75 ft. of
water. The electrical power consumed will be 19.2 kwh/day for 1
mgd, 192 kwh/day for 1O mgd and 1916 kwh/day for 100 mgd.
The surface spray will operate for about 15 minutes per day and
will be sized for 1.42 gpm/sq. ft. Thus, the power consumed for
surface spray will be 3.24 kwh/day at 1 mgd, 32.4 kwh/day at 10
mgd, and 324 kwh/day at 100 mgd. The total power consumption for
the carbon columns will, therefore, be 371 kwh/day at 1 mgd, 3511
kwh/day at 10 mgd, and 31,548 kwh/day at 100 mgd.
The amount of granular carbon to be regenerated is about 350 lb/
million gallons treated. The recommended loading rate for the
regeneration furnace is 100 Ib/day/sq. ft. of hearth area or 4.17
Ib/hr/sq. ft. At the 1 mgd size the smallest standard size re-
generation furnace (85 sq. ft.) will be capable of regenerating
67
-------
the spent carbon, operating an average of one hour per day. At
the 10 mgd size, a furnace with 168 sq. ft. of hearth area will
be capable of regenerating the carbon, operating 5 hours per day.
At the 100 mgd size, a furnace with 351 sq. ft. will be able to
regenerate the carbon if it operates 24 hours per day.
At the Lake Tahoe plant a regeneration furnace with about 62 sq.
ft. of hearth area was used. The maximum capacity of this furnace
was 6000 Ib/day or about 100 Ib/day/sq. ft. The amount of power
expended for carbon regeneration was 169 kwh/day. If we estimate
the amount of carbon to be regenerated as 35O Ib/mg, the furnace
would be operated for about 10 hours per day. Using the relation-
ship for power consumption for a multiple hearth incinerator, the
power consumption for the regeneration furnace alone would be about
83 kwh/day. Thus, the total power used, which would include trans-
port of the carbon, is about twice that used by the regeneration
furnace alone. Using this information, we can estimate the power
requirements for the 1 mgd plant as 20 kwh/day at the 1 mgd size,
155 kwh/day at the 10 mgd size, and 1175 kwh/day for the 1OO mgd
size.
The principal consumptive use of electrical power for biological
nitrification is the additional air required. The amount of oxygen
required to convert ammonia nitrogen to nitrate can be computed
from the following chemical relationship;
2NH* + 40 »~ 2NO" + 2H O + 4H+
^t £-*• J £
The ratio of oxygen required per pound of nitrogen converted to
nitrate is, therefore, 64/14 or 4.57. If we take the concentration
of ammonia nitrogen as 20 mg/1, we can compute that 761 pounds of
oxygen is required per million gallons treated. If diffused air
is used to supply the oxygen, the amount of air needed can be cal-
culated as follows;
scf/day = (Ib 0 /day)/.075/.21/aeration efficiency
68
-------
If we take the aeration efficiency as a nominal 5%, the amount
of air needed for nitrification is 0.967 scf/gallon treated. This
is essentially the same as the amount of air assumed for the acti-
vated sludge process. An additional expenditure of electrical
energy will be required to supply about 50% recycle and for final
settling.
The denitrification process will require power to keep the floe
in suspension and for recycle. The power needed for mixing is
about one-half horsepower per mgd. Thus, the power consumed will
be about 10.2 kwh/day at the 1 mgd size, 102 kwh/day at the 10
mgd size and 1O20 kwh/day at the 100 mgd size. Recycle will be
taken as 50% of the main stream.
Where demineralization of the water is required, electrodialysis
or reverse osmosis can be used. From EPA report WP-20-AWTR-18
the cost of supplying DC power to the electrodialysis process was
given as 0.85 kwh/1000 gallons. The cost of pumping the main stream
through the electrodialysis stacks was estimated as 0.491 kwh per
1000 gallons. Thus, the total for reducing the TDS of the water
from 850 mg/1 to 500 mg/1 is 1.341 kwh/1000 gallons.
