A Case of Utilizing Results
Identifying the Emission Factors of Dinitrogen Oxide in Sewage
Treatment Processes and Reflecting Them in Greenhouse Gas Inventory
YAMASHITA Hiromasa , Head; SHIGEMURA Hiroyuki , Senior Researcher; MICHINAKA
Atsuko (Dr. Env.), Researcher; ONISHI Shohei , Researcher; KAWASUMI Ryota ,Researcher
Wastewater and Sludge Management Division, Water Quality Control Department
MATSUHASHI Manabu , Researcher
Wastewater System Division, Water Quality Control Department

1. Introduction
Of the greenhouse gas emissions from sewerage works,dinitrogen oxide (N2O) accounts for about 10% 1) and,therefore, needs to be reduced. However, there are twomain issues: one is that the N2O emission factors of sewage
treatment facilities used in the Cabinet Order for the Law
for the Promotion of Measures to Deal with Climate
Change and Greenhouse Gas Inventory are greatly
uncertain due to the variation in measurement data used as
the basis of factor calculation, and the other is that thefactors are unified values and do not vary according totreatment methods, and, therefore, do not reflect the actual
situation. Therefore, in order to promote climate changecountermeasures, we conducted a survey to identify thegeneration of N2O from sewage treatment processes andestimated more accurate emission factors from the study
findings. Moreover, we present an outline of theGreenhouse Gas Inventory that we revised based on thefindings of this study.
2. Survey on N2O emissions and estimation ofemission factors
We conducted 37 field surveys of 18 sewage treatment
facilities in terms of main sewage treatment methods(conventional activated sludge process, circulating
denitrification process, anaerobic-aerobic activatedsludge process, pseudo-anaerobic-aerobic process,anaerobic-aerobic process, OD process, MBR process,etc.). As shown in the Figure, the measured values inmost sewage treatment facilities were lower than thecurrent N2O emission factor of 160 mg-N2O /m3. The
reason for this is that the current N2O emission factor wascalculated as an average for a limited number of data, i.e.
8 cases of data from 5 treatment facilities. Therefore, it
may be overestimated given the extraordinarily highvalue (approx. 1,000 mg-N2O /m3) affected the average.
In this survey as well, a certain number of extraordinarily
high values were measured in the processes without
nitrogen removal, and the average value calculated, 137
mg-N2O /m3, was close to the current N2O emission
factor. In contrast, in the treatment methods with nitrogen
removal, there were no extraordinarily high values
detected and the average was low at 9 mg-N2O /m3. Thus,
the value of the N2O emission factor differed greatly
between treatment with and without nitrogen removal.

N2O emission factor(mgN2O/m3)

Key words: Climate change, dinitrogen oxide, sewage treatment

Current:

Processes without nitrogen Processes with nitrogen
removalremoval- A2O process- Conventional activated- Anaerobic endogenous
sludge process
denitrification process- Anaerobic-aerobic- Step-feed biological nitrogenprocess (AO method)
removal process-Modified Bardenpho process
MBR process

Figure: Current Values and Estimated Values
from Survey Results
3. Reflection in Greenhouse Gas Inventory
Emission factors according to wastewater treatment
methods were newly developed, as shown in the Table,using the data of this survey and other surveys. 2) In
response to these values, the factors of "N2O Emissions
from Treatment of Household / Commercial Wastewater(Sewage Treatment Facilities)" in the Greenhouse Gas
Inventory were revised 3) and incorporated into Japan's
greenhouse gas emissions reports up to fiscal 2011. We
will continue to work to promote climate change
countermeasures.
Table: Revised N2O Emission Factors in2)
Sewage Treatment Facilities
Conventional activatedsludge process

Anaerobic-aerobic activatedsludge process

142

29.2

Anaerobic-anoxic-oxic
process
Circulating denitrification
process
11.7Circulating nitrification
denitrification type
Membrane separation
activated sludge process
0.5(Unit: mgN2O/m3)[Reference]
1) Miyamoto et al, "Collection of Presentations of Studies
on Wastewater Systems," 2010, pp. 155-157.
2) Ministry of the Environment Task Force for Reviewing
Greenhouse Gas Emissions Calculation Method,"Results of Review concerning Greenhouse Gas
Emissions Calculation -- Improvement of theCalculation Method Used for the Waste Treatment,
March 2013, p. 3.
3) National Greenhouse Gas Inventory Report of Japan,April 2013.