EPA
United States
Environmental Protection
Agency
Office of
Research and
Development
Environmental Research
Laboratory
Corvallis, Oregon 97330
EPA-600/7-78-001
January 1978
ENERGY CONSUMPTION OF
ADVANCED WASTEWATER
TREATMENT AT ELY,
MINNESOTA
-1 I « <,.„«!
Interagency
Energy-Environment
Research and Development
Program Report
-jrf, N. J. 08817
PROTilCFiON AGENCY
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-600/7-78-001
January 1978
ENERGY CONSUMPTION OF ADVANCED WASTEWATER
TREATMENT AT ELY, MINNESOTA
by
Donald J. Hernandez
Criteria and Assessment Branch
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
-------
DISCLAIMER
This report has been reviewed by the Corvallis Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
-------
FOREWORD
Effective regulatory and enforcement actions by the Environmental
Protection Agency would be virtually impossible without sound scientific
data on pollutants and their impact on environmental stability and human
health. In addition, it is necessary that energy utilization be evaluated
to assure that these actions are not contrary to the energy conservation
efforts of our Nation. Responsibility for building this data base has
been assigned to EPA's Office of Research and Development and its 15
major field installations, one of which is the Corvallis Environmental
Research Laboratory (CERL).
The primary mission of the Corvallis laboratory is research on the
effects of environmental pollutants on terrestrial, freshwater, and
marine ecosystems; the behavior, effects, and control of pollutants in
the lake systems; and the development of predictive models on the
movement of pollutants in the biosphere.
This report quantifies the energy used as a result of operating an
advanced wastewater treatment plant which includes phosphorus removal.
Other reports are being prepared which describe the impact upon the
Shagawa Lake ecosystem due to the reduction in phosphorus loading.
A. F. Bartsch
Director, CERL
m
-------
ABSTRACT
This report analyzes energy use for the advanced wastewater treatment
plant at Ely, Minnesota, and breaks it down into three major categories;
plant operation, support services, and indirect use. It provides a
detailed analysis of plant operation, process by process and shows that
energy used in the operation of the treatment process is minimal when
compared to support services and indirect use.
This report covers a period from April 1, 1973 to March 31, 1974 and
work was completed as of March 31, 1974.
IV
-------
CONTENTS
Page
I Introduction 1
II Wastewater Treatment Plant 3
III Direct Energy Utilization 6
Wastewater Treatment 7
Sludge Handling 9
Chemical Feed 10
Support Services 11
IV Indirect Energy Utilization 12
V Discussion and Summary 14
VI Literature Cited 19
VII SI Units and Conversion Factors Used 20
-------
ACKNOWLEDGEMENTS
The author wishes to thank R. M. Brice for his considerable help in
supplying information on the operation of, and equipment located at, the
treatment facility. This paper would not have been possible without his
assistance. In addition, I would like to thank fir. F. Frigiola, Ecodyne
Corporation; Mr. D. T. Prew, Tolz, King, Duvall, Anderson and Associ-
ates; and Mr. M. Preiss, of Cardox Corp., for supplying information and
reviewing the draft manuscript. Additionally, Dr. John Sheehy, Mr. R.
Smith and Dr. G. D. Zarnett provided useful comments on the manuscript.
vi
-------
SECTION I
INTRODUCTION
The art of decision making in any given area has become increasingly
complex as our society has become more and more interdependent and as
technology has advanced. This is particularly true in the areas of
pollutant generation and impact and energy development and utilization.
Unfortunately most decisions in these areas have been made in the past,
and still are, on the basis of "how to put out the fire" not "how to
prevent the fire". It has also been found that in resolving a problem,
new problems are often created, some of which are harder to deal with
than the original. A classic example is air pollution. One often used
solution has been to utilize wet scrubbers; this transfers the problem
from the air to the water. One then proceed to treat the water, which
transfers the problem from the water to the sludge. The sludge often is
disposed to the land or to the sea, which again transfers the problem.
This time it is in a form with which scientists are still trying to
deal. An exercise like this takes time, uses resources and employs
people but may never really solve the problem. True problem resolution
may be (and usually is) at the point of origin where the problem may be
minimized or prevented.
Energy consumption at wastewater treatment plants may, in the
future, be a significant input to the decision makers when determining
the extent or type of treatment. Smith (1973) studied energy consumption
in primary, secondary and tertiary municipal wastewater treatment plants.
His work is based upon both theoretical and actual plants. However, he
did not evaluate indirect energy consumption such as that used in pro-
duction of chemicals. Zarnett (1975) used the direct energy consumption
data compiled by Smith and added his own calculations for indirect
energy consumption. This paper deals with actual energy utilization at
one specific facility, the Advanced Wastewater Treatment (AWT) plant at
Ely, Minnesota, and is a follow on to the environmental impact study by
Kibby and Hernandez (1976). An evaluation is made of direct and indirect
operational energy consumption, but does not include energy utilized in
construction. That is an area which must eventually be dealt with, but
is beyond the scope of this paper.
To put this study into perspective, a brief history of the initia-
tion of the AWT plant and a description of the plant itself is necessary.
