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CHAPTER 6

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CONSTRUCTED WETLANDS

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Contents

4

5
6Constructed wetlands ...................................................................................................................................... 4

6

6.1

7
8

Introduction ............................................................................................................................................ 4

6.1.1
6.2

Methane emissions from constructed wetlands ...................................................................................... 9

6.2.1

9

Relation to 2006 IPCC Guidelines ..................................................................................................... 7

Methodological issues ........................................................................................................................ 910

6.2.1.1

Choice of method ....................................................................................................................... 911

6.2.1.2

Choice of emission factors ....................................................................................................... 1212

6.2.1.3

Choice of activity data ............................................................................................................. 12

13

6.2.2

Time series consistency.................................................................................................................... 13

14

6.2.3

Uncertainties .................................................................................................................................... 13

15

6.2.4

QA/QC, Completeness, Reporting and Documentation ................................................................... 14

16

6.3

Nitrous oxide emissions from constructed wetlands ........................................................................... 15

6.3.1

17

Methodological issues ...................................................................................................................... 15

18

6.3.1.1

Choice of method ..................................................................................................................... 16

19

6.3.1.2

Choice of emission factors ....................................................................................................... 17

20

6.3.1.3

Choice of activity data ............................................................................................................. 17

21

6.3.2

Time series consistency.................................................................................................................... 19

22

6.3.3

Uncertainties .................................................................................................................................... 19

23

6.3.4

QA/QC, Completeness, Reporting and Documentation ................................................................... 20

24

6.2

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Equation 6.1

CH4 emissions from constructed wetlands ......................................................................... 1027

Equation 6.2

CH4 emissions factor for constructed wetlands .................................................................. 1228

Equation 6.3

Total organically degradable material in domestic wastewater.......................................... 13

29

Equation 6.4

Total organically degradable material in industrial wastewater ......................................... 1330

Equation 6.5

N2O emissions from constructed wetlands......................................................................... 16

31

Equation 6.6

Total nitrogen in domestic wastewater effluent ................................................................. 18

32

Equation 6.7

Total nitrogen in industrial wastewater effluent................................................................. 18

Figures33

34

Figure 6.1

Classification of constructed wetlands for wastewater treatment ........................................ 535

Figure 6.2

Constructed wetlands for wastewater treatment................................................................... 536

Figure 6.3

Wastewater treatment systems and discharge pathways ...................................................... 837

Figure 6.4

Decision tree for CH4 emissions from constructed wetland ............................................... 11

38

Figure 6.5

Decision tree for N2O emission from constructed wetland ................................................ 17

Tables

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Table 6.1

Selected factors impacting CH4 and N2O emissions in constructed wetlands...................... 6

41

Table 6.2

Conversion rate of CH4-C and N2O-N in the initial loadings of TOC and TN .................... 7

42

Table 6.3

Coverage of wastewater types and GHG gases ................................................................... 943

Table 6.4

Methane Correction Factors by types of constructed wetlands .......................................... 1244

Table 6.5

Default uncertainty ranges for domestic and industrial wastewater ................................... 1445

Table 6.6

Example of N content in some industrial wastewater ........................................................ 1946

Table 6.7

Nitrous oxide methodology default uncertainties .............................................................. 20

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6 CONSTRUCTED WETLANDS

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6.1

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DEFINITION

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Wetland ecosystems can act as sources, sinks, or transformers of nutrients and carbon (Mitsch and Gossenlink,1993). This ability of wetlands has lead to a widespread use of natural and constructed wetlands for water quality
enhancement.

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Natural wetlands are characterized by anaerobic conditions and low turnover rates for organic matter, and arethus important terrestrial sinks for carbon and nitrogen (Augustin et al., 1998). Polluted water may be discharged
into wetland sites and a significant improvement in water quality obtained (Brix, 1997). "Semi-natural treatment
wetlands" for wastewater treatment are natural wetland systems that have been modified for this purpose. The
modifications made within these systems usually are based on increasing the volume reserved (i.e. dams) andconstructing channels for targeting the influent and effluent. These systems can be found in both freshwater andcoastal wetlands.

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Constructed wetlands systems are fully human-made wetlands for wastewater treatment, which apply various
technological designs, using natural wetland processes, associated with wetland hydrology, soils, microbes andplants. Thus, constructed wetlands are engineered systems that have been designed and constructed to utilize thenatural processes involving wetland vegetation, soils, and their associated microbial assemblages to assist intreating wastewater. Synonymous terms to “constructed” include “man-made”, “engineered” or “artificial”
wetlands (Vymazal, 2007).

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APPLICATION OF CONSTRUCTED WETLANDS FOR WASTEWATERTREATMENT

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Constructed wetlands are used to improve the quality of point and nonpoint sources of water pollution, includingstormwater runoff, domestic wastewater, agricultural wastewater, and coal mine drainage. Constructed wetlands
are also being used to treat petroleum refinery wastes, compost and landfill leachates, fish pond discharges, andpretreated industrial wastewaters, such as those from pulp and paper mills, textile mills, and seafood processing.
For some wastewaters, constructed wetlands are the sole treatment; for others, they are one component in asequence of treatment processes (US EPA, 2000).

