In 2011 Oasen started to use rapid, biological iron removal in dry filters at purification station Lekkerkerk. This was the first time a drinking water company in the Netherlands used this technique. After a year of research we have found a way to tackle the nitrification problem in the filters of the station. But how have we done this exactly? And, what is biological iron removal anyway? Oasen explains this proces in a short visual writing video.