oEPA
EPA/600/R-18/280 | June 2019 | www.epa.gov/research
United States
Environmental Protection
Agency
Life Cycle Assessment and Cost
Analysis of Distributed Mixed Wastewater &
Graywater Treatment for Water Recycling in
the Context of an Urban Case Study
Membrane
Bioreoctor
Office of Research and Development
Washington, D.C.
Constructed
Wetland
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SEPA
United States
Environmental Protection
Agency
Life Cycle Assessment and Cost
Analysis of Distributed Mixed
Wastewater and Graywater Treatment
for Water Recycling in the Context of an
Urban Case Study
Ben Morelli and Sarah Cashman
Eastern Research Group, Inc.
110 Hartwell Ave
Lexington, MA 02421
Prepared for:
Cissy Ma, Jay Garland, Diana Bless, Michael Jahne
U.S. Environmental Protection Agency
National Exposure Research Laboratory
National Risk Management Research Laboratory
Office of Research and Development
26 W. Martin Luther King Drive
Cincinnati, OH 45268
Date: June 7, 2019
Draft Report: EPA Contract No. EP-C-16-015, Task Order 0003
Report Revisions: EPA Contract No. EP-C-15-010, Work Assignment 3-32
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Although the information in this document has been funded by the United States Environmental
Protection Agency under Contract EP-C-16-015 to Eastern Research Group, Inc. (Draft Report)
and EPA Contract No. EP-C-15-010 to Pegasus Technical Services, Inc. (Report Revisions), it
does not necessarily reflect the views of the Agency and no official endorsement should be
inferred.
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Abstract
ABSTRACT
Communities such as San Francisco, California are promoting decentralized wastewater
treatment coupled with on-site, non-potable reuse (NPR) as a strategy for alleviating water
scarcity. This research uses life cycle assessment (LCA) and life cycle cost assessment (LCCA)
to evaluate several urban building and district scale treatment technologies based on a suite of
environmental and cost indicators. The project evaluates aerobic membrane bioreactors
(AeMBRs), anaerobic membrane bioreactors (AnMBRs), and recirculating vertical flow
wetlands (RVFWs) treating both mixed wastewater and source separated gray water. Life cycle
inventory (LCI) data were compiled from published, peer reviewed literature and generated
using GPS-X™ wastewater modeling software. Several sensitivity analyses were conducted to
quantify the effects of system scale, reuse quantity, AnMBR sparging rate, and the addition of
thermal recovery on environmental and cost results. Results indicate that the volume of treated
graywater is sufficient to provide for on-site urban NPR applications, and that net impact is
lowest when the quantity of treated wastewater provides but does not considerably exceed NPR
demand. Of the treatment options analyzed, the AeMBR and RVFW both demonstrated similarly
low global warming potential (GWP) impact results, while the AeMBR had the lowest estimated
system net present value (NPV) over a 30-year operational period. The addition of thermal
recovery considerably reduced GWP impact for the AeMBR treatment process it was applied to,
and similar benefits should be available if thermal recovery were applied to other treatment
processes. The AnMBR treatment system demonstrated substantially higher GWP and
cumulative energy demand (CED) results compared to the other treatment systems, due primarily
to the need for several post-treatment processes required to prepare the effluent for disinfection.
When the quantity of treated wastewater closely matches NPR demand, the environmental
benefit of avoiding potable water production and distribution (for non-potable applications) leads
to net environmental benefits for the AeMBR and RVFW treatment systems. The same benefit is
possible for the AnMBR if intermittent membrane sparging can successfully prevent membrane
fouling.
1
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List of Acronyms
LIST OF ACRONYMS
AeMBR
Aerobic membrane bioreactor
ALH
Administrative labor hours
AnMBR
Anaerobic membrane bioreactor
BOD
Biological oxygen demand
BV
Bed volume
CAS
Conventional activated sludge
CED
Cumulative energy demand
CHP
Combined heat and power
CPI
Consumer price index
COD
Chemical oxygen demand
COP
Coefficient of performance
CSTR
Continually stirred tank reactor
CT
Contact time
CV
Coefficient of variation
DHS
Downflow hanging sponge
EOL
End-of-life
EPA
Environmental Protection Agency (U.S.)
ERG
Eastern Research Group, Inc.
GE
General Electric
GHG
Greenhouse gas
gpm
Gallons per minute
gpd
Gallons per day
GW
Graywater
GWP
Global warming potential
HDPE
High-density polyethylene
HHV
Higher heating value
HRT
Hydraulic retention time
IPCC
Intergovernmental Panel on Climate Change
ISO
International Standardization Organization
LCA
Life cycle assessment
LCCA
Life cycle cost assessment
LCI
Life cycle inventory
LCIA
Life cycle impact assessment
LMH
Liters per m2 per hour
LRT
Log reduction target
LRV
Log reduction value
MBR
Membrane bioreactor
MCF
Methane correction factor
MGD
Million gallons per day
MLSS
Mixed liquor suspended solids
NPR
Non-potable reuse
NPV
Net present value
11
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List of Acronyms
O&M
Operation and maintenance
P
Phosphorus
psi
Pounds per square inch
PVDF
Polyvinylidene fluoride
RVFW
Recirculating vertical flow wetland
SCFM
Standard cubic feet per minute
SOTE
Standard oxygen transfer efficiencies
SRT
Solids retention time
TKN
Total kjeldahl nitrogen
TSS
Total suspended solids
TRACI
Tool for the Reduction and Assessment of Chemical and Environmental Impacts
U.S. LCI
United States Life Cycle Inventory Database
UV
Ultraviolet
vss
Volatile suspended solids
WW
Wastewater
WRRF
Water resource recovery facility
111
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Table of Contents
TABLE OF CONTENTS
Page
1. Study Goal and Scope 1-1
1.1 Background and Study Goal 1-1
1.2 Functional Unit 1-2
1.3 Case Study Building and District Scenarios 1-2
1.4 Case Study Water Reuse Scenarios 1-4
1.5 Water Quality Characteristics 1-6
1.6 System Definition and Boundaries 1-7
1.6.1 Aerobic Membrane Bioreactor 1-7
1.6.2 Aerobic Membrane Bioreactor with Thermal Energy
Recovery 1-8
1.6.3 Anaerobic Membrane Bioreactor 1-9
1.6.4 Recirculating Vertical Flow Wetland 1-10
1.7 Background Life Cycle Inventory Databases 1-11
1.8 Metrics and Life Cycle Impact Assessment Scope 1-12
2. Life Cycle Inventory Methods 2-1
2.1 Pre-Treatment 2-1
2.2 Aerobic Membrane Bioreactor 2-2
2.2.1 Thermal Energy Recovery for the AeMBR 2-5
2.3 Anaerobic Membrane Bioreactor 2-8
2.3.1 Membrane Fouling and Sludge Output 2-12
2.3.2 Biogas Utilization 2-13
2.3.3 Post-Treatment 2-13
2.4 Recirculating Vertical Flow Wetland 2-17
2.5 Disinfection 2-20
2.5.1 Ozone 2-23
2.5.2 Ultraviolet 2-25
2.5.3 Chlorination 2-26
2.6 Water Reuse Scenarios 2-26
2.6.1 Wastewater Generation and On-site Reuse Potential 2-27
2.6.2 Recycled Water Distribution Piping 2-28
2.6.3 Recycled Water Distribution Pumping Energy 2-30
2.6.4 Displaced Potable Water 2-34
2.6.5 Centralized Collection and WRRF Treatment 2-35
2.7 District-Unsewered Scenario 2-35
2.7.1 Dewatering - Screw Press 2-35
2.7.2 Composting 2-36
2.7.3 Compost Land Application 2-36
2.8 LCI Limitations, Data Quality & Appropriate Use 2-38
3. Life Cycle Cost Analysis Methods 3-1
3.1 LCCAData Sources 3-1
iv
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Table of Contents
TABLE OF CONTENTS (Continued)
Page
3.2 LCCA Methods 3-1
3.2.1 Total Capital Costs 3-1
3.2.2 Unit Process Costs 3-2
3.2.3 Direct Costs 3-2
3.2.4 Indirect Costs 3-2
3.2.5 Total Annual Costs 3-4
3.2.6 Net Present Value 3-4
3.3 Unit Process Costs 3-5
3.3.1 Full System Costs 3-5
3.3.2 Fine Screening 3-6
3.3.3 Equalization 3-7
3.3.4 Primary Clarification 3-8
3.3.5 Sludge Pumping 3-8
3.3.6 AeMBR 3-9
3.3.7 An VI BR 3-11
3.3.8 RVFW 3-16
3.3.9 Building & District Reuse 3-17
3.3.10 Ozone Disinfection 3-18
3.3.11 UV Disinfection 3-18
3.3.12 Chlorine Disinfection 3-18
3.3.13 Thermal Recovery System 3-20
3.3.14 DistrictUnsewered 3-20
4. Building Scale Mixed Wastewater Results 4-1
4.1 Mixed Wastewater Summary Findings 4-1
4.2 Detailed Results by Impact Category 4-3
4.2.1 Global Warming Potential 4-3
4.2.2 Cumulative Energy Demand 4-5
4.2.3 Life Cycle Costs 4-6
5. Building Scale Graywater Results 5-1
5.1 Graywater Summary Findings 5-1
5.2 Detailed Results by Impact Category 5-3
5.2.1 Global Warming Potential 5-3
5.2.2 Cumulative Energy Demand 5-4
5.2.3 Life Cycle Costs 5-5
6. Sensitivity Analyses and Annual Results 6-1
6.1 AnMBR Biogas Sparging 6-1
6.2 Full Utilization of Treated Water 6-3
6.3 Thermal Recovery Hot Water Heater 6-6
6.4 Annual Results 6-8
6.5 Life Cycle Cost Results Considering Avoided Utility Costs 6-11
v
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Table of Contents
TABLE OF CONTENTS (Continued)
Page
7. District Scale Mixed Wastewater and Graywater Results 7-1
7.1 Mixed Wastewater Summary Findings 7-1
7.2 Detailed Results by Impact Category 7-2
7.2.1 Global Warming Potential 7-2
7.2.2 Cumulative Energy Demand 7-2
7.2.3 Life Cycle Costs 7-3
7.3 Graywater Summary Findings 7-5
7.4 Detailed Results by Impact Category 7-6
7.4.1 Global Warming Potential and Cumulative Energy Demand 7-6
7.4.2 Life Cycle Costs 7-7
8. Conclusions 8-1
9. References 9-1
Appendix A: Life Cycle Inventory and Life Cycle Cost Analysis Calculations
Appendix B: Life Cycle Cost Analysis Detailed Results
Appendix C: Life Cycle Inventory
vi
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List of Tables
LIST OF TABLES
Page
Table 1-1. Baseline Scenarios for Decentralized Wastewater Treatment 1-3
Table 1-2. Distribution of Indoor Water Use in Residential Buildings 1-5
Table 1-3. Fraction of Treated Wastewater and Graywater Reused On-site (Indoor and
Outdoor) - Replacing Municipal Potable Water Use 1-5
Table 1-4. Mixed Wastewater and Graywater Influent Characteristics 1-6
Table 1-5. California Electrical Grid Mix 1-12
Table 1-6. Environmental Impact and Cost Metrics 1-12
Table 1-7. Description of LCA Impact Categories 1-13
Table 2-1. AeMBR Design Parameters 2-3
Table 2-2. Thermal Recovery System Design and Performance Parameters 2-8
Table 2-3. AnMBR Design and Operational Parameters 2-9
Table 2-4. Operational Parameters of AnMBRs Treating Domestic Wastewater 2-11
Table 2-5. Downflow Hanging Sponge Design and Operational Parameters 2-15
Table 2-6. Zeolite Ammonium Adsorption Sytem Design and Performance Parameters 2-16
Table 2-7. Wetland Treatment Performance 2-19
Table 2-8. Mixed Wastewater and Graywater Wetland Design Parameters 2-20
Table 2-9. Wetland Greenhouse Gas Emissions 2-20
Table 2-10. Log Reduction Targets for 10"4 Infection Risk Target, Non-Potable Reuse:
Wastewater and Graywater51 2-20
Table 2-11. Log Reduction Values by Unit Process and Disinfection Technology for
Viruses, Protozoa and Bacteria 2-21
Table 2-12. Disinfection System Specification for Aerobic and Anaerobic MBRs: Mixed
Wastewater 2-22
Table 2-13. Disinfection System Specification for Aerobic and Anaerobic MBRs:
Graywater 2-22
Table 2-14. Disinfection System Specification for Recirculating Vertical Flow Wetland:
Mixed Wastewater 2-22
Table 2-15. Disinfection System Specification for Recirculating Vertical Flow Wetland:
Graywater 2-23
Table 2-16. Rapid Ozone Demand of Wastewater Constituents 2-23
vii
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List of Tables
LIST OF TABLES (Continued)
Page
Table 2-17. Calculated Breakpoint and Chlorine Dose Requirements 2-26
Table 2-18. On-site Wastewater Generation and Reuse Potential 2-27
Table 2-19. Building Pipe Network Characteristics 2-30
Table 2-20. Pipe Unit Weights 2-30
Table 2-21. Reuse Water Pumping Calculations, Large Mixed-Use Building 2-32
Table 2-22. Reuse Water Pumping Calculations, Six-Story District Building 2-32
Table 2-23. Reuse Water Pumping Calculations, Four-Story District Building 2-32
Table 2-24. Potable Water Pumping Calculations, Large Mixed-Use Building 2-33
Table 2-25. Potable Water Pumping Calculations, Six-Story District Building 2-33
Table 2-26. Potable Water Pumping Calculations, Four-Story District Buildinga 2-34
Table 2-27. Finished Compost Specifications 2-37
Table 2-28. Agricultural Emissions per Cubic Meter of Wastewater Treated 2-38
Table 3-1. Direct Cost Factors 3-2
Table 3-2. Indirect Cost Factors 3-3
Table 3-3. Administration and Laboratory Costs 3-6
Table 4-1. Summary Integrated LCA, LCCA and LRV Results for Building Scale
Configurations Treating Mixed Wastewater (Per Cubic Meter Mixed
Wastewater Treated) 4-2
Table 4-2. Process Contributions to Global Warming Potential for Building Scale Mixed
Wastewater Treatment Technologies 4-5
Table 4-3. Process Contributions to Cumulative Energy Demand for Building Scale
Mixed Wastewater Treatment Technologies 4-6
Table 5-1. Summary Integrated LCA, LCCA and LRT Results for Building scale
Configurations Treating Graywater (Per Cubic Meter Graywater Treated) 5-2
Table 6-1. Annual Global Warming Potential Results for Low Reuse Scenario by
Treatment Stage for Mixed Wastewater (WW) and Graywater (GW) Systems
(kg CO2 eq./Year) 6-9
Table 6-2. Annual Cumulative Energy Demand Results by Treatment Stage for Low
Reuse Scenario for Mixed Wastewater (WW) and Graywater (GW) Systems
(MJ/Year) 6-10
viii
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List of Tables
LIST OF TABLES (Continued)
Page
Table 7-1. Summary Integrated LCA, LCCA and LRT Results for District scale AeMBR
Configurations Treating Mixed Wastewater (Per Cubic Meter Mixed
Wastewater Treated) 7-1
Table 7-2. Summary Integrated LCA, LCCA and LRT Results for District scale AeMBR
Configuration Treating Graywater (Per Cubic Meter Graywater Treated) 7-6
IX
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List of Figures
LIST OF FIGURES
Page
Figure 1-1. System boundaries for aerobic membrane bioreactor 1-8
Figure 1-2. System boundaries for aerobic membrane bioreactor with thermal energy
recovery 1-9
Figure 1-3. System boundaries for anaerobic membrane bioreactor analysis 1-10
Figure 1-4. System boundaries for recirculating vertical flow wetland analysis 1-11
Figure 2-1. Daily fluctuation in the use of potable water 2-1
Figure 2-2. AeMBR simplified process flow diagram 2-2
Figure 2-3. AeMBR subprocess configuration 2-2
Figure 2-4. System diagram for the water-to-water heat pump thermal recovery system 2-6
Figure 2-5. AnMBR simplified process flow diagram 2-9
Figure 2-6. Diagram depicting the process flow of the recirculating vertical flow wetland 2-17
Figure 2-7. Diagram depicting the cross-section of the recirculating vertical flow wetland 2-18
Figure 2-8. Side view of the modeled building piping networks 2-28
Figure 2-9. Top view of the modeled building piping networks 2-29
Figure 4-1. Comparative LCA and LCCA results for building scale configurations
treating mixed wastewater, presented relative to maximum results in each
impact category 4-3
Figure 4-2. Global warming potential for building scale mixed wastewater treatment
technologies 4-4
Figure 4-3. Cumulative energy demand for building scale mixed wastewater treatment
technologies 4-6
Figure 4-4. Net present value for building scale mixed wastewater treatment technologies
in the low reuse scenario. Results shown by treatment process designation 4-7
Figure 4-5. Net present value for building scale mixed wastewater treatment technologies
in the low reuse scenario. Results shown by cost category 4-8
Figure 5-1. Comparative LCA and LCCA results for building scale configurations
treating graywater, presented relative to maximum results in each impact
category 5-3
Figure 5-2. Global warming potential for building scale graywater treatment
technologies 5-4
Figure 5-3. Cumulative energy demand for building scale graywater treatment
technologies 5-5
x
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List of Figures
LIST OF FIGURES (Continued)
Page
Figure 5-4. Net present value for building scale graywater treatment technologies in the
low reuse scenario. Results shown by treatment process designation 5-6
Figure 5-5. Net present value for building scale graywater treatment technologies in the
low reuse scenario. Results shown by cost category 5-7
Figure 6-1. AnMBR biogas sparging global warming potential sensitivity analysis for the
treatment of mixed wastewater and graywater at the building scale 6-1
Figure 6-2. AnMBR biogas sparging cumulative energy demand sensitivity analysis for
the treatment of mixed wastewater and graywater at the building scale 6-2
Figure 6-3. AnMBR biogas sparging net present value sensitivity analysis for the
treatment of mixed wastewater and graywater at the building scale 6-2
Figure 6-4. Global warming potential sensitivity analysis of full utilization of treated
water. Results are compared according to treatment process designation
across building scale mixed wastewater (WW) and graywater systems (GW) 6-4
Figure 6-5. Cumulative energy demand sensitivity analysis of full utilization of treated
water. Results are compared according to treatment process designation
across building scale mixed wastewater (WW) and graywater (GW) systems 6-5
Figure 6-6. AeMBR - thermal recovery global warming potential sensitivity analysis for
the treatment of mixed wastewater and graywater at the building scale 6-7
Figure 6-7. AeMBR - thermal recovery cumulative energy demand sensitivity analysis
for the treatment of mixed wastewater and graywater at the building scale 6-8
Figure 6-8. Net present value for building scale mixed wastewater treatment technologies
in the low reuse scenario compared to avoided utility fees. Results shown by
treatment process designation 6-11
Figure 6-9. Net present value for building scale graywater treatment technologies in the
low reuse scenario compared to avoided utility fees. Results shown by
treatment process designation 6-12
Figure 7-1. Global warming potential for district scale mixed wastewater treatment
technologies 7-2
Figure 7-2. Cumulative energy demand for district scale mixed wastewater treatment
technologies 7-3
Figure 7-3. Net present value for district scale mixed wastewater treatment technologies.
Results are shown by treatment process designation 7-4
Figure 7-4. Net present value for district scale mixed wastewater treatment technologies.
Results are shown by cost category 7-5
XI
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List of Figures
LIST OF FIGURES (Continued)
Page
Figure 7-5. LCA results for district scale graywater treatment technologies. Results
shown by life cycle stage (a) global warming potential and (b) cumulative
energy demand 7-7
Figure 7-6. Net present value for district scale graywater treatment technologies. Results
shown by (a) life cycle stage and (b) cost category 7-8
Xll
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1—Study Goal and Scope
1. STUDY GOAL AND SCOPE
The occurrence of increased instances of severe drought in some regions across the U.S.
coupled with increased pressure on aging centralized water treatment infrastructure has created a
need to find novel wastewater treatment and reuse solutions. Some urban communities such as
San Francisco have adopted ordinances requiring all new commercial, mixed-use or multi-family
building projects treat on-site wastewater or gray water for non-potable reuse (NPR) (SFPUC
2018). This study examines the environmental and cost effects of implementing various mixed
wastewater or graywater treatment configurations for new mixed-use building scale or district
scale NPR projects. While such projects are inevitably moving forward to ensure community
resiliency, the findings of this study can be used to help optimize the environmental and cost
performance of on-site treatment and reuse.
1.1 Background and Study Goal
As one of the largest federal water research and development laboratories in the United
States, the Environmental Protection Agency (EPA) generates innovative solutions that protect
human health and the environment. The Office of Research and Development's (ORD) Safe and
Sustainable Water Resources (SSWR) Program is the principle research lead seeking metrics and
tools to compare the tradeoffs between economic, human health and environmental aspects of
current and future municipal water and wastewater services. Changes in drinking water and
wastewater management have historically focused on developing and implementing additions to
the current treatment and delivery schemes. However, these additions are generally undertaken in
the absence of a system's holistic view and result in transferring issues from one problem area to
another (Ma et al. 2015). Future alternatives need to address the whole water services physical
system to shift towards more sustainable water services such that water scarcity is alleviated.
Furthermore, these sustainable systems should be based on water resource recovery facility
(WRRF) concepts such as decentralized water treatment and recovery, energy recovery, and
nutrient recovery. Therefore, a range of integrated metrics and tools need to be used to evaluate
the multifaceted solutions and identify "next-generation" sustainable water systems.
The purpose of this study is to develop environmental life cycle assessments (LCAs) and
life cycle cost analyses (LCCA) associated with decentralized (also referred to as distributed)
water treatment and reuse systems. LCA and LCCA are tools used to quantify sustainability-related
metrics from a systems perspective. EPA previously developed a report entitled "Life Cycle
Assessment and Cost Analysis of Water and Wastewater Treatment Options for Sustainability:
Influence of Scale on Membrane Bioreactor Systems" (Cashman et al. 2016). In this study, EPA
conducted a theoretical evaluation of aerobic and anaerobic membrane bioreactors (MBR) as a
sewer mining transitional strategy and investigated the impacts of different scales (0.05-10
million gallons per day), population density (2,000-10,000 people per square mile) and climate
and operational factors (e.g., temperature and methane recovery). MBRs represent a promising
technology for decentralized wastewater treatment and can produce recycled water to displace
potable water or non-potable water. In the current report, EPA builds upon the previously
developed MBR models to develop LCAs and LCCAs of MBRs and other decentralized
wastewater technology options in the context of an urban case study, using San Francisco
California as the case study city. The study focuses on one key commercial treatment
technology, aerobic MBRs (AeMBR). The AeMBR results are compared to alternative
1-1
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1—Study Goal and Scope
technologies including anaerobic membrane bioreactors (AnMBR), AeMBRs with thermal
energy recovery, and recirculating vertical flow wetlands (RVFW). While Cashman et al. (2016)
only investigated treatment of mixed wastewater, this current study considers treatment of both
mixed wastewater as well as source separated graywater.
This study assumes NPR projects are inevitably moving forward in certain water-stressed
regions due to drivers aimed at increasing community-level resiliency and reliability. Therefore,
we focus on comparative findings of different NPR configurations rather than comparing NPR to
conventional centralized collection and treatment systems. Previous studies have examined the
life cycle implications of urban NPR systems versus conventional collection and treatment
(Kavvada et al. 2016).
This study design follows the guidelines for LCA provided by ISO 14044 (ISO 2006).
The following subsections describe the scope of the study based on the treatment system
configurations selected and the functional unit used for comparison, as well as the system
boundaries, life cycle impact assessment (LCIA) methods, and datasets used in this study.
1.2 Functional Unit
A functional unit provides the basis for comparing results in an LCA. The key
consideration in selecting a functional unit is to ensure the treatment system configurations are
compared on a fair and transparent basis and provide an equivalent end service to the
community. The functional unit for this study is the treatment of one cubic meter of either
municipal wastewater or graywater with the influent wastewater characteristics shown in Section
1.5. Treatment configurations for graywater are only compared to other treatment systems for
graywater and are not directly compared to treatment systems for mixed wastewater in the
baseline results. In the baseline results, the centralized treatment of the separated blackwater for
the graywater systems is outside the study scope. The sensitivity analysis presented in Section
6.2 does directly compare mixed wastewater and graywater systems by displaying results on the
basis of treatment of a cubic meter of wastewater produced at the building and incorporating the
separated blackwater centralized treatment into the scope. All treatment configurations were
developed to ensure that guidelines for indoor NPR were met (Sharvelle et al. 2017).
1.3 Case Study Building and District Scenarios
Table 1-1 shows the total flow rate of wastewater produced by each source area, the
quantity of water treated, and the source water type. We developed configurations to be
representative of building or block size, building density, and water use in San Francisco's South
of Market district based on comparisons with existing building statistics and satellite imagery of
the area. All scenarios are modeled as transitional solutions that are connected to the sewer for
centralized solids handling. For district scale mixed wastewater treatment, an unsewered scenario
is incorporated for local solids handling via off-site windrow composting.
1-2
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1—Study Goal and Scope
Table 1-1. Baseline Scenarios for Decentralized Wastewater Treatment
Mixed Wastewater
Separated Graywater
Large Mixed Use
(Office/Residential)
District
Large Mixed Use
(Office/Residential)
District
Total Wastewater Flow Rate
0.025 MGD
V
~
0.05 MGD
~
V
Flow Rate of Treated
Wastewater or Graywater
0.016 MGD
0.025 MGD
V
0.031 MGD
V
0.05 MGD
~
Sewer Connection
Sewered
V
~
~
V
Unsewered
Total Building Occupants8
1,100
2,300
1,100
2,300
Residential Occupants
520
990
520
990
Office Workers
590
1,300
590
1,300
Building Footprint (Roof Area)
20,000
160,000
20,000
160,000
Total Building Area (sq. ft.)
380,000
760,000
380,000
760,000
Residential Building Area
270,000
510,000
270,000
510,000
Commercial Building Area
110,000
250,000
110,000
250,000
a Sum of residential occupants and office workers.
Acronyms: MGD = million gallons per day
Details of the building and district configurations related to the split between residential
and office space were determined based on total wastewater flowrates, listed in Table 1-1, using
the per capita floor area requirements and indoor water use estimates discussed below.
We assumed that an average of 195 ft2 of floor area was required per office worker
(Heschmeyer 2013). Residential floor requirements were based on an average household size of
2.42 persons (BOC 2016) and an apartment area of 1,000 ft2. Residential per capita indoor water
use was assumed to be 35.8 gallons per day (gpd). This value is approximately 69 percent of the
national average, 52 gpd per capita (DeOreo et al. 2016), and was selected to match the target
flowrate of 0.025 million gallons per day (MGD) while reflecting the focus on water
conservation in the San Francisco region. This can be compared to high-efficiency water use
household survey results from DeOreo et al. (2016) that indicate an indoor water use rate of 112
gpd per household, or 40.5 gpd per capita based on an average household size of 2.76 persons
across the survey region. Commercial indoor water use was set at 11.3 gpd per worker, which is
a value adapted by Schoen et al. (2018) to reflect the implementation of water conservation
efforts based on original values from DeOreo et al. (2016).
1-3
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1—Study Goal and Scope
The resulting mixed-use building is 19 stories tall with a floor area of 20,000 ft2,
corresponding to a total building area of 380,000 ft2. Seventy percent of building floor space was
allocated to private residences, with the remaining 30 percent of floor area designated as office
space. The hypothetical district configuration occupies a typical San Francisco block area of
approximately 230,000 ft2 (5 acres). Sixty-nine percent of block area was assumed to be covered
by mixed use buildings, with the remainder of the space being reserved for sidewalks, parking,
and recreational or municipal open space. Forty and 29 percent of block area was assumed to be
developed as four and six story mixed-use commercial and residential building spaces. Floor
space in the four-story building was split equally between commercial and residential uses. The
bottom floor was reserved for commercial use in the six-story building.
Blackwater was assumed to comprise 28 percent of residential indoor wastewater
generation, while the remaining 72 percent consists of graywater (DeOreo et al. 2016). Office
workers use less water overall (gpd), but a greater fraction of this water contributes to blackwater
flows. For office wastewater generation, blackwater was assumed to comprise 63 percent of
indoor water generation, while the remaining 37 consists of graywater generation based on
survey results from four commercial office buildings (Dziegielewski et al. 2000). Faucets and
miscellaneous indoor uses are the two primary graywater sources in office buildings. Residential
and commercial indoor wastewater generation estimates do not include water for irrigation or
operation of centralized cooling systems, neither of which will contribute directly to wastewater
flows, either infiltrating to groundwater or evaporating. Further detail on wastewater generation
and on-site reuse potential is provided in Section 2.6.
1.4 Case Study Water Reuse Scenarios
This study assumed that recycled water from mixed wastewater and graywater treatment
is used for toilet flushing, laundry, and on-site irrigation displacing drinking water treatment and
delivery. Low reuse and high reuse scenarios were analyzed to assess the sensitivity of LCA
results to reuse quantity and to reflect uncertainty regarding the quantity of wastewater that will
ultimately be reused. A sensitivity scenario that looks at LCA results when 100% of treated
wastewater is reused is presented in Section 6.2.
The end use fractions in Table 1-2 were used to estimate the share of treated residential
wastewater and graywater that can be reused on-site. The selected study values represent a wider
range of on-site reuse potential than do the corresponding values from DeOreo et al. (2016),
which are provided for comparison. The reuse potential of commercial buildings was estimated
based on toilets' 63% share of indoor water use (Schoen et al. 2018).
1-4
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1—Study Goal and Scope
Table 1-2. Distribution of Indoor Water Use in Residential Buildings
Water Use
Category
Water
Type
Average Ef
iciency Users
High Efficiency Users
Study
Values3
(DeOreo et al.
2016)
Study
Valuesb
(DeOreo et al.
2016)
Toilet
Blackwater
28%
24%
15%
19%
Dishwashing
1.4%
1.2%
1.7%
2.0%
Bath
Graywater
1.8%
2.6%
6.5%
5.9%
Laundry
23%
16%
11%
19%
Faucet
16%
19%
17%
19%
Shower
18%
19%
31%
23%
Leakage
10%
13%
18%
10%
Other
2.2%
4.3%
0.8%
1.3%
Estimated Reuse Fraction
51%
41%
26%
38%
a (Tchobanoglous et al. 2014)
b (Sharvelle et al. 2013)
Note: DeOreo et al. (2016) values are only provided for reference and are not used in this analysis.
Table 1-3 shows the fraction of treated wastewater that was estimated for onsite reuse,
displacing treated drinking water. The low reuse scenario recognizes that reduced flow-toilets,
washing machines, and water efficient landscapes reduce on-site reuse potential. Values in Table
1-3 include indoor and irrigation water use. Further details on the assumptions that contribute to
calculation of reuse fractions are provided in Section 2.6. As an example of how to read Table
1-3, in the mixed wastewater-high reuse scenario, on-site NPR requires 72% of treated
wastewater, and only 35% in the low reuse scenario.
Table 1-3. Fraction of Treated Wastewater and Graywater Reused On-site
(Indoor and Outdoor) - Replacing Municipal Potable Water Use
Wastewater Scenario
Building
Configuration
High reuse8
Low reuseb
Mixed Wastewater
Mixed Use Building
72%
35%
District
72%
35%
Separated Graywater
Mixed Use Building
100%
55%
District
100%
57%
a Representative of buildings with average efficiency appliances.
b Representative of buildings with high efficiency appliances.
For the water reuse scenarios in this analysis, only the separated graywater systems for
buildings with average efficiency appliances could achieve recycling of 100 percent of the
treated water. In most scenarios, and especially for the mixed wastewater treatment systems,
more water is treated on-site than is demanded by the building or district. A sensitivity analysis
is presented in Section 6.2 modeling a theoretical scenario with 100 percent recycling of all
treated water. This may be achievable through sharing recycled water with adjacent buildings or
storing water for future uses (e.g., fire suppression). Alternatively, the building could opt to not
treat the full amount of wastewater or graywater produced. We did not investigate this scenario
1-5
-------
1—Study Goal and Scope
in the current study, but it could be a consideration when faced with surplus volumes of recycled
water.
1.5 Water Quality Characteristics
Table 1-4 presents water quality characteristics for mixed wastewater and separated
graywater entering the treatment facility. Separated graywater can consist of wastewater from
showers, baths, faucets in the kitchen and bath, laundry machines, and dishwashing machines. In
the U.S., graywater is usually defined as from bathroom faucets, showers, baths, and laundry
machines, and excludes water from kitchen sink and dishwasher (Sharvelle et al. 2013).
Graywater characteristics in Table 1-4 follow this definition.
Mixed wastewater characteristics were primarily based on values for medium strength
domestic wastewater from Tchobanoglous et al. (2014), highlighted in bold in Table 1-4. The
primary graywater characteristics, also in bold in Table 1-4, were calculated as the median of
values reported in literature reviews of graywater treatment and reuse studies (Eriksson et al.
2002; Li et al. 2009; Boyjoo et al. 2013; Ghaitidak and Yadav 2013). The GPS-X™ influent
characterization mass-balance feature was used to determine the other reported wastewater
characteristic values based on the primary input values in bold. The calculated values in Table
1-4 can be compared to corresponding values from Tchobanoglous et al. (2014) and the
graywater literature review in Appendix Table A-l.
Differences in mixed wastewater strength between residential and commercial sources
were not accounted for in the study. Mixed wastewater influent values are expected to be more
representative of residential generation, which accounts for 71% and 74% of water use in the
large building and district scenarios, respectively. Adjustment to reflect higher wastewater
strength for the commercial fraction is likely to increase the environmental impact of wastewater
treatment, but will have less of an effect on comparative results across systems.