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There are various types of constructed wetlands used for treatment of different wastewater, and following
subchapter highlights the main classification of constructed wetlands.

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TYPE OF CONSTRUCTED WETLANDS FOR WASTEWATER TREATMENT

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Constructed wetlands may be categorized according to the various design parameters, but the three mostimportant criteria are hydrology (water-surface flow and subsurface flow), macrophyte growth form (emergent,
submerged, free-floating) and flow path (horizontal and vertical) (Fig. 6.2 and Fig. 6.3; Vymazal 2007, 2011).
Different types of constructed wetlands may be combined (which are called hybrid or combined systems) toutilize the specific advantages of the different systems. For instance, to guarantee more effective removal ofammonia and total nitrogen, during the 1990s and 2000s an enhanced design approach combined vertical andhorizontal flow constructed wetlands to achieve higher treatment efficiency (Vymazal, 2011).

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Figure 6.1

Classification of constructed wetlands for wastewater treatment

Constructedwetlands

Free floating
plantsFloating leaved
plantsEmergent plants

Surface flow
(Free water surface)

Submerged plants

Sub-surface flow
Vertical flow
(downflow or upflow)

Horizontal Flow

Hybrid systems
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Note: Adopted from Vymazal, 2001

87

Figure 6.2

Constructed wetlands for wastewater treatment

A)

C)

D)
B)

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Note: Adopted from Vymazal, 2001. A) constructed wetland with free-floating plants (FFP), B) constructed wetland with free water surface
and emergent macrophytes (FWS), C) constructed wetland with horizontal sub-surface flow (HSSF, HF), D) constructed wetland withvertical sub-surface flow (VSSF, VF)

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Constructed Wetlands with Surface Flow

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Constructed Wetlands with Subsurface Flow

Constructed wetlands with surface flow (SF), known as free water surface constructed wetlands (FWS CWs),
contain areas of open water and floating, submerged, and emergent plants (Kadlec and Wallace 2008). The
shallow water depth, low flow velocity, and presence of the plant stalks and litter regulate water flow and,especially in long, narrow channels, ensure plug-flow conditions (Crites et al 2005). The most common
application for FWS constructed wetlands is for tertiary treatment of municipal wastewater and also forstormwater runoff and mine drainage waters (Kadlec and Knight 1996; Kadlec and Wallace 2008). FWS
wetlands are suitable in all climates, including the far north (Mander and Jenssen 2003).
In horizontal subsurface flow constructed wetlands (HF CWs), the wastewater is fed in at the inlet and flows
slowly through the porous medium under the surface of the bed planted with emergent vegetation to the outlet
where it is collected before leaving via a water level control structure (Vymazal et al 1998). During passage thewastewater comes into contact with a network of aerobic, anoxic, and anaerobic zones. Most of the bed is

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anoxic/anaerobic due to permanent saturation of the beds. The aerobic zones occur around roots and rhizomesthat leak oxygen into the substrate (Brix 1987). HF CWs are commonly sealed with a liner to prevent seepage
and to ensure the controllable outflow. HF CWs are commonly used for secondary treatment of municipal
wastewater but many other applications have been reported in the literature (Vymazal and Kröpfelova 2008).
The oxygen transport capacity in these systems is insufficient to ensure aerobic decomposition, thus, anaerobic
processes play an important role in HF CWs (Vymazal and Kröpfelova 2008). HF CWs having the ability toinsulate the surface of the bed are capable of operation under colder conditions than FWS systems (Mander andJenssen 2003).

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Vertical flow Constructed Wetlands
Vertical flow constructed wetlands (VF CWs) comprise a flat bed of graded gravel topped with sand planted withmacrophytes. Contrary to HF CWs, VF CWs are fed intermittently with large batches, thus flooding the surface.
Wastewater then percolates down through the bed and is collected by a drainage network at the bottom. The bed
drains completely which allows air to refill the bed. Thus, VF CWs provide greater oxygen transfer into the bed,
thus producing a nitrified (high NO3-) effluent (Cooper et al 1996; Cooper 2005). On the other hand, VF CWs do
not provide suitable conditions for denitrification to complete conversion to gaseous nitrogen forms which
escape to the atmosphere.

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In recently developed tidal (“fill and drain”) flow systems better contact of wastewater with the microorganisms
growing on the media is guaranteed. This significantly enhances the purification processes (Vymazal 2011).

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Hybrid Constructed Wetlands

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Another configuration is the HF-VF system. The large HF bed is placed first to remove organics and suspended
solids and to provide denitrification. An intermittently loaded small VF bed is used for additional removal oforganics and suspended solids and to nitrify ammonia to nitrate. To maximize removal of total nitrogen, however,the nitrified effluent from the VF bed must be recycled to the sedimentation tank (Vymazal 2011).

