CO2 and N2O from water resource recovery facilities: Evaluation of emissions from biological treatment, settling, disinfection, and receiving water body

D Caniani; M Caivano; R Pascale; G Bianco; I M Mancini; S Masi; G Mazzone; M Firouzian; D Rosso

doi:10.1016/j.scitotenv.2018.08.150

CO₂ and N₂O from water resource recovery facilities: Evaluation of emissions from biological treatment, settling, disinfection, and receiving water body

Sci Total Environ. 2019 Jan 15:648:1130-1140. doi: 10.1016/j.scitotenv.2018.08.150. Epub 2018 Aug 13.

Authors

D Caniani¹, M Caivano², R Pascale², G Bianco³, I M Mancini², S Masi², G Mazzone², M Firouzian⁴, D Rosso⁵

Affiliations

¹ Engineering School, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy. Electronic address: donatella.caniani@unibas.it.
² Engineering School, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
³ Dipartimento di Scienze, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
⁴ Civil & Environmental Engineering Department, University of California, Irvine, CA 92697-2175, USA.
⁵ Civil & Environmental Engineering Department, University of California, Irvine, CA 92697-2175, USA; Water-Energy Nexus Center, University of California, Irvine, CA 92697-2175, USA.

PMID: 30340259
DOI: 10.1016/j.scitotenv.2018.08.150

Abstract

Water resource recovery facilities (WRRFs) contribute to climate change and air pollution, as they are anthropogenic potential sources of direct and indirect emission of greenhouse gases (GHGs). Studies concerning the monitoring and accounting for GHG emissions from WRRFs are of increasing interest. In this study, the floating hood technique for gas collection was coupled with the off-gas method to monitor and apportion nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from both aerated and non-aerated tanks in a municipal water resource recovery facility, in order to investigate its carbon footprint (CFP). To our knowledge, this is the first time that the chamber technique was applied to evaluate gas fluxes from the settler, where an emission factor (EF) of 4.71 ∗ 10^-5 kg_CO2,eq kg_bCOD^-1 was found. Interesting results were found in the disinfection unit, which was the major contributor to direct N₂O emissions (with a specific emission factor of 0.008 kg_CO2,eq kg_bCOD^-1), due to the chemical interaction between hydroxylamine and the disinfectant agent (hypochlorite). The specific emission factor of the biological aerated tank was 0.00112 kg_CO2,eq kg_bCOD^-1. The average direct CO₂ emission was equal to 0.068 kg_CO2 kg_bCOD^-1 from the activated sludge tank and to 0.00017 kg_CO2 kg_bCOD^-1 from the secondary clarifier. Therefore, taking into account the contribution of both direct N₂O and CO₂ emissions, values of 0.069 kg_CO2,eq kg_bCOD^-1, 0.008 kg_CO2,eq kg_bCOD^-1 and 0.00022 kg_CO2,eq kg_bCOD^-1_, were found for the net CFP of the aerated compartment, the disinfection unit and the clarifier, respectively. The plant energy Footprint (eFP) was also evaluated, confirming that the aeration system is the major contributor to energy consumption, as well as to indirect CO₂ emission, with a specific eFP of 1.49 kWh kg_bCOD^-1.

Keywords: Carbon dioxide; Carbon footprint; Emission; Greenhouse gas; Nitrous oxide; Wastewater treatment.