Graywater and wastewater temperatures were assumed to be the same in winter and
summer as the wastewater travels a short distance between the source and treatment location. We
modeled the treatment system as housed in a climate-controlled building.
Table 1-4. Mixed Wastewater and Graywater Influent Characteristics
Influent Values
Target Effluent Quality
Water Quality Characteristics
Mixed
WW
Separated GW
Both
Medium
Characteristic
Unit
Strength
(Building
Low Pollutant
Load with
Effluent Quality for
Unrestricted Urban
&
District)3
Laundry3
Use
Suspended Solids
mg/L
220
94
<5
Volatile Solids
%
80
47
-
CBOD5
mg/L
200
170
-
BODs
mg/L
240
190
<10
Soluble BODs
mg/L
140
120
-
1-6
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1—Study Goal and Scope
Table 1-4. Mixed Wastewater and Graywater Influent Characteristics
Influent Values
Target Effluent Quality
Water Quality Characteristics
Mixed
WW
Separated GW
Both
Medium
Characteristic
Unit
Strength
(Building
Low Pollutant
Load with
Effluent Quality for
Unrestricted Urban
&
District)3
Laundry3
Use
Soluble CBOD5
mg/L
120
100
-
COD
mg/L
510
330
-
Soluble COD
mg/L
200
150
-
TKN
mg N/L
35
8.5
-
Soluble TKN
mg N/L
21
6.9
-
Ammonia
mg N/L
20
1.9
-
Total Phosphorus
mg P/L
5.6
1.1
-
Nitrite
mg N/L
0
0
-
Nitrate
mg N/L
0
0.64
-
Average Summer
deg C
23
30
-
Average Winter
deg C
23
30
-
Chlorine Residual
mg/L
n/a
n/a
0.5-2.5
a Values in bold were used as inputs to the GPS-X™ influent advisor.
Acronyms: BOD - biological oxygen demand, C - Celsius, COD - chemical oxygen demand, GW - graywater, N -
nitrogen, n/a - not applicable, P - phosphorus, TKN - total kjeldahl nitrogen, WW - wastewater
1.6 System Definition and Boundaries
1.6.1 Aerobic Membrane Bioreactor
Figure 1-1 presents the system boundaries for the AeMBR analysis. The system boundary
starts at the collection of wastewater from sources such as toilet flushing, laundry, sinks,
dishwashers, showers, and baths. Additional infrastructure needs to be installed for the collection
of graywater from showers, baths, laundry, and bathroom sinks. The MBR was assumed to be in
the building basement. The collected mixed wastewater or graywater is first stored in an
equalization chamber, such that a consistent flow can be treated. After the equalization chamber,
the mixed wastewater or graywater goes through pre-treatment via fine screening and grit
removal prior to MBR operation. Ultraviolet (UV) treatment was modeled as the primary
disinfection step, with chlorine subsequently added to establish a residual. For all building scale
results, it was assumed that the solids from biological processes are sent to centralized treatment.
Under a district scale sensitivity analysis, the solids are dewatered and then undergo windrow
composting followed by land application to replace the need for commercial fertilizers. The
recycled water is pumped to the applicable NPR points. Section 2.2 provides more detail on the
AeMBR process.
1-7
-------
1—Study Goal and Scope
Graywater Collection
Gravity System
Wastewater Collection
Gravity System
Demanded
Drinking Water
Treatment and
Delivery
Displaced Potable Water
Treatment and Delivery
Influent
Mixed
Wastewater
Equalization
Influent
Graywater
Fine
Screening and
Grit Removal
Screening and Grit to
Landfill
Water from dewatering step'
Key
Displaced unit
process
Unit process
within system
boundary
Or gate
(multiple inputs)
Unit process
| outside system
j_ boundary
Or gate
(multiple outputs)
Notes
a Unsewered scenario only considered for district-level analysis treating mixed wastewater.
End Use
Dishwasher
and Kitchen
Showers and
Baths
Bathroom
Sinks
Recycled
water
Pumping
Laundry
Toilet
Flushing
Irrigation
Aerobic
Membrane
Bioreactor
Disinfection
Chlorination
Dewatering
Sludge to Municipal
Wastewater T reatment
Sludge
Transport
Displaced
Fertilizer
Production
Windrow
Composting
^ Flow within system
boundaries
w Flow outside
system boundaries
Displaced product
Land Application ^
of Compost3
Figure 1-1. System boundaries for aerobic membrane bioreactor.
1.6.2 Aerobic Membrane Bioreactor with Thermal Energy Recovery
Figure 1-2 presents the system boundaries for the analysis of AeMBR with thermal
energy recovery. The boundary is the same as discussed in Section 1.6.1, except for the thermal
recovery step. A heat pump is installed prior to MBR treatment to recover thermal energy from
either the graywater or mixed wastewater. Thermal energy recovery was modeled as occurring
prior to MBR treatment to avoid potential heat loss from the mixed wastewater or graywater. The
recovered thermal energy is used for hot water heating, replacing the need for natural gas or
electricity. Section 2.2.1 provides more detail on heat pump energy recovery.
1-8
-------
1—Study Goal and Scope
Graywater Collection
Gravity System
Wastewater Collection
Gravity System
Displaced Potable Water
Treatment and Delivery
Influent
Mixed
Wastewater
End Use
Dishwasher
and Kitchen
Sink
Showers and
Baths
Bathroom
Sinks
Laundry
Toilet
Flushing
Demanded
Drinking Water
Treatment and
Delivery
«
Irrigation
Storage
Recycled
Water
Pumping
s
Influent
Graywater
Fine
Screening and
Grit Removal
Equalization
Aerobic
Membrane
Bioreactor
UV
Disinfection
Sludge to Municipal
Wastewater Treatment
Screening and Grit to
Landfill
Heat Pump
Building Hot
water Heating
Key
Displaced unit
process
Unit process
within system
boundary
Or gate
(multiple inputs)
Unit process
outside system
boundary
Or gate
(multiple outputs)
Flow outside
system boundaries
Displaced product
flow
Displaced Natural
Gas for Water
Heating
Figure 1-2. System boundaries for aerobic membrane bioreactor with thermal energy
recovery.
1.6.3 Anaerobic Membrane Bioreactor
Figure 1-3 presents the system boundaries for the AnMBR analysis. Most of the system
boundaries are similar to those presented for the AeMBR with some key differences. Methane in
the headspace of the reactor is recovered for building water heating purposes, and it was assumed
that the recovered methane reduces the buildings' overall natural gas demand. Methane in the
permeate is also recovered via a downflow hanging sponge (DHS), which simultaneously
recovers methane, thus avoiding greenhouse gas (GHG) emissions, performs chemical and
1-9
-------
1—Study Goal and Scope
biological oxygen demand (COD/BOD) removal, and provides partial nitrification. However,
additional post-treatment, using zeolite adsorption, is still required to remove ammonium in
order to establish a free chlorine residual. The resulting brine from the adsorption step is
transported off-site for underground injection. Section 2.3 provides more detail on the AnMBR
process.
Gray water Collection
Gravity System
Demanded
Drinking Water
Treatment and
Delivery
End Use
Dishwasher
and Kitchen
Showers and
Baths
Wastewater Collection
Gravity System
Bathroom
Recycled
Water
Pumping
Laundry
Displaced Potable Water
Treatment and Delivery
Toilet
Flushing
Influent
Irrigation
Mixed
Wastewater
Chlorination
Fine
Screening and
Grit Removal
Anaerobic
Membrane
Bioreactor
Downtlow
Hanging
Sponge
Zeolite
Adsorption
Equalization
influent
Gray water
UV
Disinfection
Methane from Methane
Heads pace from Permeate
t>[==}0
Transport and
Underground
Injection of
Brine
Methane
Recovery for
Heat
Screening and Grit to
Landfill
Sludge to Municipal
Wastewater Treatment
Flow within system
boundaries
Displaced
Natural Gas for
Water Heating
Building Hot
Water Heating
Flow outside
system boundaries
Displaced unit
process
Unit process
within system
boundary
Unit process
outside system
boundary
Or gate
multiple inputs)
Or gate
(multiple outputs)
Displaced product
flow
Figure 1-3. System boundaries for anaerobic membrane bioreactor analysis.
1.6.4 Recirculating Vertical Flow Wetland
Figure 1-4 presents the system boundaries for the RVFW analysis. For the RVFW, pre-
treatment steps include fine screening and grit removal, followed by slant plant clarification and
equalization. These pre-treatment steps ensure consistent inflow and reduce suspended solid
concentration, minimizing the potential for clogging of the media bed. After RVFW treatment,
1-10
-------
1—Study Goal and Scope
disinfection is required, which varies between the mixed wastewater and graywater systems. For
the mixed wastewater, ozone treatment is followed by UV disinfection and chlorination to
establish a residual. Ozone treatment is not required for the graywater systems. Section 2.4
provides more detail on the RVFW processes.
Delivery
and Kitchen
Bathroom
Sinks
Recycled
Water
Pumping
Laundry
Displaced Potable Water
Treatment and Delivery
Toilet
Flushing
Storage
Influent
Mixed
Wastewater
Irrigation
Fine
Screening and
Grit Removal
Chlorination
Slant Plate
Clarifier
Recirculating
Vertical Flow
Wetland
Equalization
Influent
Graywater
Screening and Grit to
Landfill
Sludge to Municipal
Wastewater Treatment
UV
Disinfection
Ozone
Treatment3
Key
Flow within system
boundaries
Unit process
within system
boundary
Unit "process"
outside system
boun_da_ry____
Displaced unit
process
Flow outside
system boundaries
Or gate
(multiple inputs)
Or gate
(multiple outputs)
Displaced product
flow
Notes
a Applicable only to systems treating mixed wastewater.
Figure 1-4. System boundaries for recirculating vertical flow wetland analysis.
1.7 Background Life Cycle Inventory Databases
Several background life cycle inventory (LCI) databases were used to provide
information on upstream processes such as electricity inputs, transportation, and manufacturing
of chemical and material inputs. Ecoinvent 2.2 serves as the basis for most of the upstream
infrastructure inputs and chemical and avoided fertilizer manufacturing (Frischknecht et al.
1-11
-------
1—Study Goal and Scope
2005). The U.S. Life Cycle Inventory (U.S. LCI) database was used to represent the manufacture
of some chemical and energy inputs in cases where applicable U.S. specific processes were
available in the database (NREL 2012).
All foreground (i.e., on-site) unit processes were modeled using the 2016 California
electrical grid mix (Table 1-5).
Table 1-5. California Electrical Grid Mix
Percent
Energy Source
Contribution
Natural gas
42.7%
Hydropower
13.8%
Nuclear
10.7%
Wind
10.6%
Solar
9.5%
Geothermal
5.1%
Coal
4.8%
Biomass
2.6%
Cogeneration
0.2%
Oil
0.01%
Reference: (CEC 2017)
1.8 Metrics and Life Cycle Impact Assessment Scope
Table 1-6 summarizes the metrics calculated for each treatment system option, together
with the method and units used to characterize results. Most of the LCIA metrics are generated
using U.S. EPA's LCIA method the Tool for the Reduction and Assessment of Chemical and
Environmental Impacts (TRACI), version 2.1 (Bare et al. 2002; Bare 2011). TRACI incorporates
a compilation of methods representing current best practice for estimating ecosystem and human
health impacts based on U.S. conditions and emissions information provided by LCI models.
Global warming potential (GWP) is estimated using the 100-year characterization factors
provided by the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report,
which are the GWPs currently used by the U.S. EPA for international reporting (Myhre et al.
2013). In addition to TRACI, the ReCiPe LCIA method is used to characterize water use and
fossil fuel depletion potential (Goedkoop et al. 2009). To provide another perspective on energy,
cumulative energy demand (CED), which includes the energy content of all non-renewable and
renewable energy resources extracted throughout the supply chains associated with each
treatment configuration, is estimated using a cumulative inventory method adapted from one
provided by Althaus et al. (2010). Table 1-7 provides a description of each impact category. The
LCCA is calculated using a net present value (NPV) method, discussed in Section 3.
Table 1-6. Environmental Impact and Cost Metrics
Metric
Method
Unit
Acidification Potential
TRACI 2.1
kg S02 eq.
Cost (Net Present Value)
LCCA
USD (2016)
Cumulative Energy Demand
Ecoinvent
MJ
1-12
-------
1—Study Goal and Scope
Table 1-6. Environmental Impact and Cost Metrics
Metric
Method
Unit
Eutrophication Potential
TRACI 2.1
kg N eq.
Fossil Depletion Potential
ReCiPe
kg oil eq.
Global Warming Potential
TRACI 2.1
kg C02 eq.
Particulate Matter Formation Potential
TRACI 2.1
kg PM2.5 eq.
Smog Formation Potential
TRACI 2.1
kg O3 eq.
Water Use
ReCiPe
m3
Acronyms: LCCA - life cycle cost assessment, USD - United States Dollars
Table 1-7. Description of LCA Impact Categories
Impact/Inventory
Category
Description
Unit
Acidification
Potential
Acidification potential quantifies the acidifying effect of
substances on their environment. Acidification can damage
sensitive plant and animal populations and lead to harmful effects
on human infrastructure (i.e. acid rain) (Norris 2002). Important
emissions leading to acidification include SO2, NOx, and NH3.
Results are characterized as kg SO2 eq. according to the TRACI 2.1
impact assessment method.
kg SO2 eq.
Cumulative Energy
Demand
The cumulative energy demand indicator accounts for the total
usage of non-renewable fuels (natural gas, petroleum, coal, and
nuclear) and renewable fuels (such as biomass and hydro). Energy
is tracked based on the heating value of the fuel utilized from point
of extraction, with all energy values reported on a MJ basis.
MJ
Eutrophication
Potential
Eutrophication potential assesses the impact from excessive
loading of macro-nutrients to the environment and eventual
deposition in waterbodies. Excessive macrophyte growth resulting
from increased nutrient availability can directly affect species
composition or lead to reductions in oxygen availability that harm
aquatic ecosystems. Pollutants covered in this category are
phosphorus and nitrogen based chemicals. The method used is
from TRACI 2.1, which is a general eutrophication method that
characterizes limiting nutrients in both freshwater and marine
environments, phosphorus and nitrogen respectively, and reports a
combined impact result.
kg N eq.
Fossil Fuel
Depletion
Fossil fuel depletion captures the consumption of fossil fuels,
primarily coal, natural gas, and crude oil. All fuels are normalized
to kg oil eq. based on the heating value of the fossil fuel and
according to the ReCiPe impact assessment method.
kg oil eq.
1-13
-------
1—Study Goal and Scope
Table 1-7. Description of LCA Impact Categories
Impact/Inventory
Category
Description
Unit
Global Warming
Potential
The global warming potential impact category represents the heat
trapping capacity of GHGs over a 100-year time horizon. All
GHGs are characterized as kg CO2 eq. using the TRACI 2.1
method. TRACI GHG characterization factors align with the IPCC
4th Assessment Report for a 100-year time horizon.
kg CO2 eq.
Particulate Matter
Formation Potential
Particulate matter formation potential results in health impacts such
as effects on breathing and respiratory systems, damage to lung
tissue, cancer, and premature death. Primary pollutants (including
PM2.5) and secondary pollutants (e.g., SOx and NOx) leading to
particulate matter formation are characterized as kg PM2.5 eq. based
on the TRACI 2.1 impact assessment method.
kg PM2.5
eq.
Smog Formation
Potential
Smog formation potential results determine the formation of
reactive substances that cause harm to human respiratory health
and can lead to reduced photosynthesis and vegetative growth
(Norris 2002). Results are characterized as kg of ozone (O3) eq.
according to the TRACI 2.1 impact assessment method. Some key
emissions leading to smog formation potential include CO, CH4,
NOx, NMVOCs, and SOx.
kg O3 eq.
Water Use
Water use results are based on the volume of freshwater inputs to
the life cycle of products within the treatment configuration
supply-chain. Water use results include displaced potable water.
Water use is an inventory category, and does not characterize the
relative water stress related to water withdrawals. This category has
been adapted from the water depletion category in the ReCiPe
impact assessment method.
3
111
Acronyms: GHG - greenhouse gas, IPCC - Intergovernmental Panel on Climate Change, TRACI - Tool for the
Reduction and Assessment of Chemical and Enviromnental Impacts
1-14
-------
2—Life Cycle Inventory Methods
2. LIFE CYCLE INVENTORY METHODS
This chapter describes the data sources, assumptions, and parameters used to establish the
LCI values in this study. Appendix Table C-l provides a summary table of the baseline LCI
developed for each wastewater treatment system.
2.1 Pre-Treatment
Pre-treatment includes an equalization chamber and fine screening. The equalization
chamber was sized such that the treatment systems receive a consistent hourly flow of
wastewater despite the daily fluctuations in household water use depicted in Figure 2-1. Water
use peaks between the hours of seven and eight AM during which time a household typically
consumes 15 percent of daily, indoor water use (Omaghomi et al. 2016). We estimated
infrastructure requirements for the equalization tank using tank dimensions assuming reinforced
concrete construction. Floating aerators provide simultaneous mixing and aeration. We sized
floating aerators using the CAPDETWorks™ approach, which is based on an oxygen transfer
efficiency per unit of mixing power. We specified a minimum dissolved oxygen content of 2
mg/L in the model.
16%
* 14%
E 12%
Hs 10%
cz
S 8%
I 6%
-------
2—Life Cycle Inventory Methods
Where:
Annual Electricity Use = Expressed in kWh/year
Qavg = Average daily flowrate, in MGD
2.2 Aerobic Membrane Bioreactor
The AeMBR LCI model was primarily based on modeling simulations in
CAPDETWorks™ design and costing software and GPS-X™. Figure 2-2 depicts a simplified
process flow diagram for the AeMBR treatment system. Figure 2-3 identifies subprocesses
associated with AeMBR operation.
Chlorination
AeMBR
Figure 2-2. AeMBR simplified process flow diagram.
Permeate Pumping
Screened Influent
Aeration
Blower
Sludge, to Sewer
Figure 2-3. AeMBR subprocess configuration.
The AeMBR system combines a continually stirred tank reactor (CSTR) with a
submerged membrane filter. No internal recycle was required. Energy from the diffused aeration
system was assumed to be sufficient to keep mixed liquor suspended solids (MLSS) in
suspension. Wasted sludge is disposed of via the sanitary sewer. Aeration blowers provide both
biological and membrane scour air. The AeMBR treatment unit is organized as three parallel
trains, as shown in Figure 2-2, each designed to treat 50 percent of the average daily flowrate.
Two of the three units will typically be in operation, with the third unit reserved as a standby unit
for use during routine maintenance or in the case of system failure.
2-2
-------
2—Life Cycle Inventory Methods
Table 2-1 presents design and operational parameters of the AeMBR process. A solids
retention time (SRT) of 15 days was specified in the GPS-X™ model. Design SRT of MBR unit
processes can vary between 10 and 50 in practice. An SRT of 20 days is typical for municipal
MBR systems (Yoon 2016). A representative hydraulic retention time (HRT) of 5 hours was
selected for the combined biological and filtration process. HRT typically ranges between 2 and
6 hours for combined aeration and filtration MBR processes (Yoon 2016). We calculated tank
dimensions based on HRT and GPS-X™ default depth-to-volume and length-to-width ratios. We
specified a permeate flux of 20 liters per m2 per hour (LMH) in the GPS-X™ model.
Table 2-1. AeMBR Design Parameters
Parameter
Mixed WW,
Building
Mixed
WW,
District
Graywater,
Building
Graywater
District
Units
SRTa
15
days
HRTa
5.0
hours
Biological SOTEb
0.07
perm
submergence
Scour SOTEc
0.02
perm
submergence
Biological SOTEb
0.16
0.20
0.15
0.18
total
Cross-flow SOTEc
0.06
0.08
0.06
0.07
total
Dissolved Oxygen
Setpoint
2.0
mg O2/L
Membrane flux
20
LMH
Backflush fluxd
40
LMH
Membrane area,
operation
200
390
130
240
m2
Membrane area, total
300
590
190
370
2
m
Biological airflow
66
85
17
30
m3/hr
Scour airflow
44
89
28
55
m3/hr
Tank depth,
operational
2.7
3.4
2.7
3.0
m
Tank length
3.3
4.0
2.1
3.4
m
Tank width6
1.1
1.5
1.1
1.2
m
Tank volume,
operational
20
39
13
24
3
m
Scour air demand
0.23
Nm3/m2/hr
MLSS
12,000
12,000
11,000
11,000
mg/L
Physical cleaning
interval1
10
minutes
2-3
-------
2—Life Cycle Inventory Methods
Table 2-1. AeMBR Design Parameters
Parameter
Mixed WW,
Building
Mixed
WW,
District
Graywater,
Building
Graywater
District
Units
Physical cleaning
duration1
45
seconds
Chemical cleaning
interval1
84
hours
a (Yoon 2016)
b SOTE - Standard Oxygen Transfer Efficiency (Tarallo et al. 2015)
0 SOTE - Standard Oxygen Transfer Efficiency (Sanitaire 2014)
d Backflush flowrate is twice the permeate flux (Yoon 2016).
e Refers to individual process train. Three trains per system.
f (Best 2015)
Acronyms: HRT - hydraulic retention time, LMH - liters per m2 per hour, MLSS - mixed liquor suspended solids,
SOTE - standard oxygen transfer efficiency, SRT - solids retention time, WW - wastewater
We estimated operational and total membrane area based on system flowrate and
membrane flux. The hollow fiber membrane is made of polyvinylidene fluoride (PVDF) (Cote et
al. 2012). The quantity of PVDF used in the membrane was calculated based on
CAPDETWorks™ results for the total surface area of membrane required for each size system
and manufacturer specifications for the inner and outer diameter of a hollow fiber (Suez 2017b).
An ecoinvent dataset for polyvinyl fluoride was used to model PVDF (Frischknecht et al. 2005).
Manufacture of MBR cassettes was not included in the model as data were not available, and
infrastructure typically is a small impact contributor in LCAs when amortized over the
equipment lifetime and compared to daily operational requirements. Membrane lifetime was
estimated to be 10 years (Cote et al. 2012).
Aeration requirements were estimated based on standard oxygen transfer efficiencies
(SOTE) for fine and course bubble aeration per unit depth. Fine bubble aeration systems have a
SOTE of 0.07 per meter (0.02 per foot) of submergence (Tarallo et al. 2015). Coarse bubble
aeration was specified for cross membrane airflow, and has an SOTE of 0.02 per meter (0.0075
per foot) of submergence (Sanitaire 2014). Diffusers are located 0.3 meters (1 foot) above the
floor of the treatment unit. Because of the process configuration, airflow intended for membrane
cleaning serves to reduce total biological air requirements within the unit process, but is subject
to a lower transfer efficiency. Table 2-1 lists the total SOTE of biological and cross-flow (scour)
air input into GPS-X™. The GPS-X™ model was used to estimate aeration electricity
requirements using the approach described in Section A. 1.4.
Cross-flow aeration was determined based on a scour air demand of 0.225 m3/m2/hour.
This value is the average of the default CAPDETWorks™ scour air demand estimate, of 0.3
m3/m2/hour and the General Electric (GE) eco-aeration scour rate of 0.15 m3/m2/hour. The GPS-
X™ model was used to estimate MLSS concentration as a function of the specified SRT. The
GPS-X™ model was set to operate simulating a 45 second backflush at 10 minute intervals. We
determined the backflush flowrate assuming a flux twice the normal permeate flux, or 40 LMH
(Yoon 2016).
2-4
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2—Life Cycle Inventory Methods
We estimated permeate pumping energy requirements using Appendix Equation A-l and
Equation A-2 assuming a differential head of 14 meters (45 ft) (Suez 2017a). An additional
electricity consumption factor of 25 percent was applied to the sum of aeration, permeate
pumping, and sludge pumping energy use to represent additional miscellaneous energy
requirements providing better alignment with energy consumption estimates specified in
literature summary that follows. Using this factor, total electricity consumption for the AeMBR
process, treating mixed wastewater, is 0.62 kWh/m3 of treated wastewater, which aligns closely
with the average energy consumption range reported in other studies (Krzeminski et al. 2012).
Other studies often report specific energy consumption for the full treatment system (i.e.
including pre- and post-treatment), with values for AeMBR based systems ranging from 0.4 to 4
kwh/m3 (Cornel and Krause 2004; Martin et al. 2011; Krzeminski et al. 2012). Typical values are
in the range of 0.8 to 1.75 kWh/m3. Total electricity consumption for the mixed wastewater,
AeMBR treatment system is 0.87 kWh/m3 in this analysis.
We assumed that sodium hypochlorite (NaOCl) is used for periodic membrane cleaning
every 84 hours. The LCI quantity was estimated assuming that 950 L of 12.5 percent NaOCl is
required per year per 1,650 m2 (17,760 ft2) of membrane surface area (Suez 2017a).
Process emissions of methane (CH4) and nitrous oxide (N2O) are estimated for the
AeMBR treatment systems using Appendix Equation A-7 and Equation A-8, as presented in the
IPCC Guidelines for National Inventories (Doom et al. 2006). We used GPS-X™ to estimate
BOD and total kjeldahl nitrogen (TKN) loads entering the AeMBR as inputs to these equations.
2.2.1 Thermal Energy Recovery for the AeMBR
We modeled a scenario where low-grade heat from the mixed wastewater and graywater
is recovered using a water-to-water heat pump prior to AeMBR treatment. Figure 2-4 presents a
system diagram of the heat pump used for thermal recovery.
Thermal recovery was assumed to directly follow wastewater screening to eliminate heat
loss that would occur during the wastewater treatment process. Additionally, the lag in thermal
recovery that would occur due to system HRT would challenge the system's ability to supply
heat at times of peak demand.
Filtered graywater and wastewater is pumped into a heat exchanger called the evaporator.
The evaporator contains a refrigerant, R-134a, which absorbs heat from the effluent causing the
refrigerant to evaporate. Gaseous refrigerant is compressed in the heat pump causing its
temperature to rise. Compressed refrigerant then enters a second heat exchanger called the
condenser where heat is transferred from the refrigerant to the hot water supply. An expansion
valve is used following the condenser to reduce the pressure and temperature of the refrigerant
before the cycle begins again.
2-5
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2—Life Cycle Inventory Methods
Compressor
1 Evaporator
Expansion
Valve
Figure 2-4. System diagram for the water-to-water heat pump thermal recovery system.
Table 2-2 lists the design and operational parameters used to model thermal recovery for
the wastewater and graywater AeMBR treatment systems. Wastewater and graywater
temperatures entering the evaporator are 23 and 30°C (WWmji), respectively. Temperature
differences realized on the evaporator and condenser sides of the heat pump were based on
Kahraman and Celebi (2009). The Kahraman and Celebi study reports the temperature difference
between the inlet and outlet of the condenser side heat exchanger (ATC) for three refrigerant
recirculation flowrates and influent wastewater temperatures of 10, 20 and 30°C. The lowest
refrigerant recirculation rate demonstrated the best performance, and the 20 and 30°C
experimental runs were used for the mixed wastewater and graywater, respectively.
The average coefficient of performance (COP) for the appropriate influent wastewater
temperature and the lowest refrigerant recirculation rate were used to estimate condenser and
pump energy requirements, using Equation 2 (Kahraman and Celebi 2009). Electricity
consumption was estimated assuming an electrical efficiency of 78% which is representative of
screw and reciprocating type compressors commonly used in heat pumps. A separate COP
specific to the compressor alone was used to estimate compressor power (WComP) (Studer 2007).
Compressor COP was scaled to reflect the effect of influent wastewater temperature (Kahraman
and Celebi 2009).
COP=- ^ r
{y^comp Wpump)
Equation 2
2-6
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2—Life Cycle Inventory Methods
Where:
Qww — Obtainable thermal power in wastewater or graywater
COP = Combined coefficient of performance, unitless
Wcomp = Compressor power
Wpump = Pump power
Total thermal energy transferred to the building hot water system is the sum of Qww and
compressor power (Wcomp) imparted to the working fluid minus internal losses (Cipolla and
Maglionico 2014). Obtainable wastewater thermal energy was calculated based on the
temperature difference between water entering and exiting the evaporator side heat exchanger
(ATe) by working backwards from ATC (Kahraman and Qelebi 2009) using the reported COPs
(Equation 3). The reported ATC values include system losses, so there is no need to consider them
explicitly.
QwW — mwwcp^Te
Equation 3
Where:
Qww = Obtainable thermal power in wastewater or graywater, watts
mww = Mass flowrate of wastewater or graywater, kg/sec
cp = Specific heat of water, 4180 J/kg-°C
ATe = Inlet and outlet wastewater or graywater temperature difference, evaporator
side, °C
Environmental benefits of the thermal recovery system were estimated by avoiding either
natural gas combustion or electricity use for water heating. Unlike the biogas recovery system
for the AnMBR where biogas combustion leads to a similar emission profile to that of natural
gas (see Section 2.3.2), the thermal recovery system avoids all natural gas combustion emissions.
Storage water heater (i.e. not on demand) options were compared based on delivered
energy (Ed) (Equation 4) exclusive of pipe network losses, which are expected to be equivalent
between the three systems. Energy factors of 0.69 and 0.925 were used to model the natural gas
and electric hot water heaters (Hoeschele et al. 2012). Energy factors provide an estimate of the
energy efficiency of a water heating system that includes thermal efficiency and standby losses.
Standby losses are greater in natural gas storage tanks due to the presence of a central flue.
Standby losses for the heat pump system were assumed to be equivalent to those of the electric
hot water heater, which were calculated to be six percent assuming a 98 percent thermal
efficiency. Avoided energy (fuel) consumption was calculated by dividing Ed by the appropriate
energy factor. Natural gas quantity was calculated assuming a higher heating value (HHV) of
40.6 MJ/m3 (U.S. DOE 2017).
2-7
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2—Life Cycle Inventory Methods
Delivered Energy (ED) = (Qww + Wcomp) x (1 - SL)
Equation 4
Where:
Ed = Energy delivered by the thermal recovery system, kWh
Qww = Obtainable thermal power in wastewater or graywater
Wcomp = Compressor power
Sl = Standby losses, fraction
Heat pump infrastructure estimates and GHG emissions were based on the inventory for
water-to-water heat pumps presented in Greening and Azapagic (2012). Fugitive emission of R-
134a were assumed to be three and six percent during manufacture and annual operation,
respectively.
Table 2-2. Thermal Recovery System Design and Performance Parameters
Parameter
Mixed
Wastewater
Graywater
Units
Mass Flowrate (m„„)
1.1
0.70
kg/sec
Temperature, in evaporator (WWm,h)
23
30
°C
Temperature, out evaporator (WW0Ut,c)
19
26
°C
AT, evaporator (ATe)
4.2
4.3
°c
Water specific heat (cp)
4180
J/kg-°C
Obtainable thermal power (Q„„)
19
13
kW
Compressor coefficient of performance
3.0
3.1
Combined coefficient of performance3
2.5
2.6
Compressor power
10
6
kW
Compressor efficiency
0.78
Heat pump electricity consumption
150,000
91,000
kWh/year
AT, condenser (ATC)
6.2
6.3
°C
Total thermal energy to hot water system
250,000
160,000
kWh/year
Natural gas, HHV
40.6
MJ/m3
Water heater thermal efficiency
0.9
Avoided natural gasb
31,000
20,000
m3/year
Avoided electricity0
260,000
170,000
kWh/year
a Includes compressor and fluid recirculation pump.
b Corresponds to scenario for the natural gas fired water heater.
0 Corresponds to scenario for the electric water heater.
Acronyms: HHV - higher heating value
2.3 Anaerobic Membrane Bioreactor
The AnMBR unit process was analyzed as an alternative treatment system for the
building scale water reuse scenario. A simplified process flow diagram for the modeled AnMBR
configuration is shown in Figure 2-5, with the required post-treatment processes described in
Section 2.3.3. The AnMBR is a psychrophilic process intended to operate at ambient
temperatures (approximately 23°C). Operating at ambient temperature has the benefit of
2-8
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2—Life Cycle Inventory Methods
eliminating influent heating energy demand required for mesophilic or thermophilic operation.
Psychrophilic reactors are possible with MBR reactors due to their ability to decouple HRT and
SRT, facilitating accumulation of slower growing psychrophilic organisms (Smith et al. 2013).
The anaerobic reactor was modeled as a CSTR, the most frequently used AnMBR configuration
(Song et al. 2018), based on the design of a continuously-stirred anaerobic digester. The unit
consists of a cylindrical concrete tank and floating cover with mechanical mixing. The system
utilizes a series of three external, submerged membrane tanks each of which are designed to
handle 50 percent of the average daily flowrate, making it a two-stage AnMBR. Two stage
designs are the most commonly studied pilot-scale AnMBR systems (Song et al. 2018). Only two
of the three tanks are intended to be in continuous operation. Membrane tank dimensions are
based on the Z-MOD L Package Plants (Suez 2017a). Table 2-3 provides a comparison of basic
design and operational parameters for the mixed wastewater and gray water AnMBR treatment
systems.
.
ft
,
Fine
Equalization
AnMBR
Zeolite
Adsopti on
Downfl ow
Hanging
Sponge
UV
Chi ori nation
Figure 2-5. AnMBR simplified process flow diagram.
