2.1 Methane (CH4) emission calculating principles

Estimation of organically degradable material in domestic wastewater, estimation of methane emission factor (EF) for domestic wastewater, and estimation of CH4 emissions from domestic wastewater are steps for calculating CH4 emissions.

In wastewater treatment technologies like activated sludge, membrane methods are not feasible enough for widespread application in rural areas [2]. Constructed wetlands however are attracting great concern due to lower cost, easy operation, and less maintenance requirements as a reasonable option for treating wastewater in rural areas. They are designed and constructed to mimic natural wetland systems for removing contaminants which are basically composed of vegetation, substrates, soils, microorganisms, and water, utilizing complex processes involving physical, chemical, and biological mechanisms (e.g., sedimentation, filtration, precipitation, volatilization, adsorption, plant uptake, and various microbial processes) [3].

While the treatment performance of CWs is critically dependent on the optimal

The greenhouse effect of major greenhouse gases, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) all produced in wastewater treatment operations, is weighted by their global warming potentials (GWP). Over a period of 100 years, 1 ton of methane and nitrous oxide will have a warming effect equivalent to 25 and 298 ton of CO2, respectively [4]. In the same direction, it is stated that

operating parameters (water depth, hydraulic retention time and load, feeding mode and design of setups, etc.) which could result in variations in the removal efficiency of contaminants, plant species and media types are crucial influencing factors for the treatment in CWs as they are considered to be the main biological component of CWs. Emergent, submerged, floating-leaved, and free-floating plants are commonly planted among 150 macrophyte species. The most common used emergent species reported are Phragmites spp. (Poaceae),Typha spp. (Typhaceae), Scirpus spp. (Cyperaceae), Iris spp. (Iridaceae), Juncus spp. (Juncaceae), and

Eleocharis spp. (Spikerush) [3].

Operation sequence for sequential batch reactor [1].

Figure 1.

Water Chemistry

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The direct methane emissions are a function of the amount of degradable carbon in the wastewater and sludge and an emission factor. As can be seen from Eq. (1) (Eq. (1): Eq. 6.2 of IPCC, 2006:CH4 emission factor for each domestic wastewater treatment/discharge pathway or system), the emission factor is a function of the maximum CH4 producing potential (Bo) and the methane correction factor (MCF). The Bo value of 0.6 kg CH4/kg BOD removal, the uncertainty range of �30%, and the MCF value of 0.05 are recommended [4].

disposal of effluent into waterways, lakes, or the sea. The emission factor (0.005) is taken for domestic wastewater nitrogen effluent, referring to the default value recommended by IPCC [4]. The factor 44/28 is the conversion of kg N2O-N into kg N2O. A simplified equation is given in Eq. (5). Emission factors of N2O were

ð Þ¼ NEFFLUENT ðP∙Protein∙FNPR∙FNON�CON∙FIND�COMÞ � NSLUDGE

N2O emissions from wastewater effluent

where N2O emissions, N2O emissions in inventory year, kg N2O/year; NEFFLUENT, nitrogen in the effluent discharged to aquatic environments, kg N/year, EFEFFLUENT, emission factor for N2O emissions from discharged to wastewater, kg N2O-N/kg N; 44/28, the factor 44/28 is the conversion kg N2O-N into kg N2O.

The two main factors causing CO2 production from wastewater treatment plants are the type of treatment process and electricity consumption. During anaerobic treatment, the BOD5 in the wastewater is either converted to CO2 or CH4, or some of it enters the biomass and is also converted to CO2 and CH4 by endogenous respiration. Other sources of carbon dioxide emissions are caused by sludge digesters and digestion gas combustion. In aerobic process, CO2 is produced by decomposition of organic substances. Since CO2 emissions from the wastewater treatment plant are biogenic, they are not included in the national total emissions and are not considered in the IPCC Guidelines. Biogenic origin means that it is part of the natural carbon cycle and the food chain passing from plants to animals and

2.3 Carbon dioxide (CO2) emission calculating principles

3. Emission calculating principles for constructed wetlands

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

humans, or natural atmospheric CO2 source.