Prior to initiation of the AWT, phosphorus entering Shagawa Lake was
discharged from the secondary facility operated by the City of Ely. The
U. S. Environmental Protection Agency (EPA), in cooperation with the
City of Ely, funded construction of an advanced wastev/ater treatment
facility to demonstrate that a reduction in phosphorus from a point
source could reduce the trophic status of Shagawa Lake (Malueg et al.
1975). The tertiary plant which began operation in the spring of 1973
was designed to limit the phosphorus content of the effluent to 0.05q/m3
-------
(mg/1) or less. Operating data since that time indicate that the efflu-
ent from the plant does indeed meet design criteria. Both the resultant
water quality and the limnological characteristics of Shagawa Lake have
been reported in the literature by Malueg e_t aJL (1975) and by Larsen ejt
al. (1975) and will not be discussed here.
It should be recognized that the Ely AWT was designed and constructed
as a research facility with very high phosphorus removal efficiency.
However, this did not significantly increase the level of energy utili-
zation; therefore, a comparison with non-research facilities is valid.
-------
SECTION II
WASTEWATER TREATMENT PLANT
Prior to construction of the tertiary treatment plant, the Ely,
Minnesota, waste treatment facility consisted of a conventional secondary
treatment operation. Wastewater entered the facility, passed through
two parallel grit chambers, and then through a bar screen and comminuter.
The waste proceeded through a primary clarifier, trickling filter, and
secondary clarifier. After the effluent left the secondary clarifier,
it was chlorinated and discharged into Shagawa Lake (Brice, 1975).
Historically, sludge from the secondary clarifier was returned to
the influent line of the primary clarifier and sludge from the primary
clarifier was digested and discharged to sludge drying beds. Although
the plant was designed to use digester gas to heat the digester, it was
also necessary to use supplemental gas (Brice, 1975).
The tertiary treatment system was constructed as a research facility
with a maximum of operational flexibility. Because of this, it is
possible to pump almost any part of the waste "from anywhere to anywhere."
Chemicals can also be introduced at many points in the system. However,
much of this capability is not used and a standard procedure, which is
working quite satisfactorily, was developed. It is this normal operating
procedure which will be described. A plant flow schematic is shown in
Figure 1.
The effluent from the secondary treatment facility is pumped to a
solids-contact clarifier at a rate of 4,164 m3/d (1.1 mgd) (Sheehy and
Evans, 1976). Flow from this clarifier goes to a second, similar clari-
fier and then to a flow splitter box which feeds by gravity to four dual
media filters.
The filters polish the effluent by removal of suspended solids
containing phosphorus. Use of dual media (anthracite and sand) permits
longer filter runs while still achieving excellent solids retention
capability. Backwash water is returned to the secondary plant influent
line. The filter effluent is chlorinated and discharged to Shagawa Lake
or pumped back to the plant for use as process water.
It should be noted that an activated carbon feed capability is
available for the removal of soluble organic phosphorus, or other uses
as indicated. However, due to normal plant efficiency activated carbon
is seldom used; consequently, the analyses which follow do not include
an assessment of the activated carbon system.
Chemical sludge is withdrawn from the tertiary system at both
clarifiers and pumped to a gravity sludge thickener. Organic sludge
from the primary and secondary clarifiers goes to the sludge thickener
-------
where it is mixed with the chemical sludge from the tertiary plant.
From the thickener the sludge is pumped to a rotary belt vacuum filter
and trucked to an approved sanitary landfill. In the event of equipment
failure the sludge can bypass any given treatment facility and be dis-
charged to a sludge holding pond. Filtrate from the vacuum filter and
slurry from the vacuum are discharged to the equalization tank and
returned to the head of the plant.
The tertiary treatment plant was designed to treat 5,678 m3/d
(1.5 mgd) and from April 1, 1973 - March 31, 1974 was treating 4,164
m3/d (1.1 mgd). All data in this paper are for this time period.
Overall plant performance relative to certain parameters is presented in
Table 1 (Sheeny and Evans, 1976).
TABLE 1. ELY AWT PLANT PERFORMANCE
Influent Effluent Removal
g/m3
(mg/1)
Total P
Suspended Solids
Alkalinity (as
7.
202.
181.
1
0
0
g/m3
(mg/D %
0
1
41
.05
.30
.90
99.
99.
76.
4
4
9
g/m3
(mg/1 )
7.
201.
139.
02
0
0
kg/d
29.
837.
579.
2
0
0
Mg/yr
10.7
306.0
211.0
CaC03)
BOD 90.0 12.30 86.3 78.0 325.0 119.0
-------
Exhaust
CHLORINE FEED
SYSTEM
Air blower,
CARBON DIOXIDE
FEED SYSTEM
FEED SYSTEM
RBON
y^J L^ 1
Ejector water I J
pumps ^^^..^tf '
Metering-
pumps
FERRIC
FEED i
\
"|N
.•:'• ' ' '•.
• CHL
~YSTl
=fc—
ORIDE
-M
~~ '
Process water
^-
1
^ -^ A,_
— •_
_ POLYMER i
FEED SYSTEM
nt j[ jf
I I
Lift
station
Storm flow oni
septic drainage
from Stinky Creek
Sludge pump
station
Sludge holding
tanks
Figure 1.