For the reverse osmosis process the principal consumptive use of
electrical power is for pumping the main stream through the mem-
brane. The pressure drop through the reverse osmosis process is
about 500 psig. About 10% of the feed stream is wasted with the
rejected salts and a small amount of power could be recovered by
using this stream to drive a turbine. This scheme, however, has
not been shown to be cost/effective and it will not be considered
here. At the 1 mgd size, the power consumed will be 5903 kwh/day.
At the 10 mgd size, the corresponding value is 55,836 kwh/day and
at the 100 mgd size, the power consumption would be 497,811 kwh/day.
69
-------
ELECTRICAL POWER REQUIREMENTS FOR ADVANCED PROCESS TRAINS
Estimates of electrical power consumption for various alternative
tertiary treatment trains are shown in Tables XI-XIII. Train VIII
represents the set of processes used at Lake Tahoe. For the
ammonia stripping process, it was assumed that the process will
operate 65% of the year. Trains III and IV represent the sets
of processes which are most likely to be used in the near future
for control of nutrients such as nitrogen and phosphorus. Values
for electrical power consumption shown in Tables XI-XIII for
trains without demineralization are shown in graphical form in
Figure 14.
The power requirements for treatment train III are roughly 20%
less than the activated sludge plant using sludge handling
scheme II. The Lake Tahoe system shown as train VII is 2O-40%
more expensive in terms of electrical power than the activated
sludge plant.
71
-------
TABLE XI
ESTIMATED ELECTRICAL POWER COrlSU?'iTTIO.\' FOR ALTERNATIVE TERTIARY TREATMENT TRAINS AFTER SECONDARY TREAT f>Ei\T
Plant Size -
1
ADVANCED PROCESSES USED
•" i i.c ror. c ra«n i rivi
Alum At:
-------
TABLE XII
ESTIMATED ELECTRICAL, POWER CONSUMPTION FOR ALTERNATIVE TERTIARY TREATMENT TRAINS AFTER SECOMDARY TREAT MEi\T
Plant Sirze - 10 mgd
ADVANCED PROCESSES USED
> 1:. c r o L~. c x & -2 n i n .1
Alu.;, Ace it ion and
Ext ra S lud -R I I:\ndl incj
LiKft Clarification
Lime Sludrje Dswataring
Lina R^calcination
Rcca rbonati on
A'Ui^-onia Stripping
,'\ i 1 r :". :J i c s. t i o n
Donf-'crii ication
Mwl'ci- Madia Filtration
i
Granular Carbon Adsorption
Carbon Regeneration
j
Electrooialysis
Reverse Osmosis
Total Power Consumption, kwh/cay
I
375
375
II
333
III
333
6235 6235
102
6670
1O2
953
7623
IV
611
637
1570
-
953
3771
V
VI
611 [ 611
637
157O
953
3511
155
7437
637
157O
953
3511
'155
13,410
20,847
VII
953
55,836
57,239
VIII
1
i
]
611
:
637
157O
:
936
4368
953
3511
155
12,741
-------
TABLE XIII
ESTTMAfED ELECTRICAL TOWER CONSUMPTION! FOR ALTERNATIVE TERTIARY TREATMENT TRAINS AFTER SECONDARY TREATISE NT
Plant Size - 100 mgd
-~J
.p-
ADVAwCED PROCESSES USED
|
" ':'. c r or o r-.-:s : i :_ -MI
Alu:n A'K.ltJ.ori ix'id
Extra SliKi.>~ !r-'.ndliaq
L J. m 2 C 1 a r i J I c ;A t i o n
• Li ~.e Sludge D;:vtering
Li'.n> Racalci nation
R ; _• c a r b o 1 1 a t i o n
A--;MO ni a S r, ri ppi nq
;\lY.ri..'ica iiou
D c- n i -critic a t i o n
fCal'ci-.'.^dir,. Fil trj.tion
Granular Carbon Adsorption
Carbon Regeneration
Electrodialysis
Ra v ••• rse Osmo;; is
Total Power Consumption, kwh/day
I
1,200
1,200
II
2,518
60,255
1,020
63 , 797
_L J. JL
2,518
60,25&
1,020
8 , 743
72,540
I, .