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The VF-HF and HF-VF constructed wetlands are the most common hybrid systems, but in general, any kind of
constructed wetlands could be combined to achieve higher treatment effect (Vymazal 2007).

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GREENHOUSE GASES EMISSIONS FROM VARIOUS TYPES OFCONSTRUCTED WETLANDS

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Emissions of greenhouse gases (GHGs) such as methane (CH4) and nitrous oxide (N2O) are a “byproduct” ofconstructed wetlands which importance has been increasing recently. Among several environmental factors
controlling the GHG emissions, availability of C and nutrients (especially N) which directly depends on
wastewater loading, temperature, hydrological regime (pulsing vs steady-state flow), groundwater depth,
moisture of filter material (water filled soil pores (WFSP)) , and presence of aerenchymal plants play asignificant role (see Table 6.1).

Various types of constructed wetlands may be combined to achieve higher removal efficiency, especially for
nitrogen. The design consists of two stages, several parallel VF beds followed by 2 or 3 HF beds in series (VFHF system). The VF wetland is intended to remove organics and suspended solids and to provide nitrification,
while in the HF wetland denitrification and further removal of organics and suspended solids occurs.

TABLE 6.1
SELECTED FACTORS IMPACTING CH4 AND N2O EMISSIONS IN CONSTRUCTED WETLANDS
Factors/processes

CH4

N2O

Higher water/soil/air temperature

Increase in most cases

No clear relationship

Higher moisture of soil or filter material(higher value of WFSP)

Clear increase

Decrease

Higher wastewater loading

Increase

Increase

Presence of aerenchymal plants

Increase

Increase

Pulsing hydrological regime(intermittent loading)

Clear decrease

Increase (decrease in some FWS
CWs)

Deeper water table (from surface) in
HSSF CWs

Decrease

Increase

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Table 6.2 shows CH4 and N2O conversion rate derived from literature-based relationship between the initial(input) C and N loading and respective CH4 and N2O emissions in main types of constructed wetlands. There is asignificant positive correlation (p < 0.05) between the initial loading and CH4 and N2O emissions in both FWS
and VSSF constructed wetlands, whereas no correlation was found for HSSF types. Seemingly, high variabilityof conditions and combination of several factors in HSSF constructed wetlands may be the reason for that. Also,
limited number of data did not allow derive reliable relationship for HSSF constructed wetlands. These sharescan be used as base for calculation of emision factors for Tier 1 and Tier 2. High emission factor for CH4 in FWS
CWs (Table 6.4) is caused by the additional CH4 from sediments accumulated in the bottom of surface flow
wetlands . Due to the lack of data, no clear relationship has been found between the emission of CH4 and N2Oother environmental factors.
TABLE 6.2
CONVERSION RATE OF CH4-C AND N2O-N IN THE INITIAL LOADINGS OF TOC AND TN
Type of CW

CH4-C

N2O-N

FWS

40 (5.9)

0.24 (0.10)

VSSF

1.44 (0.24)

0.021 (0.005)

HSSF

5.1 (2.4)

1.0 (0.5)

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Soil/air temperature and the soil moisture (WFSP, depth of (ground) water level) are the most significant factors
affecting emission of CH4 in constructed wetlands (Mander et al 2003; Van der Zaag 2010). Several
investigations show that the water table deeper than 20 cm from the surface of wetlands and/or water-logged
soils oxidizes most CH4 fluxes (Soosaar et al 2011; Salm et al 2012). Fluxes of N2O, however do not show clear
correlation with soil/air temperature and significant emissions of N2O from constructed wetlands has been
observed in winter (Søvik et al 2006). Likewise, freezing and thawing cycles enhance N2O emissions (Yu et al2011). Hydrological regime also plays a significant role in GHG emissions from constructed wetlands. Altor and
Mitsch (2008) and Mander et al (2011) demonstrated that the intermittent loading (pulsing) regime andfluctuating water table in constructed wetlands enhance CO2 emissions and significantly decreases CH4emissions. N2O emission, in contrary, does not show a clear pattern regarding pulsing regime.

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6.1.1

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This chapter is a supplement to Chapter 6 WASTEWATER TREATMENT AND DISCHARGE in the 2006
Guidelines. The 2006 Guidelines (2006 Guidelines, IPCC, 2006) included a new section to estimate CH4
emissions from uncollected wastewater. This section is expanded to cover CH4 emissions from constructedwetlands and semi-natural treatment wetlands. This Supplement on Wetland includes nitrous oxide (N2O)
emissions from constructed wetlands and semi-natural treatment wetlands. Emission factors of CH4 and N2Ofrom constructed wetlands and semi-natural treatment wetlands treating industrial wastewater are the same as
domestic wastewater treating ones. CO2 emissions are not included in GHG emissions from wastewater
treatment as CO2 from wastewater is considered biogenic.

