Abstract
Data about Greenhouse Gas (GHG) emissions from settling units in wastewater treatment plants (WWTPs) are limited, probably because of the increased difficulties in evaluating direct emissions when there is absence of an induced air stream through the liquid volume (Caivano et al. 2016). Particularly, gas samples collection is not immediate and easy due to the low off-gas flow leaving the liquid surface.
In this study, a modified off-gas apparatus is proposed, to avoid these experimental problems. A floating hood was connected to a blower to simulate the wind action and encourage the gas stripping. The incoming air flow rates were fixed to 4, 9, and 16 Nl min−1, simulating a wind velocity of 1.05, 2.36, and 4.19 m/s, respectively, in order to measure GHG emissions from a full-scale plant in several conditions. The same experimental conditions and a reproducible sampling apparatus were employed to measure GHG emissions also from a pilot plant. The monitoring of the full-scale plant shows that the concentrations of N2O and CO2 in the off-gas change rapidly, demonstrating the stripping effect induced by the blower air flow. A peak is reached and then a rapidly decrease is observed, proving a gradual decrease of mass transfer phenomena. As expected, the peak value increases with increasing the wind speed, whereas the time at which the peak is observed decreases. Regarding the pilot-scale plant, the results show the slow diffusion phenomena occurring in a closed system, preventing the mass transfer from the liquid to the gaseous phase.
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References
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Acknowledgments
This research was carried out in the framework of the project ‘Smart Basilicata’ (Contract n. 6386 - 3, 20 July 2016). Smart Basilicata was approved by the Italian Ministry of Education, University and Research (Notice MIUR n.84/Ric 2012, PON 2007-2013 of 2 March 2012) and was funded with the Cohesion Fund 2007–2013 of the Basilicata Regional authority. Part of this study was funded by the Italian Ministry of Education, University and Research (MIUR) through the Research project of national interest PRIN2012 (D.M. 28 dicembre 2012 n. 957/Ric – Prot. 2012PTZAMC) entitled “Energy consumption and GreenHouse Gas (GHG) emissions in the wastewater treatment plants: a decision support system for planning and management” (http://ghgfromwwtp.unipa.it) in which Donatella Caniani is responsible of the Unibas Research Unit.
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Caivano, M. et al. (2017). N2O and CO2 Emissions from Secondary Settlers in WWTPs: Experimental Results on Full and Pilot Scale Plants. In: Mannina, G. (eds) Frontiers in Wastewater Treatment and Modelling. FICWTM 2017. Lecture Notes in Civil Engineering , vol 4. Springer, Cham. https://doi.org/10.1007/978-3-319-58421-8_65
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DOI: https://doi.org/10.1007/978-3-319-58421-8_65
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