.
2,958
6,370
10,374
8,743
28,445
*
2,958
6,370
10,374
8,743
31,548
1,175
61,168
VI
2,958
6,370
10,374
8,743
31,548
1,175
134,100
195,268
vn:
.
> 8 , 743
497,811
506,554
VII I
i
(
(
2,958
6,370
10,374
9,355
43,680
i
8,743
31,548
1,175
:•-,'
114,203
-------
ELECTRICAL ENERGY CONSUMPTION FOR TERTIARY WASTEWATER TREATMENT TRAINS
versus
PLANT SIZE
1OO,OOO
I
c
0
•H
en
C
VI
1
rt
o
•H
M
^
0
01
10,000 ;io
1,000
100
10
9
8
7
6
b
4
3
2
10
<)
6
5
4
3
2
10
9
8
7
6
6
4
3
Z
pq
-
~1
-.
=
/
^
^
^
~"
~
~|
4?
1
q
F
/
^
/
£
• — •
r-,
H
^
^
^
^
=
-
,,
—
HffiBffi
^ ::::::::::! — :
H-— :-r;:::::::I:;::
-rS-^^iil:!::!
i 1 ;
^ --. i I....IL---:
_l_ __tf
^
1 j2--
~t 'T
r~ ~W~
fflii^i^ii:E??
|jE|~;;i!! ?~
L_-?«..,!
< ?' " ?
,? ^ Ix
s s v -
/ S ;;n
/ <' T
i^r n" irati1 I
rz:i:jffi:-:i^::
i-L--?--4ff-5|— -
^_. -. - -.
p==t±:-::::::::::.=C = i
S^^^ffiUtt
_. ^^
**
Js___ _ 1 _
a.'* :::::::::::::: -i
2 3
1 1 1 Hum1! |-| 1 1 1 1 1 1~
— ±
:::-:-:::::-=----"-
t
/
;j _ ^ ;;
Sz 3
L
,' ~ > >
,?.. ,<4'
..../. _.,^Z_H
iSi'^^li-
:::EE;;;iig?EEEft-
:::::;! :;!---Hv4.,^
- - ,i!.( . N <
^i /
. ' i ^
e . jt -. — 1 0-1 — 1 —
t — ? 3
: :±::::::: ^ ~±~
:;?^::::::. — -:::::q
— 1
.,---. _^
*e. - - -
* —
4 5 678910
10
-SS::::JWi
StM i «
^wH^t
Pf^-^|:|4yffi
f- i'-)''
_,£ j?
? /r
:^^v.-.::::::;^
-•£--/ \ j'fT
zz x — •'' "
t'
?
^ r
_ — ^ —
_^ 1
>
— — j|E:EE:"i":==
1 "~ ~7*
E=,EEJ\J:,|:E,:
t j,''- t- ---
t 1 —
2 3
/
1 1 1 1 1 1 II 1 1 1 1 1 1 I |>gL.(
2 T
- ; "if1
-•£±---trt-A — =p£f •
>'- r-;i'3Z-- + i
— • j ^-[- ^ — — 1 1-
----/-/i
ij^pjfjf i;^^!
— ;''
f ~[~ T
::::::: :::i— :::::,
EE:EEEi:|E:-EEEEEEE
-:"g±|^r:|=E
fflw^ffl
-{--
_.. I __ _.
0 *
£--|l±-5»''!--t:--
T ;|l if
— ,.:!
.•'-..... -L -
;! _±_.