Table 2-3. AnMBR Design and Operational Parameters
System
Component
Parameter
Mixed
Wastewater
Graywater
Units
SRT
60
davs
HRT
8.0
hours
MLSS concentration
12
g/L
COD/BOD removal
90%
of influent
concentration
Anaerobic Reactor
Tank diameter
4.0
3.5
m
Tank height
4.8
4.0
m
Mixing power
0.84
0.53
HP
Biogas production
14
6.3
m3/day
Biogas recirculation3
120
76
m3/hour
2-9
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2—Life Cycle Inventory Methods
Table 2-3. AnMBR Design and Operational Parameters
System
Component
Parameter
Mixed
Wastewater
Graywater
Units
Sludge production
0.69
0.44
m3/day
Electricity consumption13
0.81
0.82
kWh/m3
Membrane Tank
Flux
7.5
LMH
Membrane area, operational
530
340
m2
Membrane area, total
790
500
nr
Tank depth, per train
3.7
m
Tank length, per trainc
0.73
0.47
m
Tank width, per trainc
2.7
m
NaOCl, membrane cleaning
440
280
kg 15% solution
Effluent
COD
47
31
mg/L
BOD
14
9.3
mg/L
TSS
2.0
2.0
mg/L
Ammonia
35
8.5
mg/L
a For membrane cleaning.
b Includes energy use for tank mixing, permeate pumping, membrane cleaning and sludge pumping.
0 The system has three parallel membrane tanks.
Acronyms: BOD - biological oxygen demand, COD - chemical oxygen demand, HRT - hydraulic retention time,
MLSS - mixed liquor suspended solids, SRT - solids retention time, TSS - total suspended solids
Anaerobic digestion of wastewater leads to the formation of biogas. Typical biogas has a
methane content of 60 to 70 percent (Wiser P.E. et al. 2010). The higher end of this range, 70
percent (by volume), was assumed in this analysis as several studies cite high methane content
for biogas from psychrophilic reactors (Hu and Stuckey 2006; David Martinez-Sosa et al. 2011).
Biogas and associated methane production were estimated as a function of COD loading and
removal within the anaerobic reactor using the following assumptions. Methane production rates
of 0.25 and 0.26 kg CHVkg COD removed were estimated for the 23°C and 30°C reactors, by
linearly scaling based on values reported in David Martinez-Sosa et al. (2011). This value is
further supported by literature documenting operational parameters of AnMBRs treating
domestic wastewater as reported in Table 2-4. A COD removal rate of 90 percent was used to
estimate methane production (Ho and Sung 2009; Ho and Sung 2010; Chang 2014). Effluent
BODs concentration was calculated assuming a BOD/COD ratio of 0.3, based on the higher end
of the reported range of 0.1 to 0.3 (Tchobanoglous et al. 2014). Nitrogen and phosphorus have
negligible removal rates in anaerobic reactors (Mai et al. 2018). All influent TKN was assumed
to be released in the form of ammonia. The AnMBR was assumed to achieve an effluent TSS
concentration of less than 2 mg/L (Christian et al. 2010).
2-10
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2—Life Cycle Inventory Methods
Table 2-4. Operational Parameters of AnMBRs Treating Domestic Wastewater
Source
Influent
COD"
Strength
(mg/L)
COD"
Removal
(%)
Reactor
Temperature
(°C)
HRTb
(day)
Reactor
Volume
(m3)
Biogas
production
(m3 CTL/kg
COD)
(Baek et al. 2010)
-
64
-
0.5-2
0.01
-
(Berube et al.
2006)
-
70-90
11-32
-
-
-
(Chang 2014)
342-600
90
20-30
1-25
0.06-0.35
0.25-0.35
(Chu et al. 2005)
383-849
-
-
6.0
-
-
(Gao et al. 2010)
500
-
-
2.1
-
-
(Gimenez et al.
2011)
445 ± 95
87 ±3.4
33±0.2
0.25-
0.88
1.3
0.29 ±0.04
(Ho and Sung
2009)
500
>90
25
0.25-
0.50
0.004
0.21-0.22
(Ho and Sung
2010)
500
85-95
15-25
3.8-15
0.004
-
(Hu and Stuckey
2006)
460±20
>90
35
2.0
0.003
0.22-0.33
(Huang et al. 2011)
550
>97
25-30
0.33-0.5
0.006
0.14-0.25
(Kim et al. 2011)
513
99
35
0.18-
0.25
0.003
-
(Lew et al. 2009)
540
88
25
0.25
0.18
-
(Lin et al. 2011)
425
90
30±3
0.42
0.08
0.24
(Martin et al.
2011)
400-500
-
35
0.33-.58
-
0.29-0.33
(D. Martinez-Sosa
et al. 2011)
750±90
90
35±1
0.80-2.0
0.35-0.80
0.20-0.36
(David Martinez-
Sosa et al. 2011)
603±82
80-90
20-35
0.8
0.35
0.23-0.27
(Saddoud et al.
2007)
685
88
37
0.63-2.5
-
-
(Salazar-Pelaez et
al. 2011)
350
80
-
0.16-
0.50
-
-
(Smith et al. 2011)
440
92
15
0.67
-
(Smith et al. 2014)
430
85-90
15-25
0.33
-
0.35
(Wen et al. 1999)
100-2600
97
12-25
0.16-
0.25
-
-
Acronyms: COD - chemical oxygen demand, HRT - hydraulic retention time; SRT - solids retention time
Note: table reproduced from Cashman et al. (2016).
An 8 hour (0.33 day) HRT at the average daily flowrate was used to size the anaerobic
reactor. Song et al. (2018) cites several studies that consider similar HRTs for AnMBR treatment
systems. SRT for AnMBRs is typically between 40-80 days, with a MLSS concentration
between 10 and 14 g/liter. This study assumes an SRT of 60 days and a MLSS concentration of
12 g/L.
2-11
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2—Life Cycle Inventory Methods
Membrane surface area was determined by dividing the average daily flow by the
average net flux of 7.5 LMH reported in a literature review by Chang (2014) for AnMBR
systems and confirmed through personal communication with a GE AnMBR product manager
(Nelson Fonseca, GE Power and Water Lead Product Manager for Anaerobic MBR, August 18,
2015). Other authors have noted that increases in membrane flux are a possibility, and may
provide benefits associated with reduced energy consumption for membrane fouling systems and
lower membrane capital cost (Smith et al. 2014).
Mechanical mixing is required to ensure adequate digestion. Mixing horsepower
requirements were estimated assuming 0.5 HP per 28.3 m3 (1000 ft3) of reactor volume. A motor
efficiency of 88 percent was modeled (Harris et al. 1982).
2.3.1 Membrane Fouling and Sludge Output
Requirements for preventing membrane fouling, as indicated by previous work, were
assumed to be independent of wastewater strength (Smith et al. 2014). Biogas sparging and
periodic backflushing were modeled for membrane fouling control. A biogas recirculation rate of
0.23 Nm3/m2/hr was specified (Smith et al. 2014). Continuous biogas sparging was used to
generate baseline results, as it is expected to yield better system performance. Intermittent
sparging is examined as a sensitivity analysis, assuming 15 minutes of sparging every 2 hours
(Feickert et al. 2012). Backflushing is carried out for 45 seconds every ten minutes. The
backflush flowrate was estimated assuming a flux twice that of the AeMBR permeate flux, 40
LMH (Yoon 2016). NaOCl is used for periodic membrane cleaning and was estimated assuming
950 L of 12.5 percent NaOCl per year per 1650 m2 (17,760 ft2) of membrane surface area (Suez
2017a). Table 2-3 lists membrane surface area and annual NaOCl requirement for each AnMBR
system.
The amount of sludge returned to the municipal sewer system to be treated downstream at
the centralized WRRF was calculated using Equation 5 from Tchobanoglous et al. (2014).
Solving for Qw obtains the volume of sludge wasted per day.
Va = volume of anaerobic reactor (m3)
Vm = volume of membrane separation tank (m3)
Xa = solids concentration in the anaerobic reactor (mg/L)
Xm = solids concentration in the membrane separation tank (mg/L)
Qw = waste sludge flow rate (m3/day)
Equation 5
Where:
2-12
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2—Life Cycle Inventory Methods
2.3.2 Biogas Utilization
The recovered methane from the headspace was assumed to be converted to thermal
energy to supplement natural gas demand for building hot water use. Biogas cleaning and
compression was not included in this model due to lack of available data. A methane destruction
efficiency of 99% was modeled for biogas combusted in an energy/thermal device (e.g., dual fuel
biogas/natural gas boiler or flare) (IPCC 2006), with five percent of produced biogas escaping as
fugitive emission (UNFCCC 2012). Avoided natural gas production and fossil carbon dioxide
emissions are calculated based on fuel heat content using Equation 6. Other emissions resulting
from biogas combustion are assumed to be equivalent to those of the replaced natural gas given
equivalent combustion technology and appropriate biogas cleaning (Darrow et al. 2017).
2.3.3 Post-Treatment
2.3.3.1 Permeate Methane
A portion of produced methane is dissolved in solution and leaves the system in the
permeate (Smith et al. 2012). While supersaturation of dissolved methane occurs in some types
of anaerobic reactors, this has not been found in AnMBR systems (Cookney et al. 2016). Thus,
the amount of methane per liter of permeate was calculated based on Henry's Law and the van't
Hoff-Arrhenius relationship along with coefficients for methane used to calculate Henry's
constant for methane.
Van't Hoff Arrhenius Relationship, solved for Henry's Constant (Tchobanoglous et al.
2014) is shown in Equation 7 and Equation 8:
EPcm — (PRch4 X HHVCH4) x
Equation 6
Where:
EPCH4
PRCH4
HHVch4
Br,
Thermal energy from recovered headspace methane in kW
Methane production rate (grams CH4/second)
Higher heating value methane (modeled as 55.5 kJ/g)
Boiler thermal efficiency, 80 percent (using HHV) (Harris et al. 1982)
hCH4 = io(-r+B)
Equation 7
Where:
Hch4 = Henry's constant for methane at a given reactor temperature
A = 675.75
B = 6.880
T = reactor temperature in Kelvin
2-13
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2—Life Cycle Inventory Methods
Henry's Law (adapted from Smith et al. (2014)):
CUndissolved ~
Equation 8
Where:
CH4 , dissolved concentration of dissolved methane in solution (g/liter)
Pch4 = 0.65 atm, the partial pressure of methane in biogas
Hch4 = Henry's constant, as calculated for a given reactor temperature
M = 55.5 mol/liter, the molarity of water
MWCH4 = 16.04 g/mol, the molecular weight of methane
The concentration of methane dissolved in permeate varies depending on the temperature
of the reactor. Based on these calculations, approximately 21 and 27 percent of produced
methane is dissolved in permeate for the mixed wastewater and graywater systems, respectively.
Other authors have reported that between 24 and 58 percent of produced methane is dissolved in
permeate (Song et al. 2018).
Recent publications have noted that permeate methane recovery is a relatively young
technology that is not yet proven to be commercially or energetically viable (Smith et al. 2014).
However, several technologies haven proven effective at the lab or pilot scale (Hatamoto et al.
2011; Cookney et al. 2012; Matsuura et al. 2015). A downflow hanging sponge system was
modeled for permeate methane recovery in this analysis as described in Section 2.3.3.2.
2.3.3.2 Downflow-Hanging Sponge
A two-stage DHS was selected as the methane recovery method to simultaneously
recover or oxidize permeate methane, perform further COD/BOD removal and provide partial
nitrification. Basic design and operational parameters for the modeled DHS system are included
in Table 2-5, and are based on the work of Matsuura et al. (2015). The interior of the DHS
reactor is lined with triangular blocks of polyurethane sponge that house the biofilm. The sponge
itself occupies 44 percent of reactor volume (includes void space), having a void space of
approximately 98 percent (Onodera et al. 2016). Each of the two DHS stages has an HRT of 2
hours, calculated based on total sponge volume. A standard tank height of 2 meters was
specified. Tank diameter was adjusted to achieve the target volume. The DHS configuration of
Matsuura et al. (2015) is a closed/flooded reactor, relying on active aeration for methane
stripping and oxidation.
The first-stage reactor is a counter flow unit where AnMBR permeate enters at the top of
the reactor with airflow entering at the bottom. The flows move opposite of one another, with
recovered biogas being collected at the top of the reactor. Seventy-three percent of permeate
methane is recovered in the first-stage DHS (Matsuura et al. 2015). Stage one has a relatively
low air flowrate of 313 liters/m3 reactor volume/day to avoid reducing the methane concentration
in the recovered biogas below the 30 percent threshold required for successful combustion.
2-14
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2—Life Cycle Inventory Methods
Biogas recovered from the first-stage reactor is combined with biogas from the main anaerobic
reactor and used to provide thermal energy for building hot water systems.
Wastewater effluent and air both enter at the top of the second-stage DHS reactor. The
second-stage reactor is not intended for methane recovery, and instead oxidizes the permeate
methane to reduce methane off-gassing within the building's plumbing system. A methane
destruction rate of 99 percent was assumed (Matsuura et al. 2015). Calculation of dissolved
permeate methane entering the DHS reactor is described in Section 2.3.3.1. Airflow entering the
second-stage reactor is 2,500 liters/m3 reactor volume/day. The pumping energy requirement was
estimated using Appendix Equation A-l, assuming a head loss of 6 meters (1.5 times reactor
height). Blower power requirement was estimated using Appendix Equation A-3, assuming
diffuser submergence of 2 meters.
Overall the DHS process achieves a 55 and 73 percent reduction in influent COD and
BOD concentration, respectively. A 22 percent reduction in influent ammonia concentration
results from partial nitrification.
Table 2-5. Downflow Hanging Sponge Design and Operational Parameters
Parameter
Mixed Wastewater
Graywater
Units
Reactor HRTa
2.0
hours
Reactor volume
18
11
m3
Sponge volume
7.9
5
m3
Reactor height
2.0
m
Reactor diameter
3.4
2.7
m
Methane recovery, first-stage
73%
of dissolved CH4
Airflow rate, first-stage
313
L/m3/day
Methane destruction, second-stage
99%
of dissolved CH4
Airflow rate, second-stage
2500
L/m3/day
Total airflow
2.1
1.3
m3/hr
COD removal
55%
of influent concentration
BOD removal
73%
of influent concentration
Ammonia removal
22%
of influent concentration
Effluent COD
21
14
mg/L
Effluent BOD
3.8
2.5
mg/L
Effluent ammonia
27
6.6
mg/L
Fugitive methane emissions
5.0
2.9
kg/yr
Avoided natural gas
500
280
m3/yr
a DHS HRT was calculated using sponge volume, and not total reactor volume.
Acronyms: BOD - biological oxygen demand, COD - chemical oxygen demand, HRT - hydraulic retention time
2.3.3.3 Ammonium Adsorption - Zeolite
A zeolite ammonium adsorption (ion-exchange) system is used following the DHS
reactors to remove the majority of effluent ammonium, thereby reducing the quantity of NaOCl
required to establish a free chlorine residual. The ammonium adsorption system consists of an
upflow, packed bed zeolite reactor. A sodium chloride (NaCl) solution is circulated through the
packed bed to regenerate the zeolite once effluent ammonium concentrations exceed five percent
2-15
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2—Life Cycle Inventory Methods
of the influent concentration. The point at which the effluent ammonium concentration exceeds
the designated threshold, five percent, is termed "breakthrough." Design and operational
parameters of the ammonium adsorption system, listed in Table 2-6, are based on the work of
Deng et al. (2014).
Table 2-6. Zeolite Ammonium Adsorption Sytem Design and Performance Parameters
Parameter
Mixed
Wastewater
Graywater
Units
Ammonium removal rate
95%
of influent
Zeolite adsorption capacity
3.
mg NH^/g zeolite/cycle
Influent ammonium concentration
27
6.6
mg NH4/litcr
Effluent ammonium concentration
1.4
0.33
mg NH4/litcr
Ammonium load
2.6
0.40
kg NH4/dav
Zeolite requirement3
800
125
kg per reactor
Design flowrate
6
Bed volumes
Additional zeolite to meet design
flowrateb
340
600
kg per reactor
Total reactor zeolite
1100
730
kg
Zeolite bed volume
0.66
0.42
m
Number of regeneration cycles
9
count
Daily zeolite replacement
34
6.8
kg
Annual zeolite requirement
12400
2500
kg
NaCl solution strength
10
g/liter
NaCl consumption
7800
1200
kg/year
NaOH consumption
6900
4400
kg/year
a Minimum zeolite required to adsorb 95 percent of influent ammonium load.
b The zeolite requirement based on adsorption capacity was not sufficient to attain a flowrate of 6 BV per hour.
Additional zeolite was specified to increase the volume of the zeolite bed.
As wastewater flows over the packed bed, the positively charged ammonium ions are
adsorbed to the surface of the zeolite. The adsorption capacity of the zeolite bed depends on
several factors including the type of zeolite, ammonium ion concentration, the presence of
competing ions, and use history (age) of the zeolite medium. As the reactor functions, potential
adsorption-sites become occupied and the removal efficiency of the system will decrease. The
continuous column, pilot scale reactor was able to achieve 95 percent removal efficiency over
the course of nine regeneration cycles when operating at a flowrate of between four and eight
bed volumes (BV) per hour. This analysis assumed a flowrate of six BV per hour.
The initial adsorption (exchange) capacity of the natural zeolite medium was 3.1 mg
NH4-N/g of zeolite. At the end of nine regeneration cycles, the exchange capacity had dropped
by 39 percent to 1.9 mg NTU-N/g zeolite. The elapsed time to reach breakthrough decreased
from 42 hours initially, to 12 hours at the conclusion of nine regeneration cycles. The average
adsorption capacity of 2.4 mg NTU-N/g (3.1 mg NFU/g) zeolite, over the nine regeneration
cycles, was used to estimate the required zeolite quantity. An additional quantity of zeolite was
specified to reach the target flowrate of six BVs. One tenth of the required zeolite quantity is
replaced at the conclusion of each regeneration cycle (the oldest medium) such that the average
2-16
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2—Life Cycle Inventory Methods
adsorption capacity is maintained over time. The average breakthrough time over nine cycles is
21 hours.
It was assumed that regeneration occurs once daily for a two hour period. Installation of
two zeolite columns was specified and the units are expected to be used in alternating fashion. A
10 g/1 NaCl solution with a pH of 12 is used as the regenerating fluid. The high concentration of
sodium ions displaces the ammonium, thereby regenerating the zeolite for continued use. The
brine solution was assumed to be disposed of by deepwater injection. We assumed a transport
distance of 100 km to the injection well. Brine injection requires 1.8 kWh of electricity
consumption per m3 of fluid injected. Sodium hydroxide (NaOH) is used to raise the pH of the
NaCl solution, which was shown to considerably decrease the required NaCl concentration. The
NaCl requirement is 3.5 g of Na+ per gram of adsorbed NH4. The NaOH dose used in the
analysis was 0.2 kg per m3 of treated wastewater (Deng et al. 2014). An effluent ammonium
concentration of less than 1.5 mg/L is expected for the mixed wastewater and graywater systems.
2.4 Recirculating Vertical Flow Wetland
The RVFW system is analyzed for the building scale scenario and was modeled
according to Figure 2-6. The wetland basins are preceded by a fine screen, slant plate clarifier
and equalization basin to ensure consistent inflow and reduce suspended solid concentration,
minimizing the potential for clogging of the media bed. Suspended solids removal exceeds 95
percent in slant plate clarifiers, and requires minimal floor area. The mixed wastewater and
graywater RVFW systems require two and three 40 gallon per minute (gpm) clarifiers to ensure
adequate flow capacity during peak water use hours. Clarifier infrastructure requirement was
approximated based on a unit mass of 1,600 kg assuming all steel construction. Sludge is
pumped from the slate plate clarifier and disposed of in the sanitary sewer. Sludge flowrate was
estimated based on influent TSS concentration, design removal rate, and an assumed sludge
solids content of 1.2 percent. We calculated the sludge wastage rate to be 0.37 and 1.6 m3/day for
the graywater and wastewater systems, respectively. Appendix Equation A-l was used to
estimate pump power requirements and associated electricity consumption.
To Reuse
Ozone
*Mixed
JT7F Only
Fine Slant Hate
Screen Clarifier
Equalization
Tank
Chi ori nation
RVFW
Figure 2-6. Diagram depicting the process flow of the recirculating vertical flow wetland.
The equalization tank has an 18 hour retention time to allow the RVFWs to be operated
in batch mode (safety factor of 1.5). Clarified wastewater fills the equalization tank during the 12
hour wetland treatment cycle. Section 2.1 describes the approach used to estimate infrastructure
and energy consumption associated with the equalization basin and fine screens.
The RVFW was designed as a modular adaptation of a pilot-scale wetland with bed
dimensions of 30 m by 2 m. RVFW wetlands utilize a pumped re-circulation of treated graywater
2-17
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2—Life Cycle Inventory Methods
or wastewater to meet treatment goals, while minimizing space requirements. Basic design
parameters are from the work of Sklarz et al. (2010).
Figure 2-7 depicts a cross-section of the modeled wetland configuration, excluding the
cement structure. The wetland consists of an upper bed that is filled with limestone, gravel and a
top layer of soil that is planted with emergent, wetland vegetation. We estimated primary
infrastructure material requirements for the wetland treatment system based on unit dimensions
assuming reinforced concrete construction, and a wall thickness of 0.23 m (9 in). Unit weights
were used to estimate the steel requirement for rebar, steel grating, and pumps. Piping was
assumed to be made of high-density polyethylene (HDPE).
Clarified wastewater and recirculation flow is distributed evenly over the surface of the
gravel layer via a manifold and distribution pipes. Water travels vertically, downwards through
the media layers for treatment. It is assumed that the units are planted, but plant material is not
reflected in the LCI as the plants do not notably contribute to treatment and are expected to be
present in landscaping regardless of the decision to use constructed wetlands for wastewater
treatment. Depth of the planted media basin is 0.6 meters.
The upper bed is supported by stainless steel grating and is suspended above a 1 meter
deep collection and pumping basin. A minimum distance of 0.5 meters is maintained between the
lower edge of the planted bed and the water surface below. Water falls freely from the planted
bed into the lower basin, facilitating aeration. Determination of the flow rate per unit area was
based on Gross et al. (2007a), which suggests that 8-12 hours of recirculation is sufficient to reach
steady-state TSS and BOD removal when recirculating 300 L of water over 1 m2 of wetland area.
This corresponds to a treatment rate of 0.6 m3 of wastewater per m2 of wetland area per day,
which was used to calculate required wetland area.
0.6 m
0.4 m
0.1 m
0.5 m
ibark mulch
- ;;
gravel
limestone
1111
Figure 2-7. Diagram depicting the cross-section of the recirculating vertical flow wetland.
2-18
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2—Life Cycle Inventory Methods
We used a recirculation rate equal to 1.5 meters (depth) per hour, which corresponds to
the optimal recirculation rate identified by Sklarz et al. (2010). The recirculation rate is equal to
60 times the influent flowrate. Following treatment in the wetland, water is pumped back into the
building into a series of storage tanks prior to disinfection.
Large variability in influent graywater quality was shown not to have a significant effect
on resulting effluent quality from RVFW systems Alfiya et al. (2013), when expressed as percent
removal. The average removal rate from the studies reported in Table 2-7 were taken as the
modeled removal rate.
Table 2-7. Wetland Treatment Performance
Study
Flow Rate
Recycle Rate
TSS (mg/1)
BOD (mg/1)
(m3/d)
(m3/h)
In
Out
Rem (%)
In
Out
Rem (%)
(Alfiya et al. 2013)
0.16
0.30
n/a
166
1.6
99%
(Alfiya et al. 2013)
0.11
0.30
136
4.6
97%
(Alfiya et al. 2013)
0.16
0.30
229
2.7
99%
(Gross et al.
2007a)
0.45
0.39
158
3.0
98%
466
0.7
100%
(Gross et al.
2007b)
0.01
0.06
46
3.0
93%
n/a
(Gross et al. 2008)
0.30
2.50
97
9.5
90%
122
5.0
96%
(Gross et al. 2008)
0.40
2.50
158
3.0
98%
105
1.0
99%
(Sklarz et al. 2009)
0.30
4.50
90
10
89%
120
5.0
96%
(Sklarz et al. 2010)
0.30
2.50
103
6.8
93%
178
6.2
97%
(Sklarz et al. 2010)
0.30
2.50
103
3.3
97%
178
5.2
97%
Average Removal
94%
98%
Acronyms: BOD - biological oxygen demand. Rem - removal, TSS - total suspended solids
Pump power and electricity requirements are calculated using Appendix Equation A-l
and Equation A-2, respectively. A high-flow, low head pump is required for this application. The
pumps run continuously. A combined pump and motor efficiency of 60 percent was assumed
(Tarallo et al. 2015). Pipe head loss was estimated using the Hazen-Williams equation (Equation
A-6). Piping was sized based on fluid flowrate and target pipe velocity. The smallest available
diameter of HDPE pipe was selected for the vertical pipe and manifold such that the associated
fluid velocity is less than 1.5 m/sec (5 ft/sec). We assumed a maximum flow velocity of 0.61
m/sec (2 ft/sec) for horizontal distribution piping to limit energy demands associated with
friction head loss. HDPE pipe with a 5.8 inch inner diameter was modeled for all wetland piping
based on these requirements. Table 2-8 presents basic design parameters of the mixed
wastewater and graywater wetland systems.
2-19
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2—Life Cycle Inventory Methods
Table 2-8. Mixed Wastewater and Graywater Wetland Design Parameters
Parameter
Mixed Wastewater
Graywater
Units
System flowrate, English
0.025
0.016
MGD
System flowrate, metric
95
61
m3/day
Wetland area, minimum required
160
100
9
m
Minimum beds required
3
2
Count
Wetland area, modeled
180
120
m2
Pump size, per bed
0.43
HP
Recirculation flowrate, per bed
90
m3/hour
Acronyms: HP - horsepower, MGD - million gallons per day
Process GHG emissions of N2O and biogenic carbon dioxide (C02-biogenic) were
estimated for the RVFW system (Teiter and Mander 2005). We used Appendix Equation A-7 to
estimate CH4 emissions using the IPCC method (Ebie et al. 2013). The average methane
correction factor for vertical subsurface flow constructed wetlands of 0.01 was applied. Table
2-9 presents emission factors used in the analysis.
Table 2-9. Wetland Greenhouse Gas Emissions
Parameter
Value3
Units
Methane
0.006
kg CHo/kg BODb
CC^-biogenic
3.4
kg C02/m2/yr
Nitrous oxide
6.0E-3
kg N20/m2/yr
a Calculated as average of values presented in Teiter and Mander (2005)
b Refers to kg of BOD entering the treatment wetland
Acronyms: BOD - biological oxygen demand
2.5 Disinfection
We selected disinfection processes for each treatment system to meet or exceed log
reduction targets (LRTs) identified for indoor NPR (Sharvelle et al. 2017). Table 2-10 presents
LRTs for domestic wastewater and graywater to achieve risk level of 1 in 10,000 infections per
person per year. Separate LRTs are specified for each of three general pathogen types: viruses,
protozoa, and bacteria.
Table 2-10. Log Reduction Targets for 10~4 Infection Risk Target, Non-Potable
Reuse: Wastewater and Graywater3
Enteric
Viruses
Parasitic
Protozoa
Enteric
Bacteria
Indoor Use
Domestic Wastewater
8.5
7.0
6.0
Graywater
6.0
4.5
3.5
Unrestricted
Irrigation
Domestic Wastewater
8.0
7.0
6.0
Graywater
5.5
4.5
3.5
a Table reproduced from Table 3-3 in Sharvelle et al. (2017).
2-20
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2—Life Cycle Inventory Methods
Log reduction values (LRVs) listed in Table 2-11 were used to select disinfection
technologies and dosage rates required to meet LRTs in Table 2-10. Effective dosage rates are a
function of disinfection method and physical and chemical characteristics of the treated
wastewater as described in Sections 2.5.1 through 2.5.3. General wastewater characteristics such
as temperature and pH were not treated explicitly in the calculation of dosage rates, and were
assumed to be within the range required for effective disinfection. In all cases, we developed
process configurations that meet the LRTs and provide multiple disinfection barriers.
Table 2-11. Log Reduction Values by Unit Process and Disinfection Technology for
Viruses, Protozoa and Bacteria
Enteric
Viruses
Parasitic
Protozoa
Enteric
Bacteria
Units
Membrane Bioreactor8
Log Reduction
5
5
5
log
Wetland
0.5
1.0
0.8
log
Free Chlorine
1 Log io
n/a
2000-2600
0.4-0.6
mg-min/L
2 Log io
1.5-1.8
n/a
0.8-1.2
mg-min/L
3 Log io
2.2-2.6
n/a
1.2-1.8
mg-min/L
4 Log io
3-3.5
n/a
1.6-2.4
mg-min/L
Ozone
1 Log io
n/a
4-4.5
0.005-0.01
mg-min/L
2 Log io
0.25-0.3
8-8.5
0.01-0.02
mg-min/L
3 Log io
0.35-0.45
12-13
0.02-0.03
mg-min/L
4 Log io
0.5-0.6
n/a
0.03-0.04
mg-min/L
UV Radiation
1 Log io
50-60
2-3
10-15
mJ/cm2
2 Log io
90-110
5-6
20-30
mJ/cm2
3 Log io
140-150
11-12
30-45
mJ/cm2
4 Log io
180-200
20-25
40-60
mJ/cm2
a An LRV of five was used as a conservative estimate. Sharvelle et al. (2017) lists MBR LRV as >6.
Acronyms: UV - ultraviolet
Note: table compiled from Tables 4-3, 4-4, and 4-5 in Sharvelle et al. (2017).
Table 2-12 through Table 2-15 present the disinfection scenarios developed for each
treatment system and wastewater type, listing disinfection technologies, dosage rates, and
associated LRVs. LRVs are independent of treatment process scale and are applicable to both
building and district scenarios. Disinfection processes and design dosages are identical for
AeMBR and AnMBR treatment processes. The RVFW requires additional disinfection processes
and higher dosage rates to meet LRTs for indoor and outdoor NPR. Pathogen log reductions
within the wetland are considerably lower than those associated with the MBR process
technologies. A minimum UV dose of 30 mJ/cm2 was used (BGLUMR 2014). A free chloride
residual of 1 mg/L was specified for all systems, based on California residual chlorine
requirements for NPR (Sharvelle et al. 2017). A standard chlorine contact time of 30 minutes
was used for dose calculations (BGLUMR 2014).
2-21
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2—Life Cycle Inventory Methods
Table 2-12. Disinfection System Specification for Aerobic and
Anaerobic MBRs: Mixed Wastewater
Organism
Virus
Protozoa
Bacteria
LRT
8.5
7.0
6.0
Technology
LRV
LRV
LRV
Dose
Dose Units
Membrane bioreactor
5.0
5.0
5.0
n/a
n/a
Ozone
-
-
-
-
-
UV
-
4.0
2.0
30
mJ/cm2
Chlorination
4.0
-
4.0
32
mg-min/L
Total LRV
9.0
9.0
11
Acronyms: LRV- log reduction value, UV - ultraviolet
Table 2-13. Disinfection System Specification for Aerobic and
Anaerobic MBRs: Gray water
Organism
Virus
Protozoa
Bacteria
LRT
6.0
4.5
3.5
Technology
LRV
LRV
LRV
Dose
Dose Units
Membrane bioreactor
5.0
5.0
5.0
n/a
n/a
Ozone
-
-
-
-
-
UV
-
4.0
2.0
30
mJ/cm2
Chlorination
4.0
-
4.0
32
mg-min/L
Total LRV
9.0
9.0
11
Acronyms: LRV - log reduction value, UV - ultraviolet
Table 2-14. Disinfection System Specification for Recirculating
Vertical Flow Wetland: Mixed Wastewater
Organism
Virus
Protozoa
Bacteria
LRT
8.5
7.0
6.0
Technology
LRV
LRV
LRV
Dose
Dose Units
RVFW
0.50
1.0
0.80
n/a
n/a
Ozone
4.0
2.0
4.0
8.3
mg-min/L
UV
1.0
4.0
4.0
55
mJ/cm2
Chlorination
4.0
-
4.0
32
mg-min/L
Total LRV
9.5
7.0
13
Acronyms: LRV - log reduction value, UV - ultraviolet
2-22
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2—Life Cycle Inventory Methods
Table 2-15. Disinfection System Specification for Recirculating
Vertical Flow Wetland: Gray water
Organism
Virus
Protozoa
Bacteria
LRT
6.0
4.5
3.5
Technology
LRV
LRV
LRV
Dose
Dose Units
RVFW
0.50
1.0
0.80
n/a
n/a
Ozone
-
-
-
-
mg-min/L
UV
2.0
4.0
4.0
95
mJ/cm2
Chlorination
4.0
-
4.0
32
mg-min/L
Total LRV
6.5
5.0
8.8
Acronyms: LRV - log reduction value, UV - ultraviolet
2.5.1 Ozone
Ozone disinfection was only required for the RVFW system treating mixed wastewater.
A three zone contact basin was modeled for disinfection, providing a total contact time of eight
minutes (Tchobanoglous et al. 2014). Total reactor volume is 530 liters, based on the 0.025
MGD flowrate. The first basin has a contact time of two minutes, which is used to satisfy
instantaneous ozone demand associated with COD. Table 2-16 presents ozone demand estimates
for select wastewater constituents (Eagleton 1999). The primary constituents expected to
contribute to ozone demand for the RVFW are COD or total organic carbon (TOC). Due to the
overlap between the two constituents and availability of data on wastewater COD, only ozone
demand of COD was estimated. Nitrogen is expected to be primarily in the form of nitrate, which
has no associated ozone demand.
Table 2-16. Rapid Ozone Demand of Wastewater
Constituents
Constituent
O3 Demand (mg O3/L
per constituent unit)
Constituent Units
TOC
4.0
mg C/L
CODa
2.0
mg/L
Iron
0.43
mg Fe/L
Manganese
0.88
mg Mn/L
Sulfide
6.0
mg S/L
Nitrite
2.0
mg NO2/L
a (Absolute Ozone 2018)
Acronyms: COD - chemical oxygen demand, TOC - total organic carbon
The second and third contact zones each have a contact time of three minutes. Equation 9
estimates ozone decay. Lambda was calculated based on an ozone half-life of 20 minutes at 20°C
(Lenntech 2018).