Note: Average and standard error (in brackets) are presented

Relation to 2006 IPCC Guidelines

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Figure 6.3

Wastewater treatment systems and discharge pathways

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Domestic and Industrial Wastewater
Collected

Uncollected

Untreated

Rivers, Lakes,
Estuarine, Sea

TreatedStagnant
sewer

Aerobic treatment
SludgeAnaerobic
Digestion

Seweredto plant

Treated on site
Domestic: latrine,
septic tankIndustrial: On site plant

Anaerobic treatment
ReactorLand
DisposalTreated

LagoonUntreated
Rivers, Lakes,
Estuarine,Sea

To ground

ConstructedWetlands, Semi‐
natural treatment
Wetlands

Landfill orIncineration

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Note: Emissions from boxes with bold frames are accounted for 2006GLs. Supplement provides EF for black color box; ConstructedWetlands and semi-natural treatment wetlands for treatment of collected wastewater.

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Coverage of wastewater types and gases

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Chapter 6 of the 2006 IPCC Guidelines provide guidance on estimation of CH4 and N2O emissions fromdomestic with emission factor based on treatment technology. Constructed wetland is an additional treatment
technology in this supplement to 2006 IPCC Guidelines. The emission factors described in this chapter coverconstructed wetlands and semi-natural treatment wetlands (collected and treated) see Fig. 6.1.

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The methodology is provided for calculation of CH4 and N2O emissions from both domestic and industrial
wastewater. The indirect N2O emissions from potential wastewater such as runoff from agricultural land arecovered in the 2006 IPCC Guidelines. Emissions from agro-industrial wastewater (except manure management)
and mine drainage are considered as industrial wastewater. As for solid waste landfill leachate, CH4 emissions
have already been taken into account in solid waste disposal on land (6A) in the 2006 IPCC Guidelines, and are
not included in section 6.2, while N2O emissions are considered in section 6.3”

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TABLE 6.3
COVERAGE OF WASTEWATER TYPES AND GHG GASESType of Wastewater

MethaneNitrous oxide

Domestic wastewater

Included in this supplement with
provision of MCF and correction
factors for temperature and vegetation

Included in this supplement with
provision of EF

Industrial wastewater including
agro-industrial and dairy farm
wastewater

Included in this supplement with
provision of MCF and correction
factors for temperature and vegetation

Included in this supplement with
provision of EF

Runoff from agricultural land

Negligible

Covered in 2006 IPCC Guidelines(Vol.4 Chapter 11)

Leachate from landfill

Covered in the 2006 IPCC Guidelines

Included in this supplement

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6.2

METHANE EMISSIONS FROM CONSTRUCTEDWETLANDS

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6.2.1

Methodological issues

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Methane emissions are a function of the organic materials loaded into constructed wetlands and an emission
factor to which the waste generate CH4.

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Three tier methods for CH4 from constructed wetlands are summarized below.
The Tier 1 method applies default values for the emission factor and activity parameters. This method is
considered good practice for countries with limited data.
The Tier 2 method follows the same method as Tier 1 but allows for incorporation of country specific emission
factor and country specific activity data. For example, a specific emission factor based on field measurements
can be incorporated under this method.
The Tier 3 method could be used by countries with good data and advanced methodologies. A more advanced
country-specific method could be based on plant-specific data from operating constructed wetland treatment
system.
Constructed wetlands can be operated under anaerobic and aerobic conditions. But CH4 generated at such
facilities is not usually recovered and combusted in a flare or energy device. So CH4 recovery is not consideredhere.
The amount of vegetation harvesting from constructed wetland is generally very small and their impact to total
emissions from constructed wetlands is considered insignificant. Moreover, the harvesting is usually not
performed on regular basis and the quantity of harvested biomass is commonly not recorded so it is notconsidered in this supplement.
Emissions from semi-natural treatment wetlands treating uncollected wastewater are also estimated using thesame methodology.

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6.2.1.1

C HOICE OF METHOD

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A decision tree for domestic or industrial wastewater is included in the Figure 6.4.
The general equation to estimate CH4 emissions from constructed wetland treating domestic or industrial
wastewater is as follows.

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EQUATION 6.1
CH4 EMISSIONS FROM CONSTRUCTED WETLANDS
CH4 Emissions = TOW  EF
Where:

234

CH4 emissions=

CH4 emissions in inventory year, kg CH4/yr

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TOW

=

total organics in wastewater treated by constructed wetland in inventory

236

year, kg BOD/yr or kg COD/yr
EF

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=

emission factor, kg CH4/kg BOD or kg CH4/kg COD

TOW and EF for estimation of CH4 emissions from constructed wetlands can be integrated in equation 6.1 foremission from domestic wastewater and equation 6.4 for emission of industrial waste in 2006 IPCC Guidelines

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Figure 6.4

Decision tree for CH 4 emissions from constructed wetland

Start

Are data on
wastewater
treatment in CW
available?