Ely, Minnesota, Wastewater
Treatment Plant Normal Flow
Schematic
Thickened sludge
pump station
-si Sludge conveyor
Sludge hoppers
Truck to landfi
-Effluent
sampler
.Effluent to
'Shagawa Lake
Effluent pump
station
Process piping
Chemical feed piping
-------
SECTION III
DIRECT ENERGY UTILIZATION
Direct energy utilization, for the purposes of this paper, is that
energy which is utilized directly in the operation of the facility for
such uses as pumps, motors, chemical feed equipment, lighting, and heat-
ing. It does not include energy utilized in the production of chemicals
or other resources.
To arrive at actual (or estimated) energy utilization by various
plant processes it is necessary to make certain assumptions and establish
standard procedures for calculations. Since electrical meters and duty
cycles are not available on most pumps, motors, etc., it is usually
necessary to calculate power consumption on the basis of pump or motor
characteristics, and normal operating efficiencies. These calculations
were carried out in the same manner as was done by Smith (1973).
A major part of electrical consumption at a treatment plant is due
to pumping the main stream or ancillary streams from one level to a
higher level. The horsepower consumed in pumping water is given by the
following relationship:
Pumping Horsepower =
x
8.34 Ib/gal
33,000 ft-lb
mi n•hp
mgd = volume of water pumped, millions of gallons per day
H = total dynamic head, ft. of water
e. = hydraulic efficiency
This can be simplified as follows:
Pumping Horsepower = mgd x 0.1755 x H/e.
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. This information was not available in
most instances at this plant. Therefore, rough averages for hydraulic
efficiency were used as presented by Smith (1973):
up to 1000 gpm
1000 - 7000 gpm
over 7000 gpm
70% hydraulic efficiency
74 % hydraulic efficiency
83% hydraulic efficiency
-------
When converting pumping or motor horsepower to electrical power consump-
tion the electrical power in kilowatts is expressed as: kilowatt hours
= 0.85 (eff.) x horsepower x hours operating as was done by Smith (1973).
These basic formulae and assumptions are used throughout this report.
WASTEWATER TREATMENT
Primary - Secondary Plant
There are four sources of wastewater which make up the influent to
this treatment facility and average 4,164 m3/d (1.1 mgd): tertiary
plant return streams from lift station number 1, 195.8 m3/d (51,744
gpd); water from lift station number 2, which pumps water from "Stinky
Ditch" creek containing some septic tank drainage and also some runoff
from the sludge holding pond, 87 m3/d (23,000 gpd); swamp water from
lift station number 3, 142.8 m3/d (37,720 gpd); and municipal wastewater
from the City of Ely, 3,738 m3/d (987,536 gpd).
Lift station number 1 has two 200 gpm pumps designed to operate
against a total dynamic head of 55 feet. In pumping an average of 195.8
m3/d (51,744 gpd) this station utilized 52.2 MJ/d (14.5 kWh/d). Lift
station number 2 has two 100 gpm pumps designed to operate against a
total dynamic head of 40 feet. It pumps an average of 87 m3/d (23,000
gpd) and utilizes 16.9 MJ/d (4.7 kWh/d). Lift station number 3 has two
100 gpm pumps designed to operate against a total dynamic head of 30
feet, and pumps an average of 142.8 m3/d [37,720 gpd) and utilizes 20.9
MJ/d (5.8 kWh/d). The municipal waste water from the City of Ely enters
the plant by gravity flow so no pumping energy is utilized.
The total energy used for influent pumping is 90 MJ/d (25.0 kWh/d)
for a plant treating an average of 4164 m3/d (1.1 mgd). If all influent
flows were reduced proportionately the energy consumption for influent
pumping would be 81.7 MJ/d (22.7 kWh) for 3,785 m3/d (1.0 mgd). Flow
through the primary and secondary treatment plant is by gravity.
Throughout this paper, energy used for treatment of 4,164 m3 (1.1
mgd) is converted to probable energy use for 3,785 m3/d (1.0 mgd). This
is done to provide a comparison with the work done by Smith (1973).
Preliminary treatment includes a grit chamber, bar screen and
comminuter. The grit chamber and bar screen are manually cleaned, and
this use no electrical power. The comminuter was designed for 5,678
m3/d (1.5 mgd), with a peak flow of 28,387 m3/d (7.5 mgd). It is oper-
ated 24 hours a day by a 1.5 hp motor with energy consumption of 110.2
MJ/d (30.6 kWh/d) independent of flow.
From the comminuter the sewage flows by gravity to the primary
clarifier. This is a 15.2 m (50 foot) diameter circular settling basin
with mechanical equipment for sludge and scum removal, operated by a 0.5
-------
hp motor. This unit operates 24 hours a day with an energy consumption
of 36.7 MJ/d (10.2 kWh/d) independent of flow.
Flow from the primary clarifier is by gravity to the trickling
filter. This is an 18.3 m (60 foot) diameter, 1.8 m (6 foot) deep
filter consisting of rock varying in size from 7.6 - 10.2 cm (3 - 4
inches) in diameter. Wastewater is distributed over the surface of the
filter by a four-arm reaction type rotary distributor, so no additional
energy is used. Recirculation of a portion of the filter effluent can
be carried out, but is not.