2-23
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2—Life Cycle Inventory Methods
[0]t = [°]oe At
Equation 9
Where:
[O]o = Ozone concentration at time zero, mg O3/L
[0]t = Ozone concentration at time t, mg O3/L
A = Ozone decay constant, 0.035, unitless
t = Elapsed time, minutes
The ozone dose that affects disinfection in the wastewater was calculated as the product
of average ozone concentration in the second and third contact zones times the duration of
contact (Equation 10). No disinfection was assumed to occur in zone one due to instantaneous
demand. The required ozone dose was divided by an 85 percent transfer efficiency to calculate
the quantity of ozone that must be generated on-site (Summerfelt 2003).
[Oin] = Ozone concentration entering second contact zone, mg O3/L
[Oout] = Ozone concentration exiting the contact basin, mg O3/L
t = Duration of contact in second and third contact zones, minutes
We modeled on-site ozone generation requirements for electricity consumption and liquid
oxygen based on manufacturer specifications for the Primozone® GM-series of ozone generators
(Primozone® 2014). The outcome of the calculations described above indicates a facility ozone
demand of approximately two kg/day or 83 grams/hour. Two Primozone® GM1 units were
specified, each having a maximum ozone generation rate of 60 grams/hour. Energy consumption
at 100 percent capacity is 0.6 kW per unit. Product literature shows that energy use is roughly
proportional to capacity utilization (Primozone® 2013). The average ozone requirement
constitutes 69 percent of generation capacity, corresponding to 0.8 kW of power consumption,
and 7,200 kWh of annual electricity consumption. Approximately 0.4 normalized m3/hr of
oxygen are required to produce 83 grams/hour of ozone, corresponding to an annual oxygen
requirement of 4,600 kg.
We assumed 75 percent steel and 25 percent aluminum construction for each 40 kg unit
and an expected lifespan of 20 years. The ozone contact basin was modeled assuming reinforced
concrete construction and a 0.1 m (4 in) wall thickness.
mg * min
Required Ozone Dose
Equation 10
Where:
2-24
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2—Life Cycle Inventory Methods
2.5.2 Ultraviolet
UV disinfection was specified for all treatment scenarios. A minimum UV dose of 30
mJ/cm2 was used (BGLUMR 2014). UV dose is a function of delivered UV intensity and contact
time. Nominal UV intensity (In) is a measure of bulb output, and is typically reported as a
function of wastewater transmittance. Delivered intensity (Id) is augmented according to
intensity reduction factors as applied in Equation 11. Only a fraction of bulb output is in the UV
spectrum, and can range for 30 to 100 percent of bulb output (Tchobanoglous et al. 2014). A
lamp UV output factor (UV0Ut) of 0.85 was used in the analysis. A quartz sleeve transmittance
(Ts) of 0.85 was used (Pirnie et al. 2006). Lamp UV output decreases over time with bulb age. A
lamp aging factor (A) of 0.7 was selected, and represents UV output after 7000 hours of use
(Hiltunen et al. 2002). The UV dose, in mJ/cm2, received by the wastewater was calculated using
Equation 12, as a function of delivered UV intensity (Id) and contact time (CT). Contact time is
measured in seconds.
Id = In Ts X UV0Ut X A
Equation 11
Dose = ID x CT
Equation 12
Where:
Id = Intensity delivered, mW/cm2
In = Nominal intensity, mW/cm2
Ts = Quartz sleeve transmittance, 0.85 (unitless)
UVout = Lamp UV output, 0.85 (unitless)
A = Lamp aging factor, 0.7 (unitless)
CT = Contact time, seconds
Electricity consumption estimates for UV system operation were based on power use
figures for the commercially available Sanitron® UV purifiers produced by Atlantic Ultraviolet
Corporation. Two Sanitron® S50C units were modeled for building scale MBR systems,
delivering the prescribed 30 mJ/cm2 dose at their rated flowrate of 20 gpm. Only one unit is
required to be online under typical operational conditions. Each unit has a rated power
consumption of 54 watts, which corresponds to 470 kWh of annual electricity consumption. The
RVFW systems treating mixed wastewater and gray water require higher design dosages of 55
and 95 mJ/cm2, respectively. The RVFW treating mixed wastewater requires two 40 gpm
Sanitron® UV systems, of which one is expected to be in continuous operation. Power
consumption for the 40 gpm unit is 0.14 kW, or approximately 1200 kWh of annual electricity
consumption. Two of the 83 gpm Sanitron® S5,000C UV units were required for the RVFW
system treating graywater. Power consumption for the 83 gpm unit is 0.28 kW, or approximately
2400 kWh of electricity consumption per year. Infrastructure requirements for each UV system
were based on manufacturer reported unit mass, assuming all steel construction and a 30 year
unit lifespan.
2-25
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2—Life Cycle Inventory Methods
2.5.3 Chlorination
Chlorination was modeled for all treatment systems to provide a one mg/L free chlorine
residual. A standard chlorine contact time of 30 minutes (BGLUMR 2014) and system flowrate
was used to size the chlorine contact vessel. A liquid NaOCl solution, containing 15 percent
available chlorine, was used as the disinfectant. Instantaneous chlorine demand needs to be
satisfied before a free residual can be established. The instantaneous demand of wastewater TOC
content was estimated using an approach outline in the GPS-X™ technical reference
(Hydromantis 2017). Instantaneous demand of ammonia, required to reach the breakpoint, was
estimated using the influent ammonia concentration and a chlorine demand factor of 7.6 mg
Ch/mg NH4-N (Tchobanoglous et al. 2014). We used a first-order rate equation to estimate
chlorine decay, assuming a decay constant of 0.42. Total chlorine dose is the sum of
instantaneous demand, decay, and the specified one mg/L CI2 residual. The calculated free
chlorine requirement was converted into the corresponding quantity of NaOCl. Table 2-17 lists
the calculated breakpoint and chlorine dose requirements for each treatment system. The
building scale AnMBR treating mixed wastewater has considerably greater influent ammonia
concentrations than other treatment systems, leading to elevated breakpoint demand.
Table 2-17. Calculated Breakpoint and Chlorine Dose Requirements
System
Breakpoint Chlorine
Chlorine Dose
Requirement (mg Cb/L)
(mg Cb/L)
AeMBR Building, Graywater
1.90
3.05
AeMBR Building, Mixed Wastewater
2.28
3.43
AnMBR, Building, Graywater
2.87
4.21
AnMBR, Building Mixed Wastewater
10.70
11.85
RVFW, Building, Graywater
0.30
1.45
RVFW, Building, Mixed Wastewater
0.35
1.50
AeMBR District, Graywater
1.93
3.08
AeMBR District, Mixed Wastewater
2.33
3.48
We estimated electricity consumption required for NaOCl injection assuming continuous
operation of a 0.2 kW peristaltic pump, which corresponds to 1,800 kWh of annual electricity
use. Infrastructure was estimated assuming reinforced concrete construction of the chlorine
contact basin based on a wall thickness of 0.1 m (4 in).
2.6 Water Reuse Scenarios
The analysis investigated reuse of treated mixed wastewater and graywater for on-site
landscape irrigation and indoor NPR. In all scenarios, reuse water was assumed to replace
potable drinking water, reducing water use at the point of extraction for the local water utility,
and avoiding environmental burdens of potable water treatment. We analyzed two reuse
scenarios that vary assumptions related to the fraction of treated wastewater that can be reused
on-site, termed the high reuse and low reuse scenarios.
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2—Life Cycle Inventory Methods
2.6.1 Wastewater Generation and On-site Reuse Potential
The high and low wastewater reuse scenarios assess the sensitivity of LCA impacts to
reuse quantity, and reflect uncertainty regarding the quantity of wastewater that can ultimately be
reused. The high reuse scenario represents NPR associated with current, average water demand.
The low reuse scenario represents NPR in a region or development employing high efficiency
fixtures. Table 2-18 indicates the quantity of wastewater generated and treated on-site and on-site
reuse potential. On-site reuse potential is expressed as a percentage of available, treated
wastewater or graywater. On-site wastewater generation considers a mixture of residential and
commercial building occupants and associated wastewater generation rates for the mixed-use
building and district configurations described in Section 1.3.
The fraction of treated wastewater that can be reused was modeled as the sum of toilet
flushing, laundry water, and irrigation water associated with the building or district. We assumed
that for the high reuse scenario toilet and laundry water constitute 28 and 23 percent of total
indoor water use, respectively (Tchobanoglous et al. 2014). For the low reuse scenario, toilet and
laundry water constitute 15 and 11 percent of total indoor water use (Sharvelle et al. 2013). We
estimated annual irrigation water use for the high reuse scenario assuming 3.4 gallons/ft2 of
residential floor area and 6.0 gallons/ft2 of commercial floor area (Refocus 2015). Building floor
areas devoted to these two use categories are listed in Table 1-1, and were calculated based on
reported estimates of indoor water use per occupant. The low reuse estimate for district irrigation
water was developed based on landscape water demand calculations assuming that 26 percent of
the district block area is landscaped using version 1.01 of California's Water Budget Workbook
(CDWR 2010). Section A. 1.2 provides additional parameter values input into the irrigation water
budget workbook. Building scale irrigation water use for the low reuse scenario was estimated
by scaling the high reuse irrigation water estimate by the ratio between district irrigation water
use in the low and high reuse scenarios.
Table 2-18. On-site Wastewater Generation and Reuse Potential
Wastewater Scenario
Building
Configuration
High Reuse
Low Reuse
On-site Wastewater
Generation (million gallons
per year)
Mixed WW
Mixed Use Building
9.1
Graywater
5.7
Mixed WW
District
18
Graywater
11
On-site Reuse Potential
(million gallons per year)
Indoor Non-potable
Mixed Use Building
4.9
2.5
Irrigation
1.6
0.6
Indoor Non-potable
District
9.9
5.1
Irrigation
3.2
1.3
Fraction of Mixed WW Reused On-site
Mixed Use Building
72%
35%
District
72%
35%
Fraction of Graywater Reused On-site
Mixed Use Building
100%
55%
District
100%
57%
Acronyms: WW - wastewater
2-27
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2—Life Cycle Inventory Methods
2.6.2 Recycled Water Distribution Piping
A typical commercial or residential building will contain separate plumbing networks for
hot and cold potable water distribution as well as wastewater disposal. Distribution of recycled
wastewater requires its own pipe system. Graywater reuse systems require a second additional
plumbing network for graywater collection. A simple pipe network was modeled for the large
mixed-use building, and the four and six-story district buildings to approximate the additional
on-site infrastructure requirement.
Hot and cold potable water, wastewater, and irrigation plumbing networks are present
regardless of whether water reuse is practiced, and were therefore excluded from the analysis.
While it may be possible to reduce pipe size in these networks with the adoption of wastewater
recycling, this potential was not considered. We assumed that all domestic hot water was
provided using the potable water supply, regardless of scenario. Given these considerations, the
material requirement of the two additional plumbing networks were quantified based on the pipe
network depicted in Figure 2-8 (side view) and Figure 2-9 (top view).
Large Multi-Use Building (side-new)
oo
| Utility Shaft: elevators, common area, utility closets
O O Duplex booster Pumps
Vertical Water Riser
Water supply common area zone piping network
F6
F5
F4
F3
F2
F1
6 Story Building (side view)
OQ
Figure 2-8. Side view of the modeled building piping networks.
2-28
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2—Life Cycle Inventory Methods
Residential Unit
Piping:
Common area distribution pipe Reuse Water
] Elevators and utility space Graywater
Commercial Unit
Figure 2-9. Top view of the modeled building piping networks.
The large mixed-use building was divided into three pressure zones to satisfy the
maximum and minimum zone pressures listed in Table 2-19. Maximum zone pressure defines
the highest pressure that will be seen by a plumbing fixture, and should be kept at or below 70
pounds per square inch (psi) to maintain reasonable flow velocities and to avoid damaging
fixtures (Steele 2003). A minimum amount of pressure is required for proper fixture functioning.
Static differential pressure describes the pressure required to move water from the building
basement up to the highest floors. Section 2.6.3 describes pressure calculations used to determine
required pumping energy.
The pipe networks include a main vertical riser, zone risers, floor mainlines, unit
mainlines, and in-unit distribution pipes. The main vertical riser connects the treatment systems
to zone risers, which distribute recycled water to each floor. Floor mainlines distribute water
between commercial and residential units. In-unit mainlines run along two walls of each unit,
and are connected to distribution pipe that connects directly to necessary fixtures. Specific
fixture requirements were not considered in the analysis.
2-29
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2—Life Cycle Inventory Methods
Table 2-19. Building Pipe Network Characteristics
Parameter
Large Mixed-
Use Building
Six-story
Building
Four-story
Building
Units
Building Height3
290
110
82
ft
Potable Water Pressure13
85
85
85
psi
Pressure Lossc
17
13
12
psi
Static Differential Pressured
120
47
36
psi
Distribution Zones
3
1
1
Maximum Distribution
Pressure
70
70
70
psi
Minimum Distribution
Pressure
30
30
30
psi
a Assumes average height per floor of 13.7 ft and a basement depth of 27 ft.
b Pressure of distribution network at street.
0 Includes losses due to pipe friction, water meter, valves and backflow prevention.
d Measure of the pressure required to pump to the top of the building. Excluding losses.
We modeled two inch polyvinyl chloride (PVC) pipe for both the main vertical and zone
risers. One inch PVC pipe was modeled for floor mains. One inch and 0.5 inch crosslinked
polyethylene (PEX) pipe was specified for in-unit main and distribution piping, respectively.
Mainline pipe was sized based on the expected peak flowrate and a maximum flow velocity of
1.5 m/sec (5 ft/sec). Greater flow velocities increase friction losses and can lead to undesirable
pipe noise (Steele 2003). Peak flowrate for all water and wastewater categories, in gpm, was
estimated assuming that 15 percent of building water use occurs during a one hour period when
people are waking up and getting ready for the day (Omaghomi et al. 2016). In-unit pipe size
was based on standard pipe dimensions used in domestic high-rise buildings (Beveridge 2007).
Table 2-20 presents unit weights used to estimate material requirements for the LCI.
Table 2-20. Pipe Unit Weights
Pipe Type
Unit Weight (kg/m)
PVC, 2 inch
1.1
PVC, 1 inch
0.50
PEX, 1 inch
0.25
PEX, 0.5 inch
0.08
Acronyms: PEX - crosslinked polyethylene, PVC - polyvinyl chloride
2.6.3 Recycled Water Distribution Pumping Energy
Distribution of reuse water requires additional on-site pumping energy beyond what
would be necessary if potable water were used to make up for the distribution pressure of the
potable water supply. This analysis assumes a potable water distribution pressure, at the street, of
85 psi (Beveridge 2007). Following on-site treatment, water is placed in temporary storage to
await reuse at ambient pressure. Pumping scenarios assess the differential pumping energy that is
required to distribute the two potential water sources.
2-30
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2—Life Cycle Inventory Methods
Four water use categories were considered to meet the buildings' total water demand
including: potable water, domestic hot water, indoor NPR water, and irrigation water. Building
and district scale reuse scenarios calculate potable water requirements by subtracting reuse
quantities presented in Table 2-18 from total indoor water use. Domestic hot water use
constitutes 33 percent of total potable water demand. We derived this estimate by dividing a
residential hot water demand of 17 gpd (Parker et al. 2015) by average residential indoor water
use (51 gpd). Required pumping energy was calculated for each source category using Equation
13 (Beveridge 2007). The supply pressure factors, Psupply andFstreet, do not apply to recycled
water.
Ppump ~ (.P.static Pdist P'min) — (^suppiy * — ^street)
Equation 13
Where:
Ppump — Required pumping pressure, in psi
Pstatic = Static differential pressure, based on building height, in psi
Fdist = Friction loss, in psi
Pmin = Minimum distribution pressure at the end of each zone, in psi
Psupply = Supply pressure of the potable water system, in psi
F street — Friction loss from the water main to the building, in psi
Pump energy was estimated assuming continual pump operation at the daily average
flowrate. A pump efficiency of 60 percent was assumed (Tarallo et al. 2015). Table 2-21 through
Table 2-26 list pumping energy requirements per cubic meter of water use and supporting
parameter values for each reuse scenario according to water use category. The highest energy
requirement is 0.51 kWh/m3 for indoor reuse water in the large mixed-use building. For the large
mixed-use building, potable water pumping requires 0.27 kWh/m3 due to the supply pressure of
the water distribution system. The four-story building does not require any pumping energy to
distribute potable water.
The net difference in pumping energy between the status-quo scenario (i.e. 100 percent
reliance on potable water use) and the building and district reuse scenarios was calculated using
the weighted average pump energy demand per cubic meter of water use. Weighting was based
on the fraction of water use in each category. The net increase in pumping energy required for
recycled water distribution is included in the LCI. The avoided centralized treatment and
distribution processes were used to assess the avoided pumping energy from the centralized
treatment facility to the building or district.
2-31
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2—Life Cycle Inventory Methods
Table 2-21. Reuse Water Pumping Calculations, Large Mixed-Use Building
Indoor -
Indoor -
Potable
Domestic Hot
Irrigation
Water -
Recycled
Recycled Water
Water
Water
Scenario Parameter
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Peak Flowrate (gpm)
17
34
30
19
15
10
64
160
Daily average flowrate (gpm)
4.8
9.4
8.4
5.3
4.2
2.7
1.2
3.0
Required pumping pressure
(psi)
160
160
86
86
86
86
42
42
Minimum pipe diameter,
inner (in)
1.2
1.7
1.6
1.2
1.1
0.9
2.3
3.6
Pumping energy requirement
(kW)
0.56
1.1
0.52
0.33
0.26
0.17
1.9
4.8
Pumping duration (hr/vr)
8,760
8,760
8,760
8,760
8,760
8,760
170
170
Electricity use (kWh/yr)
4,900
9,600
4,600
2,900
2,300
1,400
330
800
Electricity use (kWh/m3)
0.51
0.51
0.27
0.27
0.27
0.27
0.13
0.13
Fraction of building water use
26%
46%
45%
26%
22%
13%
7%
15%
Table 2-22. Reuse Water Pumping Calculations, Six-Story District Building
Indoor -
Recycled Water
Indoor -
Potable Water
Domestic Hot
Water
Irrigation Water -
Recycled"
Scenario Parameter
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Peak Flowrate (gpm)
5.7
11
9.8
6.2
4.9
1.6
130
320
Daily average flowrate (gpm)
1.6
3.1
2.7
1.7
1.4
0.86
42
42
Required pumping pressure
(psi)
80
80
4.8
4.8
4.8
4.8
3.3
5.1
Minimum pipe diameter, inner
(in)
0.68
0.95
0.89
0.71
0.63
0.36
3.3
5.1
Pumping energy requirement
(kW)
0.09
0.18
9.6E-
3
6.0E-3
4.8E-
3
3.0E-
3
3.9
9.6
Pumping duration (hr/vr)
8,760
8,760
8,760
8,760
8,760
8,760
170
170
Electricity use (kWli/yr)
800
1,600
84
53
42
26
660
1,600
Electricity use (kWMn3)
0.25
0.25
0.02
0.02
0.02
0.02
0.13
0.13
Fraction of building water use
28%
54%
48%
30%
24%
15%
n/aa
n/aa
a Irrigation water use applies to the whole district
Table 2-23. Reuse Water Pumping Calculations, Four-Story District Building
Indoor -
Recycled
Indoor -
Potable
Domestic Hot
Water
Water
Water
Scenario Parameter
Low
High
Low
High
Low
High
Reuse
Reuse
Reuse
Reuse
Reuse
Reuse
Peak flowrate (gpm)
3.6
7.0
6.2
3.9
3.1
0.98
Daily average flowrate (gpm)
0.99
1.9
1.7
1.1
0.86
0.54
Required pumping pressure (psi)
67
67
-
-
-
-
Minimum pipe diameter, inner (in)
0.54
0.76
0.71
0.56
0.50
0.28
Pumping energy requirement (kW)
0.05
0.09
-
-
-
-
2-32
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2—Life Cycle Inventory Methods
Table 2-23. Reuse Water Pumping Calculations, Four-Story District Building
Indoor -
Recycled
Indoor -
Potable
Domestic Hot
Water
Water
Water
Scenario Parameter
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Low
Reuse
High
Reuse
Pumping duration (hr/yr)
8,760
8,760
8,760
8,760
8,760
8,760
Electricity use (kWh/yr)
430
830
-
-
-
-
Electricity use (kWh/m3)
0.22
0.22
-
-
-
-
Fraction of building water use
28%
54%
48%
30%
24%
15%
Table 2-24. Potable Water Pumping Calculations, Large Mixed-Use Building
Indoor -
Recycled
Water
Indoor -
Potable
Water
Domestic Hot
Water
Irrigation
Water -
Recycled
Scenario Parameter
Low and High Reuse
Peak flowrate (gpm)
42
21
64
Daily average flowrate (gpm)
12
5.8
1.2
Required pumping pressure (psi)
86
86
-33
Minimum pipe diameter, inner (in)
1.8
1.3
2.3
Pumping energy requirement (kW)
None
0.65
0.22
-0.93
Pumping duration (hr/yr)
8,760
8,760
170
Electricity use (kWli/yr)
9,500
3,200
-
Electricity use (kWh/m3)
0.27
0.27
-
Fraction of building water use - Low Reuse
62%
31%
7%
Fraction of building water use - High Reuse
57%
28%
15%
Table 2-25. Potable Water Pumping Calculations, Six-Story District Building
Indoor -
Recycled
Water
Indoor -
Potable
Water
Domestic
Hot Water
Irrigation
Water -
Recycled
Scenario Parameter
Low and High Reuse
Peak flowrate (gpm)
None
45
22
n/aa
Daily average flowrate (gpm)
12
6.2
n/aa
Required pumping pressure (psi)
4.8
4.8
-
Minimum pipe diameter, inner (in)
1.9
1.3
n/aa
Pumping energy requirement (kW)
0.03
0.01
-
Pumping duration (hr/yr)
8,760
8,760
170
Electricity use (kWli/yr)
380
190
-
Electricity use (kWh/m3)
0.02
0.02
-
Fraction of district water use - Low Reuseb
33%
17%
7%
Fraction of district water use - High Reuseb
30%
15%
15%
a Quantity of irrigation water varies for the low and high reuse scenarios, but no pumping energy is
required due to sufficient supply pressure from the water delivery system.
b Values total 100% when added to four-story water use fractions in Table 2-26.
2-33
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2—Life Cycle Inventory Methods
Table 2-26. Potable Water Pumping Calculations, Four-Story District
Building3
Indoor -
Recycled
Water
Indoor -
Potable
Water
Domestic
Hot Water
Scenario Parameter
Low and High Reuse
Peak flowrate (gpm)
None
19
3.0
Daily average flowrate (gpm)
5.4
5.8
Required pumping pressure (psi)
-
-
Minimum pipe diameter, inner (in)
1.3
0.49
Pumping energy requirements (kW)
-
-
Pumping duration (hr/yr)
8,760
8,760
Electricity use (kWli/yr)
-
-
Electricity use (kWMn3)
-
-
Fraction of water use - Low Reuseb
29%
14%
Fraction of water use - High Reuseb
26%
13%
a Irrigation water is accounted for in Table 2-25.
b Values total 100% when added to six-story water use fractions in Table 2-25.
2.6.4 Displaced Potable Water
The impacts of drinking water production, which are displaced in this study for non-
potable uses, were derived from LCI data provided in Cashman et al. (2014a) since there was not
an existing LCI specific to the San Francisco drinking water treatment and delivery system
available for use in the model. The displaced potable water LCI model was adapted to operations
and conditions in San Francisco to the extent possible. The water treatment system is originally
based on the Greater Cincinnati Water Works (GCWW) Richard Miller Treatment Plant. The
data in the GCWW model was adjusted to reflect the potable water treatment system in San
Francisco (Presidio Trust 2016). The Hetch Hetchy Reservoir provides high quality source water
to the city of San Francisco that is delivered to the treatment facility through a gravity system.
The model includes source water acquisition, flocculation, sedimentation, conditioning,
conventional UV primary disinfection, fluoridation, and addition of sodium hypochlorite to
establish a residual. The system boundaries for drinking water include water losses during
distribution to the consumer and the distribution pipe network infrastructure. There is an
estimated 18.7 percent loss of potable water to the consumer during delivery and an additional
0.3 percent loss of fresh water during the treatment process (Cashman et al. 2014a). No water
loss was modeled for distribution of the recycled water at the building scale. Electricity
requirements for distribution of the displaced potable water are based on the median value of
literature sources (EPRI 1996; IAMU 2002; Lundie et al. 2004; Hutson et al. 2005; Carlson and
Walburger 2007; Lassaux et al. 2007; DeMonsabert et al. 2008; Maas 2009; Amores et al. 2013).
Water treatment and finished water distribution electricity demands were modeled using the
2016 California electrical grid mix (Table 1-5).
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2—Life Cycle Inventory Methods
2.6.5 Centralized Collection and WRRF Treatment
In all scenarios connected to the sewer, the solids/sludge from fine screening and
biological processes are sent to centralized WRRF treatment via a gravity collection system.
Blackwater treatment, via the centralized sewer, was considered to be outside of the system
boundary in the baseline graywater treatment scenarios. The impact of blackwater treatment is
incorporated in the system boundary in the Section 6.2 "Full Utilization of Treated Water"
sensitivity analysis and in the Section 6.4 "Annual Results" to allow direct comparison between
graywater and mixed wastewater treatment systems. The collection system infrastructure is based
on Cashman et al. (2014b). Centralized WWRF operations were modeled using the conventional
plug-flow activated sludge treatment process LCI from U.S. EPA (2018). This is similar to the
wastewater treatment process operations at San Francisco's two main WRRFs (SFWPS 2017a;
SFWPS 2018). Biogas produced from anaerobic digestion of wastewater solids is combusted in a
combined heat and power (CHP) system for energy recovery. The CHP system provides on-site
energy and heat to the WRRFs. The resulting sludge may be sent to landfill or used for beneficial
purposes such as composting or land application. Our model used the simplifying assumption
that all produced sludge is sent to landfill after dewatering. Treated effluent is discharged
directly into the Pacific Ocean. Because the effluent is released into a marine environment and
not an at-risk freshwater system, advanced nutrient removal technologies, which may increase
WRRF energy and chemical inputs, are not required. WRRF electricity demands were modeled
using the 2016 California electrical grid mix (Table 1-5).
2.7 District-Unsewered Scenario
Sensitivity results are generated for a scenario in which the district scale AeMBR
discharges no waste to the municipal WRRF. The main treatment processes and performance are
the same as those described elsewhere in Section 2. Solids removed from the AeMBR are
dewatered in a screw press, stored on-site and trucked to a windrow composting facility
approximately 130 km northeast of San Francisco. Finished compost was assumed to be
transported 100 km, and land applied to agricultural fields as a soil amendment, replacing
chemical fertilizer.
2.7.1 Dewatering - Screw Press
A screw press was selected as a low energy and low maintenance technology for
producing a dewatered cake ready for transport to composting. The unit processes 2.6 m3 of
waste activated sludge per day, with an influent solids' concentration of 13,200 mg/L. The screw
press produces a dewatered cake with 18 percent (w/w) solid concentration (Huber Technology
2018). The unit reduces sludge transport volume by approximately 94 percent. Liquid removed
from the sludge stream is returned to the AeMBR for reprocessing. Infrastructure estimates for
the screw press are based on a unit mass of 1,080 kg assuming all steel construction. Electricity
consumption for screw press operation is 20 kWh per dry short ton of solids processed (Huber
Technology 2018). Influent and effluent nitrogen and phosphorus concentrations in the sludge
stream are estimated using GPS-X™, and are linked to the composting unit process to estimate
emissions and avoided fertilizer quantities. A solids capture rate of 90 percent was assumed.
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2—Life Cycle Inventory Methods
2.7.2 Composting
Dewatered biosolids are trucked 130 km to a windrow composting facility in a
neighboring community. The composting process is intended to achieve an initial pile moisture
content of 55 percent and a C:N ratio of approximately 30:1. Nitrogen and phosphorus content of
the dried cake was estimated using GPS-X™. We assumed that carbon comprises 73 percent of
cake dry solids based on values reported for raw sludge (Maulini-Duran et al. 2013). Woodchips
and dry leaves are used as a supplemental organic material to increase the C:N ratio and decrease
moisture content. No shredding of dewatered biosolids cake is required prior to composting.
Windrows are turned regularly using a self-propelled compost turner. To be classified as
Class A biosolids it is necessary to maintain compost pile temperatures at 55°C for a minimum
period of 15 days with 5 turnings during this time (U.S. EPA 2002). It was assumed that compost
is left on-site for a total period of 14 to 16 weeks for curing with an additional two turnings
during this time. Finished compost is screened to ensure a uniform product. The inventory
assumes that 1.4 liters of diesel fuel are consumed for screening and compost turning per ton of
dry material composted. Miscellaneous electricity use was assessed assuming 0.13 kWh per dry
ton (ROU 2007).
Measured and estimated emissions of CH4 and N2O during the composting process range
widely within the published literature. Some authors indicate that no methane is released (U.S.
EPA 2006; ROU 2007), while others indicate that up to 2.5 percent of incoming carbon content
in the composting feedstock can be lost as methane during the composting process (SYLVIS
2011). The 2006 IPCC Guidelines for National GHG Inventories suggest that less than one
percent to over four percent of incoming carbon content can be released as methane. The
potential emission range for N2O indicates that between 0.5 and 5 percent of initial nitrogen
content will be released as N2O-N (IPCC 2006).
Other LCA work by the authors of this report has demonstrated that climate change
impact potential of WRRFs employing composting as a biosolids stabilization strategy is
sensitive to selection of compost emission factors (Morelli and Cashman 2017). This study uses
the average value reported across several studies, assuming that 0.78 and 2.1 percent of C and N
entering the compost facility are lost as CH4 and N2O, respectively (Hellmann et al. 1997;
Hellebrand 1998; Fukumoto et al. 2003; SYLVIS 2011; Maulini-Duran et al. 2013). The range of
results reported in the cited studies is similar to that suggested in IPCC guidelines. Ammonia
(NH3), non-methane volatile organic compounds (NMVOC), CO2 and carbon monoxide (CO)
emissions are also included in the inventory. Emission of CO2 does not contribute to climate
change potential as the carbon is biogenic in origin.
2.7.3 Compost Land Application
The LCI includes 100 km of transportation from the compost facility to farm fields where
it applied as a fertilizer and soil amendment. Table 2-27 lists specifications of the finished
compost. Nitrogen and phosphorus content of the compost was calculated by subtracting
emissions during composting from GPS-X™ output values for biosolid nutrient content. The
model estimates that approximately nine percent of initial cake nitrogen is lost as N2O and NH3
during composting.
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2—Life Cycle Inventory Methods
Table 2-27. Finished Compost Specifications
Parameter
Value
Unit
Total N
2.7
% of dry matter
Total P
0.69
% of dry matter
Total Ka
0.20
% of dry matter
a Potassium values is from (ROU 2007)
We assumed that 1.06 liters of diesel fuel are required to spread one ton of finished
compost (ROU 2007). Field emissions were based on a compost application that provides 110 kg
N/ha (98 lb N/acre) and 44 kg P20s/ha (40 lb P20s/acre) of plant available nutrient assuming a
fertilizer replacement value of 55 percent (Smith and Durham 2002; Rigby et al. 2016). The
fertilizer replacement value is based on the total quantity of mineralized nitrogen available over a
three-year period. Negligible additional mineralization typically occurs after three years when
biosolids are applied at typical agronomic rates (Rigby et al. 2016). The same fertilizer
replacement value was used for P2O5 as a proxy. Compost was assumed to replace urea, rock
phosphate, and potassium chloride avoiding the production of these fertilizers.
Field emissions of N2O, NH3, NO3, and P were estimated assuming that increased
quantities of N and P are applied to agricultural fields to achieve equivalent plant available
nutrients. The fertilizer replacement value was used to calculate the additional N and P
requirement if compost is used to replace chemical fertilizers. The methods used to estimate field
emissions are based on total nutrient application rates, and therefore lead to higher estimated
agricultural emissions as nutrient applications increase.
Table 2-28 lists the agricultural LCI emission factors calculated. N2O, NH3, and NO3
emissions were calculated using approaches adapted from the IPCC method (De Klein et al.
2006). Emissions of N2O include direct emissions due to fertilizer application and indirect
emissions from volatized and leached nitrogen. Indirect emissions associated with land
occupation for agricultural activities are equivalent regardless of fertilizer type and application
quantity, and are excluded from the analysis. Phosphorus and NOx emissions were based on
approaches outlined in an ecoinvent agricultural LCI report (Nemecek and Kagi 2007). Carbon
sequestration was estimated based on the BEAM model (The Biosolids Emissions Assessment
Model (BEAM) 2011), which indicates that 0.25 metric tons of CO2 are sequestered per dry
metric ton of compost land applied. The carbon sequestration credit was applied to the full
quantity of compost produced, as chemical fertilizers do not contain carbon.
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2—Life Cycle Inventory Methods
Table 2-28. Agricultural Emissions per Cubic Meter of Wastewater
Treated.