Use the 2006 IPCC Guidelines
for the estimation of emissions
from other wastewater
treatment processes

No

Yes

Are measurement
or bottom-up data
available for CW
treatment?

Is a countryspecific method
available?

Yes

Yes

Estimateemissions using
bottom-up data

Box 3: Tier 3NoNo

Are countryspecific EF
available for CW
treatment?

Yes

Estimate emissions using
country specific EF

Box 2: Tier 2

No

Is this a key
category?

Yes

Estimate country-specific
Bo and MCF

No
Estimate emissions using
default emission factors

Box 1: Tier

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6.2.1.2

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The emission factor for a wastewater treatment by constructed wetland is a function of maximum CH4 producing
potential (Bo) and the methane correction factor (MCF).

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EQUATION 6.2
CH4 EMISSIONS FACTOR FOR CONSTRUCTED WETLANDS

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C HOICE OF EMISSION FACTORSEF = Bo  MCF  VCF  TCF
Where:

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EF=

emission factor, kg CH4/kg BOD or kg CH4/ kg COD

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Bo

=

maximum CH4 producing capacity, kg CH4/kg BOD or kg CH4/ kg COD

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MCF

=

methane correction factor (fraction)

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VCF

=

vegetation correction factor (fraction)

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TCF

=

temperature correction factor (fraction)

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Good practice is to use country-specific data for Bo, where available, expressed in term of kg CH4/kg BOD
removed for domestic wastewater or kg CH4/ kg COD removed for industrial wastewater to be consistent withthe activity data. If country specific data is not available, the following default values can be used.
The 2006 IPCC Guidelines provide default maximum CH4 producing capacity (Bo) for domestic and industrial
wastewater: 0.6 kg CH4/kg BOD and 0.25 kg CH4/kg COD.
Methane Correction Factor (MCF) indicates the extent to which CH4 producing capacity (Bo) is realized in eachtype of constructed wetland. It is an indication of the degree to which the system is anaerobic. The proposed
MCF for each type of constructed wetland treating domestic and industrial wastewater, derived from literature
based analysis of CH4 conversion rate (table 6.2) is provided below.
TABLE 6.4
METHANE CORRECTION FACTORS BY TYPES OF CONSTRUCTED WETLANDS
CW type

MCF

Range

FWS
HSSF
VSSF (intermittent loading)

0.35
0.1
0.03

0.32-0.37
0.064-0.227
0.025-0.048

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Anaerobic condition generally occurred in wetlands. The unknown type of semi-natural treatment wetlands canuse the default MCF of 0.35. CH4 emission for wastewater treated by natural wetland and coastal wetland, MCF
is considered to be also 0.35

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6.2.1.3

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The activity data for this source category is the amount of organic materials in the wastewater treated byconstructed wetland (TOW). This parameter is a function of population served by constructed wetland systemand biochemical oxygen demand (BOD) generation per person per day. BOD default values for selected
countries are provided in the 2006 IPCC Guidelines (Table 6.4, Chapter 6). In case of industrial wastewater,
COD loading to the constructed wetland system per day (kg COD/day) can be used. Examples of industrial
wastewater data from various industries are provided in Table 6.9, Chapter 6 of the 2006 IPCC Guidelines.

Vegetation Correction Factor (VCF) depends on the type of vegetation grown in constructed wetland. If
aerenchymal plant types are used, default VCF of 1.0 can be used. For non-aerenchymal, VCF of 0.6 is assumed
as a default value. Aerenchyma is an air channel in the root of some plants, which allows exchange of gases
between the shoot and the root.
Temperature Correction Factor (TCF) varies according to the climate zone in which constructed wetland islocated. For tropical or subtropical zone, TCF of 1.0 is assumed as the default value. For temperate and boreal
climate, TCF of 0.6 is set as a default value.

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If industrial wastewater is released into domestic sewers, it is estimated together with domestic wastewater.
The equation for TOW is:

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EQUATION 6.3
TOTAL ORGANICALLY DEGRADABLE MATERIAL IN DOMESTIC WASTEWATERTOW = P  BOD  I  0.001  365

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EQUATION 6.4
TOTAL ORGANICALLY DEGRADABLE MATERIAL IN INDUSTRIAL WASTEWATER

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TOW = COD  W  365
Where:
TOW

350

=

351

total organics in domestic or industrial wastewater treated in constructed wetland ininventory year (kg BOD/year or kg COD/year)

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P

=

population in the country

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BOD

=

country-specific per capita BOD generation in inventory year (g BOD/person/day)

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I

=

correction factor for additional industrial wastewater discharged into sewers (for355

collected the default is 1.25, for uncollected the default is 1.00 as recommended in the3562006 IPCC Guidelines)

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COD

=

COD concentration in industrial wastewater treated by constructed wetland ininventory year (kg COD/m3)

358=

Daily flow rate of industrial wastewater treated by constructed wetland, m3/d

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W

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6.2.2

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The same method and data sets should be used for estimating CH4 emissions from constructed wetland treating
wastewater for each year. The MCF for different treatment systems should not change from year to year, unlesssuch a change is justifiable and documented. If the share of wastewater treated in different treatment systems
changes over the time period, the reasons for these changes should be documented.