Flow from the trickling filter is by gravity to the secondary
clarifier, this is a 15.2 m (50 foot) diameter circular settling basin,
similar to the primary clarifier, with mechanical equipment for sludge
and scum removal operated by a 0.5 hp motor. This unit operates 24
hours a day with an energy consumption of 36.7 MJ/d (10.2 kWh/d), inde-
pendent of flow.
Tertiary Plant
Flow from the secondary clarifier is by gravity to the 208.2 m3
(55,000 gallon) wetwell which dampens flow variation and allows nearly
constant hydraulic loading of the tertiary treatment units. Pumping
from the wetwell is accomplished by two variable speed 1,100 gpm pumps
designed to operate against a total dynamic head of 65 feet. In pumping
4,315 m3/d (1.14 mgd} this station utilized 1291 MJ/d (358.5 kWh/d). If
the primary plant influent flows were reduced to 3,785 m3/d (1.0 mgd)
the energy use would be reduced to 1132 MJ/d (314.5 kWhd).
Wastewater is pumped from the tertiary influent wetwell, and all
flow through the tertiary system is by gravity. The tertiary treatment
system includes first and second stage lime clarifiers in series, each
with a 3 hp motor driven scraper and an 8 hp variable speed (21-84 rpm)
pump. The first clarifier is 16.7 m (55 feet) in diameter with a height
of 5.9 m (19.5 feet). The second clarifier is also 16.7 m (55 feet) in
diameter, but is 5.0 m (16.5 feet) in height. Both units have a hydrau-
lic capacity of twice the design flow, 11,355 m3/d (3 mgd). Flow goes
from the second clarifier to four parallel dual media gravity filters,
each 3.7 m3 (12 feet) in diameter and 4.9 m (16 feet) high. Media depth
is 0.9 m (3 feet), and air scour and backwashing is automatic. All of
this system is operated through a single control system. Energy con-
sumption was calculated as 354.6 MJ (98.5 kWh) per day for each of the
clarifiers, 14.0 MJ (3.9 kWh) per day for sludge pumping from the clari-
fiers, and 110.2 MJ (30.6 kWh) per day for the sludge thickener. Filter
operation (air compressors, backwashing, etc.) uses approximately 125.6
MJ (34.9 kVJh) per day. Information provided by Ecodyne Corporation
indicates energy consumption for the tertiary plant (not including
influent pumping) is 959.0 MJ (266.4 kWh) per day.
8
-------
Service Mater
The treatment plant requires large quantities of water in its
operation which includes such uses as lime slurry water and other
chemical feeds, plus plant cleanup, etc. Two water sources are avail-
able for this with primary reliance placed upon using plant effluent
water, with Ely Municipal water for potable water uses plus backup for
the use of plant effluent water. Two 300 gpm pumps designed to operate
against a total dynamic head of 120 feet are used to pump 852 m3/d
(225,000 gpd) of plant effluent service water. These utilize 585 MJ
(138.0 kWh) per day. If the 4,164 m3/d (1.1 mgd) was reduced to 3,785
m3/d (1-0 mgd} it would be approximately 531 MJ (147.7 kWh) per day. It
is difficult to allocate this power use back to each process so it is
left as a single item use.
SLUDGE HANDLING
Sludge Pumping and Thickening
Approximately 6.4 m3/d (1,680 gpd) of sludge are pumped from the
secondary to the primary clarifier by a 50 gpm sludge pump designed to
operate against a total dynamic head of 37 feet. Energy use is approx-
imately 1.4 MJ (0.37 kWh) per day. This would reduce to 1.2 MJ (0.34
kWh) per day at 3,785 m3/d (1.0 mgd). A total of 12.7 m3 (3,360 gal.)
of sludge per day is pumped from the primary clarifier to the sludge
thickener by a 85 gpm sludge pump designed to operate against a total
dynamic head of 23 feet. Energy use is approximately 1.7 MJ (0.47 kWh)
per day which would reduce to 1.6 MJ (0.43 kWh) at 3,785 m3/d (1.0 mgd).
Sludge from the two lime clarifiers goes to a single pumping station
containing two variable speed (04-420 rpm) sludge pumps designed to
operate against a total dynamic head of 30 feet (estimated). 67.7 m3
(17,900 gal.) and 28.4 m3 (7,500 gal.) per day are pumped, from the
first and second stage clarifiers respectively, to the sludge thickener.
Energy use is 16.5 MJ (4.6 kWh) per day which would reduce to 15.0 MJ
(4.2 kWh) at 3,785 m3/d (1.0 mgd).
The sludge thickener is 7.9 m (26 feet) in diameter and is provided
with a 1.5 hp motor which drives the scraper. Energy consumption is
110.2 MJ (30.6 kWh) per day. Sludge pumping from the sludge thickener
is accomplished by two variable speed (84-420 rpm) sludge pumps designed
to operate against a total dynamic head of 30 feet (estimated). The
energy utilized is 16.6 MJ (4.6 kWh) per day.
