Definition: Tertiary treatment (of waste water)
Treatment (additional to secondary treatment) of nitrogen and/or phosphorous and/or any other pollutant affecting the quality or a specific use of water: microbiological pollution, colour etc . For the purpose of this questionnaire, the following minimum treatment efficiencies define a tertiary treatment: organic pollution removal of at least 95% for BOD and 85% for COD, and at least one of the following:
- nitrogen removal of at least 70%
- phosphorus removal of at least 80%
- microbiological removal achieving a faecal coliform density less then 1000 in 100 m.
Eurostat, "Data Collection Manual for the OECD/Eurostat Joint Questionnaire on Inland Waters and Eurostat regional water questionnaire", version 4 (2018), Luxembourg, 2018