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6.2.3

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374
375
376
377
378
379
380

Chapter 3, Uncertainties, in Volume 1 of 2006 IPCC Guidelines provides advice on quantifying uncertainties inpractice. It includes guidance on eliciting and using expert judgments which in combination with empirical data
can provide overall uncertainty estimates. Table 6.7 and 6.10 in Chapter 6 of Volume 5 provides default
uncertainty ranges for emission factor and activity data of domestic and industrial wastewater respectively. The
following parameters are believed to be very uncertain:The quantity of wastewater is treated in constructed wetland or semi-natural treatment wetlands receiving
wastewater.

381
382



The fraction of organics that is converted anaerobically to CH4 during wastewater collection. This will
depend on hydraulic retention time and temperature in the wastewater collection pipeline, and on other

Time series consistency

Activity data that are derived from population data, which is available for all countries and all years, countries
need to determine the fraction of population served by constructed wetland systems. If data on the share ofwastewater treated are missing for one or more years, the surrogate data and extrapolation/interpolation splicing
techniques described in Chapter 5, Time Series Consistency, of Volume 1 General Guidance and Reporting canbe used to estimate emissions. Emissions from wastewater treated in constructed typically do not fluctuatesignificantly from year to year.

Uncertainties

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factors including the presence of anaerobic condition in the wastewater collection pipeline and possiblycomponents that are toxic to anaerobic bacteria in some industrial wastewater.

385
386



The amount of industrial TOW from small or medium scale industries that is discharged into constructedwetland in developing countries might be difficult to quantify.

387
388



Different types of vegetation applied in constructed wetlands that involved in gas exchange due to thiers
physical structure of Aerenchyma.

389
TABLE 6.5
DEFAULT UNCERTAINTY RANGES FOR DOMESTIC AND INDUSTRIAL WASTEWATER
Parameter

Uncertainty range

Emission factor
Maximum CH4 producing capacity (Bo)± 30%

Methane correction factor (MCF)

FWS: -8%,+14%,
VSSF: -16%, +60%
HSSF: -36%, +127%

Vegetation Correction Factor (VCF)

This data can be very uncertain depended on type of plantused in CWs. An uncertainty of -50% to +100% issuggested (Expert judgement : Authors)Temperature Correction Factor (TCF)* This data can be very uncertain depended on type ofplant used in CWs. An uncertainty of -30% to +30% issuggested. (Expert judgement : Authors)

Activity data390

Human population± 5%

BOD per person± 30%

Correction factor for additional industrial
BOD discharged into sewers (I)For uncollected, the uncertainty is zero %. For collected
the uncertainty is ± 20%

COD loading from industrial wastewater

± 30%

6.2.4

391

QA/QC, Completeness, Reporting andDocumentation

392
393
394
395
396
397

It is good practice to conduct quality control checks and quality assurance procedures as outlined in Chapter 6,
QA/QC and Verification, of Volume 1. Below, some fundamental QA/QC procedures include:

398
399
400



401
402
403
404
405
406
407
408
409
410

Activity Data
 Make sure that the sum of wastewater flows of all types of wastewater treatment processes including
constructed wetland equal 100 percent of wastewater collected and treated in the country.
Inventory compilers should compare country-specific data on BOD in domestic wastewater to IPCC default
value. If inventory compilers use country-specific values they should provide documented justification why
their country-specific values are more appropriate for their national circumstances.

Emission Factors
 For domestic wastewater, inventory compilers can compare country-specific values for Bo with the IPCC
default value (0.25 kg CH4/kg COD or 0.6 kg CH4/kg BOD). Although there are no IPCC default values forthe fraction of wastewater treated anaerobically, inventory compilers are encouraged to compare values for
MCFs against those from other countries with similar wastewater handling practices.


6.14

Inventory compilers should confirm the agreement between the units used for degradable carbon in thewaste (TOW) with the units for Bo. Both parameters should be based on the same units (either BOD or COD)
in order to calculate emissions. This same consideration should be taken into account when comparing theemissions.

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412



For countries that use country-specific parameters or higher tier methods, inventory compilers shouldcrosscheck the national estimates with emissions using the IPCC default method and parameters.

413
414



For industrial wastewater, inventory compilers should cross-check values for MCFs against those from othernational inventories with similar constructed wetland types

415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442

Completeness for estimating emissions from industrial wastewater depends on an accurate characterization ofindustrial sectors that produce organic wastewater and the organic loading applied to constructed wetland system.
So the inventory compilers should ensure that these sectors are covered. Periodically, the inventory compilers
should re-survey industrial sources, particularly if some industries are growing rapidly. This category should
only cover industrial wastewater treated onsite. Emissions from industrial wastewater released into domestic
sewer systems should be addressed and included with domestic wastewater.

