&EPA
United States
Environmental Protection
Agency
Office of Municipal
Pollution Control (WH-546)
Washington DC 20460
July 1986
Water
Energy in Municipal Waste
Water Treatment
An Energy Audit Procedure
and Supporting Data Base
Final Report
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ENERGY IN MUNICIPAL WASTEWATER TREATMENT
AN ENERGY AUDIT PROCEDURE AND SUPPORTING DATA BASE
FINAL REPORT
Contract Number 68-01-6433
Submitted To:
U.S. Environmental Protection Agency
Municipal Construction Division (WH547)
Office of Water Programs
Attention: Mr. James Wheeler
401 M Street, SW
Washington, D.C. 20460
Submitted By:
CARLTECH ASSOCIATES, INC.
OVERLOOK CENTER, SUITE 301
5457 TWIN KNOLLS ROAD
COLUMBIA, MD 21045
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TABLE OF CONTENTS
1. SUMMARY 1
2. INTRODUCTION 2
3. METHODOLOGY 4
3.1 Introduction 4
3.2 Project Plans 4
3.3 Task 1 4
3.4 Task 2 5
3.5 Task 3 7
Exhibit 3-1 8
Exhibi t 3-2 9
Exhibit 3-3 10
4. RESULTS 14
4.1 Operating Plant Energy Survey Method 14
4.2 Operating Energy Estimation Method 14
4.3 Acquisition Energy Estimation Method 15
4.4 Case Examples 15
Exhibit 4-1 16
5. CONCLUSIONS AND RECOMMENDATIONS 17
5.1 Conclusions 17
5.2 Recommendations 17
6. FUTURE WORK 19
7 . REFERENCES 20
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SECTION 1
SUMMARY
EPA regulations require a methodology for determining energy requirements of
municipal wastewater treatment because treatment plant construction and
operation consume significant amounts of energy. Energy is a major driver
of both operating and capital costs. In addition, most of the energy
consumed is drawn from irreplaceable natural resources. In recognition of
these factors, EPA requires analysis of the energy effectiveness of
alternative types of wastewater treatment. The purpose of this project was
to develop appropriate procedures to perform this analysis.
Two types of energy were addressed during this project:
o Operating Energy - energy expended during routine operation of a
wastewater treatment plan;
o Acquisition Energy - energy expended during the construction phase
of a wastewater treatment plant.
A means was developed to:
o Evaluate energy consumption of operating wastewater treatment
plants;
o Estimate operating energy requirements of planned and operating
wastewater treatment plants; and
o Estimate acquisition energy of wastewater treatment plants.
The energy evaluation method enables wastewater treatment staff to prepare
estimates of energy use for existing plants and compare them to operating
experience of typical plants of similar design. Methods have been developed
for planners to estimate acquisition and operating energies of planned
wastewater treatment alternatives to compare among process alternatives.
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SECTION 2
INTRODUCTION
A methodology for determining total energy requirements of municipal waste-
water treatment plants is needed to satisfy requirements of EPA's May 12,
1982 Regulation, "Grants for Construction of Treatment Works" 35.2030(b)
(3)(VI) "Facilities Plan Contents." The regulation requires evaluation of
the energy effectiveness of alternative technologies considered by
municipalities and other submitting organizations.
Energy is an important contributor to both operating and capital costs of
wastewater treatment plants and has a major effect on the cost effectiveness
of treatment alternatives. Data on total energy consumption of wastewater
treatment are found in many diverse sources and have not been assembled or
analyzed on a unified basis.
In recognition of this situation, EPA has adopted regulations requiring
development of a means to analyze the energy effectiveness of types of
wastewater treatment. This project has been performed in response to the
regulations. The goals of the project were to collect data concerning
energy consumption of wastewater treatment plant construction and
operation; to present data on a consistent basis; and to develop a
methodology which can be used by planners to evaluate wastewater treatment
process alternatives and by operators to calculate actual operating energy
and to evaluate changes in operating procedures.
The project was divided into three tasks:
o Task 1 - Obtain, aggregate, and analyze data; evaluate the CAPDET
computer program (previously developed by EPA and the U.S. Army
Corps of Engineers).
o Task 2 - Develop a methodology for energy evaluation and apply it
to case studies.
o Task 3 - Aggregate Task 1 and Task 2 results, and
present as Final Report.
