The 10th International Workshop on Decentralized Domestic Wastewater Treatment in Asia, A-2
4th November, 2022

Comparison of greenhouse gas (GHG)
reduction effects of decentralized
wastewater treatment facilities
Dr. Masahiro Furuichi
Director of Department of Education and Planning,
Japan Education Center of Environment

2Outline１．Introduction
２．Method
３．Result & Discussion
４．Summary１．INTRODUCTION

3

Background
SDGs： Halve the proportion of untreated wastewater globally
Paris Agreement： Reduction of greenhouse gas (GHG) emissions
It also affects the spread of wastewater treatment facilities※ High population density area→Centralized wastewater treatment facility※ Low population density area→Decentralized wastewater treatment facility

Need for knowledge on the environmental impact of decentralized wastewater treatment
facilities
Challenges for the diffusion of decentralized
wastewater treatment facilities overseas

standard value of Japan
Asian country①Septic Tank（ Widespread in the world ）150② Differences in domestic wastewateramong countries and regions➣Asian countries: 131 mg/L (low)➣EU: 337 mg/L (High)

Ave. of Asian countries：
BOD 131，T-N 73

Thailand➣effluent BOD: 145～912mg/L

Asian countries
T-N（mg/L)

cf: Small-scale sewage treatment facility （ＥＵ）
cf: Johkasou（Japan）➣ Good effluent water quality

EUAverage value of EU

France100
Australia
Malaysia

50

England0100

Germany

China

Vietnam
0ＥＵ

Ave. of ＥＵ：
BOD 337，T-N 67
Standard value of Japan：
BOD 200，T-N 45

200300BOD（mg/L）

400

500

Figure -1 Characteristics of Domestic Wastewater in Japan and Overseas

１．INTRODUCTION
Necessary knowledge
 GHG emissions considering discharged pollutant load
 Environmental Impact of Decentralized wastewater treatment facilities bytreatment method

Expected effect Widespread use of wastewater treatment facilities that aim to comprehensively
reduce the environmental impact according to the region➣ To contribute the achievement of the SDGs and the Paris Agreement

Purpose of this research
Promoting the spread of environmental load-reducing wastewater treatment facilities thatboth achieve the water environment conservation and prevention of global warming
Comprehensive comparison and analysis on the effect of reducing environmental impact
under the same usage conditions as in the EU, where the concentration of pollutants indomestic wastewater is the highest.
➣ This makes it possible to apply it to Asian countries, etc.

4

２．METHODS
1.

5Setting conditions for the decentralized wastewater treatment facilities
subject to environmental impact assessment① Facility scale：Minimum PE for individual house (5 PE)② Utilizing condition ： Equivalent to performance evaluation test by EU
regional standard EN12566-3+A2
Table -1 Outline of each decentralized wastewater treatment facility assumed in this presentation
Category
Septic tankEU type wastewater
treatment facility
Johkasou made inJapanClassificationin this study
Septic tank

Process of treatment
Solid-liquid separation
process

BOD removal type
Nitrogen removal
type
Applied to overseas
usage

Target of the wastewater

Combination ofanaerobic and aerobic
treatment

Domestic wastewater(Both Black water andGray water)

２．METHOD
2. Condition to set up a calculation model of environmental load from eachdecentralized wastewater treatment facility① EU - BOD removal type (Arithmetic Mean of 3 Models: from Literature)② EU – Nitrogen removal type (Arithmetic Mean of 5 Models: from Literature)③ Johkasou made in Jpan applied to overseas usage (Same BOD volume load asJapanese specification)④ Vietnam Septic tank (5 years after desludging, average 4.9 years for 37 units: fromLiterature)3.

Evaluation method of effluent pollutant load to water environment andsludge discharge① testing method: Performance evaluation test according to EU standard EN125663+A2. With regard to the septic tank the field survey conducted (inflow conditions
equivalent to EU standards)② Monitored pollutant amount in effluent: BOD and T-N (Johkasou made in Japanapplied to overseas usage was monitored by Total Kjeldahl Nitrogen)6２． METHOD
4.

Assessment of greenhouse gas emissions

Table -2 Types and main emission sources of GHG from wastewater treatment facilities focusedin this study
Types of categor
Main emission sources
GHG
y＜Energy-related＞
Emissions from fuel combustion (heavy oil, kerosene, gasoline, etc.)
ACO2
B
Emissions from the use and purchase of electricity (Not include in-house power generation etc.)＜Non-Energy-related＞
CH4

C

Emissions associated with wastewater treatment (domestic wastewater treatment facility: Johkasou)

D

Emissions from wastewater treatment (domestic wastewater treatment facility: anaerobic treatment)

E
Emissions associated with sludge treatment (night soil treatment facility)F
Natural decomposition of untreated wastewater＜Non-Energy-related＞

N2O

G

Emissions associated with wastewater treatment (domestic wastewater treatment facility: Johkasou)