443

6.3

NITROUS OXIDE EMISSIONS FROMCONSTRUCTED WETLANDS

445

6.3.1

Methodological issues

446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464

Nitrous oxide (N2O) emissions can occur as direct emissions from wastewater treatment constructed wetlands
through nitrification and denitrification. Emissions are a function of the total nitrogen loaded into constructedwetland and an emission factor to which the wastewater generate N2O.

CompletenessCompleteness can be verified on the basis of the degree of utilization of a treatment or discharge system orpathway (T) for all wastewater treatment system used. The sum of T should equal 100 percent. It is a goodpractice to draw a diagram for the country to consider all potential anaerobic treatment and discharge systems
and pathways, including collected and uncollected, as well as treated and untreated. Any high strength
wastewater treated in domestic wastewater treatment facilities should be included in the collected category. In
general, the amount of vegetation harvested from constructed wetland is very small. If vegetation biomass isremoved for the purpose of composting, incineration and burning, disposal in landfills or as fertilizer on
agricultural lands, the amount of biomass should be consistent with data used in the relevant sectors.

Reporting and documentation
It is good practice to document and report a summary of the methods used, activity data and emission factors.
Worksheets are provided at the end of this volume. When country-specific methods and/or emission factors areused, the reasoning for the choices as well as references to how the country-specific data (measurements,
literature, expert judgment, etc.) have been derived (measurements, literature, expert judgment, etc.) should be
documented and included in the reporting.
More information on reporting and documentation can be found in the 2006 IPCC Guidelines in Volume 1,
Chapter 6, Section 6.11 Documentation, archiving and reporting.

444

Two tier methods for N2O from this category are summarized below.
The Tier 1 method applies default values for the emission factor and activity parameters. This method is
considered good practice for countries with no country specific data.
The Tier 2 method follows the same method as tier 1 but allows for incorporation of country specific emission
factor and country specific activity data. For example, a specific emission factor based on field measurements
can be incorporated under this method. Nitrogen is taken up by plant and the degree of vegetation coverage area
in constructed wetlands affects the emission. The plant uptake of nitrogen reduces the potential of N2O emission
via nitrification and denitrification.
The methodology was provided assuming typical vegetation harvesting practice condition. However, the amountof biomass harvested from constructed wetland is generally very small and the harvested biomass is commonly
not recorded so the harvesting practice is not considered as an influencing factor in the estimation of emission.

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467

Emissions from semi-natural treatment wetland treating uncollected wastewater are also estimated using thesame methodology. Indirect N2O emission from domestic wastewater treatment effluent that is discharged into
aquatic environments has already been covered in 2006 IPCC Guidelines.

468

6.3.1.1

469
470
471
472
473

A decision tree for domestic or industrial wastewater is included in the Figure 6.5.

474
475
476

EQUATION 6.5
N2O EMISSIONS FROM CONSTRUCTED WETLANDSN2O Emissions = NEFFLUENT  EF  44/28

C HOICE OF METHOD

The general equation to estimate N2O emission from constructed wetland treating domestic or industrial
wastewater is as follows:

477
478

Where:N2O Emissions=

N2O emission in inventory year, kg N2O/yr

479

NEFFLUENT=

total nitrogen in wastewater treated by constructed wetland in inventory year,

480

kg N/year
EF

481

=

emission factor, kg N2O-N/kg N

482

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484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515

Figure 6.5

Decision tree for N 2 O emission from constructed wetland

Start

Are data on
wastewater
treatment in CW
available?

Use the 2006 IPCC Guidelines
for the estimation of emissions

No

Yes

Are measurement
or bottom-up data
available for CW
treatment?

Yes

Is a countryspecific EF
available?

Yes

Estimateemission using
country-specificEF
Box 2: Tier 2

No

No

Estimate emissions
using default EF
Box 1: Tier 1

516

6.3.1.2

C HOICE OF EMISSION FACTORS

517
518
519
520
521
522

The default IPCC emission factor for N2O emissions from domestic and industrial wastewater is 0.00075 kg
N2O-N/kg N. This value is based on data provided in the literatures and can be used for different types of
constructed wetlands. They are influenced by the extent of nitrification and denitrification taking place inconstructed wetlands, the coverage of vegetation in constructed wetlands and climatic conditions. Good practiceis to use country-specific data for emission factor, where available, expressed in term of kg N2O-N/kg N loadedfor domestic and industrial wastewater to be consistent with the activity data.