This report concerns the conduct of all three tasks. The report is
organized in the following fashion:
o Section 1 contains the summary of work performed.
o Section 3 discusses the methodology used to conduct this study.
o Section 4 presents and discusses results:
description of the methodology for estimation of operating
and acquisition energies;
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description of the operating plant energy survey method; and
- operating and acquisition energies for unit processes dis-
cussed in Task 1 (1).
o ' Section 5 presents conclusions and recommendations.
o Section 6 describes relevant future work.
o Section 7 contains references.
o Appendix A presents the energy estimation and survey procedures.
o Appendix B presents illustrative case examples.
o Appendix C presents alternative methodologies.
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SECTION 3
METHODOLOGY
3.1 INTRODUCTION
This section describes the overall approach of this project. It is divided
into subsections as follows:
o Project Plans;
o Task 1;
o Task 2; and
o Task 3.
3.2 PROJECT PLANS
Projects plans for this study were prepared and delivered in 1981 and 1982.
They discussed development of acquistion and operating energy procedures,
tables, and equations for use by planning and operating personnel.
3.3 TASK 1
Task 1 consisted of :
o Choosing unit processes for analysis;
o Literature review;
o Data analysis; and
o CAPDET evaluation.
Unit processes were chosen starting with the list of processes addressed in
EPA publications. Input from the EPA Project Officer was then used to
reduce the number of candidate processes to about 75 unit processes. These
processes were further examined to assess the quantity of data available
from other contractors and from the literature. Approximately 25
technologies were rejected because of insufficient data; the remaining 50
unit processes are discussed in this report.
The literature review consisted of:
o Database searches - we examined more than 900 titles from eight
databases and selected about 100 for this study;
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o EPA Small Wastewater Flows Clearing House - we examined more than
1000 different titles pertaining to small wastewater flows and
selected about 20 for use in this study.
o Knowledgeable Individuals - we conducted telephone interviews
with knowledgeable•individuals who furnished valuable information.
Data was also obtained from the literature on the selected wastewater
treatment unit processes. Both acquisition and operating energy data was
identified for treatment plant design flow in the range of 0.5 to 100.0
million gallons per day.
Acquisition energies were calculated using a building block approach based
upon 1967 wastewater treatment plant costs for commodities (materials used
in plant construction and operation). These acquisition energies are
included in the manual portion of this report.
Literature data on operating energies were found and examined for nearly all
of the 50 unit processes discussed in this report. Data presented in the
literature varied so widely (1) that comparison among authors and with our
calculated values was not possible. Insufficient data were available for
smal1-wastewater-flow treatment unit processes and for recovered energy.
These were, therefore, not addressed in this study. Data are currently
being generated for these processes and we believe that both small flows and
energy recovery equipment can be covered by future studies.
The applicability of the CAPDET computer program was reviewed by calculating
acquisition energies using the 1981 version of CAPDET. Results indicated
that:
o CAPDET calculates construction costs for 25 unit processes (1)
using non-parametric equations.
o CAPDET appears to adjust internally generated costs via use of
adjustment factors of 10 to 15 percent.
Task 2 consisted of using data obtained during Task 1 to develop a means to
estimate both acquisition and operating energies of wastewater treatment
units.
3.4 TASK 2
3.4.1 Operating Plant Energy Evaluation Methodology
The energy survey method developed during this project is presented in the
manual (Appendix A). This method was developed from data obtained in Task 1
(1), past energy audits of wastewater treatment plants furnished by EPA
(2,3) and from University of Wisconsin course notes (4) instructing
municipal officials in audit procedures for public facilities, including
wastewater treatment plants. Charts, tables and methods of analysis were
examined and synthesized to produce the manual.
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3.4.2 Energy Estimation Methodology
A methodology was developed to calculate acquisition and operating energies
which uses tables as a shortcut whenever possible. This methodology
includes step by step instructions for use by both planning and operating
personnel and is presented as a manual in Appendix A of this report.
The methodology developed is divided into two parts:
o Acquisition Energy and
o Operating Energy.
These are subdivided into simplified and detailed methods. Acquisition
energies are those energies consumed in the development of the facility
itself, including energies of materials and construction. Operating
energies are those energies required to perform wastewater treatment once
the plant is in place.
