4.2 Horizontal subsurface constructed wetland's GHG emissions

Eight-month average (April–December) methane and nitrous oxide emissions at the outlet of full-scale constructed wetland were calculated by using Eqs. (6)–(8). Table 3 gives the calculated GHG emissions in terms of CH4 and N2O [18].


#### Table 1.

emissions from constructed wetlands) and Eq. (7) (Eq. (7): Eq. 6.2 of IPCC, 2014:

TOWj � EFj � � þ<sup>X</sup>

where CH4 emissions, CH4 emissions in inventory year, kg CH4/year; TOWj

B0, maximum CH4 producing capacity, kg CH4/kg BOD or kg CH4/kg COD; MCFj

Nitrogen oxides are associated with microbial conversion of nitrogen compound in wastewater and emerge as emissions from wastewater discharge to waterways, lakes, or seas and treatment plants or wastewater. The emission factor (0.005) is taken for domestic wastewater nitrogen effluent, referring to the default value recommended by IPCC [16]. The factor 44/28 is the conversion of kg N2O-N into kg

Nj � EFj � <sup>44</sup>=<sup>28</sup> � � <sup>þ</sup><sup>X</sup>

where N2O emissions, N2O emissions in inventory year, kg N2O/year; Nj, total nitrogen in domestic wastewater entering CWs in the inventory year, kgN/year; Ni,j, total nitrogen in industrial wastewater entering CWs in the inventory year,

used in an industrial sector, this factor would need to be a Ni,j weighted average: i, industrial sector; j, type of CW; 44/28, the factor 44/28 is the conversion of kg

Eqs. (1)–(3) and default maximum CH4 producing capacity for domestic wastewater of 0.6 kg CH4/kg BOD and 0.25 kg CH4/kg COD and (Ti,j) values given in Table 6.5 of IPCC, "Suggested values for urbanization and degree of utilization of treatment discharge pathway or method (Ti,j) for each income group for selected countries," are used for the calculation of methane emissions from

, emission factor, kg N2O-N/kg N. If more than one type of CW is

i,j

, emission factor, kg CH4/kg BOD or kg CH4/kg COD; j, type of CWs;

total organics in wastewater entering CW in inventory year, kg BOD/year or kg COD/year; EFj, emission factor, kg CH4/kg BOD (for domestic wastewater only) or kg CH4/kg COD (for domestic and industrial wastewater). If more than one type of CW is used in an industrial sector, this factor would need to be a TOWij weighted

ij

TOWij � EFj

� � (6)

� � <sup>¼</sup> B0∙MCFj (7)

Ni,j � EFj � <sup>44</sup>=<sup>28</sup> � � (8)

,

,

CH4 emission factor for constructed wetlands), respectively.

<sup>ð</sup>CH4 emissionsÞ ¼ <sup>X</sup>

average: i, industrial sector; j, type of CW.

methane correction factor (fraction).

N2O. A simplified equation is given in Eq. (8).

<sup>ð</sup>N2O emissionsÞ ¼ <sup>X</sup>

N2O emissions from constructed wetlands

j

4.1 SBR wastewater treatment plant's GHG emissions

where EFj

Water Chemistry

kgN/year; EFj

4. Results

SBR WWTP [4].

88

N2O-N into kg N2O.

CH4 emissions from constructed wetlands

j

CH4 emission factor for constructed wetlands EFj

3.2 Nitrous oxide (N2O) emission calculating principles

N2O methodology default data [4].


#### Table 2.

Total emissions of the SBR wastewater treatment plant.


#### Table 3.

Horizontal subsurface constructed wetland's GHG emissions.
