2.3 Carbon dioxide (CO2) emission calculating principles

The two main factors causing CO2 production from wastewater treatment plants are the type of treatment process and electricity consumption. During anaerobic treatment, the BOD5 in the wastewater is either converted to CO2 or CH4, or some of it enters the biomass and is also converted to CO2 and CH4 by endogenous respiration. Other sources of carbon dioxide emissions are caused by sludge digesters and digestion gas combustion. In aerobic process, CO2 is produced by decomposition of organic substances. Since CO2 emissions from the wastewater treatment plant are biogenic, they are not included in the national total emissions and are not considered in the IPCC Guidelines. Biogenic origin means that it is part of the natural carbon cycle and the food chain passing from plants to animals and humans, or natural atmospheric CO2 source.

### 3. Emission calculating principles for constructed wetlands
