Biomass, plant and animal matter used to provide power or energy,
is broadly defined in Japan as renewable organic resource generated
from plant and/or animal matter, and there are several kinds of
Biomass such as waste material like livestock waste, sewage sludge,
etc. unused plant like rice straw, remaining material from wood
processing, etc. and crops like sugarcane, sugar beat, etc.
These kinds of biomass can be utilized as fuel, biomass plastic,
biogass, compost, etc.

As biomass is carbon neutral, meaning that the same amount of
carbon dioxide emitted by burning it was absorbed by plants that
went into producing it, utilization of biomass is effective for
reduction of greenhouse gas emissions and prevention of global
warming

For this reason, in 2002, Biomass Comprehensive Strategy in Japan
was decided by the cabinet. Basic policy for application and
utilization of Biomass was set up, and lots of activities have
been conducted in diverse ways.

In 2003, the Basic Plan for Establishing the Recycling-based
Society was also decided by cabinet, and the target of the plan
was decided to halve the final disposal amount of waste in 2001
by 2010.

In Kyoto Protocol ratified in 2005, goals for reducing greenhouse
gas emissions for each participating country were established,　and
Japan Government has decided policies for prevention of global
warming.

One of policies regarding Kyoto Protocol was Renewable Portfolio
Standard Law which was established in 2003 for power utilities.
By this law, each power utility should utilize specific amount of
new energy source such as wind power, solar energy, biomass, and
geothermal energy for electric power generation to promote the
biomass utilization. In other business field such as iron and steel
industry, paper manufacture, and oil trade which lots of fossil
fuel is consumed, several studies for utilization of biomass fuel
were also conducted for reducing greenhouse gas emission and fuel
quantity consumed.

In the field of sewage works, more approach for utilization of
biomass is also expected for prevention of global warming and
creation of a recycling society.

Under these circumstances, the project utilizing the sewage sludge
as a biomass fuel is now widely being studied. This project is
to make a solid fuel from drying or carbonization sewage sludge,
and utilize it as a fuel in coal thermal power plant after
mixing with coal.

Sewage sludge is a carbon-neutral biomass and an effective
resource for prevention of global warming. Among lots of
biomass, sewage sludge has an advantage that the generated
amount and quality is almost constant throughout the year, so
in business field which lots of fossil fuel is used, sewage
sludge has been considered as an effective new energy resource
for prevention of global warming.

In this sewage sludge biomass fuel project, municipalities, which
promote sewage works can expect several advantages such as
increase of sewage sludge recycling rate, reduction of the final
disposal sludge amount, and reduction of green house gas generated
from incineration of sewage sludge.

Also, for thermal power plant, CO2 emission and fossil fuel
consumption can be reduced and the utilization of new energy
using biomass can be promoted. Especially, recently, the price
of fossil fuel has been increasing.

In Japan, there are 73 coal thermal power plants with total
generation capacity, 30 million KW. The possible amount to
utilize sewage sludge in coal power plant with generation
capacity, 1 million KW, is about 1,000 t of dewatered cake from
Wastewater Treatment Plant. This amount of sludge is equal to
the generated amount in WTP of which sewered population is
almost 3 million.

The form of sewage sludge, which can be used in coal boiler
as fuel, is mainly classified in two types, sludge
carbonization and dried sludge, and Japan Sewage Works Agency
has conducted several research concerning Solid Fuel from sewage
sludge.

Sludge carbonization is a technology for producing carbonized
sludge composed of “carbon + minerals” that retains the carbon
content by thermal decomposition of low or zero oxygen, while
in the case of incineration, carbon in the sludge is completely
burnt with oxygen in incinerator.

Japan Sewage Works Agency and private company have conducted
joint research on developing carbonization furnace and obtained
lots of patent. The generated carbonized sludge is odor-free
and its calorie is about 3000kcal/kg. The temperature in
carbonization furnace is about 800 degrees Celsius.
　
As the calorific power will increase when the sludge is
carbonized under low temperature, fuel manufacturing system
using carbonized sludge under low temperature is now being
developed. The development objectives are optimization of
energy balance, assurance of safety of produced carbonized
sludge regarding self-heating, etc.

Carbonized Sludge
Carbonization Furnance Cross Section
from leaflet of Konan Cyubu Treatment plant in Shiga Pref.


Dried sludge has more calorific value than carbonized sludge,
and final product of dried sludge is large in quantity compared
with carbonized sludge. Then, pelletization solid fuel system
using dried sludge can retain much more energy which is contained
in sludge than carbonized sludge. Japan Sewage Agency has been
developing the system for improvement of odor and assurance of
safety of produced carbonized sludge regarding self-heating and
conducting a research to make solid fuel from sludge in
Nakaminato WTP in Kitakyusyu City from 2006. Generated solid
fuel is used for practical purposes in coal fired power
generation plant which is constructed in iron mill in Kitakyusyu
City.

Photo-1 Pelletization Solid Fuel System Using Dried Sludge


Tokyo Metropolitan Government has moved into action to utilize
carbonized sludge made from generated 300t sludge in Eastern
Sludge Treatment Center managed by TMG, as a fuel in actual
coal power plant of Tokyo Electric Power Co. This project
will start from 2007, and produced solid fuel will be traded
as valuable resource.

Also, Aichi Prefecture starts the joint research on sewage
sludge fuel using carbonization furnace with Cyubu Electric
Power Company from 2008. In this research, carbonized sludge
will be produced in Kinuura Tobu WTP managed by Aichi pref.
and examine the practicality of carbonized sludge in actual
coal power plant. Japan Sewage Works Agency will cooperate
with this research to make carbonized sludge.

The amount of generating sludge has been increasing year by
year with promotion of sewage works, and 20% of industrial
waste in Japan is sewage sludge.
Presently, final sewage sludge treatment is classified into
effective utilization and disposal by sanitary landfill,
and 64% generated sludge in Japan in 2004 was reused and
other 36% was disposed by land reclamation. In future, it
will be more difficult to secure landfill site and effective
utilization of sewage sludge should be promoted.

There are several ways for effective utilization of sewage
sludge, and among them solid fuel from sewage sludge is
considered as useful measures in respect of prevention of
global warming and energy saving. Also, sewage sludge has
an advantage for user that solid fuel can be constantly
produced in WTP and its quality is stable compared with
other biomass.


Sludge Carbonation System and Pelletization Sludge Solid
Fuel System developed by Japan Sewage Works Agency have
converted the sewage sludge which had been difficult to
dispose, into new energy recourse to prevent global warming
and save energy.

>>Category top