SEPA
United States
Environmental Protection
Agency
Errata to:
Life Cycle and Cost Assessments of
Nutrient Removal Technologies in
Wastewater Treatment Plants
Prepared for:
U.S. Environmental Protection Agency
Standards and Health Protection Division
Office of Water, Office of Science and Technology
1200 Pennsylvania Avenue NW (4305T)
Washington, DC 20460
Prepared by:
Eastern Research Group, Inc.
110 Hartwell Ave
Lexington, MA 02421
June 2023
EPA 832-R-21-006ES
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Errata
Errata
ERG identified an error in Appendix F of the Life Cycle and Cost Assessments of
Nutrient Removal Technologies in Wastewater Treatment Plants (EPA 832-R-21-006), dated
August 2021. Equation F-3, the equation used to calculate nitrous oxide (N20) emissions from
wastewater treatment processes, included an incorrect molecular weight conversion factor of N
to N20 of 44/14. The correct conversation factor is 44/28.
This error only affects N20 emission from biological treatment. The corrected emissions
are half as much as those presented in the report, as shown in Table 1 below. Emissions of N20
only affect the global warming potential (GWP) impact category but are reflected in all related
charts and discussion (Figures 6-5, 8-1 and 9-3 and Tables 8-1 and 8-3). Figure 1 compares the
GWP impact of treatment systems before and after correction of the N20 conversion factor
(Figure 6-5 in the report).
Table 1. Comparison of N2O Emissions from Biological Treatment
System
C onli^ui'iitioii
I.CM'I
VO Kmillcd by Process (k« VO/yr)
()ri»in:il Kslimitle'
Corrected Kstiniiile
1
6.6E+02
3.3E+02
2-1
2.9E+03
1.5E+03
2-2
3.9E+02
1.9E+02
3-1
7.8E+03
3.9E+03
3-2
3.0E+03
1.5E+03
4-1
8.2E+03
4.1E+03
4-2
7.7E+03
3.9E+03
5-1
7.8E+03
3.9E+03
5-2
7.7E+03
3.9E+03
a - Estimates included in Table F-2 of Life Cycle and Cost Assessments of
Nutrient Removal Technologies in Wastewater Treatment Plants (UPA 832-
R-21-006.
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Errata
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Errata
Because the error affected the calculation of biological treatment emissions, which are included
for all systems, it has a limited effect on the comparative results between systems. Correction of the
error alters the height of the biological treatment bars of each system. Prior to correction of the error,
N20 emissions from biological treatment contributed between 0.8% and 15% of total GWP emissions.
• The largest contribution of N2O to GWP is observed for treatment levels 3-1, 4-1, and 4-2 (14-
15%). Using the updated conversion factor the contribution of N2O to GWP drops to between 7
and 8%.
• More moderate contributions are observed for treatment levels 2-1, 3-2, 5-1 and 5-2 (6-8%).
Using the updated conversion factor the contribution of N2O to GWP drops to between 3 and
4%.
• The smallest contribution of N2O to GWP is observed for treatment levels 1 and 2-2 (0.8-3%).
Using the updated conversion factor the contribution of N2O to GWP drops to between 0.4 and
1.3%.
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