Vacuum Filter
The vacuum filter operation has a number of energy consumers. It
is operated six days a week and averages 3.6 hours per day over the
-------
year. The filter is a continuous fabric type having a 1.8 m (6 foot)
diameter drum 2.4 m (8 feet) wide. The drum is driven by a 1 hp motor
using 11.0 MJ (3.1 kWh) per day. Two other motors are also used in
filter operation, a 1 hp agitator motor and a 3/4 hp motor for driving
the discharge roll. These use 11.2 MJ (3.1 kWh) and 8.3 MJ (2.3 kWh)
per day, respectively. The vacuum pump is powered by a 30 hp motor and
utilizes 330.5 MJ (91.8 kWh) per day. The filtrate pump is a 120 gpm
pump designed to operate against a total dynamic head of 38 feet, has a
3hp motor, and utilizes 21.3 MJ (5.9 kWh) per day. Total energy use in
the vacuum filter operation is 382.4 MJ (106.2 kWh) per day.
Sludge Cake Handling
After filtration the sludge cake drops onto a conveyor belt oper-
ated by a 2 hp motor which uses 22.0 MJ (6.1 kWh) per day. The belt
discharges to two sludge hoppers where it is stored for trucking to a
sanitary land fill. The trucks which haul the sludge use an average of
0.0254 m3 (6.7 gallons) per day, or a direct energy consumption of 900
MJ (857.5 x 103 BTU) per day. This would reduce to 828 MJ (779.5 x 103
BTU) per day for a 3,785 m3/d (1.0 mgd) flow rate.
CHEMICAL FEED
The lime feed system consists of two storage hoppers with vibrators,
a dust collection system, two gravimetric feeder slaker units, two
centrifugal pumps, and two hydraulic ejectors. The slaker feeder (1/4
hp), mixer (1/2 hp), and conveyor (1/4 hp) utilize 73.4 MJ (20.4 kWh)
per day. The 5 hp motor that drives the 60 gpm pumps utilizes 367.2 MJ
(102 kl-Jh) per day.
Ferric chloride is stored in a 23 m3 (6,000 gallon) tank which
supplies two 0.11 m3 (30 gallon) day tanks. Two flow proportional
diaphragm pumps feed from the day tanks. Pumping energy is minimal, but
the 1.5 hp motor which drives the mixer uses 110.2 MJ (30.6 kWh) per
day.
Activated carbon and polymer are seldom used and consume essen-
tially no energy.
Sulphuric acid (for pH control) is fed by pumps similar to the
ferric chloride pumps, with minimal energy consumption.
Liquid carbon dioxide, used for pH control, is stored in a 22
metric ton (24 ton) refrigeration unit and fed by dissolving in recycled
plant effluent. Based upon information obtained from Cardox (Chemetron
Corp.), approximately 110.5 MJ (30.7 kWh) per day are required for
vaporization. A 6,000 Ib. per day 75 watt feeder uses 6.5 MJ (1.8 kWh)
per day. Total carbon dioxide energy use is 117 MJ (32.5 kWh) per day.
10
-------
Chlorine is fed by a unit similar to the carbon dioxide feeder and
uses 6.5 MJ (1.8 kWh) per day.
SUPPORT SERVICES
Energy consumption for direct operation of a waste treatment facil-
ity may be comparable at various locations in the country. Support
services, however, could have significantly different energy consumption
levels. Direct electrical energy consumption for the treatment process
at Ely was 4,388 MJ (1,219 kWh) per day, and direct electrical energy
consumption for support services was 3,348 MJ (930 kWh) per day. This
includes indoor and outdoor lighting; operation of tools, office and
laboratory equipment; blowers for heating units; and miscellaneous other
equipment and uses.
Calculations were made using the same procedure as used by Smith
(1973) for outdoor lights and indoor square footage. He cites planning
figures of 2-4 watts per square foot of floor space. Primarily because
of extreme weather conditions almost all of this plant is covered (in-
doors). There are approximately 2,060 m2 (22,170 square feet) of indoor
space at this plant. Based upon 3 watts per square foot and a 10 hour
day, electrical consumption would be 2,394 MJ (665 kWh) per day. With
outdoor lighting this would increase to 2,448 MJ (680 kWh) per day.
Actual electrical use, as stated before, was approximately 3,348 MJ (930
kWh) per day. Calculations based upon 4 watts per square foot would
give an approximate electrical use of 3,240 MJ (900 kWh) per day which
is very near actual. Although a 10 hour day was used, it must be recog-
nized that an operator was present at the tertiary plant 24 hours a day,
and many items such as lights, blowers, etc. often operate on a 24 hour
basis.
Heating was the other large energy user in support services. Over
the year an average of 0.652 m3 (172.6 gal) per day of fuel oil was
used. This amounted to 27,677 MJ (26.235 x 106 BTU) per day.
This plant was designed to treat 5,678 m3 (1.5 mg) per day and
treated 4,164 m3 (1.1 mg) per day. Regardless of quantity treated (more
or less), energy consumption for the support services would remain essen-
tially the same at this plant.