3.4.3 Acquisition Energy Calculation
The acquisition energy estimation method used in the manual was discussed in
the Task 1 Report (1). Design assumptions affecting acquisition energies
are presented in Exhibit 3-1. Using detailed commodity estimates for each
treatment unit process, commodity requirements are multiplied by appropriate
unit embodied energies, their sum resulting in the treatment unit
acquisition energy.' Acquisition energy tables were prepared using this "
method and they are presented in the manual as a simplified method for the
eleven wastewater treatment unit processes studied. The detailed method is
also presented in the manual to estimate acquisition energies for unit
processes lacking tables.
3.4.4 Operating Energy Calculation
Operating energies were calculated for 50 unit processes during this project
using data supplied by Culp/Wesner/Culp. Operating energy values for the
following eight additional unit processes were obtained from an EPA report
(5) Comminutors; Grit Removal (nonaerated); Pumping (Raw Wastewater);
Lagoons (Aerated); Land Treatment (Slow Rate and Overland Flow);
Microstraining; Overland Flow; and Sludge Transport (Truck). These operating
energy requirements include power and fuel. Twenty one unit processes
include embodied energy of consumable chemicals (Exhibit 3-2). Electrical
energy values were converted using 3.413 MBtu/MWatt. Project operating
energy requirements are based on design assumptions which include detention
times, raw wastewater strength, treated wastewater analysis, et cetera.
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Important engineering parameters (other than flow) which affect operating
energies were identified. These are found in Exhibit 3-3. Equations were
developed to adjust operating energy values for these parameters and to
calculate energy use ranges. These were aggregated into tables for
presentation in the energy estimation manual. The tables present:
o Average or typical operating energy requirements for each waste-
water treatment unit;
o High and low extremes of operating energy;
o Parameters affecting operating energies and values for typical,
high, and low energy use designs; and
o Equations for using these parameters to adjust the typical opera-
ting energies.
3.4.5 Case Examples
Twenty-five case examples were prepared to illustrate the use of the
methodology developed during this study. Examples consist of three
acquisition energy problems and 22 operating energy problems. Eleven
operating energy examples were based on the literature and others were
developed independently. Methods and use of tables was displayed in the
case examples to clarify the steps needed to calculate energies.
3.5 TASK 3
Task 3 consisted of incorporation of client comments on the Task 2 Report
and preparation of the Draft Final Report. Concurrent with conduct of Task
3 (as initially defined) we completed work on additional unit processes
funded by a contract modification. Discussion of the additional processes
is included in the Draft Final Report.
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EXHIBIT 3-1
DESIGN PARAMETER VALUES FOR ACQUISITION ENERGIES
UNIT PROCESS NAME
Activated Sludge
Basins
Sub. Turbine
Anaerobic Digesters
Centrifugation
Clarifiers
Filtration
Incinerators,
Multiple Hearth
Pure Oxygen
Activated Sludge
Con. Basins
Dissol. System
Cryo. Generation
Rotating Biological
Contactors
Sludge Pumping
Trickling Filters
Vacuum Filtration
UNITS 0.5 mgd
HYDRAULIC CAPACITY
1.0 mgd 10 mgd
100 mgd
cu ft 24
hp
cu ft 12
gpm
sq ft
sq ft
sq ft
cu ft 3
ton/day
ton/day
sq ft 500
gpm
cu ft 9
sq ft
,000
25
,000
3
850
70
50
,200
.45
.45
,000
3
,000
11
48,000
50
23,000
6
1,700
140
100
6,500
.85
.85
1,000,000
5
18,000
22
460,000
440
230,000
60
17,000
1,400
1,000
62,000
8.0
8.0
10,000,000
45
180,000
220
3,900,000
3,800
2,300,000
600
170,000
140,000
5,800
520,000
61
61
100,000,000
360
1,800,000
2,200
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EXHIBIT 3-2
UNIT PROCESSES INCLUDING EMBODIED ENERGY
OF CONSUMABLE CHEMICALS IN OPERATING ENERGIES
Alum Addition
Lime Addition
Chlorination
Granular Activated Carbon Regeneration
Biological Nitrification, Trickling Filter
Biological Nitrification,
Biological Nitrification,
Centrifugal Dewatering,
Centrifugal Dewatering,
Dewatering,
Thickening,
Thickening,
Thickening,
Press
Centrifugal
Centrifugal
Centrifugal
Centrifugal
Belt Filter
RBC's
Suspended Growth
Basket Centrifuge
Low G Solid Bowl Centrifuge
High G Solid Bowl Centrifuge
Basket Centrifuge
Low G Solid Bowl Centrifuge
High G Solid Bowl Centrifuge
Diaphragm Filter Press
Breakpoint'Chlorination
SO Dechlorination
Vacuum Filtration
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EXHIBIT 3-3
IMPORTANT OPERATING ENERGY PARAMETERS
Technology or Subtechnology
Important Parameters
Activated Sludge
o Submerged Turbine
o Pure Oxygen
o Diffused Air
o Mechanical Aeration
Biological Nitrification
o RBC's
NaOH Feed System
o Suspended Growth
Aeration System
NaOh Feed System and NaOH
o Trickling Filter
Recycle Pumping
NaOH Feed System and NaOH
Breakpoint Chlorination
o Mixer
o NaOH/Feed System
Chemical Addition
o Alum
o Lime
Chlorination
Clarifiers
Dechlorination (S07)
Oxygen Transfer Eff.
