Industrial wastewater

Industrial wastewater may be treated on site or released into domestic sewer systems. If it is released into the domestic sewer system, the emissions are to be included with the domestic wastewater emissions. This section deals with estimating CH4 emissions from on-site industrial wastewater treatment. Only industrial wastewater with significant carbon loading that is treated under intended or unintended anaerobic conditions will produce CH4. Organics in industrial wastewater are often expressed in terms of COD, which is used here. Choice of method

A decision tree for industrial wastewater is included in Figure 6.3.

Figure 6.3 Decision Tree for CH4 emissions from industrial wastewater treatment

Figure 6.3 Decision Tree for CH4 emissions from industrial wastewater treatment

Wastewater Data

1. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

1. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Assessment of CH4 production potential from industrial wastewater streams is based on the concentration of degradable organic matter in the wastewater, the volume of wastewater, and the propensity of the industrial sector to treat their wastewater in anaerobic systems. Using these criteria, major industrial wastewater sources with high CH4 gas production potential can be identified as follows:

• pulp and paper manufacture,

• meat and poultry processing (slaughterhouses),

• alcohol, beer, starch production,

• organic chemicals production,

• other food and drink processing (dairy products, vegetable oil, fruits and vegetables, canneries, juice making, etc.).

Both the pulp and paper industry and the meat and poultry processing industries produce large volumes of wastewater that contain high levels of degradable organics. The meat and poultry processing facilities typically employ anaerobic lagoons to treat their wastewater, while the paper and pulp industry also use lagoons and anaerobic reactors. The non-animal food and beverage industries produce considerable amounts of wastewater with significant organic carbon levels and are also known to use anaerobic processes such as lagoons and anaerobic reactors. Anaerobic reactors treating industrial effluents with biogas facilities are usually linked with recovery of the generated CH4 for energy. Emissions from the combustion process for energy should be reported in the Energy Sector.

The method for estimating emissions from industrial wastewater is similar to the one used for domestic wastewater. See the decision tree in Figure 6.3. The development of emission factors and activity data is more complex because there are many types of wastewater, and many different industries to track. The most accurate estimates of emissions for this source category would be based on measured data from point sources. Due to the high costs of measurements and the potentially large number of point sources, collecting comprehensive measurement data is very difficult. It is suggested that inventory compilers use a top-down approach that includes the following general steps:

Step 1: Use Equation 6.6 to estimate total organically degradable carbon in wastewater (TOW) for industrial sector i

Step 2: Select the pathway and systems (Figure 6.1) according to country activity data. Use Equation 6.5 to obtain emission factor. For each industrial sector estimate the emission factor using maximum methane producing capacity and the average industry-specific methane correction factor.

Step 3: Use Equation 6.4 to estimate emissions, adjust for possible sludge removal and or CH4 recovery and sum the results.

The general equation to estimate CH4 emissions from industrial wastewater is as follows:

Equation 6.4 Total CH4 emissions from industrial wastewater


CH4 Emissions = CH4 emissions in inventory year, kg CH4/yr

Ri total organically degradable material in wastewater from industry i in inventory year, kg COD/yr industrial sector organic component removed as sludge in inventory year, kg COD/yr emission factor for industry i, kg CH4/kg COD

for treatment/discharge pathway or system(s) used in inventory year

If more than one treatment practice is used in an industry this factor would need to be a weighted average.

amount of CH4 recovered in inventory year, kg CH4/yr

The amount of CH4 which is recovered is expressed as R in Equation 6.4. The recovered gas should be treated as described in Section 6.2.1. Choice of emission factors

There are significant differences in the CH4 emitting potential of different types of industrial wastewater. To the extent possible, data should be collected to determine the maximum CH4 producing capacity (Bo) in each industry. As mentioned before, the MCF indicates the extent to which the CH4 producing potential (Bo) is realised in each type of treatment method. Thus, it is an indication of the degree to which the system is anaerobic. See Equation 6.5.

Equation 6.5 CH4 emission factor for industrial wastewater


EFj = emission factor for each treatment/discharge pathway or system, kg CH4/kg COD, (See Table 6.8.)

j = each treatment/discharge pathway or system

Bo = maximum CH4 producing capacity, kg CH4/kg COD

MCFj = methane correction factor (fraction) (See Table 6.8.)