523

6.3.1.3

524
525
526
527
528
529

The activity data for this source category is the amount of nitrogen in the wastewater treated by constructedwetland (TN). This parameter is a function of population served by constructed wetland system, annual per
capita protein consumption (Protein) and factor for non-consumed nitrogen added to the wastewater for domestic
wastewater. In case of industrial wastewater, TN loading to the constructed wetland system in inventory year (kgN) can be used directly. The equations for determining TN for domestic and industrial wastewater are:

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531
532

EQUATION 6.6
TOTAL NITROGEN IN DOMESTIC WASTEWATER EFFLUENTNEEFLUENT, DOM = P  Protein  FNPR  FNON-CON  FIND-COM

533
EQUATION 6.7
TOTAL NITROGEN IN INDUSTRIAL WASTEWATER EFFLUENTNEFFLUENT, IND = TN  W  365

534
535
536
537
538

Where:NEFFLUENT, DOM or IND

539=

total nitrogen in municipal or industrial wastewater treated inconstructed wetland in inventory year (kg N/year)

540

P

=

human population in the country

541

Protein=annual per capita protein consumption, kg/person/yr

542

FNPR

=

fraction of nitrogen in protein, default = 0.16 kg N/ kg protein

543

FNON-CON =544

FIND-COM=

factor for non-consumed nitrogen added to the wastewatercorrection factor for additional industrial wastewater discharged into sewers (for545

collected the default is 1.25, for uncollected the default is 1.00 as recommended in

546

2006 IPCC Guidelines

547

TN

=

548

wetland in inventory year (kg N/m3)
W

549
550
551
552
553

total nitrogen concentration in the industrial wastewater treated by constructed=daily flow rate of industrial wastewater treated by constructed wetland, m3/d

TN loading can be estimated by multiplying total volume of wastewater ( Table 6.9 Chapter 6,Volume 4 in 2006
IPCC guideline ) and N content in Table 6.6.

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TABLE 6.6
EXAMPLE OF N CONTENT IN SOME NITROGEN-RICH INDUSTRIAL WASTEWATER
Wastewater generation W(m3/ton)N Range (kg/m3)

24 (16-32)1

2.40 (0.94-3.86)2

Fish processing industry

5 (2-8)20.60 (0.21-0.98)3

Seasoning source industry

NA

0.60 (0.22-1.00)3

Meat & Poultry

13 (8-18)1

0.19 (0.17-0.20)3

Starch Production

9 (4-18)1

0.90 (0.80-1.10)4

2.89 (0.46-8.3)20.50 (0.10-0.80)2

15-25% of annual precipitation6

0.74 (0.01-2.50)5

Industry type
Alcohol refining

Nitrogen Fertilizer Plant
Landfill leachate

555
556
557

Note: Average value and range (in brackets) are presented
Sources:1 2006 IPCC GL; 2Samokhin (1986); 3Pilot Plant Development and Training Institute (1994); 4Hulle et.al (2010):
5

Kjeldsen et al (2002); 6 Ehrig (1983)

558

6.3.2

Time series consistency

559
560
561

The same method and data sets should be used for estimating N2O emissions from constructed wetland treating
wastewater for each year. If a country decides to change the estimation method from default methodology (Tier1) to country specific emission data (Tier 2), this change must be made for the entire time series.

562

6.3.3

563
564
565

Large uncertainties are associated with the IPCC default emission factors for N2O emissions from constructedwetlands due to limited number of available data.

Uncertainties

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TABLE 6.7
NITROUS OXIDE METHODOLOGY DEFAULT UNCERTAINTIESParameter

Default value

Range

0.00075 kg N2O-N/kg N

0.00015-0.03

Human population

Country-specific± 5%

Annual per capita protein consumption

Country-specific

± 10%

0.16

0.15-0.17

1.1 for countries with nogarbage disposals,
1.4 for countries withgarbage disposals
Country-specific1.0-1.5

Emission factor
Activity data

Fraction of nitrogen in protein
Factor for non-consumed nitrogen

TN loading from industrial wastewater

567

6.3.4

568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585

± 30%

QA/QC, Completeness, Reporting andDocumentation

This method makes use of several default parameters. It is recommended to solicit experts’ advice in evaluating
the appropriateness of the proposed default factors. The methodology for estimating emissions is based on
nitrogen associated with domestic and industrial discharge either collected into the collection system and treatedin constructed wetland or uncollected and discharged into semi-natural treatment wetland. This estimate can beseen as conservative estimate and covers the entire source associated with domestic and industrial wastewater
discharge.
Reporting and documentation
It is good practice to document and report a summary of the methods used, activity data and emission factors.
Worksheets are provided at the end of this volume. When country-specific methods and/or emission factors areused, the reasoning for the choices as well as references to how the country-specific data (measurements,
literature, expert judgment, etc.) have been derived (measurements, literature, expert judgment, etc.) should be
documented and included in the reporting.
More information on reporting and documentation can be found in Volume 1, Chapter 6, Section 6.11
Documentation, archiving and reporting.

586

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DRAFT 2013 Wetlands Supplement

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