Sewerage Works inYokohama

January 31st, 2024
Environmental Planning Bureau
City of Yokohama

Outline of City of Yokohama
Current Situation
Mt. FujiLandmark TowerYokohama Port

OutlineTokyo International Airport(Haneda)
Yokohama

Information (2022)
City Area
Population
HouseholdTotal Budget

30min

435 ㎢
3.8 million
1.8 million
25.4 billion USD（JPY/USD=150）
3

International City
Nissan Stadium, where the final
game of Rugby World Cup 2019 washeld.

M Meeting
I Incentive Travel
C Convention
E Event/Exhibition

Pacifico Yokohama hosts the largest
number of international conferencesin Japan by venue. (2019)

International conventions

180times (2019)4Sewerage Development

Treated Water in Yokohama BOD 3.7mg/l (2010）

ＢＯＤ Biochemical Oxygen Demand
Biochemical oxygen demand or B.O.D. is the amount of dissolved
oxygen needed by aerobic biological organisms in a body of water tobreak down organic material present in a given water sample at
6 time period.
certain temperature over a specificTreatment District & Facilities
ItemValuePopulation

3.772 million

Coverage

99.9 %

Served District

9

Wastewater Treatment Plant

11Sludge Treatment Plant

2

Major Pumping Station26Total Sewer Length
Volume of Treated Wastewater

Approx. 11,800 km
1.6mil.m3/day

Wastewater Treatment Plant (WTP)
Sludge Treatment Plant
Pumping Station

7

Environmental Deterioration in 1960’s

8Intensive investment in sewerage development
Coverage of Sewerage Service

Construction Cost (USD million)

Over USD 1 billion
USD 19 billion in total

15 years

1976

1980

1985

1990

1995

2000

2005

2010

(JPY/USD = 100)9

Principal of Cost Burden in Sewer（雨水公費・汚水私費の原則）
Treatment of Rainwater＝TAX(General Account）

Rainwater is natural phenomenon.
Therefore, general account is applied.
Wastewater = Tariff「Polluter-Pays Principle」Therefore, tariff isapplied for treatment of wastewater.

Appropriate Cost Burden（cf. Combined Sewer Line）

Subsidy by the National Gov.
Although water facilities
shall be constructed by local
government as their own
administrative works, thenational government shallpromote the sewer works
through bearing a part ofcost.

Subsidy Ratio

Sewer
Line

１／２

Treatment
Plant

５．５／１０or
１／２

Other than national subsidy, municipal bond is issued for applying theprincipal fund. Considering the life cycle of sewer facility as 40 years, Theredemption period is 30 years for considering the fairness in burden
between generations.

Budget and Personnel (2020)(JPY/USD=150)

BudgetUSD

Composition Ratio

Total

24 Billion(100％)

Sewage Works

1.7 Billion

7％

Employees

PeopleComposition Ratio

Total

44,227(100％)

Sewage Works

832

1.9％

Basic Treatment System in Yokohama
 The wastewater becomes odor‐free and clean by conventional activate sludge process.
 Sludge generated from this wastewater treatment process is transmitted to sludge treatment
system.

Excess Sludge
Released intorivers/oceanSludge treatment system
Wastewater Treatment Plant

Sewerage System

Collecting Pipes(digestion, dewatering, incineration, etc.)
13

Wastewater Treatment
Anaerobic-anoxic-oxic Process (A2O Process)
The A2O process is a method that aims to remove nitrogenand phosphorus in addition to organic substances.
Primary
settling tankFinal
sedimentation tankreactorAnaerobic Anoxic
cellcellOxic cell

Agitator

Circulating
pump

Returnpump

14

Wastewater Treatment
Average value of water quality
Water quality(mg/l)

CategoryTarget(mg/l)

Removalrate(%)

Influent

Effluent

BOD1603.625

98

COD90

8.3

2091

SS

140

2.050

99

T-N

27

8.2

3070

T-P

3.40.91

373

Nitrogen / Phosphorous removal rate（％）
Standard methods (1997）

Advanced treatment (2010）

NitrogenPhosphorous

NitrogenPhosphorous

４８５４７４８５

Sludge Treatment (General Information)
Sludge treatment is an important issue

 Treatment of sewage
generates sludge More treatment or moreadvanced treatment produces
more sludge
 Sludge treatment needs to beconsidered in combination
with sewage treatment
 Sewage treatment is theremoval of solids fromsewage, Sludge treatment isthe removal of water fromsludge.

