Iron coatings in pilot dry groundwater biofilters

摘要

In drinking water production from groundwater in the Netherlands, iron and ammonium are often removed in one dry biofiltration step. Iron removal in these filters is supposed to be a combination of two physical-chemical processes: flocculation-filtration and adsorptive oxidation. Nitrification was studied alone and in combination with iron removal in a pilot-scale dry biofilter setup, where both iron removal processes were imitated by either direct spraying or pre-oxidation of ferrous iron. Nitrification was evaluated by chemical analyses of the water and molecular techniques and iron removal by chemical analyses of the water and the filter coatings. The experiment was performed at two test locations with distinctly different water qualities. For both iron removal processes, nitrification was hindered by iron. Ammonia-oxidizing bacteria dominated over archaea in all columns. Despite equal operational conditions and loading of iron and ammonium, large differences were observed between both test location in floc formation during preoxidation and in coating formation.