(Ibs. 02/hp.-hr.)
Oxygen Transfer Eff.
(Ibs. 0 /hp.-hr.)
Type of 0^ Generation
Oxygen Transfer Eff.
(Ibs. 0 /hp.-hr.)
Oxygen Transfer Eff.
(Ibs. 0 /hp.-hr.)
Hydraulic Loading Rate (gpd/sq ft)
Dose (mg/L)
Oxygen Transfer Efficiency (Ibs/hp-hr)
Oxygen Requirement (Ibs/MG)
Dose (mg/L)
Recycle Ratio
TDH (ft)
Dose (mg/L)
Detention time (min)
Dose (MG/L)
Dosage (mg/L)
Dosage (mg/L)
Dosage (mg/L)
Overflow Rage (GPDPSF)
Dose (mg/L)
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Digestion
o Aerobic
o Anaerobic
Dissolved Air Floatation
Filtration
Granular Activated Carbon
Lagoons
o Aerated
o Facultative
Land Treatment
o Slow Rate
o Overland Flow
Microstraining
Ozonation
Preliminary Treatment
o Comminutors
o Screens
o Grit Removal
Pumping
o Raw Wastewater
o In Plant
o Sludge
RBC's
Sludge Quantity (Ibs/MG)
Oxygen Transfer Eff.
(Ibs. 09/hp. hr.)
Sludge Quantity (Ibs/MG)
Connected hp
Solids Quantity (Ibs/MG)
Loading Rate (Ibs/Sq ft-day)
TDK. (Ft)
TDK, (ft.)
Connected hp
Detention Time (days)
TDH (Ft)
TDK (Ft)
Loading Rate
(GPMPSF)
Dose (mg/L)
Connected Hp*
Mechanical Cleaning *
Detention Time (Min.)
Connected Hp*
TDH (Ft)
TDH (Ft)
TDH (Ft)
Hydraulic Loading Rate
(GPDPSF)
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Sludge Dewatering
o Basket Centrifuge
Polymer/Feed System
o Low G and High G Solid Bowl
Centrifuge
Polymer/Feed System
o Filter Press, Diaphragm
Press
Lime/Feed System
Fed /Feed System
o Filter Press, Belt
Polymer/Feed System
o Drying Beds
o Vacuum Filter
Sludge Incineration,
Multiple Hearth
Sludge Quantity (Ibs/MG)
Sludge Concentration (% solids)
Sludge Quantity (Ibs/MG)
Dose (Ibs/ton)
Sludge Quantity (Ibs/MG)
Sludge Concentration (% solids)
Sludge Quantity (Ibs/MG)
Dose (Ibs/ton)
Solids Quantity (Ibs/MG)
Loading Rate (Ibs/Sq ft-hr)
Dose (mg/L)
Solids Quantity (Ibs/Sq ft-hr)
Dose (mg/L)
Solids Quantity (Ibs/Sq ft-hr)
Sludge Quantity (Ibs)MG)
Sludge Concentration (% Solids)
Sludge Quantity (Ibs/MG)
Dose (Ibs/ton)
Solids Concentration (Percent)
Sludge Quantity (Ibs/MG)
Loading Rate (Ibs/hr/sq/Ft)
Sludge Quantity (Ibs/MG)
Dose (Ibs/ton)
Solids Concentration (Percent)
Sludge Thickening
o Basket Centrifuge
Polymer/Feed system
o Low G and High G Solid Bowl
Centrifuge
Polymer/Feed System
o Gravity
o Dissolved Air Flotation
Sludge Quantity (Ibs/MG)
Sludge Concentration (% solids)
Sludge Quantity (Ibs/MG)
Sludge Quantity (Ibs/MG)
Sludge Concentration (% solids)
Sludge Quantity (Ibs/MG)
Loading Rate (Ibs/Sq ft)
Sludge Quantity (Ibs/MG)
Solids Quantity (Ibs/MG)
Loading Rate (Ib/Sq ft-day)
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Sludge Transport
Trickling Filters
o Low Rate
o High Rate, Rock Media
o High Rate, Plastic Media
Ultraviolet Light Disinfection
Solids Concentration (Percent)
Sludge Quantity (Ibs/MG)
Distance (Mi.)