Emissions Species
Value
Units
Nitrous oxide
1.0E-4
kg N20/m3
Nitrogen oxides
4.5E-5
kg NOx/m3
Ammonia
1.1E-3
kg NHa/m3
Nitrate
6.1E-3
kg NOs/m3
Phosphorus, surface water
1.0E-4
kg P/m3
Phosphate, groundwater
3.4E-6
kg P/m3
Carbon, sequestration
-0.05
kg CO2 eq/m3
2.8 LCI Limitations, Data Quality & Appropriate Use
LCI information that falls outside of the system boundary was introduced and discussed
in Section 1.6. More general LCI limitations that readers should understand when interpreting
the data and findings are as follows:
• Transferability of Results. While this study is intended to inform decision-making
for treatment configurations of similar size and design, the data presented here relates
to the specific scenarios described, and should be considered carefully when applying
results and conclusions to work in other contexts that include:
o System scale: System scale can considerably affect impact and cost per unit
volume of wastewater treated. Results will not accurately reflect impact at
different scales.
o Building and district configuration: Several aspects of building and district
configuration impact LCI quantities and resulting LCA impacts. The split
between residential and office workers directly affects the split between
blackwater and graywater generation, subsequent treatment requirements, and
corresponding LCA impacts. Building and district configuration also directly
influences distribution and collection material and energy requirements reflected
in the developed LCI.
o Wastewater composition: Wastewater composition included in this study reflects
average municipal wastewater and a graywater source that includes laundry water.
In practice, residential and commercial/institutional sources produce wastewaters
of considerably varying strength depending on the breakdown of indoor water
uses and fixture selection (Dziegielewski et al. 2000; DeOreo et al. 2016).
o Centralized drinking water and wastewater treatment: Models for displaced
centralized drinking water treatment as well as centralized blackwater treatment
were adapted to be specific to San Francisco as described in Section 0 and 2.6.5.
Impacts for centralized treatment will vary depending on the local treatment
configurations. Displaced distribution of potable water is modeled according to
U.S. average kWh requirements and using the California electrical grid mix
(Table 1-5). Electrical grid impacts are dependent on the regional electricity
supply and will vary for different regions across the U.S. Impacts for distributing
2-38
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2—Life Cycle Inventory Methods
potable water will vary based on local topography and distance from the drinking
water treatment plant.
• Data Accuracy and Uncertainty. In a complex study with thousands of numeric
entries, the accuracy of the data and how it affects conclusions is truly a difficult
subject, and one that does not lend itself to standard error analysis techniques. The
reader should keep in mind the uncertainty associated with LCI data when
interpreting the results. Comparative conclusions should not be drawn based on small
differences in impact results.
• Process Management. WRRFs are complex facilities requiring skilled management
to achieve the level of effluent quality identified in this report as being required for
indoor NPR applications. In addition to achieving treatment goals, facility and
process management practices have the potential to dramatically alter the LCI and
associated environmental performance data detailed throughout this report. The
treatment process LCIs described in this work were developed with the intention of
selecting values that are both representative and conservative in the sense that they do
not drastically underestimate or overestimate the treatment potential of individual
technologies.
• Process Maturity and Optimization. All the treatment processes, particularly
AnMBRs and RVFWs, are yet to be widely deployed for the delivery of recycled
water for decentralized NPR applications. As such it is believed that opportunities for
optimization of process equipment performance and operational practice are
inevitable. Opportunities for cost reduction are also expected as scale appropriate
technologies and equipment standardization develop. This work is intended to guide
such developments by identifying opportunities to reduce system cost and
environmental impact, while improving or maintaining treatment performance.
Notable opportunities for optimization in equipment performance and process
operation include: AeMBR and AnMBR scour rate, RVFW recirculation rate, DHS
biogas recovery and ammonia removal, zeolite replacement rate and regeneration
efficiency, heat pump COP, and pump efficiency.
• Representativeness of Background LCI Data. Background processes are
representative of either U.S. average data (in the case of data from U.S. EPA LCI or
U.S. LCI) or European average (in the case of ecoinvent) data. In some cases,
European ecoinvent processes were used to represent U.S. inputs to the model (e.g.,
for chemical inputs) due to lack of available representative U.S. processes for these
inputs. The background data, however, met the criteria listed in the project quality
assurance project plan for completeness, representativeness, accuracy, and reliability.
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3—Life Cycle Cost Analysis Methods
3. LIFE CYCLE COST ANALYSIS METHODS
This section presents the methodology used to develop life cycle costs. Cost data was
collected and adjusted from several sources as described in Section 3.1. Basic LCCA methods
are described in Section 3.2. Section 3.3 describes unit process specific cost calculations.
3.1 LCCA Data Sources
Cost data were obtained from the following sources:
• CAPDETWorks™ Design & Costing Software;
• RS Means (2016);
• Manufacturer Cost Quotes (2017/18);
• Online vendor data (2017/18).
3.2 LCCA Methods
The LCCA uses NPV to consider capital costs and annual or otherwise periodic costs
associated with construction, operation, maintenance, and material replacement over a 30-year
time horizon. The goal of the LCCA is to compare the present value of several alternative
treatment options at the building scale. NPV results are also compared to the district scale for
unsewered versus sewered AeMBR treatment configurations for mixed wastewater. All costs are
expressed in 2016 dollars.
3.2.1 Total Capital Costs
Total capital costs include unit process costs, direct, and indirect costs. Unit process costs
were developed for each step in the treatment process and include purchased equipment and
installation. Direct costs pertain to the integration of individual unit processes within the larger
WRRF. Indirect costs include all other expenditures not typically considered a direct
construction expense, including professional services, profit, and contingency. Direct and
indirect costs were determined using cost factors applied to installed equipment cost. Equation
14 was used to calculated total capital cost.
Total Capital Cost = Unit Process Costs + Direct Costs + Indirect Costs
Equation 14
Where:
Total Capital Cost (2016 $) = Total capital costs
Unit Process Costs (2016 $) = Unit process equipment and installation cost
Direct Costs (2016 $) = Costs incurred as a direct result of WRRF integration
Indirect Costs (2016 $) = Costs incurred for professional services and miscellaneous
expenses
3-1
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3—Life Cycle Cost Analysis Methods
3.2.2 Unit Process Costs
The cost of purchased equipment was developed using sources listed in Section 3.1.
Section 3.3 describes specific data sources and estimation methods used for each unit process.
Unit process cost includes the cost associated with installation of purchased equipment. Detailed
cost data is provided in Appendix B.
3.2.3 Direct Costs
Direct costs include mobilization, site preparation, site electrical, yard piping,
instrumentation and control, and lab and administration building construction. Lab and
administration building costs were excluded from this analysis as all facilities were assumed to
be in the building basement or on existing grounds.
Table 3-1 lists the direct cost factors used for this project. The full list of direct costs
applies to newly constructed treatment processes. Equation 15 was used to calculate unit process
direct cost by applying direct cost factors to installed equipment cost. Direct costs account for
system integration and costs not directly associated with an individual unit process.
Direct Cost = Direct Cost Factor x Unit Process Cost
Equation 15
Where:
Direct Cost (2016 $) = Direct cost in excess of purchased equipment price
Direct Cost Factor (%) = Direct cost factor for each direct cost element, see Table 3-1
Unit Process Costs (2016 $) = Total unit process equipment and installation cost
Table 3-1. Direct Cost Factors
Direct Cost Elements
Direct Cost Factor (% of
Purchased Equipment Cost)
Mobilization
5%
Site Preparation
7%
Site Electrical
15%
Yard Piping
10%
Instrumentation and Control
8%
Lab and Administration Building
n/a
Note: Adapted from Hydromantis (2014)
3.2.4 Indirect Costs
Indirect costs typically include land costs, legal costs, engineering design fee, inspection,
contingency, technical costs, interest during construction, and profit. Table 3-2 lists indirect cost
factors as reported by CAPDETWorks™ engineering cost estimation software. Additional land
cost was not assumed to be required beyond that associated with the initial building or district
3-2
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3—Life Cycle Cost Analysis Methods
development, and was excluded from the analysis. Total indirect costs are the sum of all
individual indirect costs as calculated in Equation 16.
Total Indirect Cost = Indirect Cost Factor x (Unit Process Costs +
Direct Cost) + Interest During Construction
Equation 16
Where:
Total Indirect Cost (2016 $) = Sum of indirect costs
Indirect Cost Factor (%) = Indirect cost factor for each indirect cost element, see Table
3-2
Unit Process Costs (2016 $) = Total unit process equipment and installation cost
Direct Cost (2016 $) = Total direct costs
Interest During Construction (2016 $) = Calculated in Equation 17
Table 3-2. Indirect Cost Factors
Indirect Cost Elements
Indirect Cost Factor
Miscellaneous Costs
5%
Legal Costs
2%
Engineering Design Fee
15%
Inspection Costs
2%
Contingency
10%
Technical
2%
Profit
15%
Note: Adapted from Hydromantis (2014) and AACEI (2016)
Equation 17 was used to assess interest during construction. A 1.7 percent interest rate
was used in the cost analysis, corresponding to the March 2017 interest rate offered by
California's Clean Water State Revolving Fund (CWB 2018).
Ic = ^\lJnit Process Costs + Direct Costs + Remaining Indirect Costs) x Tcp
x (t)
Equation 17
Where:
Ic (2016 $) = Interest paid during construction
Unit Process Costs (2016 $) = Total unit process equipment and installation cost
Direct Costs (2016 $) = Total direct costs
Remaining Indirect Costs (2014 $) = Indirect costs, including miscellaneous items, legal
costs, engineering design fee, inspection costs, contingency, and technical
Tcp = Construction period, 3 years based on CAPDETWorks™ default construction
period (Hydromantis 2014)
ir = Interest rate during construction, %
3-3
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3—Life Cycle Cost Analysis Methods
3.2.5 Total Annual Costs
Total annual cost includes operation and maintenance labor, materials, chemicals, and
energy purchases. These treatment systems were not assumed to produce any direct revenue. The
value of avoided utility costs is considered in Section 6.5. Total annual cost was calculated using
Equation 18. Material costs include material replacement, which was assessed using the expected
lifespan of plant components and installed equipment cost. Equipment that has an expected
lifespan of 30 years or greater was outside the temporal scope of the cost analysis.
Total Annual Cost = O&M Labor + Material Cost + Chemical Cost + Energy Cost
O&M Labor (2016 $/year) = Operations and maintenance labor costs required to operate
the WRRF, including administrative and laboratory labor
Materials Costs (2016 $/year) = Material and physical service costs (e.g. sludge disposal
fee) for operation and maintenance of the WRRF, including equipment replacement
Chemical Costs (2016 $/year) = Cost of chemicals required for WRRF operation (e.g.,
NaOCl, polymer)
Energy Costs (2016 $/year) = Cost of electricity required for WRRF operation
3.2.6 Net Present Value
NPV for each treatment system was calculated using Equation 19 (Fuller and Petersen
1996). A real discount rate of three percent was used in the cost analysis. The analysis does not
include escalation rates beyond the standard inflation rate for any cost categories except for
energy costs (Fuller and Petersen 1996). The LCCA was performed in constant (non-inflated)
dollars and uses a real discount rate corresponding to the constant dollar method. Electricity was
escalated according to 2017 annual energy escalation factors in the California region (Lavappa et
al. 2017). Energy escalation factors are applied by multiplying base year energy cost by the
escalation factor corresponding to the appropriate calendar year. Energy escalation factors are
included in Appendix Table A-3.
NPV (2016 $) = Net present value of all costs and revenues necessary to construct and
operate the WRRF
Costx = Cost in future year x
i (%) = Real discount rate
x = number of years in the future
Equation 18
Where:
Net Present Value
Equation 19
Where:
3-4
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3—Life Cycle Cost Analysis Methods
3.3 Unit Process Costs
The following sections describe data sources and cost estimation assumptions for
individual unit processes. Detailed capital costs for each system are listed in Appendix B. All
costs are presented in 2016 dollars unless otherwise noted.
Several of the process technologies evaluated are not yet widely deployed in commercial
applications. Cost estimation methods specific to the 0.025 to 0.05 MGD process scale were not
in all cases available, and there is uncertainty regarding how some of the unit costs will vary at
the building and district scale. Subsections within Section 3.3 make explicit note of such
instances, referring readers to discussion of specific concerns in Section A.2.3.
3.3.1 Full System Costs
Several costs were estimated based on the full treatment system, and are not assigned to
individual unit processes.
The labor rate was determined using the average of seven 2016 labor rates for
construction trades related to WRRF construction (U.S. DOL 2017). The seven labor categories
we used and their labor rates in 2016 $ were:
• First-Line Supervisor of Construction Trades: $34.38/hr
• Construction Laborers: $17.88/hr
• Construction Equipment Operators: $23.12/hr
• Electricians: $31.60/hr
• Pipe layers, Plumbers, Pipefitters, and Steamfitters: $22.16/hr
• Construction Trades Helpers: $15.91 /hr
• Other Construction and Related Workers: $21,91/hr
The average labor rate was $23.85/hr in 2016 $, exclusive of overhead and employee
benefits. We used a multiplier of 2.1 to estimate the loaded labor rate, resulting in an average
construction labor rate of approximately $50 per hour. This labor rate was applied to unit specific
construction, operation, and maintenance labor requirements as described throughout this
section.
Administrative labor cost was estimated on the basis of system flowrate using Equation
20 (Harris et al. 1982).
0 7829
Administrative Labor Hours (ALH) = 348.7 x (Qavg)
Equation 20
Where:
Administrative labor hours (ALH), in hours per year
Qavg = Average daily flowrate, in MGD
3-5
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3—Life Cycle Cost Analysis Methods
The administrative labor rate was calculated as a function of estimated administrative
labor hours and the labor rate using Equation 21 (Harris et al. 1982).
Administrative Labor Rate = 20.92 x ALH~03210 x OLR
Equation 21
Where:
Administrative labor rate, in salary dollars per hour equivalents
ALH = Administrative labor hours, in hours per year
OLR = Operator Labor Rate, $50 per hour
The laboratory labor rate was estimated to be 110 percent of the operations labor rate, or
$55 per hour. Laboratory labor hour requirements for each system was estimated using Equation
22. The relationship is expected to be valid for system flowrates of 0.01 to 20 MGD (Harris et al.
1982). Administrative and laboratory labor hours and associated annual cost for each treatment
system are listed in Table 3-3.
f n. 0.1515
Laboratory Labor Hours = 2450 x \Qavg)
Equation 22
Where:
Laboratory labor hours, in hours per year
Qavg = Average daily flowrate, in MGD
Table 3-3. Administration and Laboratory Costs
Scenario
Administrative
Labor Hours
Annual
Administration
Cost ($/yr)
Laboratory
Labor
Hours
Annual
Laboratory Cost
($/yr)
Building Scale, Graywater
14
6,200
1,300
72,000
Building Scale, Wastewater
19
7,800
1,400
77,000
District Scale, Graywater
23
8,800
1,400
80,000
District Scale, Wastewater
33
11,000
1,600
86,000
3.3.2 Fine Screening
Bare construction cost, including installation, of the fine screen systems was estimated
based on system flowrate using Equation 23 (Harris et al. 1982). Fine screening precedes
equalization in the RVFW treatment system. Design flowrate for RVFW systems was specified
assuming a peaking factor of 3.6, which corresponds to 15 percent of daily water use (i.e.
wastewater generation) occurring in a one hour period (Omaghomi et al. 2016). Screening capital
cost for other treatment systems was calculated using the average daily flowrate, as fine
3-6
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3—Life Cycle Cost Analysis Methods
screening takes place following flow equalization. Two identical units were specified, one unit is
reserved for standby use.
(CPl 2016\
Screening Bare Construction Cost = 40,000 x Q x I —— 1
\C< r ii Q77/
fCPhoi6\
/l977>
Equation 23
Where:
Screening bare construction cost, in 2016 $s
Q = design flowrate, in MGD
Consumer Price Index (CPI) was used to adjust system cost into present dollars
Annual material costs for maintenance were estimated as 2.5 percent of bare construction
cost. Maintenance labor cost was assumed to be equivalent to material cost. Operational labor
hours were estimated based on system flowrate using Equation 24. The equation is intended to be
valid for average system flowrates between 0 and 3 MGD (Harris et al. 1982).
Operation Labor Hours = 600 x Qavg°3382
Equation 24
Electricity consumption was estimated using Equation 1 in Section 2.1.
3.3.3 Equalization
Capital costs for flow equalization include concrete, rebar, and forming for basin
construction and aeration system costs. Concrete, rebar and forming requirements were based on
unit dimensions. Material and installation cost data for concrete, rebar and forming requirements
are from the RSMeans database (RSMeans 2016). Installed aeration system costs are based on
the approach developed for the CAPDETWorks™ software using Equation 25 through Equation
27. The cost of the aeration system includes the aerator, associated electrical/mechanical
equipment, and installation labor. Direct and indirect costs are applied to the sum of unit capital
costs.
(20.7 x HPa0 2686)
Floating Aerator Cost (FEC) = AC$0 x
100
Equation 25
Where:
Floating aerator cost, installed cost
ACso = Cost of 50 HP aerator, in 2016 $s
HPa = Horsepower of installed aerator
The cost of additional electrical and mechanical equipment was calculated using
Equation 26.
3-7
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3—Life Cycle Cost Analysis Methods
Ancillary Equipment Cost = FEC x (0.589 x HPa 0 1465)
Equation 26
Where:
FEC = Floating aerator cost (installed), 2016 $s
HPa = Horsepower of installed aerator
Installation labor hours are calculated using Equation 27.
Installation Labor = (0.633 x HPa) + 40
Equation 27
Where:
Installation labor, in hours
HPa = Horsepower of installed aerator
Maintenance material and labor costs for the aerator and tank were estimated as five and
1.5 percent of bare construction costs, respectively (City Of Alexandria 2015). Operational labor
cost was assumed to be equivalent to maintenance cost, due to a lack of alternative information.
3.3.4 Primary Clarification
Primary clarification precedes equalization in the RVFW treatment system. Two and
three 40 gpm slant plate clarifiers are required to handle the peak wastewater flowrate for the
building scale graywater and mixed wastewater systems, respectively. The capital cost of
purchased equipment was based on price estimates from the M.W. Watermark Company. The
slant-plate clarifiers arrive fully assembled. Twenty-five hours of installation labor was estimated
per clarifier. Maintenance material and labor cost for the clarifier tanks were estimated assuming
a 1.5 percent cost factor applied to installed equipment cost (City Of Alexandria 2015).
Operational labor cost was estimated assuming 350 hours per year for clarifiers with a surface
area of less than 1000 ft2 (Harris et al. 1982).
3.3.5 Sludge Pumping
Sludge is pumped out of the membrane bioreactors or primary clarification vessel in the
case of the RVFW system. Equation 28 was used to estimate pump cost. The equation is valid
over a pump flowrate range from 0 to 5000 gpm (Harris et al. 1982). For AeMBR systems,
sludge flowrate was estimated using GPS-X™. For the AnMBR systems, we used Equation 5 to
estimate daily sludge wasting. The cost estimate includes specification of a backup pump. A cost
factor of 2.5 was applied to pump equipment cost to estimate total pumping cost including
installation.
A five percent cost factor was applied to installed equipment cost to estimate
maintenance material and labor cost. No additional operational cost was estimated.
3-8
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3—Life Cycle Cost Analysis Methods
Installed Pumpx Cost = 2.5 x
2.93 x Pumpx
100
0.4404
3000
Equation 28
Where:
Pumpx Cost, cost of pump with x flowrate, in gpm (2016 $s)
Pumpx, pump flowrate in gpm
PC3000, cost of a standard 3000 gpm pump, $21,000 (2016 $s) (Hydromantis 2014)
3.3.6 AeMBR
We calculated tank capital cost based on unit dimensions presented in Table 2-1 and a
wall thickness of 0.30 m (1.0 foot) estimated using Equation 29. The design assumes two layers
of #5 rebar, 1.6 cm (5/8 inch), with a unit weight of 1.6 kg/meter (1.0 lb/foot). Material and
installation cost data for concrete, rebar and forming requirements are from the RSMeans
database (RSMeans 2016).
tw = Tank wall thickness, inches
SWD = Side-water depth, ft
The biological and scour air delivery system for each tank consists of two blowers,
distribution piping, swing arm headers, and fine and coarse diffusers. Each blower was sized to
provide 115 percent of aeration demand at the daily average flowrate, as estimated by GPS-X™.
Only one unit is expected to be required under typical operating conditions. Blower cost was
calculated using Equation 30 (Harris et al. 1982). The equation is valid over a blower capacity
range of 0 to 30,000 standard cubic feet per minute (scfm). Table 2-1 lists airflow requirements
for all wastewater treatment scenarios.
tw = 7.5 + (0.5 x SWD)
Equation 29
Where:
BlowerY Cost = BC-
3000
0.6169
\ (CPI2Q16\
J \cpi20J
Equation 30
Where:
BC3000 = Standard cost of 3000 scfm blower, $ 58,000 (Hydromantis 2014)
BCX = Blowerx capacity, in scfm
3-9
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3—Life Cycle Cost Analysis Methods
The cost of distribution piping was estimated based on the design capacity of the blowers
using Equation 31. The equation is intended to be valid over a design blower capacity range of
100 to 1000 scfm (Harris et al. 1982). Several systems have an aeration demand that is lower
than the minimum recommended airflow for this parametric cost estimation equation. Figure A-l
is included to justify the use of this estimation approach at lower airflow rates.
Air Piping Cost, in 2016 $s
BCX = Design blowerx capacity, in scfm
Three swing arm headers are specified, one for each process train, to which fine and
coarse bubble diffusers are mounted to provide biological and scour airflow. Each swing arm
header is capable of handling a maximum airflow of 550 scfm, with an associated equipment
cost of $16,200 (Hydromantis 2014). Each swing arm header was estimated to require 25 hours
of installation labor, including diffuser installation. System cost for the swing arm headers is
consistent across the system scale and wastewater scenarios due to their rated airflow capacities.
We applied an additional 10 percent cost factor to swing arm and diffuser equipment price to
estimate air distribution ancillary cost.
We determined the number of diffusers required based on the installed blower capacity.
Biological air is delivered using two scfm fine bubble diffusers, at a cost of $59 per diffuser.
Scour air is delivered using 12 scfm coarse air diffusers, at a cost of $36 per diffuser
(Hydromantis 2014). We estimated membrane system cost using a cost factor of $80 per m2
($7.40 per ft2), based on membrane area requirements as summarized in Table 2-1. NaOCl for
membrane cleaning is purchased as a 15 percent solution, with a unit cost of $0.30 per kg
(Hydromantis 2014).
Permeate pump cost was estimated based on pump design flowrate, in gpm, using
Equation 28. A cost factor of 2.5 was applied to pump equipment cost to estimate total pumping
cost including installation. Two pumps were specified per process train, with one pump reserved
for standby use.
The material costs of system maintenance for the air distribution and membrane systems
were estimated using Equation 32. The equation estimates a cost factor that was then applied to
total bare construction cost of AeMBR infrastructure. Equation 32 was originally intended for
application to the air distribution system, swing-arm header, and diffuser infrastructure, but was
also applied to the membrane system in this analysis. The O&M material cost factors range
between eight and 10 percent of bare construction cost for the flowrates considered in this
analysis.
/C^2016\
\CP11 q77)
Air Piping Cost = 617.2 x (BCX)
1977
Equation 31
Where:
3-10
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3—Life Cycle Cost Analysis Methods
O&M Material Cost = 3.57 x Qavg °-2626-
Equation 32
Where:
O&M material cost, percent of bare capital cost
Qavg = Average daily flowrate, in MGD
We estimated maintenance material and labor cost for the pumps and process basins
assuming five and 1.5 percent of installed equipment costs, respectively (City Of Alexandria
2015). Operational and maintenance labor hours requirements for the MBR treatment system are
estimated as a function of design airflow using Equation 33 and Equation 34 (Harris et al. 1982).
For the building scale system, treating mixed wastewater these equations estimate a total,
average operational and maintenance labor requirement of approximately 1.4 hours per day. We
apply a labor rate of $50 per hour to estimate cost.
Operation Labor Hours = 62.36 x CFMD03972
Equation 33
Maintenance Labor Hours = 22.82 x CFMD°-4379
Equation 34
Where:
Operation and maintenance labor hours, in hours per year
CFMd = Airflow at average operating conditions, in scfm
3.3.7 AnMBR
We calculated anaerobic reactor tank capital cost based on unit dimensions presented in
Table 2-3 and Equation 35 (Harris et al. 1982). Tank wall thickness (tw) was calculated using
Equation 29.
Vcon = (0.275 x (SWD + 4.5) x Dtank x tw)/35.3
Equation 35
Where:
Vcon = Volume of tank concrete, m3
Dtank = Tank diameter, ft
tw = Tank wall thickness, inches
SWD = Side-water depth, ft
Effluent from the anaerobic tank flows into one of three external tanks for membrane
filtration. Capital cost of the membrane tanks was estimated using the dimensions listed in Table
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3—Life Cycle Cost Analysis Methods
2-3 and an assumed wall and slab thickness of 0.23 m (9 in) and 0.3 m (1 ft), respectively. The
design includes two layers of #5 rebar, 1.6 cm (5/8 inch), with a unit weight of 1.6 kg/meter (1.0
lb/foot). Material and installation cost data for concrete, rebar, and forming requirements are
from the RSMeans database (RSMeans 2016). Piping requirements for the anaerobic reactor are
estimated based on tank sidewater depth and diameter. Piping requirements for the membrane
tank are based on tank dimensions and the pipe network configuration for G.E's Z-MOD
LeapMBR system (Suez 2017a). Pipe material and installation cost are from the RSMeans
database (RSMeans 2016). Minor piping cost was estimated to be 25 percent of major piping
cost (Harris et al. 1982).
Cost of the membrane system was estimated using a cost factor of $79.70 per m2 ($7.40
per ft2), based on membrane area requirements as summarized in Table 2-3. NaOCl for
membrane cleaning is purchased as a 15 percent solution, with a unit cost of $0.30 per kg
(Hydromantis 2014).
Mechanical mixers were sized as described in Section 2.3, rounding up estimated
horsepower to the nearest whole number. One backup mixer was specified. Permeate pump cost
was estimated based on pump design flowrate, in gpm, using Equation 28. A cost factor of 2.5
was used to estimate total mechanical equipment cost including installation. Two pumps were
specified per process train, with one pump reserved for standby use. Blower size (for biogas
scouring) and installed capital cost were calculated using Appendix Equation A-3 and Equation
30, respectively, applying a 100 percent cost factor to account for equipment installation.
The anaerobic reactor is equipped with a floating cover for gas storage. The
CAPDETWorks™ floating cover cost estimation approach is presented in Equation 36. The
equation is recommended for application to systems with a tank diameter of between 30 and 70
ft, and was used to estimate the capital cost of a 30 foot floating cover. A straightline approach to
cost estimation was then applied to approximate floating cover cost for the mixed wastewater
and graywater treatment systems, as it is expected to yield a better cost estimate for tanks
between 10 and 30 feet in diameter, see Appendix A.l, Figure A-3 for further detail. A 23%
ancillary material cost was applied to the cover cost estimated using Equation 36. Labor hours
required for floating cover installation were estimated based on cover diameter (Harris et al.
1982).
Cover Cost = Cost7Qft x (0.14 x lO^°0122xDtanfe^)
Equation 36
Where:
Cost70ft = Cost of a 70 ft diameter floating cover, $280,000 (2016 $s)
Dtank = Tank diameter, feet
The anaerobic reactor and permeate methane recovery system require gas safety
equipment that includes pressure relief valves, flame traps, pressure and gas gauges, and a flare.
Gas safety equipment cost was estimated using Equation 37. Installation cost was estimated to be
90 percent of equipment capital cost (Harris et al. 1982). CAPDETWorks™ Engineering Design
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3—Life Cycle Cost Analysis Methods
& Costing software recommends 2" gas safety piping for systems with tank diameter less than 30
feet.
Safety Equipment Cost = Cost2in (0.675 + (0.1625 * Dp)
Equation 37
Where:
Cost2in = Cost of a 2 inch gas safety system, $28,000 (2016 $s)
Dp = Diameter of gas safety piping, 2 inches
Maintenance material cost factors for the anaerobic reactor, membrane tanks, and biogas
recirculation and safety systems are calculated using Equation 32. Maintenance material costs for
pumps and mixers are estimated using a 2.5 percent cost factor. Operation and maintenance
hours are estimated as a function of the biogas recirculation rate using Equation 33 and Equation
34.
3.3.7.1 Downflow Hanging Sponge Reactor
The DHS treatment process consists of first and second stage reaction vessels. Capital
cost for the tanks was based on unit dimensions presented in Table 2-5 and an assumed wall
thickness of 0.24 m (9.5 in). The design assumes two layers of #5 rebar, 1.6 cm (5/8 inch), with a
unit weight of 1.6 kg/meter (1.0 lb/foot). The tanks are closed on top with a concrete lid.
Material and installation cost data for concrete, rebar, and forming requirements are from the
RSMeans database (RSMeans 2016).
Forty-four percent of the internal volume of each tank is occupied by hanging sheets of
polyurethane sponge with a unit cost of 325 $/cubic meter (Alibaba 2018b). A 200 percent
installation labor and ancillary material cost factor was applied to the material cost of the bulk
polyurethane sponge. Lifespan of the sponge is assumed to be 10 years, using the lifespan of
filtration membrane as a proxy value.
The DHS reactor uses forced aeration to accurately control the methane stripping and
oxidation rate. Blower size and installed capital cost were calculated using Appendix Equation
A-3 and Equation 30, respectively. No standard cost estimating procedures were found to
quantify the cost of air and water distribution piping networks. Identical pipe configurations,
consisting of a manifold and three distribution pipes, were assumed for both the air and water
distribution networks, based on unit dimensions listed in Table 2-5. Pipe diameter was
determined based on wastewater flowrate and a maximum flow velocity of 1.5 m/s (5 ft/sec).
Pipe, ancillary material, and installation labor cost was estimated using RSMeans (2016). A 32
percent cost factor was applied to the installed pipe cost to estimate minor additional material
costs, based on the cost factor provided for trickling filter water distribution systems (Harris et
al. 1982). Annual electricity cost was included for pumping and blower operation as described in
Section 2.3.3.2.
Operation and maintenance labor hours were estimated using Equation 38 and Equation
39, which are intended for trickling filter systems with an average flowrate of less than one
3-13
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3—Life Cycle Cost Analysis Methods
MGD. A maintenance material cost factor of one percent is applied to installed equipment costs
for non-mechanical DHS infrastructure. Maintenance material cost for blowers was estimated
using a 2.5 percent cost factor.
Operation Labor = 128 x QaVg° 301
Equation 38
Maintenance Labor = 112 x Qav50'2430
Equation 39
Where:
Qavg = System flowrate, MGD
3.3 J.2 Zeolite Adsorption System
Capital costs for the zeolite adsorption system are based on CAPDETWorks™ modeling
approach for activated carbon adsorption. Vessel size based on the CAPDETWorks™ activated
carbon design approach was compared to that of the zeolite adsorption system to determine
applicability of the cost assessment approach. Vessel size estimated using the CAPDETWorks™
design approach is within one percent of the volume of the zeolite system. Cost estimation
Equation 40 through Equation 45 are originally intended to be applicable for a system flowrate
between 0.5 and 10 MGD. Justification of the applicability of the cost estimation approach to
smaller system flowrates is included in Appendix Section A.2.2.
Two parallel zeolite adsorption vessels are required to provide back-up capacity and to
maintain continuous operation during the two hour regeneration cycle. The cost of two stainless
steel vessels was estimated using Equation 40.
Vessel Cost = (133,000 x Qavg° S87) x (^2°16)
\Lii 11977/
Equation 40
Where:
Vessel Cost = Installed vessel cost, 2016 $s
Qavg = System flowrate
CPI is used to adjust system cost into present dollars
Feed pump, piping, wet well, and dry well cost for the zeolite system was estimated using
Equation 41.
3-14
-------
3—Life Cycle Cost Analysis Methods
Feed System Cost = (35,500 x QaVg°'6) x (rp,2°16)
\C< r ^1977/
Equation 41
Where:
Feed system cost = Installed feed system cost, 2016 $s
Qavg = System flowrate
CPI is used to adjust system cost into present dollars
The carbon adsorption system includes a cost estimation equation for a backwashing
system. Backwashing system unit cost estimated in Equation 42 was used as a proxy for the
equipment required to recirculate zeolite regeneration fluid. The carbon adsorption backwash
flowrate per unit area of media bed is approximately three times greater than the flowrate of
NaCl and NaOH regeneration fluid. The original equation showed that for every tripling of
flowrate, system cost increases by approximately 52 percent. Therefore, a factor of 1.5 was
included in Equation 42 to account for the difference in flowrate between the backwash and
regeneration systems.
Regeneration System Cost = (30'00° *Qavg ) x ^2016^
Equation 42
Where:
Regeneration system cost = Installed regeneration system cost, 2016 $s
Qavg = System flowrate
CPI is used to adjust system cost into present dollars
The carbon handling system used for activated carbon regeneration was used to estimate
the cost of similar system requirements for zeolite removal and disposal following 10
regeneration cycles. System cost includes piping, valves, fittings, spent media storage, wet well,
dry well, eductors, and eductor pumps. The eductor system is used for pneumatic conveyance of
the spent media, being suitable for both granular zeolite and activated carbon conveyance.
System cost was estimated using Equation 43.
Zeolite Handling System Cost = (19,600 x Qavg0'28) x (rp.2°16)
\C< r ^1977/
Equation 43
Where:
Zeolite handling system cost = Installed handling system cost, 2016 $s
Qavg = System flowrate
CPI is used to adjust system cost into present dollars
3-15
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3—Life Cycle Cost Analysis Methods
Operation and maintenance labor hour requirement were estimated using Equation 44.
The mixed wastewater and graywater DHS systems require an estimated 150 and 122 annual
O&M labor hours.
0&.M Labor Hours = 860 x Qavg0,473
Equation 44
Where:
O&M Labor, in hours
Qavg = Average system flowrate, in MGD
Maintenance material cost was estimated using Equation 45, which yields a maintenance
cost factor of 1.7 and 1.6 percent of installed equipment cost for the graywater and mixed
wastewater systems, respectively.
