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B-51.2.1 Field Observation for CH₄ and N₂O Balance of Solid Waste and Wastewater treatment process

[Contact Person]

Yuhei Inamori
Team Head, International Water Environment Renovation Research Team
Regional Environmental Division
National Institute for Environmental Studies
Environmental Agency
16-2 Onogawa, Tsukuba, Ibaraki, 305 Japan
Tel:+81-298-50-2400, Fax:+81-298-50-2530
E-mail:inamori@nies.go.jp

Total Budget for FY1998

3,705,000Yen

Abstract

As a nation with a low degree of self-sufficiency in food, Japan imports large quantities of nitrogen and organic materials as food or animal feed, and these are released into the environment as contaminated water or waste material. For this reason, according to the operation conditions of the treatment systems that handle the nitrogen that is emitted and the organic material produced from these sources and the changes in the states of these substances after they have been released into the environment, there is a strong possibility of these becoming emission sources with a high potential for emitting CH₄ and N₂O. But it has been pointed out that CH₄ and N₂O inventories for Japan are hampered by their extremely narrow estimation range and low estimation precision for contaminated water and waste material. As a response to this situation, this research project was a survey of an existing sewage treatment plant conducted to study the actual state of emissions of N₂O and based on this, its formation route. The results have revealed that unit quantities of N₂O produced are from 8.33 to 11.2 per person (mgN₂O-N/capita/day) and 21.2 to 29.2 per cubic meter of in flowing water (mgN₂O-N/m³ inflow) and that in some cases the quantity of N₂O-N that is emitted as gas dissolved in the discharged water accounts for almost half of this total. These results suggest that there is a high probability of N₂O dissolved in the discharged water entering the atmosphere as gas. In addition, the higher the N₂O-N accumulation rate, the higher the N₂O formation rate, the N₂O formation rate is accelerated in cases where the NH₄-N concentration is higher than the NO₂-N or NO₃-N concentrations, but that when it is lower, the N₂O formation rate is lower. Consequently, almost all N₂O formation under aerobic conditions is caused by NH₄⁺ oxidization and NO₂^- reduction, suggesting that of these, the catabolistic reduction reaction of NO₂ is the principal mechanism.

[Key Words]

CH₄, N₂O, Waste and Wastewater Treatment. Inventory, Biological Reaction