Abstract: A carrier element (1; 10; 20) for growth of biofilm thereon is designed for free-flowing in liquid to be purified and has surfaces (3; 13) for biofilm growth which are protected from the abrasion from other carrier elements or surfaces in a container containing the liquid to be purified by ridges (4; 12) having a height corresponding to a desired thickness of a biofilm intended to grow on the protected surfaces (3; 13). The ratio between the surfaces (3; 13) for biofilm growth and the area of the ridges ranges from 1:1 to 1:20.

Abstract: A process for converting ammonium (NH4+) of a mainstream of a wastewater plant to dinitrogen gas (N2), including the consecutive steps of i.) removing biodegradable carbon compounds in the mainstream, ii.) converting ammonium (NH4+) in the mainstream to nitrite (NO2?) in an aerated biological process containing ammonium oxidizing bacteria (AOB) in a nitration vessel (133a-133d); and iii.) denitrifying the resulting stream from step ii.) to dinitrogen gas in an anammox vessel (200). Growth of nitrite oxidizing bacteria (NOB) in step ii.) is prevented by periodically subjecting the bacteria in said nitration vessel (133a-133d) to water suppressing growth of nitrite oxidizing bacteria (NOB).

Abstract: A process for converting ammonium (NH4+) of a mainstream of a wastewater plant to dinitrogen gas (N2), including the consecutive steps of i.) removing biodegradable carbon compounds in the mainstream, ii.) converting ammonium (NH4+) in the mainstream to nitrite (NO2?) in an aerated biological process containing ammonium oxidizing bacteria (AOB) in a nitration vessel (133a-133d); and iii.) denitrifying the resulting stream from step ii.) to dinitrogen gas in an anammox vessel (200). Growth of nitrite oxidizing bacteria (NOB) in step ii.) is prevented by periodically subjecting the bacteria in said nitration vessel (133a-133d) to water suppressing growth of nitrite oxidizing bacteria (NOB).

Abstract: A carrier element (1; 10; 20) for growth of biofilm thereon is designed for free-flowing in liquid to be purified and has surfaces (3; 13) for biofilm growth which are protected from the abrasion from other carrier elements or surfaces in a container containing the liquid to be purified by ridges (4; 12) having a height corresponding to a desired thickness of a biofilm intended to grow on the protected surfaces (3; 13). The ratio between the surfaces (3; 13) for biofilm growth and the area of the ridges ranges from 1:1 to 1:20.