Local governments are often responsible for providing wastewater services to their communities, such as collection, septic system management, primary and secondary treatment, solids handling and effluent discharge. This section focuses only on calculating the fugitive and process CH4 and N2O emissions from septic systems and centralized wastewater treatment (WWT) facilities only. Other sections of the LGOP Protocol should be used to calculate emissions from other activities related to wastewater treatment (e.g., electricity use, stationary combustion, and vehicle fleet).
This protocol applies to local governments that have operational or financial control over a septic system or WWT facility. Local governments served by regional WWT plants have the option of quantifying these emissions and reporting them as Scope 3 emissions.
Chapter 10 of the LGOP provides guidance on calculating emissions from WWT facilities:
CH4 emissions estimations:
Stationary emissions from incomplete combustion of digester gas.
To calculate these CH4 emissions from anaerobic digestion “leaks” at WWT facilities:
- Equation 10.1 should be used if measurements of the volume of digester gas (biogas) produced and the fraction of CH4 in the biogas are obtainable.
- Equation 10.2 should be used if these site-specific data are not available.
Process emissions from WWT lagoons.
To calculate process CH4 emissions from WWT lagoons:
- Use Equation 10.3 if measurements of the average BOD5 load, BOD5 removal in primary treatment upstream of the lagoon (if primary treatment is present), and the fraction of overall lagoon removal performance are obtainable.
- Use Equation 10.4 if these site-specific data are not available.
Fugitive emissions from septic systems.
To calculate process CH4 emissions from septic systems:
- Use Equation 10.5 if measurements of the average BOD5 load are obtainable.
- Use Equation 10.6 if these site-specific data are not available.
N2O emissions estimations:
Process emissions from WWT plant with nitrification/denitrification.
To calculate process N2O from WWT plants with nitrification/denitrification, use Equation 10.7.
Please note that in Equation 10.7, the population served must be increased to represent any significant amounts of nitrogen discharged into the municipal treatment system from industrial sources.
The additional equivalent population is calculated by dividing the amount of industrial nitrogen discharged into the municipal treatment system, (expressed in kg of total nitrogen per day), by the nitrogen population-equivalent of 0.026 kg N/person/day.
Process emissions from WWT plants without nitrification/denitrification.
To calculate process N2O from WWT plants without nitrification/denitrification, use Equation 10.8.
Please note that in Equation 10.8, the population served must be increased to represent any significant amounts of nitrogen discharged into the municipal treatment system from industrial sources.
The additional equivalent population is calculated by dividing the amount of industrial nitrogen discharged into the municipal treatment system, (expressed in kg of total nitrogen per day), by the nitrogen population-equivalent of 0.026 kg N/person/day.
Process emissions from effluent discharge.
To calculate process N2O emissions from effluent discharge:
- Use Equation 10.9 if measurements of the average total nitrogen discharged is obtainable.
- Use Equation 10.10 if these site-specific data are not available.
Please note that in Equation 10.9, the population served must be increased to represent any significant amounts of nitrogen discharged into the municipal treatment system from industrial sources.
The additional equivalent population is calculated by dividing the amount of industrial nitrogen discharged into the municipal treatment system, (expressed in the kg of total nitrogen per day), by the nitrogen population-equivalent of 0.026 kg N/person/day.