H

Emissions from wastewater treatment (domestic wastewater treatment facility: anaerobic treatment)

J

Emissions associated with sludge treatment (night soil treatment facility)

K

Natural decomposition of effluent

L

Natural decomposition of untreated wastewater

7２． METHOD

8

Types of target GHG and scope of emissions calculation
Manufacturing process

Installation process

Materials used

Transportation

power consumption(Blower)

Transportation

Manufacturing

Construction

Operation & maintenancetreatment

Utilization process

Disposal process

Desludging
Sludge treatment
Wastewater treatment
process

CH4

N2O

BlowerSludge treatment process
Treated effluent
Untreated water

Energy-related
Non Energy -related
Out of scope in this study
A previous report found that
92% of emissions of GHG in
the Johkasou sector are
derived from the use stage.

Figure -2 Activity classification by stage of decentralized wastewater treatment facility

２． METHOD

9Table -3 Environmental load units and GHG emission factors used in calculations in this study
Item
Energy -related

Classification
Environmental load unit
in Table 2B
Power consumption by Blower
Vehicle fuel for maintenance inspection (privateApassenger car)AVehicle fuel for desludging (vacuum vehicle)

Non Energy related

A，B
C，G
C，G
D，HE，JKKFLSludge treatment
BOD removal type
Nitrogen removal type
Septic tank
Sludge treatment process Night soil treatment plant
Wastewater treatment
process

Natural decomposition of effluent
Natural decomposition of untreated wastewater

Unit

GHG factor(kg-CO2/kWh)

0.555(kg-CO2/PE・km)

0.188(kg-CO2/km)

0.554(kg-CO2/kL)(kg-CO2/PE・year)(kg-CO2/PE・year)(kg-CO2/PE・year)(kg-CO2/m3)(kg-N2O/kg-N)(kg-CO2/kg-N)(kg-CO2/kg-BOD)(kg-CO2/kg-N)

86
65.8
62.8
119.39
0.551
0.01
2.354
1.500
2.354

① Global Warming Potential (GWP)=> Compliant with IPCC Fourth Assessment Report （CH4：25，N2O：298）② Emission factor of wastewater treatment process with respect to influent pollutant load difference=> Emission Factor of Johkasou x Inflow amount of pollutant load into each facility / Inflow amount of pollutant
load into Johkasou③ Effluent from Septic tank=> Untreated wastewater （Higher concentration than untreated domestic wastewater in Japan, BOD 180mg/L ）３．RESULT AND DISCUSSION

10

1. Establishment of an environmental load calculation model for decentralized
wastewater treatment

Table -4 Environmental Load Calculation Model for Decentralized Wastewater Treatment Facilities
Item

Septic tank

BOD removal
type

Nitrogenremoval type

Performance evaluation testing method
Term of evaluation testing
Water temperature
Population equivalent (PE) for treatment

Field survey
4 days－40.451
112.8
525
378
59.2
323
238
36.4
－
－
1,825
16.1
1.00
1.00
000

EN12566-3+A2
38 weeks－
50.750
150.0
301
9.0
45.1
61
54.2
9.2
548
11.9
791
16.1
5.03
2.84
59
20
408

EN12566-3+A2
38 weeks－
50.750
150.0
312
9.7
46.8
61
7.9
9.2
183
11.9
365
16.1
3.622.438014416

Volume of wastewater

Test results and specifications

Water quality of influent
Water quality of effluent
BOD
Inflow amount of pollutant load
Water quality of influent
Water quality of effluent
T-N
Inflow amount of pollutant load
Operation and Interval
maintenancedistance travelledInterval
Desludging
distance travelled
Designed capacity
Volume of removed sludge
Designed power consumption
Uptime of blower（standard）
Annual power consumption

（℃）
（PE）
（m3/day）（L/PE・day)（mg/L）（mg/L）（g-BOD/PE・day）（mg/L）（mg/L）（g-T-N/PE・day）（day）（km/time）（day）（km/time）
（m3）
（m3）
（W）
（h）
（kWh）

Johkasou made inJapan applied tooverseas usage
EN12566-3+A263 weeks
－5
0.780
155.9
481
10.7
75.1
102
20.2
16.0
476
11.9
476
16.1
2.87
2.31
58
24508

 Even in the same performance evaluation testing, the inflow BOD concentration varied from 301 to 481mg/L(concentration has not been adjusted) Unification of inflow water quality is difficult. The model shown above is based on the results of the same testmethod

３． RESULT AND DISCUSSIONT-N load (g-T-N/m3)

Pollution load discharged into the water environment from wastewater
treatment facilities

BOD load (g-BOD/m3)

2.