Good practice is to use country and industry sector specific data that may be available from government authorities, industrial organisations, or industrial experts. However, most inventory compilers will find detailed industry sector-specific data unavailable or incomplete. If no country-specific data are available, it is good practice to use the IPCC COD-default factor for Bo (0.25 kg C^/kg COD).

In determining the Methane correction factor (MCF), which is the fraction of waste treated anaerobically, expert judgement is recommended. A peer-reviewed survey of industry wastewater treatment practices is one useful technique for estimating these data. Surveys should be conducted frequently enough to account for major trends in industry practices (i.e., every 3-5 years). Chapter 2, Approaches to Data Collection, in Volume 1, describes how to elicit expert judgement for uncertainty ranges. Similar expert elicitation protocols can be used to obtain the necessary information for other types of data if published data and statistics are not available. Table 6.8 includes default MCF values, which are based on expert judgment.

Table 6.8

Default MCF values for industrial wastewater

Type of treatment and discharge pathway or system





Sea, river and lake discharge

Rivers with high organics loadings may turn anaerobic, however this is not considered here.


0 - 0.2


Aerobic treatment plant

Must be well managed. Some CH4 can be emitted from settling basins and other pockets.


0 - 0.1

Aerobic treatment plant

Not well managed. Overloaded


0.2 - 0.4

Anaerobic digester for sludge

CH4 recovery not considered here


0.8 - 1.0

Anaerobic reactor

(e.g., UASB, Fixed Film Reactor)

CH4 recovery not considered here


0.8 - 1.0

Anaerobic shallow lagoon

Depth less than 2 metres, use expert judgment


0 - 0.3

Anaerobic deep lagoon

Depth more than 2 metres


0.8 - 1.0

1 Based on expert judgment by lead authors of this section Choice of activity data

The activity data for this source category is the amount of organically degradable material in the wastewater (TOW). This parameter is a function of industrial output (product) P (tons/yr), wastewater generation W (m3/ton of product), and degradable organics concentration in the wastewater COD (kg COD/m3). See Equation 6.6. The following steps are required for determination of TOW:

(i) Identify the industrial sectors that generate wastewater with large quantities of organic carbon, by evaluating total industrial product, degradable organics in the wastewater, and wastewater produced.

(ii) Identify industrial sectors that use anaerobic treatment. Include those that may have unintended anaerobic treatment as a result of overloading of the treatment system. Experience has shown that usually three or four industrial sectors are key.

For each selected sector estimate total organically degradable carbon (TOW).

Equation 6.6

Organically degradable material in industrial wastewater


TOWi i


= total organically degradable material in wastewater for industry i, kg COD/yr = industrial sector

= total industrial product for industrial sector i, t/yr

= wastewater generated, m /t product

= chemical oxygen demand (industrial degradable organic component in wastewater), kg COD/m3

Industrial production data and wastewater outflows may be obtained from national statistics, regulatory agencies, wastewater treatment associations or industry associations. In some cases quantification of the COD loading in the wastewater may require expert judgement. In some countries, COD and total water usage per sector data may be available directly from a regulatory agency. An alternative is to obtain data on industrial output and tonnes COD produced per tonne of product from the literature. Table 6.9 provides examples that could be used as default values. These should be used with caution, because they are industry-, process- and country-specific.

Table 6.9

Examples of industrial wastewater data

Industry Type

Wastewater Generation W (m3/ton)

Range for W (m3/ton)


COD Range (kg/m3)

Alcohol Refining


16 - 32



Beer & Malt


5.0 - 9.0





NA -



Dairy Products




1.5 - 5.2

Fish Processing




Meat & Poultry





Organic Chemicals


0 - 400


0.8 - 5

Petroleum Refineries


0.3 - 1.2


0.4 - 1.6

Plastics & Resins


0.3 - 1.2


0.8 - 5

Pulp & Paper (combined)


85 - 240


1 - 15

Soap & Detergents


1.0 - 5.0


0.5 - 1.2

Starch Production




1.5 - 42

Sugar Refining




1 - 6

Vegetable Oils


1.0 - 5.0


0.5 - 1.2

Vegetables, Fruits & Juices





Wine & Vinegar


11 - 46


0.7 - 3.0

Notes: NA = Not Available. Source: Doorn et al. (1997). Time series consistency

Once an industrial sector is included in the inventory calculation, it should be included for each subsequent year. If the inventory compiler adds a new industrial sector to the calculation, then he or she should re-calculate the entire time series so that the method is consistent from year to year. General guidance on recalculation of estimates through time series is provided in Volume 1, Chapter 5, Time Series Consistency.

