6 WASTEWATER TREATMENT AND DISCHARGE
6.1 INTRODUCTION
Wastewater can be a source of methane (CH4) when treated or disposed anaerobically. It can also be a source of
nitrous oxide (N2O) emissions. Carbon dioxide (CO2) emissions from wastewater are not considered in the IPCC
Guidelines because these are of biogenic origin and should not be included in national total emissions.
Wastewater originates from a variety of domestic, commercial and industrial sources and may be treated on site
(uncollected), sewered to a centralized plant (collected) or disposed untreated nearby or via an outfall. Domestic
wastewater is defined as wastewater from household water use, while industrial wastewater is from industrial
practices only.1 Treatment and discharge systems can sharply differ between countries. Also, treatment and
discharge systems can differ for rural and urban users, and for urban high income and urban low-income users.