Material Cost Factor = 0.55 — 0.664 log10 Qavg
Equation 45
Where:
Material cost factor, as a percent of installed capital cost
Qavg = Average system flowrate, in MGD
3.3.8 RVFW
We estimated material requirements for the wetland beds based on dimensions and
construction materials described in Section 2.4. Capital cost for the RVFW beds include
concrete, rebar, form material, HDPE piping, and wetland media. All bed piping is 5.8 inches
(inner diameter). Steel grating is used to support the wetland media, which includes a layer of
crushed limestone, gravel and wood chips. RVFW bed and media costs for materials and
installation were drawn from the RSMeans database (RSMeans 2016).
Recirculation pump cost was estimated based on pump design flowrate, in gpm, using
Equation 28. A cost factor of 2.5 was applied to pump equipment cost to estimate total pumping
cost including installation. Two pumps were specified per bed, with one pump reserved for
standby use. The equation is valid over a pump flowrate range from 0 to 5000 gpm (Harris et al.
1982).
Operation and maintenance labor cost was estimated assuming $100 per square meter of
wetland area (Gross et al. 2007a). We estimated maintenance material and labor cost for the
recirculation pumps using a cost factor of five percent of installed equipment costs.
Effluent is processed in batches, and requires pumping back to the building basement and
temporary storage following RVFW treatment and preceding the disinfection step. Multiple
3-16
-------
3—Life Cycle Cost Analysis Methods
5,000 gallon HDPE tanks are used for RVFW effluent storage. Three tanks, or 15,000 gallons, of
storage capacity are required for the building scale, mixed wastewater scenario. Two tanks are
required for the building scale, gray water scenario. The tanks come fully assembled. A 100
percent cost factor was applied to tank cost as an estimate of installation and ancillary equipment
cost.
Electricity cost for recirculation and pumping to the storage tanks was included in the
analysis. The cost of earthwork was not considered, and assumed to be incidental to construction
of other building and landscaping requirements. Inter-unit piping and associated instrumentation
and control costs were assessed using the direct and indirect cost factors, Sections 3.2.3 and
3.2.4.
3.3.9 Building & District Reuse
Building or district wastewater reuse requires additional constructions costs associated
with installation of the recycled water pipe network, plus a separate graywater collection system
for the graywater scenario. We estimated capital cost of these two additional plumbing networks
based on the pipe network descriptions provided in Section 2.6.2. The RSMeans database
(RSMeans 2016) provided pipe, fitting, and installation costs for PVC riser and mainline piping.
PEX pipe material cost was also available in the (RSMeans 2016). We used a 400 percent cost
factor applied to PEX pipe material cost (per meter) to estimate the cost of fittings and
installation. Even considering the high cost factor, the unit price of PEX pipe is only one third
that of PVC pipe of a similar diameter. PEX pipe is expected to have a lower unit cost due to a
reduction in the number of required fittings and a relative reduction in installation labor.
Additional pumping capacity is required to distribute reuse water within buildings and for
landscape irrigation. We estimated reuse and irrigation pump cost using Equation 28 and the
peak flowrates listed in Table 2-21 through Table 2-23. The net reduction in potable water pump
cost was subtracted from the cost of reuse and irrigation pumps to estimate the net increase in
pump cost attributable to water reuse. Booster pump cost for potable water distribution was
estimated based on pump power requirements listed in Table 2-21 through Table 2-26. We used
the retail price of Berkeley® High-Pressure Booster pumps to estimate equipment cost.
Installation and ancillary material cost for pump installation was estimated by applying a 150
percent cost factor to pump equipment cost.
We applied an additional 50 percent cost factor to installed pipe and pump costs to
estimate the cost of ancillary material and installation associated with graywater and reuse piping
networks. These costs are expected to include pump control systems, pressure reducing valves,
system venting, and additional fittings.
A five and 1.5 percent cost factor was applied to installed pump and piping cost,
respectively, to estimate annual maintenance material and labor cost. No additional operational
cost was included.
Section 6.5 compares the estimated life cycle cost of on-site treatment systems to avoided
utility fees. Avoided potable water service fees were estimated based on the 2017 residential and
commercial rate schedules for San Francisco's water service. Fees of $5.58 and $6.49 were
3-17
-------
3—Life Cycle Cost Analysis Methods
assessed per 1000 cubic foot (Ccf) of potable water provided to residential and commercial
users, respectively. Avoided wastewater service fees were estimated based on the 2017 multi-
family residential rate schedule for San Francisco's wastewater service, and were assessed at a
rate of $9.95 per 1000 cubic foot (Ccf) of wastewater discharged (SFWPS 2017b).
3.3.10 Ozone Disinfection
Capital costs for the ozone disinfection system include on-site construction of a concrete
contact basin, ozone generator, injection system and ancillary equipment and installation costs.
Installed equipment cost of an ozone generation system with a variable production capacity of up
to 1.8 kg/day (4 lb) costs approximately $26,500. Two units are specified for the RVFW system
treating mixed wastewater. An additional $19,000 is required for plumbing, electrical, and
monitoring equipment (Eagleton 1999). Material and installation costs for concrete, rebar and
forming for the ozone contact basin are from the RSMeans database (RSMeans 2016).
Estimation of ozone requirements are described in Section 2.5.1. Manufacturer
specifications for the Primozone® GM-series of ozone generators are used to estimate electricity
and liquid oxygen requirements associated with ozone generation for the appropriately sized
unit. A unit cost of liquid oxygen of 0.13 $/kg ($117/ton) was used to estimate annual material
cost (Carollo 2012). The outlet pressure of the Primozone® generators was assumed to be
sufficient for injection, such that additional electricity is not required.
Annual maintenance costs for the ozone generator are assessed on the basis of unit capital
cost, assuming three percent of installed equipment cost (City Of Alexandria 2015). The
structural maintenance cost factor of 1.5 percent was applied to the contact basin. Operational
labor cost was estimated assuming 550 labor hours per year (Hansen et al. 1979).
3.3.11 UV Disinfection
Capital costs of UV disinfection systems are based on pricing for commercially available
Sanitron® systems, produced by the Atlantic UV Corporation. The cost of UV system
installation and ancillary material requirements was estimated assuming 100 percent of
purchased equipment costs. The standard direct and indirect cost method described in Section 3.2
was used to estimate total capital cost. The annual cost of electricity was calculated based on
system specific electricity consumption and electricity unit costs per kWh of consumption
(Atlantic UV Corp. 2007). Annual maintenance cost, excluding bulb and quartz sleeve
replacement, was estimated as 1.5 percent of total capital cost (City Of Alexandria 2015). Bulb
and sleeve pricing specific to each Sanitron® unit were included assuming bulb and sleeve
lifespans of 10,000 hours and 5 years, respectively. The lifespan of UV bulbs is based on
manufacturer recommendations (Atlantic UV Corp. 2007). The lifespan of quartz sleeves is
specified in CAPDETWorks™. Lifespan of the UV housing is 30 years, as specified in
CAPDETWorks™. The operational labor requirement for the average daily flowrates of 10-20
gpm were estimated to be 24 hours per year.
3.3.12 Chlorine Disinfection
Chlorine disinfection is required for all treatment systems to provide residual disinfection
up to the point of use. Capital equipment costs for the metering pumps and injection system are
3-18
-------
3—Life Cycle Cost Analysis Methods
calculated using Equation 46 (Harris et al. 1982). Equipment includes the hypochlorite injection
system, chemical storage, flow recorders, booster pumps, and residual analyzers. The cost of
chlorination equipment is equivalent for systems with daily chlorine demand of between zero
and 50 pounds per day, which encompasses all the systems studied.
Chlorination Equipment = 4.33 x 2,700 x (cpi2016\
\CP11977J
Equation 46
Where:
Chlorination equipment = Installed equipment cost, 2016 $s
The chlorine contact basin is based on a pre-cast tank design, with a maximum capacity
of 1200 gallons. Material and installation costs for concrete, rebar and forming are drawn from
the RSMeans database (2016).
Operation and maintenance material cost was estimated using the average material and
supply cost factor, 6.5 percent, calculated across all treatment systems (see Appendix Section
A.2.4). The same cost factor was used because equipment cost is equivalent across systems.
Maintenance labor cost was estimated based on daily chlorine requirement, using Equation 47
(Harris etal. 1982).
Maintenance Labor Hours = 15.82 x CR0 3141
Equation 47
Where:
Maintenance labor hours, in hours per year
CR = Chemical requirement, in lb CI per day
Operation labor cost was estimated based on daily chlorine requirement, using Equation
48 (Harris et al. 1982).
Operation Labor Hours = 40.48 x CR0 5316
Equation 48
Where:
Operation labor hours, in hours per year
CR = Chemical requirement, in lb CI per day
NaOCl is purchased as a 15 percent solution, with a unit cost of $0.30 per kg
(Hydromantis 2014).
3-19
-------
3—Life Cycle Cost Analysis Methods
3.3.13 Thermal Recovery System
Heat pump cost and system integration was analyzed as part of a sensitivity analysis
looking at thermal recovery for building scale AeMBR treatment systems. Systems were sized
based on thermal recovery calculations presented in Section 2.2.1. Equipment costs for the
building scale graywater and mixed wastewater treatment systems were based on manufacturer
prices for 22 and 31 kW heat pumps (heating capacity), which are $13,800 and $17,500,
respectively. A cost factor of 2.5 was applied to heat pump equipment cost to estimate total
installed cost. Maintenance material and labor cost for the heat pump was estimated using a 5
percent cost factor applied to installed equipment cost.
3.3.14 District Unsewered
The district unsewered scenario includes the additional cost of on-site dewatering and
fees for disposal of dewatered biosolids. We specified two screw presses for solids dewatering.
Each unit is capable of processing between 3 and 5 kg of solids per hour. The uninstalled
equipment cost for each unit is $14,500 (Alibaba 2018a). The cost of ancillary equipment and
installation was estimated as 100 percent of screw press equipment cost. The 100 percent cost
factor is based on the cost factor provided for centrifuge dewatering, and is noted to include
conveyors, polymer feed system, pumps, and associated tankage (Harris et al. 1982). We
estimated annual polymer cost assuming 19 lb polymer per dry short ton of solids processed
(Macomber 2016). Approximately 14 short tons of solids are processed annually. Polymer unit
price is $1.30 per lb (Hydromantis 2014).
The screw press manufacturer Huber Technology indicates a maintenance requirement
for their Hub Q-Press® of less than 30 minutes per day (Macomber 2016). We estimate annual
operation labor cost assuming 20 minutes of operator time daily, or 122 hours per year.
Maintenance material and labor costs for the screw press were estimated using a 5 percent cost
factor, for general mechanical and electrical equipment, applied to bare construction cost.
Recology provides compost, trash, and recyclable collection and processing in San
Francisco. Recology charges a uniform price based on commercial bin size. The district scale
AeMBR produces approximately 1.1 m3 (1.5 yd3) of dewater solids per week. Recology charges
$446 for weekly pick-up of a 1.5 yd3 container. An additional surcharge of $0,091 per lb is
applied to 1.5 yd3 containers in excess of 205 kg (450 lb) (Recology 2017). The mass of 1.5 yd3
of biosolids is approximately 1,220 kg (2,700 lb), corresponding to a density of 1,070 kg/m3.
Total annual disposal cost was estimated to be $45,200. To incentivize composting and
recycling, Recology applies a diversion discount based on the volumetric fraction of waste that
avoids landfill disposal, however this was not applied in the cost analysis because of uncertainty
about the magnitude of the discount.
To ensure a fair comparison, we included estimated utility costs associated with disposal
of AeMBR waste activated sludge to the sanitary sewer for the district sewered scenario based
on the 2017 non-residential rate schedule for San Francisco's wastewater service (SFWPS
2017b). The non-residential rate schedule assesses cost based on the volume of wastewater
discharged plus surcharges per pound of COD, TSS and oil and grease sent to the sanitary sewer.
A fee of $6.45 was assessed per 1,000 cubic foot (Ccf) of wastewater discharged. Surcharges of
3-20
-------
3—Life Cycle Cost Analysis Methods
$0.46 and $0.87 per pound of COD and TSS were added based on output of the GPS-X™ model.
The district mixed wastewater scenario discharges 25,000 pounds of TSS and 31,000 pounds of
COD to the sanitary sewer annually. The district graywater scenario discharges 8,000 pounds of
both TSS and COD annually.
3-21
-------
4—Building Scale Mixed Wastewater Results
4. BUILDING SCALE MIXED WASTEWATER RESULTS
For the building scale, we investigated multiple mixed wastewater and gray water
treatment technologies including the AeMBR, AeMBR with thermal recovery, AnMBR, and
RVFW. As discussed in Section 1.4, two "reuse" scenarios are included, varying the building's
non-potable water demand. AnMBR results in Section 4.2 represent continuous biogas sparging
(baseline). Results for the AnMBR with intermittent biogas sparging are included in the Section
4.1 summary findings. For the AeMBR with thermal recovery, results in this section represent
use of a natural gas building hot water heater.
Section 4.1 presents summary LCA and LCCA results for the building scale mixed
wastewater treatment systems. Section 4.2 describes detailed GWP, CED and NPV results. Due
to a lack of available data, no uncertainty assessment was included in the analysis. Modest
differences in potential environmental impact should not be taken to indicate significant
differences in environmental impact when comparing treatment technologies.
4.1 Mixed Wastewater Summary Findings
Table 4-1 presents summary LCA, LCCA and LRV results for building scale systems
treating mixed wastewater. Figure 4-1 presents comparative LCA and LCCA results, relative to
the maximum impact result in each category. The AeMBR without thermal recovery
demonstrates the lowest environmental impact in five of eight impact categories. The RVFW is
the second best performing treatment system across the assessed LCA categories, but has the
highest life cycle cost. The AeMBR with thermal energy recovery achieves the lowest GWP and
fossil fuel depletion impacts, but shows increased environmental impacts in the other LCA
impact categories compared to the AeMBR system without thermal energy recovery. This is
attributable to the additional electricity required to recover the thermal energy. While natural gas
is displaced in the thermal energy recovery system, the net increase in electricity consumption
outweighs this benefit for specific impact categories such as acidification potential, particulate
matter formation potential, eutrophication potential, and smog formation potential. For the
AnMBR, results vary notably depending on whether biogas sparging is intermittent or
continuous. The AnMBR with continuous sparging demonstrates the highest environmental
impact results in six of eight impact categories. AnMBR systems with intermittent sparing have
the lowest CED, and are much more environmentally competitive with other treatment options,
but potentially result in poorer system performance as a result of increased membrane fouling.
Since the AeMBR is a current commercial technology and the alternative systems are still
emerging technologies, there are likely opportunities to optimize performance of the alternative
systems as they become commercialized.
Significant water use savings are seen for all systems. This is a primary benefit of
applying these NPR technologies. Since the overall water savings is driven almost exclusively by
the supply of recycled water, which does not vary across the compared technologies, detailed
results are not presented for the water use category. Water use savings include the direct quantity
of drinking water displaced as well as any drinking water that may have been lost during
distribution.
4-1
-------
4—Building Scale Mixed Wastewater Results
Table 4-1. Summary Integrated LCA, LCCA and LRV Results for Building Scale Configurations Treating Mixed Wastewater
(Per Cubic Meter Mixed Wastewater Treated)
Indicator
Unit
Mixed Wastewater Building
-Scale, Low Reuse"
AeMBR
AeMBR -
Thermal
Recoveryb
AnMBR -
Continuous
Sparging
AnMBR -
Intermittent
Sparging
RVFW
LCA and LCCA Results
Acidification Potential
kg SO2 eq
2.9E-4
1.8E-3
3.3E-3
2.7E-3
6.0E-4
Cumulative Energy Demand
MJ
4.9
12
8.7
2.5
7.5
Eutrophication Potential
kg N eq
3.1E-4
5.9E-4
6.3E-4
5.8E-4
4.7E-4
Fossil Depletion Potential
kg oil eq
0.06
-0.15
0.11
0.02
0.09
Global Wanning Potential
kg C02eq
0.36
0.04
0.64
0.38
0.31
Particulate Matter Formation Potential
kgPM2.5 eq
1.7E-5
1.6E-4
1.8E-4
1.4E-4
6.9E-5
Smog Formation Potential
kg 03 eq
8.8E-3
0.04
0.10
0.08
0.01
Water Use
m3 H^O
-0.43
-0.42
-0.42
-0.42
-0.42
Cost (NPV)
USD
$3,900,000
$4,100,000
$5,400,000
$5,300,000
$5,700,000
Total
LRV
Virus (LRT = 8.5)
9.0
9.0
9.0
9.0
9.5
Protozoa (LRT = 7.0)
9.0
9.0
9.0
9.0
7.0
Bacteria (LRT = 6.0)
11
11
11
11
13
a The low reuse scenario represents a building with high-efficiency appliances.
b Thermal recovery modeled as providing heat to a natural gas-based building hot water heater.
Acronyms: LRT = Log Reduction Target, LRV = Log Reduction Value, NPV = Net Present Value.
4-2
-------
4—Building Scale Mixed Wastewater Results
100%
50%
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H AeMBR - Thermal Recovery
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Figure Acronyms: AP - Acidification Potential, CED - Cumulative Energy Demand. EP - Eutrophication Potential. FDP - Fossil Depletion
Potential, GWP - Global Wanning Potential. NPV - Net Present Value, PMFP - Particulate Matter Formation Potential, SFP - Smog Formation
Potential. WU - Water Use
Figure 4-1. Comparative LCA and LCCA results for building scale configurations treating
mixed wastewater, presented relative to maximum results in each impact category.
4.2 Detailed Results by Impact Category
4.2.1 Global Warming Potential
Figure 4-2 displays GWP results for building scale treatment configurations treating
mixed wastewater for NPR. Table 4-2 lists the percent contribution of several process categories
to gross, positive GWP (i.e. calculated relative to non-negative impact).
The AnMBR demonstrates the highest net GWP impact among the presented
technologies. Continuous biogas sparging, post-treatment, and brine disposal negate the AnMBR
benefit of avoiding aeration energy. Biogas energy recovery, and associated avoided natural gas
combustion, reduces GWP by approximately 20 percent. The cumulative effect of post-treatment
processes indicate that the AnMBR system may be more practical for production of irrigation
4-3
-------
4—Building Scale Mixed Wastewater Results
water, where removing ammonia to achieve the chlorine residual required for indoor NPR would
not be necessary. Table 4-2 shows that electricity and chemical consumption and transportation
associated with post-treatment processes contribute strongly to GWP impact.
Thermal energy recovery considerably reduces GWP impact, exceeding the GWP
reduction associated with AnMBR biogas recovery. Thermal recovery was modeled as occurring
prior to wastewater treatment. Practical implementation of this sequence of unit processes needs
to be studied further. Implementing thermal recovery prior to the main biological treatment step
is likely less of an issue for gray water systems. Because thermal recovery occurs prior to
treatment, the unit could also theoretically be combined with the RVFW. Thermal recovery is not
likely to be a paired with the AnMBR, since the recovered thermal energy would reduce influent
temperatures below those recommended for psychrophilic reactor operation. The RVFW system
shows the lowest GWP results despite considerable pump energy use, infrastructure
requirements, and the need for ozone disinfection. Electricity and infrastructure impacts
contribute approximately 75 and 15 percent of positive GWP impact for the RVFW. GWP
results are sensitive to the amount of treated wastewater that can be reused, as demonstrated by
the magnitude of the water recycling credit. Avoidance of potable water production and
distribution reduces GWP impact by between 30 and 45 percent depending upon the system
considered. Net GWP benefits are seen for the AeMBR with thermal recov ery under the high
reuse scenario.
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Low High
Reuse Reuse
AeMBR
Low High
Reuse Reuse
AnMBR"
Low High
Reuse Reuse
RVFW
Low High
Reuse Reuse
AeMBR - Thermal
~ Biological Process
a Preliminary/Primary
~ Post-Treatment
ffl Chlorine Disinfection
E3UV Disinfection
~ Ozone Disinfection
¦ Water Recycling
^ Energy Recovery
0 Brine Disposal
¦ Net Impact
a AnMBR results modeled with continuous biogas sparging.
b Thermal recovery modeled as providing heat to a natural gas-based building hot water heater.
Figure 4-2. Global warming potential for building scale mixed wastewater treatment
technologies.
4-4
-------
4—Building Scale Mixed Wastewater Results
Table 4-2. Process Contributions to Global Warming Potential
for Building Scale Mixed Wastewater Treatment Technologies
Treatment
System3
Unit Process
Emissions
Chemicals
Electricity
Infrastructure
Energy Recovery
Waste Disposal
Recycled Water
Transport
AeMBR
34%
2%
58%
5%
0%
1%
-42%
0%
AnMBR
10%
27%
54%
8%
-22%
1%
-29%
24%
RVFW
6%
3%
74%
16%
0%
1%
-45%
0%
a Refers to AeMBR without thermal recovery and AnMBR with continuous sparging.
4.2.2 Cumulative Energy Demand
Figure 4-3 displays CED results for building scale treatment configurations treating
mixed wastewater for NPR. Table 4-3 lists the percent contribution of several process categories
to gross, positive CED (i.e. calculated relative to non-negative impact).
CED results are driven by electricity consumption, primarily associated with biological
processes, and the CED credit from potable water displacement. Potable water displacement
reduces net CED by between 25 and 45 percent depending on the system under consideration.
For the AnMBR treatment system, chemical use during post-treatment increases CED by 20
percent, while biogas recovery reduces CED by 20 percent. Figure 4-3 indicates that CED
increases when thermal recovery replaces hot water provided by a natural gas heater. This result
is counter-intuitive, but can be explained by the fact that the energy demand for heat pump
compressor and pump operation is greater than the thermal energy recovered when a life cycle
perspective is taken. Heat pump COPs are based on the electricity required to run a heat pump
compressor, not considering energy losses during electricity generation and distribution. This
same explanation accounts for the large reduction in CED that is realized when thermal recovery
replaces an electric hot water heater as seen in the sensitivity analysis in Section 6.3. The RVFW
CED results are higher than those seen for the AeMBR. The RVFW substitutes the space
intensity of more traditional constructed wetlands for the energy intensity of active circulation.
Ozone disinfection, only required for the RVFW treating mixed wastewater, also incrementally
increases the CED of this system.
4-5
-------
4—Building Scale Mixed Wastewater Results
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10.0
5.0
-5.0
-10.0
Low High
Reuse Reuse
AeMBR
Low High
Reuse Reuse
AnMBR"
Low High
Reuse Reuse
RVFW
~ Biological Process
l Chlorine Disinfection
i Water Recycling
Net Impact
l Preliminary/Primary
~ UV Disinfection
B Energy Recovery
Low High
Reuse Reuse
AeMBR - Thermal
Recovery11
~ Post-Treatment
~ Ozone Disinfection
0 Brine Disposal
a AnMBR results modeled with continuous biogas sparging.
b Thermal recovery modeled as providing heat to a natural gas-based building hot water heater.
Figure 4-3. Cumulative energy demand for building scale mixed wastewater treatment
technologies.
Table 4-3. Process Contributions to Cumulative Energy Demand
for Building Scale Mixed Wastewater Treatment Technologies
13
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AeMBR
0%
1%
96%
3%
0%
0%
-45%
0%
AnMBR
0%
21%
75%
3%
-21%
0%
-26%
0%
RVFW
0%
2%
88%
10%
0%
0%
-35%
0%
* Refers to AeMBR without thermal recovery and AnMBR with continuous sparging.
4.2.3 Life Cycle Costs
Figure 4-4 displays the NPV of building scale systems treating mixed wastewater.
Results in this figure are grouped according to treatment process designation. Figure 4-5 shows
the same results grouped by cost category. Baseline cost results are presented only for the low
reuse scenario, as system NPV does not vary considerably based on reuse potential. Section 6.5
4-6
-------
4—Building Scale Mixed Wastewater Results
presents additional results that compare estimates of system NPV against avoided utility costs
associated with reduced potable water consumption and wastewater treatment services that do
not figure directly into calculation of system NPV.
The AnMBR and RVFW systems have the highest life cycle costs. The AnMBR is more
expensive due to the additional post-treatment processes and increased reactor infrastructure
costs. The higher cost of the RVFW is due to additional pre-treatment infrastructure (e.g., slant
plate clarifier) and the inclusion of ozone treatment. The 'other' cost category in Figure 4-4
includes administration labor and the cost of laboratory testing, which is consistent across
treatment options.
The O&M labor cost category is the largest contributor to life cycle cost for all of the
treatment systems, followed by capital cost. Labor costs are greatest for the RVFW system due
to the addition of ozone disinfection and increased labor requirements of the larger capacity
equalization basin and fine screen. The relatively higher AnMBR material costs are attributable
to the greater membrane area of AnMBRs, relative to AeMBRs, due to their lower flux.
Additional material costs associated with the added AnMBR post-treatment processes also
contribute additional material costs.
$6,000,000
$5,000,000
vo $4,000,000
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> $3,000,000
Ph
Z
$2,000,000
$1,000,000
$0
AeMBR AnMBR3 RVFW AeMBR - Thermal
Recovery
¦ Preliminary/Primary
~ Biological Treatment
~ Post-Treatment
a Disinfection
¦ Building Reuse
¦ Other (b)
• Total
a AnMBR results modeled with continuous biogas sparging.
b Other = administrative costs.
Figure 4-4. Net present value for building scale mixed wastewater treatment technologies in
the low reuse scenario. Results shown by treatment process designation.
4-7
-------
4—Building Scale Mixed Wastewater Results
$6,000,000
$5,000,000
£ $4,000,000
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> $3,000,000
$2,000,000
$1,000,000
$0
$3,900,000
AeMBR
$5,400,000
AnMBR
$5,700,000
$4,100,000
RVFW AeMBR -
Thermal Recovery
¦ Energy
B Chemicals
~ Materials
¦ O&M Labor
~ Capital
¦ Interest During Construction
• Total
a AnMBR results modeled with continuous biogas sparging.
Figure 4-5. Net present value for building scale mixed wastewater treatment technologies in
the low reuse scenario. Results shown by cost category.
4-8
-------
5—Building Scale Graywater Results
5. BUILDING SCALE GRAYWATER RESULTS
The building scale source separated graywater system assumes the same overall
wastewater production as the building scale mixed wastewater systems, but the blackwater is
sent to a centralized WRRF instead of being treated on-site. Results shown here are presented per
cubic meter of graywater treated.
5.1 Graywater Summary Findings
Integrated summary LCA, LCCA and LRV results are shown for building scale systems
treating graywater in Table 5-1. Figure 5-1 presents comparative LCA and LCCA results,
relative to the maximum impact result in each category. Overall, net impacts are lower than those
seen for mixed wastewater. Because a larger percentage of the graywater can be reused, as
discussed in Section 2.6, a greater overall benefit is seen on a functional unit basis for
displacement of potable water. This is evident in the water use saving results in Table 5-1.
Many of the impact trends across technologies are similar to those discussed in the mixed
wastewater treatment findings with a number of exceptions. The increased benefits of avoided
potable water consumption cause impact results for the AeMBR to yield net environmental
benefits for acidification potential and particulate matter formation potential. The AeMBR with
thermal recovery yields net environmental benefits in GWP. Impact results for other treatment
technologies are reduced as well, but still lead to net impacts per cubic meter of treated
graywater. Results for the AeMBR with thermal recovery demonstrate improved environmental
performance relative to the other treatment options because of the higher graywater influent
temperature and the corresponding increase in energy recovery. When treating graywater, the
NPV of RVFW treatment is below that of the AnMBR treatment option due to a greater relative
reduction in RVFW infrastructure costs.
5-1
-------
5—Building Scale Gravwater Results
Table 5-1. Summary Integrated LCA, LCCA and LRT Results for Building scale Configurations Treating Graywater (Per
Cubic Meter Graywater Treated)
Graywater Building-Scale, Low Reuse"
Indicator
Unit
AeMBR
AeMBR -
Thermal
Recoveryb
AnMBR -
Continuous
Sparging
AnMBR -
Intermittent
Sparging
RVFW
Acidification Potential
kg SO2 eq
-2.2E-04
0.0011
0.0013
6.8E-04
1.1E-04
oe
Cumulative Energy Demand
MJ
1.49
7.24
7.17
0.84
4.27
3
5«
<
u
Eutrophication Potential
kg N eq
2.2E-04
4.9E-04
4.3E-04
3.8E-04
3.7E-04
Fossil Depletion Potential
kg oil eq
0.015
-0.23
0.091
0.0032
0.045
u
-J
Global Wanning Potential
kg C02eq
0.089
-0.29
0.34
0.083
0.11
¦a
Particulate Matter Formation Potential
kgPM2.5 eq
-2.2E-05
1.1E-04
7.6E-05
3.6E-05
3.2E-05
<
u
Smog Formation Potential
kg 03 eq
0.0012
0.032
0.037
0.025
0.0073
-J
Water Use
m3 HjO
-0.68
-0.68
-0.68
-0.68
-0.68
Cost (NPV)
USD
$4,000,000
$4,100,000
$5,000,000
$5,000,000
$4,700,000
%
-J
13
Virus (LRT = 6.0)
9.0
9.0
9.0
9.0
6.5
Protozoa (LRT = 4.5)
9.0
9.0
9.0
9.0
5.0
o
H
Bacteria (LRT = 3.5)
11
11
11
11
9.0
a The low reuse scenario represents a building with high-efficiency appliances.
b Thermal recovery modeled as providing heat to a natural gas-based building hot water heater.
Acronyms: LRT = Log Reduction Target, LRV = Log Reduction Value, NPV = Net Present Value.
5-2
-------
5—Building Scale Graywater Results
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100%
50%
0%
-50%
-100%
-150%
-200%
-250%
~ AeMBR ¦AeMBR - Thermal Recovery
~ AnMBR - Continuous Sparging ~ AnMBR - Intermittent Sparging
SRVFW
Figure Acronyms: AP - Acidification Potential. CED - Cumulative Energy Demand. EP - Eutrophicatioti Potential, FDP - Fossil Depletion
Potential. GWP - Global Warming Potential. NPV - Net Present Value, PMFP - Particulate Matter Formation Potential. SFP - Smog Formation
Potential. WU - Water Use
Figure 5-1. Comparative LCA and LCCA results for building scale configurations treating
graywater, presented relative to maximum results in each impact category.
5.2 Detailed Results by Impact Category
5.2.1 Global Warming Potential
Figure 5-2 displays GWP results for building scale treatment configurations handling
graywater for NPR. Water recycling benefits are consistent across treatment options, leading to
considerable reductions in GWP and GWP benefits in the high reuse scenario for the AeMBR
and RVFW treatment systems. These benefits indicate that the cumulative impact of the
decentralized treatment systems is less than that of the potable water systems that they replace.
The AnMBR with continuous membrane scouring generates net positive impact results for both
reuse scenarios. For all graywater systems, new collection infrastructure is required. This impact
is included in the "water recycling" stage in Figure 5-2. This increase in infrastructure has a
negligible effect on GWP results when compared to other operational requirements.
5-3
-------
5—Building Scale Gravwater Results
The lower strength of graywater, relative to mixed wastewater, leads to reduced energy
demand and process emissions for the AeMBR. For the AnMBR, lower wastewater strength
means that the system recovers less energy in the graywater scenario. The impact of brine
disposal is notably reduced for the AnMBR systems treating source separated graywater due to
the lower nitrogen content of this waste stream. Ozone disinfection is not required for the RVFW
treating source separated graywater, leading to a reduction in GWP. Greater thermal energy
recovery is possible with graywater systems due to the higher temperature of graywater
compared to mixed wastewater (30° C versus 23° C).
Low High Low High Low High Low High
Reuse Reuse Reuse Reuse Reuse Reuse Reuse Reuse
AeMBR - Thermal
AeMBR AnMBR3 RVFW Recoveryb
~ Biological Process ¦ Preliminary/Primary ~ Post-Treatment
m Chlorine Disinfection El UV Disinfection ~ Ozone Disinfection
¦ Water Recycling § Energy Recovery 0 Brine Disposal
¦ Net Impact
a AnMBR results modeled with continuous scouring.
b Thermal recovery modeled as providing heat to a natural gas-based building hot water heater.
Figure 5-2. Global warming potential for building scale graywater treatment technologies.
5.2.2 Cumulative Energy Demand
Figure 5-3 displays building scale CED results for systems treating source separated
graywater. The AeMBR has the lowest CED. The AeMBR with thermal energy recovery
demonstrates reduced CED, relative to the mixed wastewater scenario, that is nearly identical to
the net CED of the AnMBR treatment option. Because of the higher temperature of influent
wastewater, the graywater heat pump has an improved COP that requires less electricity
consumption for compressor operation per unit of thermal energy recovered. The CED increase
associated with the thermal energy recovery was described in Section 4.2.2. Thermal recovery in
the baseline results assumes the generated heat displaces a natural gas hot water heater. Section
6.3 presents results when recovered heat displaces operation of an electric-based hot water
heater. As with GWP, AnMBR systems recover less energy within the graywater scenario
5-4
-------
5—Building Scale Gravwater Results
leading to an increase in energy demand. Other CED results are similar to those discussed for
mixed wastewater.
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15.0
10.0
5.0
-5.0
-10.0
-15.0
Low High
Reuse Reuse
AeMBR
Low High
Reuse Reuse
AnMBR3
Low High
Reuse Reuse
RVFW
Low High
Reuse Reuse
AeMBR - Thermal
Recoveryb
~ Biological Process
H Chlorine Disinfection
¦ Water Recycling
¦ Net Impact
¦ Preliminary/Primary
El UV Disinfection
§ Energy Recovery
~ Post-Treatment
~ Ozone Disinfection
0 Brine Disposal
a AnMBR results modeled with continuous biogas sparging.
b Thermal recovery modeled as providing heat to a natural gas-based building hot water
Figure 5-3. Cumulative energy demand for building scale graywater treatment
technologies.
