Sewage Sludge Composting Facility (Introduced to: Biei Town, Hokkaido Prefecture)
Sewage Sludge – High Speed Composting Facility
At present, 2.2 million tons per year of sewage sludge (dry matter base) is generated in Japan, but only about 25% of it is used as biomass. (2015 Ministry of Land, Infrastructure, Transport and Tourism) Approximately 50,000 tons of phosphorous is contained in that sewage sludge. This is a huge amount, equivalent to 10% of the amount that Japan imports, so there is need to utilize this resource.
Therefore, Biei Town decided to build a composting facility in order to use sewage sludge.
There were some conditions to meet when building the facility. First, it must do high temperature fermentation reliably even in winter (when the outside temperature is -10 to -20˚ C). Second, the facility is close to tourist destinations, so it must not emit foul odors. Third, management would be outsourced, so the equipment must be easy to maintain.
This facility is located on the north side of Biei Town, which has an average annual temperature of 5.6˚ C and a minimum temperature below -20˚ C in winter, and there are tourist destinations nearby. Therefore, they selected a Miraie plant because of the features important to them, such as the fact that fermentation temperature rises reliably even in winter and ensures stable performance, and it does not pollute the outside environment with foul odors.
Sewage sludge generated from the sewage treatment facility in town is carried in closed containers to the composting facility.
Moisture content is approximately 83%. An auxiliary material (return compost) is added to it for composting.
Compost material is deposited into a high pressure aeration (EasyJet) fermentation tank, and fermentation is completed in 42 days.
It keeps the fermentation temperature above 70˚ C even in winter, enabling stable operation year round.
The finished compost has no odor, and moisture content of 40%, so it is dry and easy to use.
Compost produced at this facility is used at facilities around town, as well as for gardening and other activities.
|Odor Measurement Result||Measurement Locations and Results|
|Ammonia||5 to 6 ppm directly above the fermentation tank, 2 ppm directly below the ventilation fan|
|Methyl Mercaptan||0 ppm both directly above the fermentation tank and directly below the ventilation fan|
|Hydrogen Sulfide||0 ppm both directly above the fermentation tank and directly below the ventilation fan|
These are the results of odor measurement.
Ammonia was not detected, except for trace amounts directly above the fermentation tank.