HfflSlS
f i 1
4 5 678910
1OO
Plant Design Capacity, mgd
Note; I, II, in, iv, & VIII refer to specific treatment
trains
75
FIGURE 14
-------
COMPARISON WITH OTHER CONSUMPTIVE USES
The total production of electrical power in the United States
in 1969 has been estimated by the Department of Commerce as
1,522,229 million kwh. The total for 1971 was 1,717,520 million
kwh. Residential sales of electrical power totaled 407,922
million kwh in 1969. In 1969 the average residential consumption
of electrical power was 5,943 kwh per year and the average popu-
lation per household was 3.2 persons. Thus, the per capita resi-
dential use of power was about 5.09 kwh/day.
2
According to the Federal Power Commission , the average consumption
of electrical power varied significantly with the area of the
country from a high of 19,636 kwh/yr/household in Eugene, Oregon
to a low of 2,275 kwh/yr/household in Bronx, New York.
Commercial and industrial power were combined and divided into
small light and power and large light and power. Power usage for
small light and power was estimated by the Department of Commerce
as 286,686 million kwh in 1969 and 557,222 million kwh for large
light and power for a total of 843,908 kwh/yr for industrial and
commercial. Thus, commercial and industrial power represented
about 55% of the total power generated while residential power
represented only 27%.
The Edison Electric Institute conducted a survey of 127 companies to
determine the percentage usage of electrical power among various
industries. The results of the survey is shown in Table IX. The
principal users of electrical power are primary metals and chemicals
and allied products. The aluminum industry alone used 51,894
million kwh in 1970.
The estimated power consumption for plants, included in the 1968
12
Inventory of Municipal Waste Facilities is shown in Table X.
The average usage was 0.0573 kwh/day/capita. This amount of power
77
-------
TABLE XIV
PF.RCF.;:T-\GE DISTRIBUTION- o? MINING A:JD MAMLTACTI-RINC i-;;~HR3 FA- MAJOR CROUPS
-------
TABLE XV
CONSUMPTION OF ELECTRICAL ENERGY BASED ON THE 1968 INVENTORY OF MUNICIPAL WASTE FACILITIES
Minor Treatment
Primary Treatment
Intermediate Treatment
Activated Sludge
Trickling Filters
Ponds
Other and Unknown
Tertiary Treatment
Totals
Population Served
1,360,870
36,947,397
5,857,690
41,264,036
29,617,136
6,123,078
8,636,514
325,530
gpd/capita
122
122
122
123
89
89
89
123
kwh/day/capita
.0185
.0286
.0286
.113
.043
.O135
.0135
.226
130,132,251
kwh/day
25,176
1,056,696
167,530
4,662,836
1,273,537
82,662
116,593
73,570
7,458,600
Average kwh/day/capita = 0.0573
-------
consumed in wastewater treatment is about 1% of the average resi-
dential consumption of electrical power. This amount of power
is about equivalent to one 8 watt bulb in each household, burning
24 hours per day. If all of the population was served by activated
sludge plants, the power consumption would be about 0.113 kwh/day/
capita which is equivalent to a 15 watt light bulb, burning in each
household 24 hours per day. A desk lamp is normally equipped with
two 15 watt fluorescent lamps.
Power consumption for tertiary treatment is highly dependent on
the train of processes selected. For train V the power consumption
is roughly equivalent to the activated sludge process. For the
Lake Tahoe system, shown as train VIII, the power consumption is
roughly 40-50% greater than activated sludge. Thus, if we assume
train III or train V, the consumption of power per household would
be roughly equivalent to a 30 watt desk lamp burning for 24 hr/day.
In terms of cost per capita for activated sludge plants, the usage
would be about 0.54 cents/day/household, taking the cost of elec-
trical power as 1.5 cents/kwh. If tertiary trains III or V are
provided, an additional cost of about 0.44 cents per household day
would be incurred, making a total of roughly 1 cent/household per
day.
80
-------
ACKNOWLEDGMENTS
This study was made possible through the help and support of
various equipment manufacturers such as Westinghouse Electric
Corp., Pacific Flush Tank Division of Rex Chainbelt, Inc., Dorr-
Oliver, Inc., Bird Machine Co., Wallace and Tiernan, Environmental
Control Group, Rex Chainbelt, Inc., Allis Chalmers and others.