None of Significance
Recycle Ratio, TDH (Ft)
Recycle Ratio, TDH (Ft)
None of Significance
* Not addressed in this report
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SECTION 4
RESULTS
This section discusses the results of performance of this project,
included are:
o Method for surveying operating energy requirements of existing
plants,
o Methods for estimation of operating energies,
o Methods for estimation of acquisition energies.
4.1 OPERATING PLANT ENERGY SURVEY METHOD
The energy evaluation method developed in the course of this project is
included in the manual presented in Appendix A. This manual enables
operating plant personnel to examine and evaluate energy use by their
operating plant. The method is divided into two portions:
o Examination of motors, and
o Examination of fuel consumption (applies to incinerators, process
heat, etc.)
The plant operator is instructed to divide the plant into subunits. Each
subunit is then examined to count the motors and other fuel-using equipment.
Subunit totals are then added and compared with the overall utility bill.
Guidance is presented on measuring duty cycles to include intermittent
operations.
4.2 OPERATING ENERGY ESTIMATION METHOD
This section summarizes the methods developed for estimation of operating
energy by wastewater treatment plant operating and planning personnel. The
manual presented in Appendix A contains the result. These methods were
developed for the unit processes presented in Exhibit 4-1. They use tables
and adjustment procedures for important engineering parameters affecting the
design of wastewater treatment plants including flow rate, size, pump head,
detention time, etc. In addition, ranges of operating energy are provided
in the manual for those cases where the design parameters have not been
established or where rapid estimation is desired.
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4.3 ACQUISITION ENERGY ESTIMATION METHOD
This section summarizes the method developed for estimation of acquisition
energy. The manual presented in Appendix A is the result. A method was
developed using detailed plant designs to estimate the acquisition energies
of various types of wastewater treatment unit processes. Tables were
developed from that method for the unit processes listed in Exhibit 4-1.
Procedures to adjust the acquisition energies for flow rates are described
in the manual. In addition, the detailed method is presented so that other
unit process acquisition energies can be estimated when detailed design
information is available.
4.4 CASE EXAMPLES
Twenty-five case examples were prepared to illustrate the use of the method-
ology developed during this study. The titles of the case examples are pre-
sented in Exhibit 4-2 and the case examples are presented in Appendix B.
Examples consist of three acquisition energy problems and 22 operating energy
problems. Eleven operating energy examples were obtained from the literature
and 14 were prepared independently.
