3.1 Methane (CH4) emission calculating principles

The direct methane emissions are the function of the amount of degradable carbon in the wastewater and sludge, and an emission factor. The emission factor is a function of the maximum CH4 producing potential (Bo) and the methane correction factor (MCF) for the wastewater treatment and discharge system. The Bo value of 0.6 kg CH4/kg BOD removal and the uncertainty range of �30% is recommended by IPCC [16]. The MCF indicates that the extent to which the CH4 producing capacity is realized in each type of treatment and discharge pathway and system. The CH4 emissions from constructed wetlands and CH4 emission factors for constructed wetlands are given in Eq. (6) (Eq. (6): Eq. 6.1 of IPCC, 2014: CH4

emissions from constructed wetlands) and Eq. (7) (Eq. (7): Eq. 6.2 of IPCC, 2014: CH4 emission factor for constructed wetlands), respectively.

CH4 emissions from constructed wetlands

$$\text{(CH}\_4\text{ emissions)} = \sum\_j \left( \text{TOW}\_j \cdot \text{EF}\_j \right) + \sum\_{\vec{\eta}} \left( \text{TOW}\_{\vec{\eta}} \cdot \text{EF}\_{\vec{\eta}} \right) \tag{6}$$

Eqs. (4) and (5) and the values given in Table 1 are used for N2O emission

electricity are calculated by the use of emission factor of 0.91 tCO2e Mwh<sup>1</sup> [4]. Total emissions of full-scale SBR WWTP operated from 2012 to 2015 are given

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].

Definition Default value Range

garbage disposals1.4 for countries with garbage disposals

1.0–1.5

1.25 1.0–1.5

) Total (tCO2e)

EFEFFLUENT Emission factor (kg N2O-N/kg-N) 0.005 0.0005–0.25 P Number of people in country Country specific 10% Protein Annual per capita protein consumption Country specific 10% FNPR Fraction of nitrogen in protein 0.16 0.15–0.17

calculations. Finally, indirect GHG emissions from the consumption of

Sustainability Assessment of Wastewater Treatment Plants

DOI: http://dx.doi.org/10.5772/intechopen.88338

4.2 Horizontal subsurface constructed wetland's GHG emissions

FNON-CON Non-consumed protein adjustment factor 1.1 for countries with no

Year CH4 (tCO2e) N2O (tCO2e) Electricity usage (tCO2e Mwh<sup>1</sup>

2012 74.87 0.0143 69.34 144.22 2013 248.99 0.0143 69.34 318.34 2014 87.68 0.0143 387.1 474.79 2015 68.41 0.0143 928.2 996.62

Parameter (kg/d) 2012 2013 2014 2015 BOD 312 406 292 224 TN 45 67 23 346 CH4 emission 18.72 24.36 17.52 13.44 N2O emission 0.56 0.83 0.29 4.30

FIND-COM Co-discharge factor for industrial

Total emissions of the SBR wastewater treatment plant.

Horizontal subsurface constructed wetland's GHG emissions.

nitrogen into sewers. Higher for countries with significant fish processing plants

in Table 2 [17].

Table 1.

Table 2.

Table 3.

89

N2O methodology default data [4].

where CH4 emissions, CH4 emissions in inventory year, kg CH4/year; TOWj , 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 average: i, industrial sector; j, type of CW.

CH4 emission factor for constructed wetlands EFj � � <sup>¼</sup> B0∙MCFj (7)

where EFj , emission factor, kg CH4/kg BOD or kg CH4/kg COD; j, type of CWs; B0, maximum CH4 producing capacity, kg CH4/kg BOD or kg CH4/kg COD; MCFj , methane correction factor (fraction).