11
-------
SECTION IV
INDIRECT ENERGY UTILIZATION
Indirect energy is that energy which is consumed in the manufac-
turing or processing of a material or direct energy, which is used in
the treatment plant at Ely. This includes the energy needed to produce
lime, C02, FeCls, polymer, H2S04, C12» gasoline, electricity and fuel
oil. The quantities of various energy sources used per year are shown
in Table 2. Data was obtained from Kibby and Hernandez (1976). These
quantities have been put into common energy units and are shown in Table
5.
12
-------
TABLE 2. ENERGY SOURCES REQUIRED TO PRODUCE RESOURCES USED ANNUALLY FOR AWT FOR ELY, MINNESOTA.
RESOURCES
Lime Mg (tons)
C02 Mg (tons)
Fed 3 Mg (tons)
Polymer kg (Ibs)
Sulfuric Acid Mg (tons)
Chlorine Mg (tons)
Gasoline m3 (gal)
Electricity kWh
Fuel Oil m3 (gal)
TOTAL
Energy Elect
Fuel Oil
Gasoline
Nat gas
Prop & But
Crude oil
Coal
ENERGY SOURCES
Propane &
Use Per Year Fuel Oil Coal Natural Gas Butane
m3 (gal) Mg (ton) m3 (Cu Ft) m3 (gal)
488(538) 37.6 (9935) 73 x 103 (2.58 x 10s)
152(168)
39.9(44) nil
304(670) not known
74.4(82) nil
4.7(5.2) 0.03 (7.7) 0.14 (0.15) 447 (15.8 x 103)
9.27(2450) 42.5 (1502) 0.06 (16.6)
780,000 15.4 (4070) 326 (359)
238(63,000) 1093 (38.6 x 103) 1.62 (427.8)
53.0 (14,013)326 (359.2) 73.6 x 103 (2,636 x 103) 1 .68 (444.4)
3,413 BTU/kWh
19,000 BTU/# 8#/gal
20,750 BTU/# 6.152 #/gal
1 ,050 BTU/cu ft
95,500 BTU/gal
138,100 BTU/gal
8,500 BTU/#
Crude Oil Electricity
m3 (gal) GJ (kUh)
96.84 (26,900)
96.48 (26,800)
23.22 (6,450)
(0.94)
0.09 (24.3)
0.09 (25.2) 216.54 (60,150)
-------
SECTION V
DISCUSSION AND SUMMARY
This paper reports energy utilization required for the operation of
the AWT plant at Ely, Minnesota, and has dealt with three major areas of
energy utilization: plant operation, support services, and indirect
uses. A detailed breakdown has been make of plant operation, unit by
unit (Table 3) and of support services (Table 4). Indirect energy
utilization is shown in Table 5, and a summary of total energy utilization
is shown in Table 6.
In addition to showing operational energy use at Ely, Table 3
compares this to the data obtained by Smith (1973). There appears to be
little consistency in comparing these data, but one must recognize that
each treatment plant did use some different unit processes. It should
also be remembered that at the 3,785 m3/d (1.0 mgd) level Smith was
dealing with a "standard" plant, whereas this paper deals with a specific
operational plant and uses actual energy consumption. Another factor to
consider is that the Ely plant was designed to treat 5,678 m3/d (1.5
mgd), was being operated at 4,164 m3/d (1.1 mgd), and data have been
converted to 3,785 m3/d (1.0 mgd). If the plant were operating at
design flow, the energy utilized per 3,785 m3 (1.0 mg) would be nearer
to that calculated by Smith.
The energy utilized by support services at Ely far surpasses
energy utilization in the treatment process. This is partially due to
the geographical location. Nights are long and the weather is cold.
Almost the entire facility is enclosed and heated, so fuel is the largest
single energy use. This is of particular significance in view of rising
fuel costs and potential shortages. It should be noted that regardless
of the daily flow or level of treatment used (phosphorus removal) this
energy use would not be reduced. Smith (1973) reports an estimate of
205 MJ (57 kWh) per day for primary-secondary plant support services.
This is very close to the probable use at the Ely primary-secondary
plant. He did not show similar calculations for tertiary treatment.
14
-------
TABLE 3. DAILY DIRECT ENERGY UTILIZATION FOR AWT PLANT OPERATION AT ELY, MINNESOTA, COMPARED TO SMITH
(1973) DATA.
ELY
, MINNESOTA,
Actual
PLANT SIZE
4,164 m3
MJ
0.1 mg)
kWh
AWT PLANT
SMITH
(1973)
Converted to
3,785 m3
MJ
(1-0 mg)
kWh
3,785 m
MJ
3 (1.0 mg)
kHh
PRIMARY-SECONDARY PLANT
Influent Pumping
Preliminary Treatment
Bar Screens
Comminuter
Grit Removal
Primary Sedimentation
Trickling Filter
Recirculation Pumping
Secondary Sedimentation
90
--
110.2
--
36.7
--
36.7
25.0
--
30.6
--
10.2
--
10.2
81.7
--
110.2
36.7
--
36.7
22.7
—
30.6
—
10.2
—
10.2
551
5.5
55.1
6.1
110.2
659
110.2
153
1.5
15.3
1.7
30.1
183.