As with domestic wastewater, sludge removal and CH4 recovery should be treated consistently across years in the time series. CH4 recovery should be included only if there are facility-specific data. The quantity of recovered CH4 should be subtracted from the CH4 produced as shown in Equation 6.4. Uncertainties

Uncertainty estimates for Bo, MCF, P, W and COD are provided in Table 6.10. The estimates are based on expert judgement.

Table 6.10

Default uncertainty ranges for industrial wastewater


Uncertainty Range

Emission Factor

Maximum CH4 producing capacity (Bo)

± 30%

Methane correction factor (MCF)

The uncertainty range should be determined by expert judgement, bearing in mind that this is a fraction and uncertainties cannot take it outside the range of 0 to 1.

Activity Data

Industrial production (P)

± 25% Use expert judgement regarding the quality of data source to assign more accurate uncertainty range.

Wastewater/unit production (W)

These data can be very uncertain as the same sector might use different waste handling procedures at different plants and in different countries. The product of the parameters (W^COD) is expected to have less uncertainty. An uncertainty value can be attributed directly to kg COD/tonne of product. -50 %, +100% is suggested (i.e., a factor of 2).

COD/unit wastewater (COD)

Source: Judgement by Expert Group (Co-chairs, Editors and Authors of this sector). QA/QC, Completeness, Reporting and Documentation

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:

• For industrial wastewater, inventory compilers may review the secondary data sets (e.g., from national statistics, regulatory agencies, wastewater treatment associations or industry associations) , that are used to estimate and rank industrial COD waste output. Some countries may have regulatory control over industrial discharges, in which cases significant QA/QC protocols may already be in place for the development of the wastewater characteristics on an industry basis.

• For industrial wastewater, inventory compilers should cross-check values for MCFs against those from other national inventories with similar wastewater characteristics.

• The inventory compilers should review facility-specific data on CH4 recovery to ensure that it was reported according to criteria on measurements outlined in Chapter 2, Approaches to Data Collection, in Volume 1.

• Use a carbon balance check to ensure that the carbon contained in CH4 recovery is less than the carbon contained in BOD entering the facility that reports CH4 recovery.

• If sludge removal is reported in the wastewater inventory, check for consistency with the estimates for sludge applied to agriculture soils, sludge incinerated, and sludge deposited in solid waste disposal.

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


Completeness for estimating emissions from industrial wastewater depends on an accurate characterization of industrial sectors that produce organic wastewater. In most countries, approximately 3-4 industrial sectors will account for the majority of the organic wastewater volume, 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.

Some sludge from industrial wastewater treatment may be incinerated or deposited in landfills or on agricultural lands. This constitutes an amount of organic waste that should be subtracted from available TOW. It is good practice to be consistent across sectors: the amount of sludge that is removed from TOW should be equal to the amount of sludge disposed at landfills, applied to agricultural soils, incinerated or treated elsewhere.


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 are used, the reasoning for the choices as well as references to how the country-specific data (measurements, literature, expert judgement, etc.) have been derived (measurements, literature, expert judgement, etc.) should be documented and included in the reporting.

If sludge is incinerated, landfilled, or spread on agricultural lands, the quantities of sludge and associated emissions should be reported in the waste incineration, SWDS, or agricultural categories, respectively.

If CH4 recovery data are available for industrial wastewater treatment, these should be documented for flaring and energy recovery separately. The treatment of recovered CH4 and how to report emissions from flaring should be the same as the guidance for domestic wastewater in Section

More information on reporting and documentation can be found in Volume 1, Chapter 6, Section 6.11 Documentation, archiving and reporting.

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