5.2.3 Life Cycle Costs
NPV results for building scale graywater treatment systems are shown in Figure 5-4 by
treatment process designation and in Figure 5-5 by cost category. Baseline cost results are
presented only for the low reuse scenario, as system NPV does not vary considerably based on
reuse potential. Section 6.5 presents additional results that compare estimates of system NPV
against avoided utility costs associated with reduced potable water consumption and wastewater
treatment services that don't figure directly into calculation of system NPV.
Total costs for the AeMBR graywater system increase slightly compared to the mixed
wastewater system. While the preliminary/primary and biological treatment costs are lower for
the graywater system, the cost of the additional graywater collection and reuse piping systems
increases the overall system cost. The capital cost of these pipe networks is equivalent and
amounts to approximately $310,000 dollars for pipes, fittings, and installation plus an additional
50 percent cost factor for ancillary equipment, materials, and labor. The building reuse system
also includes the cost of water distribution pumps and effluent storage tanks.
For the AnMBR and RVFW treatment systems the total system cost is lower for the
graywater system, as the reductions in unit process costs outweigh the cost of installing a
5-5
-------
5—Building Scale Gravwater Results
graywater collection system. Disinfection and post-treatment costs decrease considerably for the
RVFW and AnMBR treatment systems. The cost to build and operate the main biological
treatment processes is lower in the graywater scenario relative to other system costs for all
treatment options. Labor costs are slightly reduced in the graywater scenario both in magnitude,
and relative to capital cost.
$6,000,000
$5,000,000
$4,000,000
vjo
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Q .
hH
z
$2,000,000
$1,000,000
$5,000,000
$4,000,000
$0
$4,700,000
$4,100,000
AeMBR
AnMBR
RVFW
AeMBR -
Thermal Recovery
¦ Preliminary/Primary
~ Biological Treatment
~ Post-Treatment
H Disinfection
¦ Building Reuse
¦ Other (b)
• Total
a AnMBR results modeled with continuous biogas sparging.
b Other = Administrative costs.
Figure 5-4. Net present value for building scale graywater treatment technologies in the low
reuse scenario. Results shown by treatment process designation.
5-6
-------
5—Building Scale Gravwater Results
$6,000,000
$5,000,000
$5,000,000
$4,000,'
& $4,000,000 -
vo
§, $3,000,000
>
£ $2,000,000
$1,000,000
$0
AeMBR AnMBRa RVFW AeMBR -
Thermal Recovery
¦ Energy
n Chemicals
~ Materials
¦ O&M Labor
~ Capital
¦ Interest During Construction
• T otal
a AnMBR results modeled with continuous biogas sparging.
Figure 5-5. Net present value for building scale graywater treatment technologies in the low
reuse scenario. Results shown by cost category.
$4,700,000
5-7
-------
6—Sensitivity Analyses and Annual Results
6. SENSITIVITY ANALYSES AND ANNUAL RESULTS
Sensitivity analyses are presented at the building scale for modeling assumptions
associated with AnMBR biogas sparging, water reuse potential, and AeMBR thermal recovery
options. Results are shown for GWP, CED and NPV. Section 6.4 also includes results presented
on an annual basis. Section 6.5 compares baseline system NPV against the avoided utility costs
of investing in on-site NPR.
6.1 AnMBR Biogas Sparging
Results of the biogas sparging sensitivity analysis are depicted in Figure 6-1 for GWP, in
Figure 6-2 for CED, and in Figure 6-3 for NPV. Summaiy results for all impact categories are
presented for the low reuse scenario in Table 4-1 for mixed wastewater and in Table 5-1 for
graywater. Intermittent membrane sparging assumes a sparging duration of 15 minutes every 2
hours based on Feickert et al. (2012), as was modeled in Cashman et al. (2016). Intermittent
sparging reduces biological treatment GWP impact by 40 to 65 percent compared to continuous
sparging. CED is even more strongly influenced by AnMBR sparging frequency, being reduced
by more than 70 percent in all four scenarios. Under the mixed wastewater scenario, intermittent
biogas sparging results in an 80 percent decrease in reactor electricity demand compared to
continuous sparging. However, this decrease in electricity consumption could result in reduced
system performance with a potential increase in membrane fouling. Cost results are insensitive to
the sparging assumptions, since AnMBR NPV is not strongly influenced by electricity
consumption.
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at
o
u
ex
Figure 6-1. AnMBR biogas sparging global warming potential sensitivity analysis for the
treatment of mixed wastewater and graywater at the building scale.
[ '/////////sss S -sjjjS//////. J
Mixed Wastewater
Graywater
~ Biological Process ¦ Preliminary/Primary ~ Post-Treatment H Chlorine Disinfection
~ UV Disinfection ~ Ozone Disinfection ¦ Water Recycling ¦ Energy Recovery
a Brine Disposal ¦ Net Impact
Low High
Reuse Reuse
Continuous Sparging
Low High
Reuse Reuse
Intermittent Sparging
Low High
Reuse Reuse
Continuous Sparging
Low High
Reuse Reuse
Intermittent Sparging
6-1
-------
6—Sensitivity Analyses and Annual Results
Low High
Reuse Reuse
Continuous Sparging
Low High
Reuse Reuse
Intermittent Sparging
Mixed Wastewater
Low High
Reuse Reuse
Continuous Sparging
Low High
Reuse Reuse
Intermittent Sparging
Gravwater
~ Biological Process
~ UV Disinfection
h Brine Disposal
¦ Preliminary/Primary
~ Ozone Disinfection
• Net Impact
~ Post-Treatment
¦ Water Recycling
1 Chlorine Disinfection
l Energy Recovery
Figure 6-2. AnMBR biogas sparging cumulative energy demand sensitivity analysis for the
treatment of mixed wastewater and graywater at the building scale.
$6,000,000
$5,000,000
$4,000,000
$3,000,000
$2,000,000
$1,000,000
$0
$5,400,000
$5,300,000
$5,000,000
$5,000,000
»
—
¦
'WXMMWMA
WKKMM
Continuous
Sparging
Intermittent
Sparging
Continuous
Sparging
Intermittent
Sparging
1
Mixed Wastewater
1
1
Graywater
1
1
B Preliminary/Primary
~ Biological Treatment
~ Post-Treatment
¦ Disinfection
a Building Reuse
H Other (a)
• Total
a Other = administrative costs.
Figure 6-3. AnMBR biogas sparging net present value sensitivity analysis for the treatment
of mixed wastewater and graywater at the building scale.
6-2
-------
6—Sensitivity Analyses and Annual Results
6.2 Full Utilization of Treated Water
Full reuse of recycled water was only achieved in the high reuse graywater scenario.
Other scenarios, specifically for the mixed wastewater systems, are generally treating more water
than is currently demanded for NPR at the building-level. This sensitivity analysis considers a
theoretical scenario in which 100 percent of the treated water can be recycled (e.g., through
exporting to other buildings). We have also included centralized WRRF treatment of the
blackwater fraction for the graywater systems, to facilitate a more direct comparison of the
mixed wastewater and graywater configurations. Results of this analysis are shown in Figure 6-4
for GWP and in Figure 6-5 for CED.
The net impact differences between the graywater and mixed wastewater systems are
smaller in this sensitivity analysis than in previously presented results. While mixed wastewater
systems have greater operational impacts, they also have greater savings associated with the
increased volume of displaced potable water. When recycling all treated water, all systems result
in approximately neutral GWP impact, with most systems achieving small GWP benefits.
The thermal recovery system shows notable GWP benefits, especially when coupled with
an electric hot water heater. There is more thermal energy recovery possible with the mixed
wastewater systems (treats a larger volume of water). However, thermal recovery occurs prior to
biological treatment in our model and, therefore, may be more practical for graywater systems.
Figure 6-5 clearly shows the effect of hot water heater type on thermal recovery CED results.
The main benefit associated with on-site treatment of the full amount of wastewater
produced by a building is the potential water savings. Approximately 1.20 m3 of potable water
use can be saved per m3 of wastewater produced in the mixed wastewater scenarios. This result
is applicable to all technology configurations. More than one cubic meter of wastewater can be
saved because NPR displaces not only the same volume of potable water, but also displaces all
the potable water losses in the distribution system and any water losses at the centralized
drinking water treatment plant. Comparatively, graywater systems can displace up to 0.79 m3 of
potable water per m3 of wastewater produced. The system treating source separated graywater
does not displace potable water for the blackwater fraction treated at the municipal WRRF.
Inclusion of treatment of blackwater at the centralized WRRF within the study results for
graywater does not have a notable effect on the results shown in Figure 6-4 and Figure 6-5. As
discussed in Section 2.6.5, biogas produced from anaerobic digestion of wastewater solids at the
WRRFs in San Francisco is combusted in a CHP system for energy recovery, making these
centralized treatment configurations relatively low GWP and CED options.
6-3
-------
'§—Sensitivity Analyses and Annual Results
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6—Sensitivity Analyses and Annua! Results
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6—Sensitivity Analyses and Annual Results
6.3 Thermal Recovery Hot Water Heater
We evaluated the effect of thermal recovery on impact per m3 of treated wastewater for
the building scale AeMBR treatment system as part of a sensitivity analysis. Thermal recovery is
performed prior to wastewater treatment, and so it is expected that similar results can be applied
to the RVFW treatment system. Figure 6-6 displays thermal recovery hot water heater GWP
sensitivity analysis results. Thermal recovery benefits and burdens were evaluated for both
natural gas and electric hot water heaters. Figure 6-7 presents CED results for the same
scenarios.
Figure 6-6 shows that the inclusion of thermal recovery yields reductions in GWP for
both types of treated wastewater and electric and natural gas hot water heaters. The amount of
thermal energy recovered is not dependent on the quantity of wastewater that can be reused
within the building, and therefore the magnitude of the process's environment benefit is the same
for both reuse scenarios. Results for both GWP and CED show that avoiding the use of electric
hot water heaters yields a greater environmental benefit compared to a natural gas based water
heater, due to the lower relative environmental performance of an electric hot water heater
operated using electricity characteristic of the San Francisco electrical grid mix.
Figure 6-7 indicates that CED per m3 increases when thermal recovery replaces hot water
provided by a natural gas heater. This result is counter-intuitive, but can be explained by the fact
that the energy demand for heat pump compressor and pump operation is greater than the
thermal energy recovered when a life cycle perspective is taken. Heat pump COPs are based on
the electricity required to run a heat pump compressor, not considering energy losses during
electricity generation and distribution. This same explanation accounts for the large reduction in
CED that is realized when thermal recovery replaces an electric hot water heater.
These results are representative of the specific heat pump and hot water heater
specifications described in Section 2.2.1. Changes in system performance parameters or the
underlying electrical grid mix will affect the reported results.
6-6
-------
6—Sensitivity Analyses and Annual Results
1.0
0.5
-0.5
-2.0
Low High Low High
Reuse Reuse Reuse Reuse
Natural Gas Electric
Hot Water Heater
Mixed Wastewater
Low High
Reuse Reuse
Natural Gas
Hot Water Heater
Graywater
Low High
Reuse Reuse
Electric
E Biological Process
¦ Chlorine Disinfection
l Water Recycling
¦ Preliminary/Primary
~ UV Disinfection
1 Energy Recovery
~ Post-Treatment
~ Ozone Disinfection
i Brine Disposal
Figure 6-6. AeMBR - thermal recovery global warming potential sensitivity analysis for
the treatment of mixed wastewater and graywater at the building scale.
6-7
-------
6—Sensitivity Analyses and Annual Results
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20
10
-10
-20
-30
-40
-50
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Low High Low High
Reuse Reuse Reuse Reuse
Natural Gas Electric
Hot Water Heater
Mixed Wastewater
Low High Low High
Reuse Reuse Reuse Reuse
Natural Gas Electric
Hot Water Heater
Graywater
~ Biological Process
0 UV Disinfection
B Brine Disposal
H Preliminary/Primary
~ Ozone Disinfection
¦ Net Impact
~ Post-Treatment
¦ Water Recycling
i Chlorine Disinfection
1 Energy Recovery
Figure 6-7. AeMBR - thermal recovery cumulative energy demand sensitivity analysis for
the treatment of mixed wastewater and graywater at the building scale
6.4 Annual Results
GWP results are shown for the low reuse scenario on an annual basis in Table 6-1 by unit
process (i.e., treatment stage). Centralized WRRF treatment of blackwater is included in the
graywater results to allow for a fair comparison between the mixed wastewater and graywater
systems. As discussed in Section 2.6.5, the centralized WRRF modeled for San Francisco is
representative of a low-impact treatment system. The tables also include district level sewered
and unsewered scenarios. The quantity of water treated on-site is not consistent between
scenarios. Building scale systems reuse approximately 15,000 to 30,000 cubic meters of
wastewater annually in the low and high reuse scenarios, respectively. This volume
approximately doubles in the district scale scenario.
6-8
-------
6—Sensitivity Analyses and Annual Results
Table 6-1. Annual Global Warming Potential Results for Low Reuse Scenario by Treatment Stage for Mixed Wastewater
(WW) and Graywater (GW) Systems (kg CO2 eq./Year)
AeMBR
AnMBRc
AeMBR - Thermal
Energy Recovery
RVFW
Sewered
Unsewered
Sewered
Sewered
Sewered
Building
District
Building
Building
Building
Treatment Stage
WW
GW
WW
GW
WW
WW
GW
WW
GW
WW
GW
Fine Screening
1,400
1,100
2,100
1,500
2,100
1,400
1,100
1,400
1,100
1,400
1,000
Flow Equalization
1,500
1,100
2,900
1,800
2,900
1,500
1,100
1,500
1,100
2,800
2,100
Primary Clarification
620
350
Membrane Bioreactor Operation
16,000
6,800
30,000
13,000
30,000
14,000
8,500
16,000
6,800
MBR Infrastructure
730
510
1,300
880
1,400
1,600
1,200
730
510
Recirculating Vertical Flow Wetland Operation
6,700
4,300
Wetland Media
2,300
1,500
Recovery of Methane (Headspace and
Permeate)
-200
-20.0
Ammonia Adsorption
7,600
4,100
Ammonia Brine Disposal
7,900
1,200
Biogas Energy Recovery
-5,500
-2,200
Thermal Recovery
-11,000
-8,400
Ozone Treatment
3,200
0
UV Disinfection
190
160
490
490
490
190
150
190
160
490
490
Chlorination
1,100
920
1,400
1,300
1,400
1,700
1,100
1,100
920
890
820
Recycled Water Pumping and Piping
410
410
780
790
840
410
410
410
410
1,100
850
Displaced Potable Water Treatment and
Delivery
-8,800
-9,000
-18,000
-18,000
-18,000
-8,800
-9,000
-8,800
-9,000
-8,800
-9,000
Dewatering
480
Windrow Composting
12,000
Land Application of Compost
-920
Centralized Blackwater Treatmentb
1,300
2,700
1,300
1,300
1,300
Totals
13,000 3,300 21,000 4,500 33,000 22,000 8,900 1,500 -5,100 11,000 3,700
a Values are rounded to two significant figures.
b Included in graywater annual results only. Applies to blackwater portion such that the graywater and mixed wastewater scenarios treat the same overall volume of water.
Centralized treatment of sewered system sludge is also incorporated and reported in the operation treatment stage.
c AnMBR modeled with continuous sparging.
Acronyms: MBR - membrane bioreactor, RVFW - recirculating vertical flow wetland, UV - ultraviolet
6-9
-------
6—Sensitivity Analyses and Annual Results
Table 6-2. Annual Cumulative Energy Demand Results by Treatment Stage for Low Reuse Scenario for Mixed Wastewater
(WW) and Graywater (GW) Systems (MJ/Year)
Treatment Stage
AeMBR
AnMBRc
AeMBR - Thermal
Energy Recovery
RVFW
Sewered
Unsewered
Sewered
Sewered
Sewered
Building
District
Building
Building
Building
WW
GW
WW
GW
WW
WW
GW
WW
GW
WW
GW
Fine Screening
28,000
23,000
39,000
31,000
39,000
28,000
23,000
28,000
23,000
28,000
23,000
Flow Equalization
33,000
23,000
65,000
40,000
65,000
33,000
23,000
33,000
23,000
63,000
47,000
Primary Clarification
2,900
3,000
Membrane Bioreactor Operation
210,000
90,000
380,000
180,000
380,000
270,000
170,000
210,000
90,000
MBR Infrastructure
4,400
3,000
8,200
5,400
8,600
11,000
7,200
4,400
3,000
Recirculating Vertical Flow Wetland
Operation
140,000
89,000
Wetland Media
30,000
20,000
Recovery of Methane (Headspace and
Permeate)
-5,900
-2,300
Ammonia Adsorption
140,000
74,000
Ammonia Brine Disposal
15,000
2,300
Biogas Energy Recovery
-90,000
-37,000
Thermal Recovery
250,000
130,000
Ozone Treatment
75,000
0
UV Disinfection
4,500
3,700
12,000
12,000
12,000
4,500
3,700
4,500
3,700
12,000
12,000
Chlorination
20,000
19,000
24,000
21,000
24,000
26,000
21,000
20,000
19,000
19,000
18,000
Recycled Water Pumping and Piping
11,000
11,000
21,000
21,000
21,000
11,000
11,000
11,000
11,000
28,000
22,000
Displaced Potable Water Treatment and
Delivery
-140,000
-140,000
-280,000
-280,000
-280,000
-140,000
-140,000
-140,000
-140,000
-140,000
-140,000
Dewatering
6,300
Windrow Composting
14,000
Tand Application of Compost
600
Centralized Blackwater Treatmentb
-5,500
-12,000
-5,500
-5,500
-5,500
Totals
170,000
27,000
270,000
18,000
290,000
300,000
150,000
420,000
160,000
260,000
89,000
a Values rounded to two significant figures
b Included in graywater annual results only. Applies to blackwater portion such that the graywater and mixed wastewater scenarios treat the same overall volume of water. Centralized
treatment of sewered system sludge is also incorporated and reported in the operation treatment stage.
c AnMBR modeled with continuous sparging.
Acronyms: MBR - membrane bioreactor, RVFW - recirculating vertical flow wetland, UV - ultraviolet
6-10
-------
6—Sensitivity Analyses and Annual Results
6.5 Life Cycle Cost Results Considering Avoided Utility Costs
Figure 6-8 and Figure 6-9 compare baseline system NPV against utility costs avoided as a
result of on-site wastewater treatment for the mixed wastewater and graywater treatment
systems. Avoided utility fees do not directly affect system NPV, but do provide a useful estimate
of alternative fees for equivalent service. Avoided utility fees include wastewater and potable
water cost estimated over the 30 year analysis period, expressed as NPV in 2016 dollars. Section
3.3.9 describes the utility rates used in the analysis. The magnitude of avoided utility costs is not
sufficient to cover the cost of investment in on-site wastewater treatment, but do considerably
reduce the relative increase in long-term expenditure for water and wastewater services for
systems treating both mixed wastewater and graywater. Comparison of results for the low and
high reuse scenarios show that while system NPV remains relatively consistent, the delivered
value of water and wastewater services, as estimated by avoided utility costs, increases with NPR
demand. Additional utility savings are possible if meter size is reduced as a result of installation
of on-site treatment.
$6,000,000
$5,000,000
$4,000,000
^ $3,000,000
$2,000,000
o
PLh
2
$5.4M
$3.9M
$1,000,000
$0
$-1,000,000
$-2,000,000
$-3,000,000
/
<5-
•4
$4.1M
$-2.4M Np
.0°
Low Reuse
$5.4M $5'7M
$4M
r
$4.1M
$-2.8M
^ od
p ¦#
,oN
High Reuse
¦ Preliminary/Primary ~ Biological Treatment ~ Post-Treatment H Disinfection
¦ Building Reuse B Other (b) s Avoided Utility Cost • Total
a AnMBR results modeled with continuous biogas sparging.
b Other = administrative costs.
Figure 6-8. Net present value for building scale mixed wastewater treatment technologies in
the low reuse scenario compared to avoided utility fees. Results shown by treatment
process designation.
6-11
-------
6—Sensitivity Analyses and Annual Results
$6,000,000
$5,000,000
$4,000,000
S? $3,000,000
S $2,000,000
> $1,000,000
Z $0
$-1,000,000
$-2,000,000
$-3,000,000
$5.1M
$4M
h
m
$4.1M $4.1M
¦
$4.2M
M
1
—
m
m
1
1
M
mm
¦
j
L
m
¦
m
u
¦
¦
$-1.6M
,
x°
c
e> .
-------
7—District Scale Mixed Wastewater and Gravwater Results
7. DISTRICT SCALE MIXED WASTEWATER AND GRAYWATER RESULTS
District scale LCA and LCCA results were generated for the AeMBR treatment process.
The district represents a hypothetical city block in San Francisco with mixed-use four and six-
story buildings. For the district scale mixed wastewater scenario, we considered a sewered
scenario where process solids are disposed of in the municipal sewer system and a scenario in
which the district is not connected to a sewer (i.e., "unsewered") and handles its solids with on-
site dewatering and off-site windrow composting followed by land application.
7.1 Mixed Wastewater Summary Findings
Table 7-1 displays the summary LCA and LCCA results for the sewered versus
unsewered scenario. Overall, impacts increase for the unsewered scenario. Eutrophication
impacts increase substantially for the unsewered scenario due to the land application of compost,
which leads to nutrient runoff, as described in Section 2.7.3. Acidification potential and
particulate matter formation potential also increase considerably due to ammonia emissions
resulting from compost and land application of the compost. Smog formation potential increases
for the unsewered scenario due to emissions associated with the truck transport of solids to the
composting location.
Results for the district scale sewered scenario are slightly lower than those in the building
scale analysis per cubic meter of treated wastewater due to economies of scale for the treatment
system and reduced pumping requirements for the recycled water. Solids processing at the
centralized WRRF was excluded from the analysis, but is expected to be minor based on results
presented in Section 6.2.
Detailed results by life cycle stage are provided for GWP, CED, and NPV in Section 7.2.
Table 7-1. Summary Integrated LCA, LCCA and LRT Results for District scale AeMBR
Configurations Treating Mixed Wastewater (Per Cubic Meter Mixed Wastewater Treated)
Indicator
Unit
Sewered
Unsewered
% Change
Acidification Potential
kg SO2 eq
1.8E-4
4.2E-3
2239%
+*
Cumulative Energy Demand
MJ
3.9
4.2
8%
3
C£
<
Eutrophication Potential
kg N eq
2.8E-4
1.2E-3
339%
Fossil Depletion Potential
kg oil eq
0.05
0.06
14%
U
u
-J
¦a
Global Wanning Potential
kg C02 eq
0.31
0.48
55%
Particulate Matter Formation Potential
kg PM2.5 eq
6.7E-6
1.5E-4
2123%
a
<
Smog Formation Potential
kg 03eq
6.6E-3
0.02
172%
u
-J
Water Use
m3 H2O
-0.43
-0.43
0%
Cost (NPV)
USD
$6,000,000
$6,500,000
8%
a
Virus (LRT = 6.0)
9.0
9.0
0%
-J
13
Protozoa (LRT = 4.5)
9.0
9.0
0%
o
H
Bacteria (LRT = 3.5)
11
11
0%
Note: Applicable to low reuse scenarios representative of buildings with high efficiency appliances.
7-1
-------
7—District Scale Mixed Wastewater and Graywater Results
7.2 Detailed Results by Impact Category
7.2.1 Global Warming Potential
Figure 7-1 presents district scale AeMBR mixed wastewater treatment GWP results for
the sewered and unsewered scenarios. While the unsewered scenario negates the needs for
centralized treatment of the sludge, and the resulting compost avoids the need for commercial
fertilizer, there is still a notable GWP increase when disconnecting from the sewer. This is
represented in the red composting/land application bar in Figure 7-1. The increase in GWP
impacts for the composting/land application life cycle stage are from nitrous oxide and methane
emissions during the windrow composting process. As discussed in Section 2.7.2, this study
assumes that 0.78 and 2.1 percent of C and N entering the compost facility are lost as CFU and
N2O, respectively. This value can vary markedly depending on the management of the compost
system. Alternate composting methods, such as the aerated static pile, could be employed to
minimize the GWP impact of composting.
¦c
QJ
-w
O
•—
o
a
£
-D
o
*
a-
o
fS
O
u
OX)
-£
0.8
0.6
0.4
0.2
-0.2
-0.4
-0.6
0.07
Low Reuse
High Reuse
AeMBR - Sewered
0.24
Low Reuse
High Reuse
AeMBR - Unsewered
~ Biological Process ® Preliminary/Primary
^ Chlorine Disinfection ~ UV Disinfection
¦ Composting/Land Application ° Net Impact
~ Post-Treatment
¦ Water Recycling
Figure 7-1. Global warming potential for district scale mixed wastewater treatment
technologies.
7.2.2 Cumulative Energy Demand
Figure 7-2 presents district scale AeMBR mixed wastewater treatment CED results for
the sewered and unsewered scenarios. Unlike results for other impact categories assessed, CED
impacts are not sensitive to the solids handling method, with results increasing only slightly in
the unsewered scenario.
7-2
-------
7—District Scale Mixed Wastewater and Graywater Results
AeMBR - Sewered
AeMBR - Unsewered
~ Biological Process
s Preliminary/Primary
n Post-T reatment
^ Chlorine Disinfection
~ UV Disinfection
¦ Water Recycling
e Composting/Land Application
° Net Impact
Low Reuse
High Reuse
Low Reuse
Figure 7-2. Cumulative energy demand for district scale mixed wastewater treatment
technologies.
7.2.3 Life Cycle Costs
Figure 7-3 presents the NPV of the sewered versus unsewered scenarios according to
treatment process designation. Figure 7-4 presents system NPV broken out by cost category.
Sludge handling and disposal costs are included in both sewered and unsewered life cycle cost
calculations. In the sewered scenario, sludge is discharged to the sanitary sewered with utility
fees assessed based on the volume and strength of wastewater discharged. Sludge handling and
disposal costs in the unsewered scenario include on-site dewater, transportation, and windrow
composting of the waste activated sludge. Disconnecting the district wastewater treatment
system from the sanitary sewer leads to an 8 percent increase in system NPV over a 30 year
period. Approximately 70 percent of sludge handling and disposal costs in the unsewered
scenario are associated with transportation and tipping feeds at the composting facility. The
remaining 30 percent of cost is associated with dewatering equipment and operation labor. Costs
associated with composting are classified as materials in Figure 7-4.
7-3
-------
7—District Scale Mixed Wastewater and Gravwater Results
$7,000,000
$6,000,000
^$5,000,000
- $4,000,000
o
> $3,000,000
Ph
Z
$2,000,000
$1,000,000
$0
¦ Preliminary/Primary
H Disinfection
^ Sludge Handling and Disposal
• Total
~ Biological Treatment
¦ Building Reuse
¦ Other (a)
a Other = administrative costs.
Figure 7-3. Net present value for district scale mixed wastewater treatment technologies.
Results are shown by treatment process designation.
Sewered
Unsewered
$6,500,000
$6,000,000
7-4
-------
7—District Scale Mixed Wastewater and Gravwater Results
$7,000,000
$6,000,000
$5,000,000
S $4,000,000
o
$3,000,000
Cm
Z
$2,000,000
$1,000,000
$0
¦ Energy
a Chemicals
~ Materials
B O&M Labor
~ Capital
¦ Interest During Construction
• T otal
Figure 7-4. Net present value for district scale mixed wastewater treatment technologies.
Results are shown by cost category.
7.3 Gravwater Summary Findings
Summary graywater LCA and LCCA results are shown in Table 7-2 for the AeMBR
district scale systems treating graywater. LCA results across impact categories are consistently
lower per cubic meter of treated graywater in the district scenario as compared to the similar
building scale AeMBR treating graywater. The fine screen, equalization basin, and chlorine
disinfection process show reduced impacts per cubic meter at the larger district scale, and are
largely responsible for reduced impacts relative to building scale results. Detailed results for
GWP, CED, and cost are shown in Section 7.4.
$6,000,000
Sewered
$6,500,000
Unsewered
7-5
-------
7—District Scale Mixed Wastewater and Gravwater Results
Table 7-2. Summary Integrated LCA, LCCA and LRT Results for District scale
AeMBR Configuration Treating Graywater (Per Cubic Meter Graywater Treated)
Indicator
Unit
AeMBR
Sewered
LCA and LCCA Results
Acidification Potential
kg SO2 eq
-3.1E-4
Cumulative Energy Demand
MJ
0.77
Eutrophication Potential
kg N eq
2.0E-4
Fossil Depletion Potential
kg oil eq
4.9E-3
Global Warming Potential
kg C02eq
0.054
Particulate Matter Formation Potential
kg PM2.5 eq
-3.1E-5
Smog Formation Potential
kg 03 eq
-2.3E-4
Water Use
m3 H20
-0.69
Cost (NPV)
USD
$6,000,000
Total
LRV
Virus (LRT = 6.0)
9.0
Protozoa (LRT = 4.5)
9.0
Bacteria (LRT = 3.5)
11
Note: Applicable to low reuse scenarios representative of buildings with high efficiency appliances.
7.4 Detailed Results by Impact Category
7.4.1 Global Warming Potential and Cumulative Energy Demand
Figure 7-5 presents detailed GWP and CED results for the district scale graywater
system. In the high reuse scenario, where the full volume of treated graywater displaces centrally
treated potable drinking water, the district scale graywater system produces net environmental
benefits in both GWP and CED. Operation of the biological treatment process is the primary
source of impact for both categories.
7-6
-------
7—District Scale Mixed Wastewater and Graywater Results
0.054
High Reuse
Low Reuse
High Reuse
Low Reuse
~ Biological Process H Preliminary/Primary ~ Post-Treatment 0 Chlorine Disinfection D UV Disinfection ¦ Water Recycling o Net Impact
Figure 7-5. LCA results for district scale graywater treatment technologies. Results shown
by life cycle stage (a) global warming potential and (b) cumulative energy demand.
7.4.2 Life Cycle Costs
Figure 7-6 shows NPV results for the district graywater scenarios on both a life cycle
stage and a cost category basis. Building reuse systems contribute significant life cycle costs to
the district scale graywater treatment system as do administrative costs associated with water
quality testing.
7-7
-------
7—District Scale Mixed Wastewater and Graywater Results
(a)
(b)
$7,000,000
$6,000,000
— $5,000,000
5 $4,000,000
53,000,000
cu
Z $2,000,000
$1,000,000
$0
$6,000,000
r/ysssyyss/jyjv//yss/s&s/rs//ss/jM^
Sewered
f/i
$7,000,000
$6,000,000
$5,000,000
$4,000,000
> $3,000,000
p.
£ $2,000,000
$1,000,000
$0
a Preliminary/Primary
~ Biological Treatment
B Disinfection
¦ Building Reuse
^ Sludge Handling and Disposal
H Other (a)
• Total
a Other = administrative costs.
$6,000,000
Sewered
* Energy
¦ Chemicals
¦ Materials
a O&M Labor
¦ Capital
a Interest During Construction
• Total
Figure 7-6. Net present value for district scale graywater treatment technologies. Results shown by (a) life cycle stage and (b)
cost category.
7-8
-------
8—Conclusions
8. CONCLUSIONS
The findings of this study describe the environmental and cost benefits and trade-offs of
several decentralized (or distributed) mixed wastewater and graywater treatment configurations
intended for NPR applications in an urban setting.
The study was structured such that the full volume of mixed wastewater or graywater
produced within the building or district is processed in the on-site treatment facility. As
demonstrated in Table 1-3, in most scenarios the volume of treated wastewater or graywater
considerably exceeds on-site demand for NPR. Only in the two high reuse graywater scenarios,
do the building or district consume the full quantity of treated water. The results presented in
Sections 4 and 5 demonstrate that, for a given treatment technology, the system treating source
separated graywater produces lower impacts per unit of treated water. This is largely explained
by the fact that for graywater systems, a larger fraction of the wastewater treated can be used for
NPR, thereby generating an avoided burden credit for potable water treatment and distribution
that would otherwise have been required. The results of the full utilization sensitivity analysis,
Section 6.2, take these observations one step further by correcting for the discrepancy in reuse
fraction and accounting for the environmental impact of centralized blackwater treatment. These
adjustments reduce the gap in environmental performance between mixed wastewater and
graywater systems. For most treatment systems, GWP and CED impact is still slightly lower for
the graywater system, however the difference is not usually large enough to indicate a substantial
difference in environmental performance. The impacts of centralized blackwater treatment are
quite small per unit of treated wastewater due to San Francisco's centralized WRRFs' use of
anaerobic digestion coupled with energy recovery. Recovered energy can substantially reduce
the environmental impact of WRRFs when displacing fossil fuel consumption. Incorporation of
centralized blackwater treatment within the graywater system boundaries may have a more
notable impact in other regions in the country where WRRFs do not practice energy recovery.
These findings indicate the benefits of decentralized wastewater treatment when the majority of
treated water can be reused. For communities with low impact centralized treatment plants, such
as San Francisco, excess water volume not required for NPR could be treated at the municipal
treatment plant at a lower cost and environmental burden.
Baseline building scale summary results for mixed wastewater show that for most impact
categories, the AeMBR treatment system has the lowest environmental impact and the lowest
system NPV. The environmental performance of the AeMBR is closely followed by that of the
RVFW. The AnMBR is associated with the highest environmental impacts, even when
employing intermittent sparging. System NPV is comparable for the AnMBR and RVFW
systems treating mixed wastewater. The life cycle cost of these two systems is approximately 40
percent greater than the comparable AeMBR treatment option for mixed wastewater. The
difference in life cycle cost across systems is reduced when treating source separated graywater.
