AWWA WKICO66069

Biological nitrification in groundwater filters is often inhibited by iron removal processes in the same filters. Nitrification can be successfully maintained in full-scale filters by use of subsurface aeration, which probably changes the iron removal mechanism and the resulting filter coatings. Several groundwater filters, with and without subsurface aeration, have been compared for mass and pore structure of the coatings on the filter materials. Cumulative pore area of filter coatings in drinking water filters has been determined by mercury-intrusion porosimetry. The results have been related to biological nitrifying activity in a standard batch test. In the non-subsurface aerated filter samples, both mass and cumulative pore area were restricted and inversely proportional to specific nitrification rate. In subsurface aerated filters, however, a strong increase in coating mass resulted in high cumulative pore area, but only a slight reduction in specific nitrification rate. Includes 9 references, tables, figures.