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EXHIBIT 4-1
A. ACQUISITION ENERGIES UNIT PROCESSES
Activated Sludge
Anaerobic Digesters
Centrifugation
Clarifiers
Filtration
Multiple Hearth Incineration
Pure Oxygen Activated Sludge
Rock Media Trickling Filter
Rotating Biological Contactor
Sludge Pumping Station
Vacuum Filtration
B. OPERATING ENERGY UNIT PROCESSES
Activated Sludge
Diffused Air, Coarse Bubble
Diffused Air, Fine Bubble
Mechanical Aeration
Submerged Turbine
Activated Sludge, Oxygen
Breakpoint Chlorination
Biological Nitrification
Suspended Growth
Trickling Filters
RBC's
Chemical Addition
Alum
Lime
Chlorination
Clarifiers
Dechlorination (S02)
Digestion
Aerobic
Anaerobic
Filtration
Granular Activated Carbon
Regeneration
Lagoons, Aerated
Land Treatment
Slow Rate
Overland Flow
Micros training
Ozonation
Preliminary Treatment
Comminutors
Grit Removal (Aerated)
Grit Removal (Nonaerated)
Screens
Pumping
In Plant
Wastewater
Sludge
Rotating Biological Contactors
Sludge Dewatering
Basket Centrifuge
Low G Solid Bowl Centrifuge
High G Solid Bowl Centrifuge
Filter Press
- Diaphragm
- Belt
Drying Beds
Sludge Incineration
Multiple Hearth
Sludge Thickening
Basket Centrifuge
Low G Solid Bowl Centrifuge
High G Solid Bowl Centrifuge
Gravity Thickening
Dissolved Air Flotation
Trickling Filters
Low Rate, Rock Media
High Rate, Plastic Media
High Rate, Rock Media
Super High Rate, Plastic Media
Ultraviolet Light Disinfection
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SECTION 5
CONCLUSIONS AND RECOMMENDATIONS
This section presents conclusions drawn during the performance of this
project and recommendations for both EPA and operating personnel to use the
methods developed during this task. These are presented below:
5.1 CONCLUSIONS
The following conclusions were drawn from this study:
o A simple energy survey of operating plants to estimate existing
energy use can be performed by plant engineers, plant superinten-
dents, etc.
o Operating energies can be estimated using two methods:
Simplified - using project-generated tables, and
Detailed - using adjustment equations.
o Acquisition energies can be estimated using two methods:
Simplified - using project-generated tables, and
Detailed - requiring detailed cost estimates.
5.2 RECOMMENDATIONS
Recommendations are as follows:
o The energy survey method should be used to estimate energy use
in operating wastewater treatment (WWT) plants.
o Our simplified acquisition energy estimation method may be
used for the unit processes covered.
o The detailed acquisition energy method must be used for other
processes.
o The simplified operating energy estimation may be used for most
energy estimates.
o The detailed operating energy estimation method may be used
whenever more accurate estimates are needed and engineering
parameters are available.
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o Estimation methods should not be extended outside the size range
.0.5 - 100 MGD design flow.
o Users should obtain engineering parametric data for cases under
study whenever this data is available.
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SECTION 6
FUTURE WORK
Future work on this project should include expansion of the methodology gen-
erated in this report to include additional unit processes. Future work
should also include validation of the modified CAPDET computer program for
estimation of both acquisition and operating energies.
Acquisition energies presented during this report were, based upon gross
estimates of unit embodied energies produced by the University of
California at Davis. These embodied energies are in turn based on material
presented by the Center for Automatic Computation (CAC) of the University of
Illinois using data gathered in 1968. Use of energy in manufacturing has
altered greatly since that time, and these figures are likely to be high.
Therefore, future work on this project should include a revalidation of the
unit embodied energy figures used in our calculations.
The methodology discussed in this report does not include small-flow unit
processes (e.g., grinder pumps, septic tanks) as data were not available.
This report also does not address recovered eaergy processes (such as
digester gas combustion and incinerator heat recovery) as data were not
available. These data are currently being generated and will be available
in the near future. Therefore, future work should include analysis of
small-flow unit and energy recovery processes when data are available.
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SECTION 7
REFERENCES
1. CARLTECH ASSOCIATES, "Energy In Municipal Wastewater Treatment — An
Energy Audit Procedure and Supporting Database - Task 1 Report"
Prepared under EPA Contract No. 68-01-6433 (March, 1982)
2. U.S. EPA Unpublished Draft Energy Audit Report - Kentucky Wastewater
Treatment Plant (1982).
3. U.S. EPA Unpublished Draft Energy Audit Report - Florida Plant (1982).
4. University of Wisconsin, "Municipal Energy Conservation Manual,"
Prepared by the University of Wisconsin - Extension, Department of
Engineering and Applied Science (1979).
5. G.M. Wesner et.al, Energy Conservation in Municipal Wastewater
Treatment, MCD 32, Prepared under EPA Contract No. 68-03-2186, Task 9
(March 1978).
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