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SBMC Newsletter
From Sewerage Business Management Center

Vol.5 No.1
April 26, 2007
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This is the 17th Issue of SBMC Newsletter provided by
Sewerage Business Management Centre quarterly.
SBMC Newsletter covers Japan's ODA information in the field
of sewage works and current situation of sewage works in
Japan.
If you wish to subscribe or unsubscribe or were subscribed
in error, please refer to the instruction below on how to
register or unsubscribe.
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The contents of this issue are as follows.
1.

COMBINED SEWER OVERFLOW (CSO) CONTROL
Advantages and Disadvantages of Combined Sewer
Systems
2.

EFFECTIVE UTILIZATION OF DIGESTER GAS
Biomass, Environment-friendly Alternative Energy
Resource
3. REPORT FROM PARTICIPANTS IN 2006 SEWAGE WORKS ENGINEERING
AND STORMWATER DRAINAGE TECHNOLOGY JICA TRAINING PROGRAM
Mr.Oni Maso
from Papua New Guinea
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1. COMBINED SEWER OVERFLOW (CSO) CONTROL
Advantages and Disadvantages of Combined Sewer Systems

There are two types of sewage (rainwater and wastewater)
collection systems, namely, separate sewer system and
combined sewer system. Separate sewer systems consist of
two pipes. One pipe conveys stormwater runoff from storm
drains to bublic water bodies, and the other pipe conveys
sanitary sewage to a local wastewater treatment plant.
combined sewer systems (CSS) have only one pipe which
conveys both wastewater and stormwater to a local
wastewater treatment plant.

In combined sewer systems, flood control and water
quality preservation in public water bodies can be expected

by construction of one pipe. Also, systems configuration is

rather simple and construction is relatively easy as only

one pipe is constructed under the road while two pipes is

needed in case of separate systems. Therefore, combined

sewer system widely adopted in large cities such as Tokyo,
and Osaka where sewage works were promoted in early stage.

In these areas, flood control and wastewater drainage had
to be accomplished at the same time.

However, during heavy rain event, overflows occur from
these combined sewers which results in stormwater runoff

and sewage being discharged into water bodies. As design
capacity of sewer systems is limited, the exceed sewage
including rainwater and rainwater and wastewater is
discharged to public water bodies from outlet installed
in sewer systems. Deposited sludge in sewer pipe is also

washed out to water bodies at the first stage of rain

event.

Therefore, in the case of CSS, Combined Sewer Overflow

(CSO) should be appropriately controlled to preserve the

water quality in water bodies.

In Japan, basically separate systems are adopted for newly
constructed sewerage systems, as only wastewater is
transported to the treatmentplant and there is no overflow
during rain event.

To solve the problems regarding CSO, in 2001, Ministry of
Land Infrastructure and Transport established "CSO Control
Studying Committee", and finalize the report on the basic
concept for rational implementation of CSO control. Also,
in 2002, based on the study of the committee, "Guideline
and Explanation for CSO Control" was published.

To promote rational CSO Control, research and technology
development is needed, and in 2003, MLIT adopt the research
topic, "Technology Development on CSO Control" as the first
topic of SPRIT 21, Sewage Project, Integrated and
Revolutionary Technology for the 21st Century which is
managed on the initiative of MLIT and focuses on important
problems in the field of sewage works where technology
development is particularly needed.

In this project, 24 technologies classified into five
categories, Debris Removal, High Rate Filtration,
Coagulation Separation, On-site Disinfections, Measurements/
Control were evaluated and Specified performance in each
technology was certified by technical committee established
in JIWET, Japan Institute of Wastewater Engineering
Technology. The project has been coordinated and managed by
JIWET under the cooperation of municipalities, private
sector and academic institution.

The result of the project is shown in the following web
page.

http://www.jiwet-spirit21.jp/confluence/eng_02.html

http://www.jiwet-spirit21.jp/confluence/eng_03.html

In 2003, partial amendment of enforcement order of the
Sewerage Law was made, and technical standards for final
effluent water quality were set up for CSO as well as the
effluent water quality from Wastewater Treatment Plant.
This regulation will be applied after 10 years from the
enforcement, and each municipality, which adopted CSS
should submit the Comprehensive CSO Control Plan to MLIT
within 10 years.

Please refer to

http://www.sbmc.or.jp/english/200407/Partial_amendment_of
Enforcement_Order_of_the_Sewerage_Law.htm

There are following conventional counter measures for CSO

in addition to the newly developed technology by SPRIT 21.
- Stormwater Storage Tank (Storage in rain event and
treatment of stored sewage after rain event)
- Permeable Pavement (Reduction of Rainwater)
- Cleaning of Sewer
- Conversion to separate sewer system from CSS, etc.

You can see the illustrated version of this topic in the

following web page.
http://www.bmc.or.jp/english/70427/Combined_Sewer_Overflow
Control.html
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2. EFFECTIVE UTILIZATION OF DIGESTER GAS
Biomass, Environment-friendly Alternative Energy Resource

Biomass, plant and animal matter providing power or energy,
which is carbon neutral and renewable organic resource, is
very effective for prevention of global warming and
promotion of a recycling-oriented society, and its
utilization is strongly required.

Digester gas, one of the useful biomass produced by
anaerobic digestion in Wastewater Treatment Plant has been
utilized as a fuel for boilers which is used for heating
of digestion tank, and excess digester gas has not been
utilitized but only burned using gas burning equipment.
However, recently, effective measures for utilization of
excess digester gas have been established and digester gas
is widely and effectively used in Japan. In this report,
effective utilization of digester gas is explained.