The Rex Chainbelt and PFT Engineering Manuals were particularly
valuable. Valuable information on plant utilities was supplied
by Black and Veatch Engineers of Kansas City and by the Cincinnati
Gas and Electric Co.
81
-------
REFERENCES
1. Evans, David R. and Wilson, Jerry C., "Capital and Operating
Costs-AWT," Jour. WPCF, Vol. 44, No. 1, pp. 1-13
2. "Typical Electric Bills," 1970, Federal Power Commission,
Washington, D. C.
3. "Process Equipment - Sewage, Water, Industrial Waste Treat-
ment," Rex Chainbelt, Inc., Milwaukee, Wisconsin, Binder
No. 315, Vol. I and II
4. Albertson, J. G., et al, "Investigation of the Use of High
Purity Oxygen Aeration in the Conventional Activated Sludge
Process," EPA Water Pollution Control Research Series,
No. 17050 DNW 05/70
5. "Waste Treatment Equipment," Pacific Flush Tank Division,
Rex Chainbelt, Inc., Chicago, Illinois
6. Personal Communication from Mr. Eugene Guidi of Bird Machine Co.
7. Unterberg, W. , Sherwood, R. J. and Schneider, G. R.,
"Computerized Design and Cost Estimation for Multiple-
Hearth Sludge Incineration," EPA Water Pollution Control
Research Series, No. 17070 EBP 07/71
8. Personal Communication from Mr. Don Parkhurst of Black and
Veatch Consulting Engineers, Kansas City, Kansas
9. Michel, Robert L., "Costs and Manpower for Municipal Waste-
water Treatment Plant Operation and Maintenance 1965-1968,"
Jour. WPCF, Vol. 42, No. 11, pp. 1883-1910
10. Seiden, L. and Patel, K., "Mathematical Model of Tertiary
Treatment by Lime Addition," Robert A. Taft Water Research
Center, Report No. TWRC-14, September 1969
11. Edison Electric Institute Publication, July 21, 1972,
"Tabulations of Industrial KWHR Sales by Investor-Owned
Companies for 1971"
12. "Municipal Waste Facilities in the United States," Statistical
Summary, 1968 Inventory, U. S. Dept. of Interior, FWQA
83
-------
APPENDIX
85
-------
Cincinnati Oas k Elactrlc Company
Fourth and Main Streets
Cincinnati, Ohio
P.U.C.O. Bo. 11
Original Sheat Ho. 16-F
Sheet 1 of 2
OSH3BAL S23VTC3 - LAR05
AVAILABILITY
Available in localities indicated on Shasta Ho. 2, S-A of thin schedul*, whsr« facilities of
suitable volttg* and adequate capacity are adjacent to tha prsmiaai to b« sarvsfi.
APPLICABILITY
Applicable to electric service required for any purpose by an individual customer on ona
premiae, whan supplied at ona point of delivery, except breakdown, standby or supplemental
earvico, or rea'als Bervlca not in conformity with Ccnpany's service regulations. When both
alngl* and thrae phase Harvice Is required by a customer tho monthly usage shall be the
arithmetical sun for three phaae and for single ph»a« aarvlce.
Th» account shall never be billed as one single phaaa account and ona three phaae account on
this rst*. alien cu»tomer'a demand for alngla phaae service has not exceeded 5 kilowatts In
evsry nonth of twelva conaecutlve months, customers will bo billed for single phaae sarvico
on R&ta General Service Small, If available.
TYPS OF 32HVICS - Alternating current 60 Hz, slngla or threa phaae at Company's itand&rd voltoga.
fTST MONTHLY BILL Computed In accordance with the following chargos: .
A. Secondary voltage service: where Company furnishes standard rating primary voltage transferees-*
and appurtenances and supplies service from Its overhead or underground ayBtama at standard
secondary voltage. Company may meter at primary or secondary voltage aa circumstances warrant.
