N2O emission in a full-scale partial nitrification/anammox process
A BSTRACT The reduction of the emission of greenhouse gases to the atmosphere will be one of the challenges that society will have to face in the coming years. Until now, all efforts have been put in improving the properties of the discharged water in a wastewater treatment plant and the efficiency of the whole process. But little effort has been done in measuring and controlling the greenhouse gas emissions. For this reason, the production of nitrous oxide when treating wastewater has become of great concern. Several measurements in laboratory scale and full scale have been done and a wide range of results have been obtained. On the other hand, Himmerfjärden wastewater treatment plant has a deammonification plant for treating rejected water produced when dewatering sludge. It consists of an efficient technology where less energy is supplied and no extra carbon source is added. However, it is unknown the efficiency of this system in terms of nitrous oxide production. For this reason, an analysis was carried out from the 19th June to the 2nd of July. In the light of the results obtained, the deammonification process has obtained better results than conventional nitrification and denitrification in terms of nitrous oxide emissions. Key words: GHG; Global Warming; nitrous oxide; deammonification; rejected water.
1. I NTRODUCTION The world’s population has considerably increased in the last fifty years and it is expected to continue with this tendency for the next decades. Meanwhile, food, heat and energy have also experienced an increasing demand that has been solved by developing new technologies. The use of artificial fertilizers in farms and croplands and nitrogen in industries have become usual as well as burning fossil fuels for heat and energy production in order to cover this high demand. However, they have a considerable environmental impact that has been of great concern for national governments and international institutions since the 70s. Concentration of nitrogenous ions in water has become higher leading to problems such as eutrophication or loss of biodiversity and the release of nitrogenous gases have produced ozone layer depletion, greenhouse effect and climate change with an impact on global scale. The main objective for the 21st Century for humanity is to minimize and reduce these environmental impacts. Treating nitrogenous compounds in wastewater has been essential for controlling eutrophication in river and lakes. New strict regulations have been approved in developed countries and have been applied since then. There are several nitrogenous compounds that can be found in wastewater (Gerardi, 2002): organic nitrogen, ammonium ions or ammonia, nitrite and nitrate. Treating these pollutants in wastewater has positive effects on the water basin where it is discharged: problems such as eutrophication or oxygen depletion are avoided or, at least, minimized. Nevertheless, this treatment process has also some drawbacks: emission of greenhouse gases such as CO2 due to electricity supply in the wastewater treatment plant (WWTP) and N2O produced in some processes when removing nitrogen. Both are greenhouse gases that should be minimized when treating wastewater.
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