Quantifying direct carbon dioxide emissions from wastewater treatment units by nondispersive infrared sensor (NDIR) – A pilot study

Abstract Treatment of nutrient-rich wastewater potentially results in direct release of greenhouse gases (GHGs) such as CO 2 , N 2 O or CH 4 – and thus affects Waste Water Treatment Plant's carbon footprint. Accurate CO 2 quantification is challenging due to various chemical, physical and operational conditions. A floating chamber equipped with a nondispersive infrared, single beam, dual wavelength sensor has been evaluated for a pilot approach to quantify fugitive CO 2 emissions above different wastewater treatment units. Total average CO 2 flux was 1182 g CO 2 ·m −2 ·d −1 with minimum and maximum fluxes of 829 g CO 2 ·m −2 ·d −1 and 1493 g CO 2 ·m −2 ·d −1 , respectively. Total observed CO 2 emissions were in 7 to 17 kg CO 2 ·PE −1 ·a −1 (average 12 kg CO 2 ·PE −1 ·a −1 ). The nitrification tank accounted for about 94.3% of the emissions, followed by secondary clarification (ca. 4.3%) and denitrification (ca. 1.4%), based on those average annual CO 2 emissions per population equivalent (PE).