Demand Chargei
First 15 kilowatt* of Demand or less
Noxt 35 Kilowatts of Demand
Haxt 50 kilowatts of Demand
Noxt 900 kilowatts of Demand
Additional kilowatts of Demand
Ensrgy Ch&rget
First 500 kilowatt hours
Naxt 1,500 kilowatt hours
Next It ,000 kilowatt hours
Haxt 60 kilowatt hours par kilowatt of Damind
?/sjct 120 kilowatt hours per kilowatt of Demand
Next 120 kilowatt hours par kilowatt of Demand
Additional kilowatt hours
40.00
at 32.00 p«r kilowatt
at SI.95 P«r kilowatt
at 31-50 per kilowatt
at $1.35 per kilowatt
at 5-12^ par kilowatt hour
at 3.12«! per kilowatt hour
at 2.13(( per kilowatt hour
at l.U2# par kilowatt hour
at I.l4jl per kilowatt hour
at .82^ per kilowatt hour
at .?!<* per kilowatt hour
Plus or minus an adjustment par kilowatt hour determined in accordance with "Tax Adjustment"
forth In Sheet Ho. 60 of this tariff.
set
Plus or minus 0.0055^ per kilowatt hour for each 0.5# par million Btu by which the average cost
of fual burned during the next preceding month is above or below 20.5^ per million Btu. Th«
average cost of fuel burned shall be that recorded on Company's books,excluolve of charge* for
unloading from the shipping medium.
A thrsa phaae euatoaer whose demand does not exceed 15 KH all! be charged an additional surcharge
of $lt.OO per month for the three ph&sa service.
Minimumi Tha Damand Charge for the Billing Demand but not le»» than $5-00.
Primary voltage aervlco: whera customer furnlshss prlnary voltaga transformers and appurtenances
and takes service from Company's ovarhead or underground By»t«m at standard primary nominal
voltage of 13 KV or higher. Billing at yats in paragraph A above subjact to th» folloaing
additional provisional
Monthly discount par kW billing deamnd
13
66 XV
10.15
kV
Undar this paragraph B, If Company elects to metor at primary voltage tha Xlloaratt hours
rsglttered on Company's m*tar will ba reduced 1-1/255 for billing purposes.
Minimum! - The Damand Charg» for the billing Damand but for not loss th&A 300 kW.
Isousd by B. John Toigar, Prsald»"t
Cincinnati, Ohio
Sffactlv® October 30, 1970
86
-------
The Cincinnati Qaa & Electric Company
Fourth and Main Streets
Cincinnati, Ohio
P.U.C.O. No. 11
ORIGINAL SHEET NO. 16-P
SHEET 2 of 2
GENERAL SERVICE - LARQE
DEMAND
1. The Demand shall be the kilowatts derived from the Company's demand meter for the fifteen
ntinut* period of customer's greatest use during the month adjusted for power factor, as provided
herein. At Company's option a demand meter may not be Installed if tha nature of the load clearly
indicates the load will have a constant demand. In which case the demand will be the calculated
demand. The Company may Install a demand meter when the consumption exceeds 2500 kilowatt houra
for two consecutive months or when the Company has reason to beliave the demand exceeds 15
kilowatts.
2. Wh»n b,oth thra» phase service and single phaae service are supplied each ehall be metered
a«parat«ly, and the Demand for billing shall be tha arithmetical sum of the demand for thra*
ph»i» servlc* and for single phaoo service,
In no tvant will the billing Demand be taken as lass than the higher of tha followingi
A. 70$ of the highest kllowstta similarly established during the preceding 11 month*.
b. 300 kilowatts for prlnary voltage service.
Pow«r factor Adjustment!
This rat« is based on a maintained power faotor of not less than 90$ lagging and If the Company
determine Customer's power factor to be less than 9056, tha billing demand will be th« number of
kilowatts equal to the kilovolt atnparea multiplied by 0.90.
