Domestic waste water

Methane emissions vary depending on the discharge pathway/treatment system and are calculated based on the concentration of degradable organic material within the waste water as measured by the biological or chemical oxygen demand (standard measures of water organic concentration).

How to use this category

Selecting an emissions scenario

To use this category, choose between 'treated' or 'untreated' modes of waste water discharge using the type drill choice, then specify the particular system using the system and context drill choices.

Specifying activity data

Waste quantity: Next, a measure of the concentration of degradable organic material within the waste water must be specified. Users can opt to express this quantity as an absolute mass (e.g. kg) of (degradable) organic material, or alternatively by using a known volume (e.g. litres) of waste water generation together with the oxygen demand of a unit volume of water (e.g. mg per litre). These measures should represent either biological or chemical oxygen demand. To specify organic discharge on the basis of a total mass, set the mass using the totalOrganicWaste profile item value. Otherwise, set the volume of waste water discharged and the associated organic concentration (oxygen demand) using the volume and massOrganicPerVolume profile item values.

Sludge removal: Where removal of solid organics (sludge) is practised, this can be deducted from the emissions calculation. To specify sludge removal, set the mass of removed sludge using the massSludge profile item value. The value returned in this case represents methane emissions associated with the waste quantity specified minus the removed sludge. If no value for sludge removal is specified, an absense of sludge removal is assumed.

Methane recovery: Where methane recovery/capture is practised, this can be deducted from the emissions calculation. To specify methane recovery, set the mass of recovered methane in the recoveredMethane profile item value. The value returned in this case represents methane/N₂O emissions associated with the waste quantity specified minus the methane recovered. If a quantity of recovered methane is specified which is greater than the emitted quantity, CarbonKit returns a value of 0, and posts an error message into the comment profile item value.

Biological or chemical oxygen demand? In calculating methane emissions associated with this category, CarbonKit assumes that quantities of organic material (either total mass or mass per volume - see above) are specified in terms of the biological oxygen demand of waste water. Users can instruct that their specified quantities alternatively represent chemical oxygen demand by setting the isCOD profile item value to 'true'.

Results and calculation

The quantities returned represent the methane emissions associated with waste water discharge into the treatment system specified. The following quantities are returned:

• CH4: absolute quantity of CH₄ emitted
• CO2e: emitted CH₄ to CO₂e converted using the appropriate global warming potential)

Notes

Sludge removal

Where removed sludge is incinerated, users are referred to the following category

• waste combustion

Methane recovery

Where recovered methane is burned for energy production, flared, or fed into a gas distribution system, users are referred to the following categories

• stationary fuel combustion

• methane flaring

• oil and gas processing