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3.1 Methane (CH4) emission calculating principles

where NEFFLUENT, total annual amount of nitrogen in the wastewater effluent, kg N/year; P, human population; Protein, annual per capita protein consumption, kg/person/year; FNPR, fraction of nitrogen in protein, default = 0.16, kg N/kg protein; FNON-CON, factor for non-consumed protein added to the wastewater; FIND-COM, factor for industrial and commercial co-discharged protein into the sewer system; NSLUDGE, nitrogen removed with sludge (default = zero), kg N/year.

<sup>ð</sup>N2O emissionsÞ ¼ NEFFLUENT∙EFEFFLUENT∙44=<sup>28</sup> (5)

(4)

evaluated by incorporating N loads in influent of the SBR WWTP.

Total nitrogen in the effluent

Sustainability Assessment of Wastewater Treatment Plants

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

Total organics in wastewater (TOW) (in inventory year, kg BOD/year) is a function of human population and BOD generation per person, and it is expressed in terms of biochemical oxygen demand (kg BOD/year). TOW was calculated by using Eq. (2) (Eq. (2): Eq. 6.3 of IPCC, 2006: total organically degradable material in domestic wastewater) [4].

CH4 emission factor for each domestic wastewater treatment= discharge pathway or system EFj � � <sup>¼</sup> B0∙MCFj (1)

where Fj emission factor, kg CH4/kg BOD; j each treatment/discharge pathway or system; B0 maximum CH4 producing capacity, kg CH4/kg BOD; MCFj methane correction factor (fraction).

$$\begin{aligned} \text{Total originally degrades material in domestic wastewater} \\ \text{(TOW)} = \text{P}\text{-BOD}\text{-}0.001\text{-}1\text{-}365 \end{aligned} \tag{2}$$

where TOW, total organics in wastewater in inventory year, kg BOD/year; P, country population in inventory year (person); BOD, country-specific per capita BOD in inventory year, g/person/day; 0.001, conversion from gram BOD to kg BOD, I, correction factor for additional industrial BOD discharged into sewers (for collected the default is 1.25; for uncollected the default is 1.00).

The general equation for estimating CH4 emissions from domestic wastewater was calculated by using Eq. (3) (Eq. (3): Eq. 6.1 of IPCC, 2006: total CH4 emissions from domestic wastewater).

Total CH4 emissions from domestic wastewater

$$\mathbf{(CH\_4\text{ emissions})} = \left[\sum\_{\vec{\eta}} \left(U\_i \cdot T\_{\vec{\eta}} \cdot EF\_j\right) \bullet (\mathbf{TOW} - \mathbf{S}) - \mathbf{R}\right] \tag{3}$$

where CH4 emissions, CH4 emissions in inventory year, kg CH4/year; TOW, total organic wastewater in inventory year, kg BOD/year; EFj, emission factor, kg CH4/kg BOD; S, organic component removed as sludge in inventory year, kg BOD/ year; Ui, fraction of population in income group i in inventory year; Ti,j, degree of utilization of treatment/discharge pathway or system, j, for each income group fraction i in inventory year; i, income group: rural, urban high income and urban low income; j, each treatment/discharge pathway or system; R, amount of CH4 recovered in inventory year, kg CH4/year.

#### 2.2 Nitrous oxide (N2O) emission calculating principles

Estimation of nitrogen in effluent, estimation of emission factor, and emissions of indirect N2O emissions from wastewater are steps for calculating N2O emissions. It is associated with the microbial conversion of nitrogen compound in the wastewater. It occurs as emissions from treatment plants or from wastewater after

Sustainability Assessment of Wastewater Treatment Plants DOI: http://dx.doi.org/10.5772/intechopen.88338

The direct methane emissions are a function of the amount of degradable carbon in the wastewater and sludge and an emission factor. As can be seen from Eq. (1) (Eq. (1): Eq. 6.2 of IPCC, 2006:CH4 emission factor for each domestic wastewater treatment/discharge pathway or system), the emission factor is a function of the maximum CH4 producing potential (Bo) and the methane correction factor (MCF). The Bo value of 0.6 kg CH4/kg BOD removal, the uncertainty range of �30%, and

Total organics in wastewater (TOW) (in inventory year, kg BOD/year) is a function of human population and BOD generation per person, and it is expressed in terms of biochemical oxygen demand (kg BOD/year). TOW was calculated by using Eq. (2) (Eq. (2): Eq. 6.3 of IPCC, 2006: total organically degradable material in

CH4 emission factor for each domestic wastewater treatment=

Total organically degradable material in domestic wastewater

collected the default is 1.25; for uncollected the default is 1.00).