Power Factor nay be determined by contlnous measurement or'by tests at Company's option; if by
continuous measurement, power factor determined during tha Interval in which tha kilowatt asuinui*
iSsaiand ia established, will be used for billing purposes) If by testa, power faotor dategtmlned
during a period in which Customer's KW demand as measured la not lesa than 90# of the measured
kilowatt maximum demand in tha next preceding billing period, will bs-uaed for billing purposes
until superseded by a poser factor determined by subsequent teat mada at tha direction of Company
or raquest of Customer.
PAYMENT
The H«t Monthly Bill is payable within fourteen (14) days from date. When not so paid, tha
Gross Monthly Bill, which is the Hat Montrtly Bill plus 5$, IB due and payable.
T2HM 0? 8ZHVICB - One (l) year for Secondary voltage service, and three (3) years for Primary volt»s«
eervloe.
SEHVIC2 REGULATIONS
Tha supplying of, and billing for, service and all conditions applying thereto, are aubjaot to
the Jurisdiction of The Public Utilities Commission of Ohio, and to Company's Sarvloe Regulation*
currently •ffaotive, as filed with Tha Public Utilities Commission of Ohio, as provided bj law.
effective October 30, 1<«70
Issued by B. John Yeagar, President
Cincinnati, Ohio
87
-------
TABLE 8.—NATIONAL WEIGHTED
AVERAGK BILLS FOR INDUSTRIAL SERVICE,
1935-1070
cities ouly3
05
00
Average bill
Ja
3t\
Ja.
Ja
Ja.
,I» i
.1 HI
Jai
JKI
.1 a I
Ja;
Ja.
Jill
Jai
Jar
Jai
Jar
Jai
Jnn
Jan
Jai
Jan
J.in
J:.n
i. 3,
i. 3.
i. 3,
i. 3,
i. 3,
. 3,
'• 3,
. 1.
• 3,
. 3,
' l!
• 3,
. 3i
- 3,
• 1,
. 1.
. 3,
. 3,
. 3,
. 1.
- 1,
1!)70
39CS
1 M',!
HH;.-',
3 Oh 4
3 9 r,:i
3 nr>2
liiho
1915
3010
Date 350 I W
"kWli
? G-l S
c::<>
c:;3
r,",i
' (I'M
fj''4
.^
G'>7
(••»o
G''l
010
012
GOG
COl
5 S3
5SO
. _. f,C5
Gli5
C12
300 }CW
Go.utjy
kV.'ti
*l|li>3
1 ! 1 r!o
i.i nt
3 , 1 CO
3JC7
1.1 -i()
3,1 ::R
1.33-1
3.12-t
1.1211
1,111
1 , 1 03
3,093
1 OsO
l.OSC
3.0-10
3 ,03i5
1.043
1.002
l,b;>5
3.000 kW
2IHI.IKK)
Si-lL'.S
3.-VJ2
3.-I07
.1.423
3,-n-t
3.442
•X2S.1
3.279
3.204
31302
3,154
3,042
3'.024
O >^(>O
2!S28
3,081
Avernpre cliarfre per k\Vh Index of avcrapc hill (1007=100)
3T.O KW
:;o.oi)0
2. 1C
2.12
2.11
2.33
2.10
2.11
2.11
2.1.-1
2.09
2. OS
2 09
2.07
2.07
2.05
2.04
2.02
2 02
2.'00
1.04
1.93
1.03
l.SS
1.88
2.04
300 kW
G<>. (nil)
k\Vli
1.97
1 .04
3.93
3.93
3.02
1.93
1.03
1.95
3 .90
l.SO
l!,S7
1.S7
1.K5
3.P4
3..S2
1.S2
1.R1
1.74
1.73
1.74
1.C7
l.CC
1.81
1.000 kW
200.000
k\\'h
1.75
1.72
3.71
1.71
1.70
1.71
1.71
3.72
3. OS
1.07
1.05
1.0-1
1.G4
l.r.2
l.f.O
1.5S
1.58
1.5S
i.r,2
1.51
1.51
1.43
1.41
1.54
ir.o i;W
"k\Vli
102.4
100.5
300.2
100.0
00.7
100 2
100.2
100.K
99.2
OS G
09.1
OS. 3
OS.l
97.3
90.7
05.7
05. C
94.9
92.1
91.3
91. G
89 3
R9.3
8C.7
300 IcW
<;o ooo
k\Vli
302.1
300.3
100.1
300.0
!.9.C
300.1
300.0
100.7
9S.4
OS.O
97.8
07.0
00.0
ij'i'.l
04.0
93.7
00.3
89.4
90.0
SG.5
85.8
93.G
1.0(10 V-W
200 (M)0
k\Vli
102.0
300.4
300 2
300.0
lob'.o
99.S
lOu.G
07.9
97.5
on!o
05.8
91.5
o:>.G
92. G
02.4
92.2
PR. 9
RS.O
gK.4
83.7
S2.G
90.0
Source: Federal"Power Commission Report FPC R-76 "Typical Electric
Bills 197O" Federal Power Commission, Washington, D. C.
