Assessment of the nitrous oxide emission in a sewage treatment plant and the river receiving its effluent water

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  • 下水処理場の水処理工程および放流河川における亜酸化窒素発生量の一体的評価
  • ゲスイ ショリジョウ ノ ミズショリ コウテイ オヨビ ホウリュウ カセン ニ オケル アサンカ チッソ ハッセイリョウ ノ イッタイテキ ヒョウカ

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Abstract

<p>In order to make clear the characteristics of the nitrous oxide (N2O) emission from a sewage treatment process, total amount of the N2O emission including the direct emission, the indirect emission and the dissolved N2O emission through the treated water was assessed based on the survey. Three daily surveys were conducted in the A-STP, which is run with Pseudo-AO process, and the river receiving its effluent in Sep.2013, Dec.2013 and Sep.2014, respectively. Based on the survey, the amounts of the N2O emission were estimated by 868 kgCO2/day in September and 3,897 kgCO2/day in December, respectively. The percentages of each origin in September were as follows: the duct gathering the gases from the grit chamber, the first settling tank and sludge treatment units was 0.3% ; the direct emission from aeration tanks was 14.8% ; the gasification of the dissolved N2O in the treated water was 0.9% ; the effluent to the river as dissolved N2O in treated water was 5.8% ; indirect emission based on the IPCC guideline was 78.2% . On the other hand, the percentages of these origins in December were 0.7% , 66.4% , 8.9% , 7.1% and 16.9% , respectively. Based on the results, by accounting for the dissolved N2O in treated water as well as the direct and the indirect emission, the correct amount of N2O emission can be calculated. Since the dissolved N2O concentrations in the aeration tanks were high in winter, the controlling of DO concentration in the aeration tanks and SRT with the monitoring of nitrite concentration, might be effective to reduce the N2O emission, especially in winter.</p>

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