30.6
TERTIARY PLANT
Influent Pumping
Lime Clarification
Clarifiers (2)
Lime Feed
Recarbonation
Multi Media Filtration
Ferric Chloride Feed
Chlorine Feed
Service Water Pumping
1,291
709
440.6
117
125.6
110.2
6.5
585
358.5
197.0
122.4
32.5
34.9
30.6
1.8
162.4
1,132
686
400.6
106.9
114.1
110.2
6.5
531
314.5
190.5
111.3
29.7
31.7
30.6
1.8
147.7
—
187.2
—
338.4
360
~
2.6
—
—
52.
--
94.
100.
—
0.7
—
SLUDGE HANDLING
Sludge Pumping
Gravity Thickener
Anaerobic Digesters
Lime Sludge Dewatering
Vacuum Filtration
kludge Hauling (857.5 x 103 BTU)
Multiple Hearth Incineration
Misc. Pumps, Motors, etc
estimated as 5% of total
TOTAL
33.5
110.2
—
--
404.3
900
--
256
5,360
9.3
30.6
--
--
112.3
250
--
71
1,489
30.6
110.2
--
--
367.5
818.2
—
232
4,873
8.5
30.6
--
—
102.9
227.3
—
65
1,353
9.6
36.7
445
230.4
205.2
--
194.4
—
3,503
2.6
10.2
123.6
64.0
57.
—
54.0
—
973
Gasoline use, not electrical
15
-------
TABLE 4. DAILY DIRECT ENERGY UTILIZATION FOR AWT PLANT SUPPORT SERVICES
AT ELY, MINNESOTA (INDEPENDENT OF FLOW)
Actual
4,164 m3 (1.1 ng)
Miscellaneous— 3.35 GJ (930 kWh)
lights, tools, blowers, etc.
2Fuel Oil (Heat) 27.68 GJ
0.62 m3 (172.6 gal) (26.235 x 106 BTU)
TOTAL 31.03 GJ
1Smith (1973) only showed primary-secondary support services.
2Smith (1973) showed no data since he did not use a specific plant at a
specific geographical location.
After fuel the next largest use of energy is indirect use for the
production of resources used. This use also far exceeds the energy used
in the treatment process. The energy use for support services may vary
greatly by geographical location of an AWT plant, but the indirect
energy use will not. Regardless of where a plant of this type is
located, this utilization will remain relatively high. It can readily
be seen that the greatest energy use is in the production of lime and
electricity. Details of energy use in production of resources are
discussed in detail by Kibby and Hernandez (1976).
A summary of total energy consumption at Ely is shown in Table 6.
This very dramatically shows the relative energy consumption of the
three major areas of energy use. As stated before, support services
energy use is disproportionately high due to the geographical location.
However, it would be high at almost any location in the United States.
Of the total 62.37 GJ used per day at Ely, 27.68 GJ are attributable to
heating the plant, 12.46 GJ are used in producing the lime, and 12.96 GJ
are used in producing the electricity used at the plant. These three
items constitute 85% of the plant energy use. Energy consumption should
be a consideration in the design of any treatment plant. This analysis
shows that maximum energy benefit can be obtained by concentrating on
conservation of electricity, heat, and lime. It should be noted that
these high energy items are, to a large degree, a reflection of the
advanced waste treatment portion of the Ely plant. This large energy
consumption, and environmental tradeoffs discussed by Kibby and Hernandez
(1976), further emphasize the necessity for thorough evaluations prior
to instituting advanced waste treatment as we know it today. An addi-
16
-------
tional factor which has not been studied is energy utilized in construc-
tion. Energy use is a direct measurement of cost, in both dollars and
natural resources. A complete and thorough evaluation should be carried
out when an advanced wastewater treatment facility is considered, and no
such facility should be built unless the study indicates a true need
with minimum adverse effects.
TABLE 6. A SUMMARY OF DAILY ENERGY UTILIZATION FOR AWT PLANT OPERATION
AT ELY, MINNESOTA
Actual Converted to Percent of
4,14 m3/d (1.1 mgd) 3,785 m3/d (1.0 mgd) Total
GJ GJ
Plant Operation 5.36 4.87 8.6
Support Services 31.03 31.03 49.7
Indirect 26.05 23.68 41.7
TOTAL 62.44 59.58 100.0
17
-------
TABLE 5. INDIRECT ENERGY UTILIZATION FOR AWT FOR ELY, MINNESOTA
Energy Used to Produce Resources
00
Per Year
RESOURCES USED
Lime Mg (tons)
C02 Mg (tons)
iFeClg Mg (tons)
2Polymer kg (Ibs)
^SOit Mg (tons)
Chlorine Mg (tons)
Gasoline m3 (gal)
3Electricity kWh
Per Year
488[538)
152(168)
39.9(44)
304(670)
74.4(82)
4.7(5.2)
9.27(2450)
780 x 103
GJ
4,548
96.5
BTU
(4,311 x 106)
(91.47 x 106)
43.6
3.5
4,727
4Fuel Oil m3 (gal) 238(63 x 103) 88.6
9.508
Per Day
4,164 m3 (1.1 mg)
nj BTU
12.46 (11.81 x 106)
0.26 (250.6 x 103)
(41.32 x 106)
(3.29 x 106)
(4481 x 106)
(83.99 x 106)
(9,012 x 109)
Negligible energy used
2Energy used not known, but probably negligible
3This is net energy, based upon 33% thermal efficiency
reduction from 4,164 m3 (1.1 mg) to 3,785 m3 (1.0 mg)
0.12 (113.2 x 103)
0.01 (9.02 x 103)
12.96 (12.28 x 106)
0.24 (0.230 x 106)
26.05 (24.69 x 106)
Converted to
3,785 m3 (1.0 mg)
GJ BTU
11.33 (10.74 x 106)
0.24 (227.8 x 103)
0.11 (10.9 x 103)
0.01 (8.2 x 103)
11.77 (11.16 x 106)
0.24 (0.230 x 106)
23.70 (22.47 x 106)
since fuel oil is used to heat the building.