Figure -3 Amount of BOD load discharged fromdecentralized wastewater treatment facilities (per m3)

BOD load of effluent (per m3)
 Septic tank ：378g-BOD/m3
34 to 42 times higher environmental impact thanother facilities
 other facilities：9～10g-BOD/ m3

Figure -4 Amount of T-N load discharged fromdecentralized wastewater treatment facilities (per m3)

T-N load of effluent (per m3)
 Septic tank ：238g-T-N/ m3
Large amount of load inflow but low removal ratio Nitrogen removal type and Johkasou made in Japanapplied to overseas usage ：lower than 20g-T-N/ m3

 The amount of BOD polluted discharged from the septic tank suggested the impact on the ecosystem and water
environment.
 To reduce the amount of T-N load, Nitrogen removal type and Johkasou made in Japan applied to overseas usage
are considered to be useful.

11３． RESULT AND DISCUSSION
3.

12Evaluation of GHG emissions from decentralized wastewater treatment plant

Table-5 GHG emissions (CO2 equivalent) per 5 PE of decentralized sewage treatment facility
Field survey
Item
Water temperature
Population equivalent (PE) for treatment
Power consumption by Blower
Operation and Maintenance
Energy Desludging
relatedSludge treatment

（℃）
（PE）

Subtotal
Wastewater treatment process（kg-CO2/unit・year）
Sludge treatment process
Non Energy Natural decomposition of effluent
relatedNatural decomposition of untreated wastewater
Subtotal
合計

EN12566-3+A2

Septic taank

BOD removaltype－50.0
0.0
1.821.5
23.3
597.0
0.1
0.0
231.7
828.8
852.0

－
5226.3
1.5
4.1
112.7
344.7
362.3
0.7
34.9
0.0
398.0
742.7

Johkasou madein Japan applied
Nitrogento overseas
removal type
usage

－
5
230.9
4.5
8.9
208.7
453.0
339.4
1.3
5.1
0.0
345.9
798.9

－
5
282.0
1.7
6.8
152.3
442.9
570.6
1.0
13.5
0.0
585.1
1,028.0

 Septic tanks have a small amount of Energy -related GHG emission, however have the largest Non energy-related
GHG emission.
 The BOD removal type (742.7 kg-CO2/unit/year) has the lowest GHG emissions, and Johkasou made in Japan applied
to overseas usage has the largest GHG emission.

Inflow pollutant load and outflow pollutant load differ depending on the test.
It is necessary to compare GHG emissions taking into account wastewater treatment capacity.

３． RESULT AND DISCUSSION

13Comparison of GHG emissions considering inflow/outflow water quality (per kg BOD removed)

Figure -5 Greenhouse gas emissions per 1kg of BOD removed,excluding the decomposition of wastewater in the natural (CO2 conversion) Johkasou made in Japan applied to overseas usage has the smallest GHG emission(7.57 kg-CO2／kg-removed BOD)
 Septic tank has a 2.7 times higher GHG emission (20.43 kg-CO2/kg-removed BOD) compared with Johkasou made inJapan applied to overseas usage.
This might be due to the low BOD removal capacity and high GHG emissions in the wastewater treatment process.
 The average value of GHG emissions for BOD removal type, nitrogen removal type, and Johkasou made in Japanapplied to overseas usage (exclude Septic tank) is 8.67 kg-CO2/kg-removed BOD.
It’s only 42% of septic tank emission when considering inflow/outflow water quality

３． RESULT AND DISCUSSION

14

Comparison of GHG emissions considering natural decomposition of effluent / untreatedwastewater

Figure -6 GHG emissions per 1kg of BOD removed considering natural decomposition ofeffluent / untreated wastewater (CO2 equivalent) Johkasou made in Japan applied to overseas usage has the smallest GHG emission (7.67kg-CO2／kg- removed BOD)
 Septic tank has a 3.7 times higher GHG emission (28.06 kg-CO2/kg-removed BOD) compared with Johkasou made inJapan applied to overseas usage.
It would be pollutant load contained in effluent from Septic tanks is high.
 The average value of GHG emissions for BOD removal type, nitrogen removal type, and Johkasou made in Japanapplied to overseas usage (exclude Septic tank) is 9.40kg-CO2／kg- removed BOD.
It’s only 34% (1/3) of septic tank emission when considering inflow/outflow water quality.

４．SUMMARY
From the perspective of the international wide spread of decentralized
wastewater treatment facilities, with regard to the environmental impact, theamount of discharged pollutant load and the amount GHG emissions was studied
in this research, and the following results were obtained.
1. The amount of BOD contamination in the effluent from the septic tank was 34 to42 times higher than that of other facilities, giving a high environmental impact.
2. The amount of GHG emissions per unit was the lowest for the EU-BOD removal
type.
3. Considering the wastewater treatment capacity of each facility, the amount ofGHG emissions per removed BOD was the lowest for Johkasou made in Japanapplied to overseas usage
4. The average value of GHG emissions per removed BOD for facilities applying
combination of anaerobic and aerobic treatments was 42% of that of Septic tank,and 34% of that of septic tanks when considering natural decomposition ofeffluent / untreated wastewater

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Thank you for your attention!