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

recovered in inventory year, kg CH4/year.

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2.2 Nitrous oxide (N2O) emission calculating principles

� � <sup>¼</sup> B0∙MCFj

where Fj emission factor, kg CH4/kg BOD; j each treatment/discharge pathway or system; B0 maximum CH4 producing capacity, kg CH4/kg BOD; MCFj methane

ð Þ¼ TOW <sup>P</sup>∙BOD∙0:001∙I∙<sup>365</sup> (2)

where TOW, total organics in wastewater in inventory year, kg BOD/year; P, country population in inventory year (person); BOD, country-specific per capita BOD in inventory year, g/person/day; 0.001, conversion from gram BOD to kg BOD, I, correction factor for additional industrial BOD discharged into sewers (for

The general equation for estimating CH4 emissions from domestic wastewater was calculated by using Eq. (3) (Eq. (3): Eq. 6.1 of IPCC, 2006: total CH4 emissions

Ui � Tij � EFj

where CH4 emissions, CH4 emissions in inventory year, kg CH4/year; TOW, total organic wastewater in inventory year, kg BOD/year; EFj, emission factor, kg CH4/kg BOD; S, organic component removed as sludge in inventory year, kg BOD/ year; Ui, fraction of population in income group i in inventory year; Ti,j, degree of utilization of treatment/discharge pathway or system, j, for each income group fraction i in inventory year; i, income group: rural, urban high income and urban low income; j, each treatment/discharge pathway or system; R, amount of CH4

Estimation of nitrogen in effluent, estimation of emission factor, and emissions of indirect N2O emissions from wastewater are steps for calculating N2O emissions. It is associated with the microbial conversion of nitrogen compound in the wastewater. It occurs as emissions from treatment plants or from wastewater after

� �∙ð Þ� TOW � <sup>S</sup> <sup>R</sup> " (3)

Total CH4 emissions from domestic wastewater

ij

(1)

the MCF value of 0.05 are recommended [4].

discharge pathway or system EFj

domestic wastewater) [4].

Water Chemistry

correction factor (fraction).

from domestic wastewater).

disposal of effluent into waterways, lakes, or the sea. The emission factor (0.005) is taken for domestic wastewater nitrogen effluent, referring to the default value recommended by IPCC [4]. The factor 44/28 is the conversion of kg N2O-N into kg N2O. A simplified equation is given in Eq. (5). Emission factors of N2O were evaluated by incorporating N loads in influent of the SBR WWTP.

Total nitrogen in the effluent ð Þ¼ NEFFLUENT ðP∙Protein∙FNPR∙FNON�CON∙FIND�COMÞ � NSLUDGE (4)

where NEFFLUENT, total annual amount of nitrogen in the wastewater effluent, kg N/year; P, human population; Protein, annual per capita protein consumption, kg/person/year; FNPR, fraction of nitrogen in protein, default = 0.16, kg N/kg protein; FNON-CON, factor for non-consumed protein added to the wastewater; FIND-COM, factor for industrial and commercial co-discharged protein into the sewer system; NSLUDGE, nitrogen removed with sludge (default = zero), kg N/year.

$$\begin{aligned} \text{N}\_2\text{O emissions from wastewater effect} \\ \text{(N}\_2\text{O emissions)} = \text{N}\_{\text{EFFLUENT}} \cdot \text{EF}\_{\text{EFFLUENT}} \bullet 44/28 \end{aligned} \tag{5}$$

where N2O emissions, N2O emissions in inventory year, kg N2O/year; NEFFLUENT, nitrogen in the effluent discharged to aquatic environments, kg N/year, EFEFFLUENT, emission factor for N2O emissions from discharged to wastewater, kg N2O-N/kg N; 44/28, the factor 44/28 is the conversion kg N2O-N into kg N2O.