The RVFW is unlike passive wetland systems, utilizing active pumping to achieve a high
recirculation rate of the treated wastewater, thereby limiting land area requirements. Active
recirculation is used to boost treatment performance and consistency, but also increases energy
demand. Electricity consumption accounts for approximately 75 percent of RVFW GWP impact.
Despite being compact for a wetland, the RVFW still has greater infrastructure demands than the
other treatment systems due in part to the batch-processing operational mode of the designed
8-1
-------
8—Conclusions
system. Batch processing is not an issue for very small systems, but even for a 0.016 MGD
graywater treatment system the storage requirements and increases in equipment size required to
achieve treatment goals tend to increase material and cost requirements. Moving away from a
batch processing format and focusing on optimization of recirculation rates are both likely to
yield reductions in cost and environmental impact. Given the potential for optimization, and the
marginally higher environmental impact of the RVFW system relative to the AeMBR, the results
presented here reflect positively on the potential use of building scale RVFW systems.
The AnMBR treatment system performance demonstrated the highest impact among the
building scale treatment systems. Biogas sparging sensitivity results presented in Section 6.1
demonstrate the influence of sparging rate (due to associated energy use) on both GWP and
CED. If the intermittent sparging rates presented by Feickert et al. (2012) are proven effective,
the results of this analysis indicate that impact results comparable to those of the AeMBR and
RVFW are possible. The need to establish a chlorine residual for indoor NPR challenges the
AnMBR due to the high ammonia content of AnMBR effluent. The resources cited in this paper
indicate the ability of DHS and zeolite post-treatment units to overcome this issue, but at the
expense of increased cost, energy, and chemical consumption. The lower nitrogen content of
graywater reduces energy and chemical demands of the post-treatment processes, while the
lower COD content of graywater reduces biogas production leading to a tradeoff that mutes both
the benefits and burdens of AnMBR utilization. None of these processes are fully
commercialized at the system scales that we have considered, and active research is ongoing to
identify optimized, low-cost solutions to help bring AnMBRs to market. Creative solutions are
required to deal with the ammonia in AnMBR effluent if indoor NPR is the goal. A simple
alternative strategy would be to utilize AnMBR technologies to produce irrigation water for
NPR, avoiding the need for extensive post-processing.
Results of the thermal recovery sensitivity presented in Section 6.3 demonstrate the
promise of this simple, innovative energy recovery option. Using thermal recovery with mixed
wastewater and even graywater does pose some practical challenges due to the consistency of the
fluid, but the energy recovery potential is great even given the modest system performance
parameters utilized in this analysis. Moreover, if thermal recovery can be successfully employed
prior to the wastewater treatment process, it is feasible to maximize the obtainable energy and
provide supplemental heat with minimal lag time at times of peak building energy demand.
The cost of these systems is not negligible, requiring ongoing operation, maintenance,
and administrative and laboratory support to ensure continued, successful operation. The capital
cost of the mixed wastewater AeMBR system is approximately $1.2 million while that of the
AnMBR and RVFW is $2.1 million. The cost of regular laboratory testing accounts for a
considerable portion of ongoing O&M labor cost. The analysis presented in Section 6.5
demonstrates that on-site treatment does have the potential to considerably reduce water and
wastewater utility bills, but the total magnitude of this benefit is not sufficient to pay back the
estimated cost of system construction and ongoing operation.
This research highlights the environmental benefit of displacing centralized potable water
production and distribution with decentralized NPR. The full utilization sensitivity demonstrates
that systems treating both mixed wastewater and graywater can be used to produce treated
effluent suitable for NPR with comparable levels of impact. The choice of which source water
8-2
-------
8—Conclusions
best suits the needs of the project can be determined based on expected demand for NPR water,
local regulations, and preferences regarding treatment system type. The results presented
highlight several challenges for RVFW and AnMBR treatment systems, indicating several
potentially valuable opportunities for system refinement. The AeMBR treatment technology
appears to be a suitable option for building and district scale wastewater and graywater treatment
for NPR applications, demonstrating low relative cost and environmental impacts among the
systems studied.
8-3
-------
9—References
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9-14
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Appendix A
Appendix A:
Life Cycle Inventory and Life Cycle Cost Analysis Calculations
-------
Appendix A
APPENDIX A: LIFE CYCLE INVENTORY AND LIFE CYCLE COST ANALYSIS
CALCULATIONS
A.l LCI Calculations
A. 1.1. Influent Wastewater Characteristics
Table A-l presents influent mixed wastewater and graywater characteristics as reported
in (Tchobanoglous et al. 2014) and the graywater literature review (Eriksson et al. 2002; Li et al.
2009; Boyjoo et al. 2013; Ghaitidak and Yadav 2013). Values in Table A-l can be compared to
study values listed in Table 1-4, which have been adjusted based on the GPS-X™ mass balance
feature. Values listed as "n/a" in Table A-l are not presented in the sources listed above.
Table A-l. Mixed Wastewater and Graywater Influent Values
Water Quality Characteristics
Mixed WW
Separated GW
Characteristic
Unit
Medium
Strength
(Residential &
District)
Low Pollutant
Load with
Laundry
Suspended Solids
mg/L
195
90
% Volatile Solids
0/
/O
78
47
cBODs
mg/L
n/a
n/a
BODs
mg/L
200
166
Soluble BODs
mg/L
n/a
100
Soluble cBODs
mg/L
n/a
n/a
COD
mg/L
508
333
Soluble COD
mg/L
n/a
153
TKN
mgN/L
35
8.5
Soluble TKN
mgN/L
n/a
n/a
Ammonia
mgN/L
20
1.9
Total Phosphorus
mgP/L
5.6
1.1
Nitrite
mgN/L
0
0
Nitrate
mgN/L
0
0.64
Average Summer
degC
23
29
Average Winter
degC
23
29
Chlorine Residual
mg/L
n/a
n/a
Acronyms: GW - graywater, WW - wastewater
A. 1.2. Irrigation Water Use
San Francisco's annual average evapotranspiration rate of 35.1 inches/year was used as
an input to version 1.01 of California's Water Budget Workbook (CDWR 2010). We assumed
that 50, 25, and 25 percent of landscaped area was occupied by plants with high, medium, and
low water use requirements, respectively. A default irrigation water use efficiency of 0.71 was
A-l
-------
Appendix A
used. We assumed a landscaped area of 58,900 ft2, which corresponds to 26% of district block
area.
A. 1.3. Pump Power Calculation
Pumping power requirement was calculated using Equation A-l. Electricity demand for
pump operation was calculated using Equation A-2.
Pump Power (P) = QxPxgxh
F v J (3.6£6)
Equation A-l
Where:
Pump Power, in kilowatts, kW
Q = Fluid flow, m3/hr
p = Fluid density, kg/m3
g = Acceleration due to gravity, 9.81 m/s2
h = Differential head, m
P
Electricity = — x t
Equation A-2
Where:
Electricity, in kWh
P = Pump Power, in kW
i] = Combined motor and pump efficiency, fraction
t = Annual pumping time, hours
A. 1.4. Blower Power Calculation
Blower power requirement was calculated using Equation A-3 (Tchobanoglous et al.
2014). A specific heat ratio of 0.23 was used for biogas recirculation. Electricity demand for
blower operation was calculated using Equation A-2.
Blower Power =
wRT
n
— -i
Pi
28.97ne
Equation A-3
Where:
w = Weight of air flowrate, kg/sec
R = Universal gas constant, 8.314 J/mol-K
T = Temperature, 296.15 K (23°C)
A-2
-------
Appendix A
n = Specific heat ratio of dry air, 0.283
e = Combined blower/motor efficiency, 0.7 (Tarallo et al. 2015)
Pi = Inlet pressure, atm
p0 = Outlet/discharge pressure, atm
Inlet pressure was calculated using Equation A-4 (Hydromantis 2017).
Inlet pressure (p£) = Ps — Apa
Equation A-4
Where:
Pi = Inlet pressure, atm
Ps = Barometric pressure, 1 atm (101.325 kPa)
Apa = Pressure drop in inlet filter and piping to blower, 0.02 atm (0.25 psi) (Tarallo et al.
2015)
Outlet pressure was calculated using Equation A-5 (Hydromantis 2017). Diffuser
submergence is based on the configuration of specific process reactors.
Outlet pressure (p0) = Ps + g x d x p x 9.86 6 + Apd
Equation A-5
Where:
p0 = Outlet/discharge pressure, atm
Ps = Barometric pressure, 1 atm
g = Gravitational constant, 9.81 m/s2
d = Diffuser submergence depth, m
p = Fluid density, kg/m3
Apd = Pressure drop in air distribution piping and diffuser, 0.17 atm (2.5 psi) (Tarallo et
al. 2015)
A. 1.5. Head loss in Pipe Networks
Total pumping head is estimated as the sum of vertical head and head loss due to friction
loss. Head loss in pipe elbows and fixtures is not included.
Head loss due to friction in piping networks is estimated using the Hazen-Williams,
empirical head loss equation, Equation A-6.
100 01.852
hf = 0.2 0 8 3 X (—)1-852
c dh
Equation A-6
A-3
-------
Appendix A
Where:
hf= Head loss due to friction, ft IHhO/lOOft pipe
c = Hazen-Williams roughness constant
Q = Fluid flow, gallons per minute
dh = Hydraulic diameter, inches
A. 1.6. Aerobic Biological Treatment Process Greenhouse Gas Emissions
Methane (CH4) and nitrous oxide (N2O) emissions were estimated for the AeMBR
treatment systems using Equation A-7 and Equation A-8, as presented in the IPCC Guidelines
for national inventories (Doom et al. 2006). The GPS-X™ model was used to estimate BOD and
TKN loads entering the AeMBR. IPCC guidelines suggest that for a well-managed aerobic
treatment plant the methane correct factor (MCF) will vary between 0 and 0.1. We used the
midpoint of this range, 0.05, as the MCF in this analysis. We used an N2O emission factor of
3.8E-3, which is the average of four emissions factors for plug-flow aerobic treatment processes
(Chandran 2012).
CH4 Emissions = BOD x B0 x MCF
Equation A-7
Where:
CH4 Emissions from AeMBR unit process, kg CH4 /yr
BOD = BOD entering biological treatment process, mg/L
Bo = maximum CH4 producing capacity, 0.6 kg CH4/kg BOD (Doom et al. 2006)
MCF = methane correction factor, fraction
44
N20 Emissions = TKN x EF x —
2 28
Equation A-8
Where:
N2O Emissions from AeMBR unit process, kg N20/yr
TKN =Total kjeldahl nitrogen entering biological treatment process, mg N/L
EF = Emission factor, fraction
A.2 LCCA Calculations
A. 2.1. Dollar Year Adjustment
In cases where cost data was found for years other than the analysis year (2016), the cost
information is scaled to the analysis year based on the national average, urban CPI. The most
recent available CPI values from the Bureau of Labor Services are record in Table 7-1. No CPI
value is yet available for 2017. For the purposes of this analysis 2016 and 2017 costs were
assumed to be equivalent.
A-4
-------
Appendix A
2016 Cost = Costv x '
CPIy
Equation A-9
Where:
2016 Cost = Cost of item x, in 2016 $
Costy = Cost of item x in year^, $
CPI2016 = CPI score for 2016, relative to 1982-84
CPIy = CPI value for year^, relative to 1982-84
Table A-2. Consumer Price Index Values:
1980-2016 (Crawford and Church 2017)
Year
CPI
Year
CPI
1980
82.4
1999
166.6
1981
90.9
2000
172.2
1982
96.5
2001
177.1
1983
99.6
2002
179.9
1984
103.9
2003
184.0
1985
107.6
2004
188.9
1986
109.6
2005
195.3
1987
113.6
2006
201.6
1988
118.3
2007
207.3
1989
124.0
2008
215.3
1990
130.7
2009
214.5
1991
136.2
2010
218.1
1992
140.3
2011
224.9
1993
144.5
2012
229.6
1994
148.2
2013
233.0
1995
152.4
2014
236.7
1996
156.9
2015
237.0
1997
160.5
2016
240.0
1998
163.0
2017
n/a
A.2.2. LCCA Energy Escalation Factors
Table A-3 presents electricity cost (real) escalation factors for the California region used
to estimate future electricity prices in constant base dollars (Fuller and Petersen 1996; Lavappa et
al. 2017).
A-5
-------
Appendix A
Table A-3. Electricity Cost Escalation Factors
Year
Electricity Escalation
Factor3
2016b
1.00
2017b
1.00
2018
0.98
2019
0.98
2020
0.98
2021
1.00
2022
1.02
2023
1.06
2024
1.07
2025
1.07
2026
1.09
2027
1.10
2028
1.10
2029
1.10
2030
1.11
2031
1.11
2032
1.12
2033
1.13
2034
1.13
2035
1.14
2036
1.15
2037
1.15
2038
1.16
2039
1.16
2040
1.17
2041
1.18
2042
1.19
2043
1.20
2044
1.21
2045
1.22
a Value for 2018-2045 from (Lavappa et al. 2017).
b Values for 2016 and 2017 assumed to be 1.0.
A.2.3. Cost Estimation Support
Several of the treatment systems being analyzed such as the AnMBR, DHS, and zeolite
adsorption system are not in wide current use, necessitating the use of proxy cost estimation
approaches. Additionally, CAPDETWorks™ cost estimation equations are not universally
applicable for system flowrates corresponding to building and district scale decentralized
WRRFs. This section provides discussion and further information on specific cost estimation
approaches that fall into these categories.
Several CAPDETWorks™ cost estimation equations are intended for cost estimation of
larger treatment systems. In some cases these equations are deemed applicable at lower flowrates
A-6
-------
Appendix A
when they continue to produce realistic decreases in system cost outside of their intended range
of application. For example, Figure A-l graphs the relationship been air piping system cost and
design airflow described in Equation 31. The equation is intended for parametric estimation of
air piping installed equipment costs for design airflow rates of 100 to 1000 scfm. The lower end
of the intended application range is identified with the yellow diamond marker at 100 scfm.
Several of the designed systems have a design airflow rate that is outside the recommended
range (i.e. less than 100 scfm). The figure shows that as system airflow increases, costs rise
rapidly before beginning to plateau. Costs per unit of air delivered are highest at lower airflow as
would be expected. Over the entire depicted airflow range for every order of magnitude increase
in system size, air piping cost increases by a factor of 1.8 (parametric cost factor).
The described parametric cost factors are an indication of the extent to which economies
of scale affect specific elements of WRRF construction. Lower cost factors indicate greater
economies of scale.
18.000
16,000
14,000
12,000
cw
2 10,000
CM
8,000
6,000
4,000
2,000
Airflow (scfm)
Figure A-l. Cost of AeMBR air piping system as a function of airflow.
A similar relationship is demonstrated in Figure A-2 for adsorption vessel cost estimated
as a function of system flowrate. Over the entire depicted range of system flowrate for every
order of magnitude increase in system size, adsorption vessel cost increases by a factor of 3.9.
System component capital costs and parametric cost factors for the zeolite adsorption system are
listed in Table A-4.
0
200
400
600
800
1000
A-7
-------
Appendix A
2500
2000
J 1500
1000
500
2
10
0
4
6
8
System Flowrate (MGD)
Figure A-2. Cost of AnMBR zeolite adsorption vessel as a function of system size.
Table A-4. Cost Summary for Zeolite Adsorption System.
System Component
Cost Parameter
AnMBR,
Mixed WW
AnMBR,
GW
Adsorption Vessel
Capital Cost
$60,420
$46,495
Parametric Cost Factor
3.S
Feed System
Capital Cost
$15,372
$11,761
Parametric Cost Factor
4.(
Regeneration System
Capital Cost
$19,265
$16,260
Parametric Cost Factor
2/
Zeolite Handling
System
Capital Cost
$27,632
$24,386
Parametric Cost Factor
1.9
Acronyms: GW - graywater, WW - wastewater
A-8
-------
Appendix A
300,000
250,000
---¦ 200.000
w
VO
" 150:000
y;
O
u
g 100,000
o
u
50,000
0 10 20 30 40 50 60 70
Cover Diameter (ft)
—CAPDET Approach —o— Straight Line
Figure A-3. Comparison of two methods for floating cover cost estimation.
Figure A-3 graphs floating cover cost as a function of tank diameter using two estimation
approaches. The standard CAPDETWorks™ approach, shown in red is intended for cover
diameters between 30 (yellow diamond) and 70 feet. A straightline approach was used to
estimate the cost of floating covers between 10 and 30 foot diameter, based on
CAPDETWorks™ estimated floating cover cost of $91,400 for a 30 foot digester.
A.2.4. Chlorination
Equation A-10 was used to estimate annual material costs for chlorine maintenance and
operation (excluding chemical cost). Table A-5 shows the daily chlorine requirement for each
system. The estimated maintenance material cost factor is applied to installed equipment cost.
6.255 x OR'0 0797
Maintenance material cost factor = ——
; 100
Equation A-10
Where:
CR = Daily chlorine requirement, in lb/day
A-9
-------
Appendix A
Table A-5. Daily Chlorine Requirements by
Treatment System (lb Cl/day)
System
Chlorine
Requirement
(lb Cl/day)
AeMBR, Building, Graywater
0.41
AeMBR, Building, Mixed Wastewater
0.72
AnMBR, Building, Graywater
0.74
AnMBR, Building Mixed Wastewater
2.5
RVFW, Building, Graywater
0.19
RVFW, Building, Mixed Wastewater
0.31
AeMBR, District, Graywater
0.80
AeMBR, District, Mixed Wastewater
1.5
A-10
-------
Appendix B
Appendix B:
Life Cycle Cost Analysis Detailed Results
-------
Appendix B
APPENDIX B: LIFE CYCLE COST ANALYSIS PET ATT,ED RESULTS
Results in this Appendix are based on the following LCCA factors (Table B-l). Detailed
NPV results by process for assessed building scale and district scale scenarios are shown in
Table B-2 through Table B-10.
Table B-l. Life Cycle Cost Analysis Factors
Description
Quantity
Value
Unit
Source
Assumed LCCA Time
Period
Years
30
years
For New Construction (Stanford University
2005)
Electricity
1 kWh
0.194
$/kWh
Annual Average Small Commercial Electricity
Rate in SF (SFWPS 2017b)
Discount rate
Time value of money
0.050
% (as decimal)
Scenario Value = 5%
Interest
During construction
period
0.017
% (as decimal)
Scenario Value = 1.7% (CWB 2018)
Oxygen Cost
Kg
0.13
$/kg
$110/ton (in 2011 $s) (Carollo 2012)
Sodium Hypochlorite
(NaOCl) '
Kg
0.30
$/kg (as 15%
solution)
9.76 $/ft3 (Hydromantis 2014)
Polymer
Lb
1.3
$/lb
CAPDETWorks™
Labor Rate
Fully loaded
50
$/hour
(U.S. DOL 2017), see report for calculations.
Laboratory Labor Rate
Fully loaded
55
$/hour
110% of labor rate (Harris et al. 1982)
Annual Maintenance
Costs3
Structural Units &
AnMBR
1.5%
of bare
construction cost
storage tanks (City Of Alexandria 2015),
material and labor cost
Annual Maintenance
Costs3
Electrical/Mechanical
Units
5.0%
of bare
construction cost
material and labor, original factor is 2.5%
(CAPDETWorks™) for materials only.
Annual Maintenance
Costs
DHS reactor
1.0%
of bare
construction cost
CAPDETWorks™ Trickling filter as proxy,
materials only
Annual Maintenance
Costs
Building GW
10%
of bare
construction cost
(Harris et al. 1982) (varies with system size)
Annual Maintenance
Costs
Building WW
9.3%
of bare
construction cost
(Harris et al. 1982) (varies with system size)
Annual Maintenance
Costs
District GW
8.8%
of bare
construction cost
(Harris et al. 1982) (varies with system size)
Annual Maintenance
Costs
District WW
7.8%
of bare
construction cost
(Harris et al. 1982) (varies with system size)
Annual Maintenance
Costs3
Disinfection
3.0%
of bare
construction cost
storage tanks (City Of Alexandria 2015),
material and labor cost
3 Includes material and labor costs of maintenance.
Acronyms: GW - graywater, WW - wastewater
B-l
-------
Appendix B
Table B-2. NPV for Mixed Wastewater Building scale AeMBR Systems
(2016 USD)
Process
Interest During
Construction
Capital
O&M
Labor
Material
Chemical
Energy
Thermal Recovery3
2,444
95,824
17,660
39,765
_
_
Equalization
2,822
110,679
48,373
34,014
_
11,252
Fine Screen
1,775
69,600
141,789
28,883
_
9,731
AeMBR
10,404
408,015
400,566
265,307
817
72,170
UV
283
11,088
19,982
2,757
_
1,588
Chlorination
2,773
108,732
65,198
40,722
4,085
6,002
Building Reuse
13,969
547,806
52,227
62,089
_
_
Administration
_
_
1,370,314
_
_
_
Totalb
34,469
1,351,743
2,116,110
473,536
4,902
100,743
a Only applicable for AeMBR systems with thermal recovery.
b Total includes cost of the thermal recovery system.
Acronyms: O&M - operations and maintenance, UV - ultraviolet
Table B-3. NPV for Graywater Building scale AeMBR Systems (2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Thermal Recovery
1,925
75,506
13,916
31,333
_
_
Equalization
2,494
97,815
44,313
31,512
_
7,875
Fine Screen
1,344
52,699
129,300
21,869
_
7,875
AeMBR
8,355
327,645
279,469
237,744
522
31,728
UV
233
9,126
19,874
1,770
_
1,296
Chlorination
2,723
106,793
55,853
40,315
2,323
6,002
Building Reuse
25,733
1,009,150
89,683
99,545
_
_
Administration
_
_
1,262,277
_
_
_
Totalb
42,808
1,678,733
1,894,684
464,088
2,845
54,776
a Only applicable for AeMBR systems with thermal recovery.
b Total includes cost of the thermal recovery system.
Acronyms: O&M - operations and maintenance, UV - ultraviolet
B-2
-------
Appendix B
Table B-4. NPV for Mixed Wastewater Building scale AnMBR Systems
(2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
2,822
110,679
48,373
34,014
_
11,252
Fine Screen
1,775
69,600
141,789
28,883
_
9,731
AnMBR3
19,278
756,000
412,518
389,112
2,176
93,639
Zeolite
8,834
346,439
137,214
44,432
110,541
5,262
DHS
3,585
140,607
70,915
26,165
_
_
UV
283
11,088
19,982
2,757
_
1,588
Chlorination
2,773
108,732
96,143
40,722
14,092
6,002
Building Reuse
13,969
547,806
52,227
62,089
_
_
Administration
_
_
1,370,314
_
_
_
Total
53,319
2,090,950
2,349,475
628,173
126,808
127,473
a Applicable for AnMBR systems withy continuous biogas sparging.
Acronyms: DHS - downflow hanging sponge, O&M - operations and maintenance, UV - ultraviolet
Table B-5. NPV for Graywater Building scale AnMBR Systems (2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
2,494
97,815
44,313
31,512
_
7,875
Fine Screen
1,344
52,699
129,300
21,869
_
7,875
AnMBR3
13,639
534,879
343,615
338,242
1,393
60,671
Zeolite
6,140
240,769
98,163
51,992
33,264
2,498
DHS
2,158
84,625
62,846
17,509
_
_
UV
233
9,126
19,874
1,770
_
1,296
Chlorination
2,723
106,793
65,313
40,315
4,204
6,002
Building Reuse
25,733
1,009,150
89,683
99,545
_
_
Administration
_
_
1,262,277
_
_
_
Total
54,464
2,135,855
2,115,385
602,753
38,861
86,216
a Applicable for AnMBR systems withy continuous biogas sparging.
Acronyms: DHS - downflow hanging sponge, O&M - operations and maintenance, UV - ultraviolet
Table B-6. NPV for Mixed Wastewater Building scale RVFW Systems
(2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
3,338
130,901
55,976
39,081
_
21,930
Clarification
4,181
163,945
292,643
11,392
_
_
Fine Screen
3,944
154,651
242,978
64,177
_
9,731
Wetland
21,568
845,809
389,182
103,926
_
47,070
Ozone
4,080
159,990
461,445
92,501
9,741
24,320
UV
580
22,736
20,626
7,087
-
4,119
B-3
-------
Appendix B
Table B-6. NPV for Mixed Wastewater Building scale RVFW Systems
(2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Chlorination
2,773
108,732
52,847
40,722
1,787
6,002
Building Reuse
13,969
547,806
52,227
62,089
_
_
Administration
_
_
1,370,314
_
_
_
Total
54,432
2,134,569
2,938,239
420,974
11,528
113,172
Acronyms: O&M - operations and maintenance, UV - ultraviolet
Table B-7. NPV for Graywater Building scale RVFW Systems (2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
2,970
116,462
51,732
36,563
_
16,445
Clarification
2,765
108,422
289,090
7,310
_
_
Fine Screen
2,986
117,097
206,010
48,593
_
7,912
Wetland
14,379
563,872
259,455
69,281
_
31,379
UV
580
22,736
_
_
_
4,119
Chlorination
2,723
106,793
20,626
7,087
1,088
6,002
Building Reuse
25,733
1,009,150
47,097
40,315
_
_
Administration
_
_
89,683
99,545
_
_
Total
52,136
2,044,531
1,262,277
_
1,088
65,856
Acronyms: O&M - operations and maintenance, UV - ultraviolet
Table B-8. NPV for Mixed Wastewater District scale AeMBR Systems - Sewered
(2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
3,739
146,633
58,586
39,950
_
22,504
Fine Screen
2,734
107,211
169,325
44,490
_
13,414
AeMBR
14,054
551,133
484,599
332,328
1,629
132,082
UV
580
22,736
20,626
8,141
_
4,119
Chlorination
2,773
108,732
80,115
40,315
8,279
6,002
Building Reuse
27,884
1,093,472
111,532
138,312
_
_
Administration
_
_
1,564,398
_
_
_
Sludge disposal3
_
_
_
624,283
_
_
Total
51,763
2,029,918
2,489,180
1,227,819
9,908
178,120
a Sludge disposal via the sanitary sewer is included in the district sewered scenario for direct comparison with the unsewered
scenario.
Acronyms: O&M - operations and maintenance, UV - ultraviolet
B-4
-------
Appendix B
Table B-9. NPV for Mixed Wastewater District scale AeMBR Systems - Unsewered
(2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
3,739
146,633
58,586
39,950
_
22,504
Fine Screen
2,734
107,211
169,325
44,490
_
13,414
AeMBR
14,062
551,444
484,599
441,099
1,629
132,317
Dewatering
3,730
146,259
125,214
60,694
5,561
_
Composting
729,706
UV
580
22,736
20,626
8,141
_
4,119
Chlorination
2,773
108,732
80,115
40,315
8,102
6,002
Building Reuse
27,884
1,093,472
111,532
138,312
_
_
Administration
_
_
1,564,398
_
_
_
Total
55,500
2,176,488
2,614,394
1,502,708
15,292
178,355
Acronyms: O&M - operations and maintenance, UV - ultraviolet
Table B-10. NPV for Graywater District scale AeMBR Systems - Sewered (2016 USD)
Process
Interest During
Construction
Capital
O&M Labor
Material
Chemical
Energy
Equalization
3,169
124,278
51,776
35,832
_
13,669
Fine Screen
2,029
79,586
153,739
33,027
_
10,748
AeMBR
10,840
425,085
360,209
274,799
1,014
63,214
UV
580
22,736
20,626
8,141
_
4,119
Chlorination
2,585
101,376
66,773
40,315
_
6,002
Building Reuse
51,124
2,004,847
185,308
212,087
_
_
Administration
_
_
1,426,843
_
_
_
Total
70,327
2,757,908
2,265,274
796,155
1,014
97,752
Acronyms: O&M - operations and maintenance, UV - ultraviolet
B-5
-------
Appendix C
Appendix C:
Life Cycle Inventory
-------
Appendix C
APPENDIX C: LIFE CYCLE INVENTORY
Table C-l presents a summary of the life cycle inventory associated with each wastewater treatment system.
Table C-l. Life Cycle Inventories
Unit
Process
Input/Output
AeMBR, Building,
Graywater
AeMBR, Building,
Mixed Wastewater
AnMBR, Building,
Graywater
AnMBR, Building
Mixed Wastewater
RVFW, Building,
Graywater
RVFW, Building,
Mixed Wastewater
AeMBR, District,
Graywater
AeMBR, District,
Mixed Wastewater
Units (per m3)
Electricity
0.107
0.084
0.107
0.084
0.107
0.084
0.075
0.058
kWh
Fine Screen
Screening Disposal
4.07E-3
9.54E-3
4.07E-3
9.54E-3
4.08E-3
9.54E-3
4.07E-3
9.54E-3
kg
Steel
1.34E-3
8.57E-4
1.34E-3
8.57E-4
1.34E-3
8.57E-4
6.91E-4
4.28E-4
kg
Concrete
1.35E-5
1.13E-5
1.35E-5
1.13E-5
1.86E-5
1.56E-5
1.12E-5
9.21E-6
m3
Equalization
Steel
8.04E-4
6.76E-4
8.04E-4
6.76E-4
5.34E-4
4.46E-4
6.68E-4
5.49E-4
kg
Electricity
0.106
0.097
0.106
0.097
0.222
0.189
0.095
0.097
kWh
HDPE
n/a
n/a
n/a
n/a
7.82E-5
7.15E-5
2.33E-5
1.69E-5
kg
Steel
3.80E-3
3.64E-3
kg
Clarification
Sludge Disposal
n/a
n/a
n/a
n/a
7.32E-3
0.017
n/a
n/a
m3
Electricity
6.41E-4
1.50E-3
kWh
Concrete
2.50E-5
2.11E-5
4.98E-5
4.01E-5
9.32E-5
8.94E-5
1.98E-5
1.69E-5
m3
Steel
1.54E-3
1.29E-3
2.66E-3
2.07E-3
0.011
0.010
1.18E-3
9.66E-4
kg
HDPE
-
-
1.04E-4
1.20E-4
8.32E-4
7.99E-4
-
-
kg
Polyvinyl Fluoride
5.92E-4
5.92E-4
1.58E-3
1.58E-3
n/a
n/a
5.92E-4
5.92E-4
kg
Lower Media,
Crushed Limestone
0.022
0.021
kg
Biological
Process
Middle Media,
Gravel
n/a
n/a
n/a
n/a
0.076
0.073
n/a
n/a
kg
Organic Cover,
Wood Chips
0.081
0.078
kg
Sodium
Hypochlorite
7.19E-4
7.20E-4
1.92E-3
1.92E-3
n/a
n/a
7.19E-4
7.19E-4
kg
Electricity
0.427
0.622
0.817
0.808
0.423
0.406
0.439
0.569
kWh
Methane
4.86E-3
5.94E-3
2.42E-3
3.50E-3
7.45E-4
9.05E-4
4.80E-3
5.94E-3
kg CH4
C-l
-------
Appendix C
Table C-l. Life Cycle Inventories
Unit
Process
Input/Output
AeMBR, Building,
Graywater
AeMBR, Building,
Mixed Wastewater
AnMBR, Building,
Graywater
AnMBR, Building
Mixed Wastewater
RVFW, Building,
Graywater
RVFW, Building,
Mixed Wastewater
AeMBR, District,
Graywater
AeMBR, District,
Mixed Wastewater
Units (per m3)
N20
5.01E-5
2.03E-4
-
-
3.26E-5
3.13E-5
5.01E-5
2.03E-4
kg N20
Sludge
8.32E-3
0.014
7.25E-3
7.26E-3
n/a
n/a
8.32E-3
0.014
ill1
Biogas
Recovery
Natural Gas,
Avoided
n/a
n/a
0.045
0.070
n/a
n/a
n/a
n/a
m3
Downflow
Hanging
Sponge
Electricity
n/a
n/a
0.035
0.035
n/a
n/a
n/a
n/a
kWh
Methane
1.29E-4
1.46E-4
kg CH4
Natural Gas
0.013
0.014
in1
Concrete
2.53E-5
2.14E-5
m3
Steel
1.19E-3
1.04E-3
kg
HDPE
2.33E-5
3.15E-5
kg
Zeolite
Zeolite
0.112
0.360
kg
NaCl (99+%)
0.055
0.227
kg NaCl
NaOH
0.200
0.200
kg NaOH
Electricity
0.034
0.045
kWh
Disposal, Brine
Injection
5.51E-3
0.023
m3
UV
Electricity
0.017
0.014
0.017
0.014
0.056
0.036
0.029
0.018
kWh
Steel
3.42E-5
3.15E-5
3.42E-5
3.15E-5
4.92E-5
3.15E-5
2.54E-5
1.57E-5
kg
Clilorination
Concrete
3.42E-6
2.97E-6
3.42E-6
2.97E-6
3.43E-6
2.97E-6
2.33E-5
1.49E-6
m3
Steel
8.53E-5
7.42E-5
8.53E-5
7.42E-5
8.53E-5
7.42E-5
5.83E-6
3.71E-5
kg
Electricity
0.081
0.052
0.081
0.052
0.081
0.052
0.042
0.026
kWh
Sodium
Hypochlorite
3.20E-3
3.60E-3
5.79E-3
0.012
1.50E-3
1.57E-3
3.23E-3
3.65E-3
kg NaOCl
Storage
HDPE
9.01E-4
8.66E-4
9.01E-4
8.66E-4
1.80E-3
1.73E-3
9.30E-4
7.21E-4
kg
Electricity
n/a
n/a
n/a
n/a
0.045
0.045
n/a
n/a
kWh
C-2
-------
SEPA
United States
Environmental Protection
Agency
PRESORTED STANDARD
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
Office of Research and Development (8101R)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
------- |