Multi-point monitoring of nitrous oxide emissions in three full-scale conventional activated sludge tanks in Europe

Supplementary material

In this document, supplementary information is provided in order to complete the technical

specifications of the sampling technique and to give the calculation method of the emission

factor (EF).

1. Schematic overview of the sampling hoods

Figure 1 - Schematic view of the sampling hoods used for the aerobic (top) and anoxic zones (bottom)

In Figure 1 (top), one of the hoods (main) was equipped with an airflow meter. Where airflow measurements were not available a cross-check between the airflow measurements at the main hood, SCADA and the aerator density in the relative area were used to obtain the best approximation.

The anoxic hood (Figure 1, bottom) uses the principle of enriching an ambient air sample by forcing it to travel counter-current along the length of the sampling area. The air sampled is dragged by the analyzer at a known airflow rate.

2. Details of the EF calculation

Once the concentrations of the ambient sample and of the off-gas sample are known, the following equation can be used to calculate the EF.

EF=

(

_∑

_{Q ∙(C}

−C

)

A

∙ A

)

∙

1

NH

−

N

Where:

 j – the area measured

 Q – the local airflow measured over the monitoring area or its best approximation. For the

anoxic zones this is the sampling flow of the N2O analyzer.



C

 C_out – the N2O-N concentration in the sample adjusted for temperature and pressure.



A

 A_{hood , j} – the area of the jth _hood.



NH

−

N

to the bioreactor and the concentration exiting the plant.

Where available, online NH4+_{-N measurements (either from SCADA or manual sampling) should be used.}

Alternatively, a known removal efficiency can be a valid substitute. The EF has the dimension of N2O-N