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Anaerobic digestion is decomposition and decay process by
which organic matter is broken down to its simpler
chemicals components under anaerobic conditions. Anaerobic
microorganisms digest the organic matter in digestion tank
in WTP under anaerobic conditions, and produce methane
(60%), carbon dioxide (35%), and small amount of hydrogen,
nitrogen, and hydrogen sulphide, as well as trace amounts
of other gases.

Generally, digester gas is utilized as a fuel for boilers
to heat the digester tank. Excess gas burns with burning
equipment and exhaust gas is released to the atmosphere.
Under the condition that lots of excess gas is obtained in
large WTP or by using high efficiency digester tank, energy
saving in total system can be expected by utilizing the gas
energy.

As for the utilization of digester gas, direct utilization
such as a fuel for sludge incinerator, and boilers for hot
water supply or air conditioning is desirable because of
its high efficiency.

Recently, power generation systems using digester gas has
been widely adopted. In WTP in Yokohama city, most of
digester gas is used as a fuel for gas engine to produce
electric power, and the generation capacity in Hokubu WTP
is about 5,000kW. Moreover, heat recovery systems from
exhaust gas or cooling water are installed in the
generation　systems, and recovered heat is effectively used
in WTP. In this system, electricity is generated by heat
engine and at the same time byproduct heat is effectively
recovered and utilized. This system is called cogeneration
system, and its energy efficiency is high.

The methane contained in digester gas can also be used as
a fuel for Fuel cells. Fuel cells are power generating
systems that produce DC electricity by combining hydrogen
anf oxygen (from the air) in an electrochemical reaction.
Usually, pure hydrogen is expensive and hydrogen is
generated from digester gas or natural gas. The principle
of fuel cell is the reverse reaction of electrolysis of
water, an electrolytic process which decomposes water into
oxygen and hydrogen gas with the aid of an electric current.
Byproduct of fuel cells is only the water and this system
is good for environment.

In Kobe City, Biogas of which methane concentration is 98%
has been successfully produced from digester gas (methane
concentration: 60%) after eliminating the impure substances.
The quality of Biogas is almost same as city gas, and the
biogas is used as a fuel for vehicles. Generally, Biogas
needs to be upgraded in order to obtain;

A higher caloric value,
No enhancement of corrosion due to high level of
hydrogen sulphide, etc.
A gas without any mechanically damaging particles.

Since 2006, municipal bus using Biogas as a fuel, has been
operated, and it is scheduled to increase the Biogas
production in WTP.

Digester gas, one of the useful biomass produced by
anaerobic digestion in Wastewater Treatment Plant can
contribute to the prevention of global warming and

sustainable development, and several effective measures
for gas utilization have been developed in Japan.

To see the illustrated version of this topic, please visit

the following web page.
http://www.sbmc.or.jp/english 070427/Effective_Utilization
of Digester_gas.html
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3. REPORT FROM PARTICIPANT IN 2006 SEWAGE WORKS ENGINEERING
AND STORMWATER DRAINAGE TECHNOLOGY JICA TRAINING PROGRAM
Mr. Oni Maso
from Papua New Guinea

Papua New Guinea is the largest island in the pacific and

it lies barely to the South of the equator just North of
Australia. It shares the land boundary with Indonesia.
The country is vastly covered with tropical rain forest,

rugged mountains and white sandy beaches. The population of

the country is 5 million and Port Moresby, the capital city
alones population is approximately 500,000.

The National Capital District Commission was established by
an Act of the Parliament and it's role was to provide better
municipal services to the rate payers of the city.

Up until 1995, the Water Supply and Sewerage Division was
part of National Capital District Commission (NCDC).
A separate entity was established in a "Built Operate

Transfer" (BOT) system and the functions of Water Supply

and Sewerage were transferred to the new company, NCD WATER

AND SEWERAGE Pty Ltd (EDA RANU) which now manages, momitor,

provide and maintain all the services of Water and Sewerage
in NCD.

The PNG Water Board is another company that operates Water

and Sewerage services in the other parts of Papua New Guinea
except for Port Moresby. In the rural/provincial towns'
areas, the local level government is responsible for the
upkeep of the water/sewerage services (septic tank
maintenance) thorough the technical division.

The Environment & Conservation and Water Resource

department are the two body's that are responsible for the
monitoring and regulating of the water quality in the
country.

As for the Local Water & Sewerage Authority, they do take

samples of water that is discharged into the lagoons and
sea to check the water quality.

The local water and Sewerage Authority has a master plan
to in place to upgrade the city's water and sewerage
system and it is currently upgrading the city's water
supply mains.

In Port Moresby, there are three existing sewerage

treatment lagoons in the Inland area and they are located
in the Western part of the city in Waigani, Morata and
Gerehu. The lagoons consist of anaerobic and facultative
ponds. The capacity of each pond is adequate for the
influent treatment and the treated effluent is at the

acceptable level for discharge into the natural system.

However in the Coastal area, the hilly areas use pumped

reticulation systems and there is no treatment plant.

The sewer generated in the coastal areas is discharged
directly into the sea via short sea outfalls, except for

one receiving station that uses grit removal before
sewerage is pumped into the sea outfall.

The present stage of sewerage system is adequate as it is

serving it's purpose. However as the city is expanding there

is a need for new sewer lines to be constructed to meet the

demand and also to enable residents who are not connected
into the system to connect into and also to do away with the
septic tank, night soil and pit latrines.
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