Research Trends and Results

Global warming countermeasure in sewage works
HARADA Ichiro, HeadYAMASHITA Hiromasa, Senior Researcher
MIYAMOTO Ayako, Researcher
TSUSHIMA Ikuo(PhD. Engineering), Researcher
OGOSHI Masashi(PhD. Engineering), Researcher
MATSUHASHI Manabu, Researcher
Wastewater and Sludge Management Division, Water Quality Control Department(Keywords) Global warming countermeasure, Nitrous oxide, Recycled water, Energy efficiency
1. Introduction
Sewage works emit greenhouse gasses directly fromwastewater treatment plants and consume much energy, andit is being a main emission source of greenhouse gasses thatcomes from office operation of the local government.
Global warming countermeasures in sewage works needmultifaceted efforts such as energy use efficiency alongwith reduction of greenhouse gas generation. In ourdepartment, investigation research has been done fromevery point of view.
2. Nitrous oxide emission control from wastewater
treatment processes
Nitrous oxide (N2O) that has 310 times the greenhouseeffect of carbon dioxide, is emitted from wastewater
treatment processes. However the emission situation at
actual plants is not understood, and specific emission
control countermeasures have not yet been established,because the generating mechanism has a lot of unclear
points.
Therefore, regarding N2O that is emitted during
wastewater treatment processing, we investigated theN2O-generation situation in actual plants with different
treatment methods (picture). As a result, there was a lot ofemission in standard activated sludge process that has shortsludge retention time, and it becomes suppressed inmembrane separation activated sludge process. Therefore it
was assumed that N2O emission becomes suppressed if
nitrification is progressed well. In the future, establishmentof emission control technology will be determined by theproceeding clarification of N2O generating mechanism
along with paying attention to microbial community
structures in reaction tanks.
3. Global warming countermeasure by use ofreclaimed wastewater
Global water resource shortage is a cause for concern anduse of reclaimed wastewater has caught attention. In thissituation, the assessment of the effect of the use ofreclaimed wastewater has also been needed from the pointof view of global warming. The department has proceeded
to develop an assessment measure of greenhouse gas
reduction effect by using reclaimed wastewater, and thefollowing results were obtained by 2013.
According to the result of an investigation of carbon
dioxide generation by life cycle assessment measure(LC-CO2), it is suggested that LC-CO2 of area-widecirculation of reclaimed wastewater is lower compared toon-site circulation within a building, and the water-saving
effect from area-wide circulation is high. Also, bycomparison by type of wastewater treatment technology, apossibility of energy saving is indicated by using membrane
bio reactors as pretreatment. It is planned to continuously
consider the structural analysis of energy consumption andassessment measures of new technology.
4. Improvement of energy efficiency by cooperation
with other businesses
To further improve energy efficiency and the reduction ofgreenhouse gasses in sewage works, cooperation with otherenergy consumers and suppliers is expected along withusing countermeasures of their facilities. With that, acooperation measure in terms of technology and businessalong with city planning that relates closely to sewage
works has been considered, and the results weresummarized. A diagnostic tool has been created that caneasily calculate prospect of profit of the project bydeveloping project feasibility study methods ofcollaborative technology along with developing the latest
technology menu that can be applicable to sewage works
and other business and arranging check items. These
achievements are planned to be published, and it is expected
to be used for consideration or assessment of collaborative
project.

Picture: Research of N2O that is emitted from the wastewater
treatment process.