-------
Comparison Between Federal Power
Commission Power Categories and
CG&E Schedule
KW Demand
kwh/day
kwh /mo
first 6000 kwh
60 x KW Demand x 1 . 42gf/kwh
120 x KW Demand x 1.14^/kwh
120 x KW Demand x 0.82^/kwh
Additional kwh x 0.71jZ?/kwh
KW Demand minus 15
First 35 KW x $2 = $70
Second 50 KW x $1.95 = $97.50
Third 9OO KW x $1.50 = $1350
Additional KW Demand x $1.35
Total Monthly Bill, dollars
Cents /kwh
Ccnts/lOOO gallons treated
1 m
kwh
ISO
3O,OOO
24,000
15,OOO
135
10O
50
gd
$/mo
157.60
127. 8O
171.
7O.
97.50
75.
698.90
2.33
10
kwh
3OO
6O , OOO
54,OOO
36, OOO
O
285
25O
2OO
mgd
$/mo
157.60
255. 6O
410 . 4O
7O.
97. 5O
300.
•
1,291.1
2.15
!
100
kwh
1,OOO
200 , OOO
194,OOO
134,OOO
14,000
985
95O
900
;
mod
$/rno
i
j
!
t
1
157.60
1
852.
i
1,368.
114. 8O
;
I
i
70.
i
i
Qv.sn i
1,35O. |
4,OO9.9O !
2.OO j
1
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No.
3. Accession No.
4. Title
ELECTRICAL POWER CONSUMPTION FOR MUNICIPAL
WASTEWATER TREATMENT
7. Author(s)
Robert Smith
9. Organization . . _ , , . .
Envxronmental Protection Agency
National Environmental Research Center
Advanced Waste Treatment Research Laboratory
Cincinnati, Ohio 45268
12. Sponsoring Organization
IS. Supplementary Notes
Environmental Protection Agency report number,
EPA-R2-73-281, July 1973.
5. Report Date Aug. 1972
6.
8. Performing Organization
Report No.
10. Project No.
11. Contract I Grant No.
13. Type of Re port and
Period Covered
16. Abstract
Electrical power consumption by most conventional and advanced processes
for treating municipal wastewater has been estimated on a unit process
basis. Electrical power for complete plants has been estimated by adding
power consumption for individual processes and plant utilities. Electrical
power consumption for wastewater treatment has been compared to other
consumptive uses of electrical power.
17a. Descriptors
*Waste water Treatment, ^Electrical Power Demand, *Electric Power Costs,
Sewage Treatment Plants, Sewage Works
17b. Identifiers
Wastevmter Treatment Processes, Electrical Power Consumption
17c. COWRK Field & Group
18. Availability
19. Security Class.
(Report)
20. Security Class.
(Page)
Abstractor Robert Smith
21. No. of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D. C. 20240
Institution
EPA
WRSIC 102 (REV. JUNE 1971 )
GP 0 9 13.26 ?
------- |