-------
LITERATURE CITED
1. Brice, R. M. 1975. Personal Communication.
2. Frigiola, F. 1976. Personal Communication.
3. Kibby, H., and Hernandez, D. J. 1976. Environmental Impacts
of Advanced Wastewater Treatment at Ely, Minnesota, EPA-600/
3-76-092. pp. 30.
4. Larsen, D. P., K. W. Malueg, D. W. Schults, and R. M. Brice (1975).
Response of Eutrophic Shagawa Lake, Minnesota, U.S.A., to Point-
Source Phosphorus Reduction. Verh. Internat. Verein. Limnol.
19:884-892.
5. Malueg, K. W., D. P. Larsen, D. W. Schults, and H. T. Mercier
(1975). A Six Year Water Phosphorus and Nitrogen Budget for
Shagawa Lake, Minnesota. Journ. of Envir. Qual. 4:236-242.
6. Prew, D. T. 1976. Personal Communication.
7. Preiss, M. 1976. Personal Communication.
8. Sheehy, J. W. and Evans, F. L. 1975. Tertiary Treatment for
Phosphorus Removal at Ely, Minnesota, AWT Plant April 1973-March
1974, EPA 660/2-76-082. pp. 123.
9. Smith, R. 1973. Electrical Power Consumption for Municipal
Wastewater Treatment. EPA-R2-73-281. pp.89.
10. Zarnett, G. D. 1975. Energy Requirements for Conventional and
Advanced Wastewater Treatment. Ministry of the Environment,
Applied Sciences Section, Pollution Control Branch, Publ. No. W47,
Toronto, Ontario, pp. 29.
19
-------
SI UNITS AND CONVERSION FACTORS USED
UNITS
length
mass
area
'^FIXFS
vU.1 i. A L-*J
flu Hi pi
rncTfiMC
.rxoiUPlo
To Convert
metre (m)
kilogram (kg)
square metre (m2)
i cation Factors
1012
109
106
103
102
101
10"1
10'2
10'3
10~6
10'9
10'12
10"15
10"18
From to
energy
volume
Prefix
tera
giga
mega
kilo
hecto
deka
deci
centi
mi 1 1 i
micro
nano
pi co
femto
atto
joule (J)
cubic met
SI Symbol
T
G
M
k
h
da
d
c
m
u
n
P
f
a
Multiply by
BTU
feet
foot2
foot3
gallon (U.S. liquid)
inches
kilowatt-hour (kWh)
pounds (Ib avoirdupois)
ton (short-2000 Ibs)
joules (J)
metre (m)
metre2 (m2)
metre3 (m3)
metre (m3)
centimeters (cm)
joules (J)
kilogram (kg)
megagrams (Mg)
1.055 x 103
0.3048
9.290 x 10"2
2.832 x 10"2
3.785 x 10~3
2.540
3.600 x 106
4.536 x 10"1
0.907
20
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-600/7-78-001
4. TITLE AND SUBTITLE
Energy Consumption of Advanced
Wastewater Treatment at Ely, Minnesota
7. AUTHOR(S)
Donald J. Hernandez
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Corvallis Environmental Research Laboratory
U.S. Environmental Protection Agency
200 SW 35th Street
Corvallis, OR 97330
12. SPONSORING AGENCY NAME AND ADDRESS
same
15. SUPPLEMENTARY NOTES
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
January 1978
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1NE625
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVERED
inhouse - final
14. SPONSORING AGENCY CODE
EPA/600/02
16. ABSTRACT
This report analyzes energy use for the advanced wastewater treatment plant at
Ely, Minnesota, and breaks it down into three major categories: plant operation,
support services, and indirect use. It provides a detailed analysis of plant
operation, process by process, and shows that energy used in the operation of
the treatment process is minimal when compared to support services and indirect
use.
17. KEY WORDS AND DOCUMENT
a. DESCRIPTORS b.lDENTI
Energy Consumption Adva
Tr
IS. DISTRIBUTION STATEMENT 19. SECU
Release to Public Uncl
20. SECU
Uncl
ANALYSIS
FIERS/OPEN ENDED TERMS C. COS ATI Field/Group
need Wastewater
eatement
=IITY CLASS (This Report) 21. NO. OF PAGES
assified 26
=tlTY CLASS (This page) 22. PRICE
assified
EPA Form 2220-1 (9-73)
21
-------
•w-GPO #799-059
------- |