How it is handled is important.

 Most of the sludge is organic matter
 Strong odors are generated attreatment facilities and during thetransportation process Sludge and methane can beconverted into fuel
 Methane emissions cause global
warming Landfills are limited and lessmoisture content required Treatment process affects disposal
volume, landfill environment, andgreenhouse gas emissions
 Economies of scale are considered16

Dewatered Sludge Disposal
1985
Until 1950s

HumanWaste

1965

1975

3,700tons

53,700 tonsDewatered
SludgeDewatered
SludgeDewatered
SludgeLandfilled

Landfilled

Incinerated(16,000tons of Ash)

165,400 tons

Fertilizer

17

Transition of Sludge Treatment Methods
De centralized processing method (1962-1987)
Concentration → Digestion → Dewatering @ WWTP
⇒ Disposal/Use as fertilizer
Rapid urbanizationPopulation
growthIncreased environmental
awareness

Centalized Processing Method (1987-)
Sludge generated from 11 WWTP is pumped throughunderground pressure pipes to two sludge recycling centers.
Concentration → digestion → dehydration → incineration/fuel⇒Utilized as fuel and construction materials@ Sludge Recycling Center-Cost-effectiveness (economies of scale)-Stable monitoring and control-Odorless treatment method-More effective use of energy and resources18

Sewage Sludge Treatment
Centralized sludge treatment since 1988
Sludge generated in 11
WWTPs conveyed to 2
Sludge Treatment Centers in
the industrial zones throughpressurized pipelines

Kouhoku
WWTP

Tsuzuki
WWTP

Kanagawa WWTP

Pressurized pipeline

Sakae II
WWTP

Pressurized pipeline (extended)Pumping
stationHokubu I WWTP
Hokubu II WWTP
Hokubu STC

Chubu WWTP
Nanbu WWTP

Wastewater Treatment Plant
Sludge Treatment Center

Seibu
WWTP

Sakae I
WWTP

Kanazawa WWTP
Nanbu STC

Total pipeline length: 153 km
19Sludge Treatment Process
Adjacent refuse
incineration plant
Digestion gas

SludgePower generation
Cementplant
Ash

Mechanicalthickening

Construction
site

Dewatering
Digestion

Incineration

Alternative to fuelTransformation
into bio‐charcoal

Coal
power
plant
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Effective Use of the Sewerage Resources
Effective use of the sewerage resources and assets
Cleaning water
Small stream

Treatedwastewater

Source for air conditioning
Electric power
Digestion gas

Sewerageresources
and assets

SludgeIncinerationash

Fuel
Improved soil for backfill
Cement raw material
Effective use of the space

Facility

Optical fiber in the sewer
21

Treated Wastewater
Water discharged into public water bodies

Used in facilities such as toilets（Sold recycled water）

Wastewater treatment plant
Usage for small streams

Heat/Cool for air conditioning

22

Sewage Sludge
Power generation using digestion gas

Digestion gas

Auxiliary fuel for incineration

Sludge treatment center

Incinerator ash
Improved soil for backfill

Coal alternative fuel23
Cement raw material

23

Digester Gas Power Generation Project under PFI Method

City of Yokohama

business plan
Electricity &Heat Supply

WWTP

sludgePFI Operator

gas holder

digestion tank

Fee Payment
Digestion gas generator

digestion Gas• Licenses to businesses• Check the management of the business

Digestion gasand treatedwater supply

Investment in equipment
renewal and operation andmaintenance costs

24Conclusion
 City of Yokohama has been developing seweragesystems from planning to construction, operation andmaintenance in collaboration with the public andprivate sectors.
 The system has helped overcome urban, sanitation,environmental, and disaster issue.
 We will use this know-how to contribute to solving
water problems by collaborating with urban cities.
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