Aerated Rock Filters for Enhanced Ammonia and Fecal Coliform Removal from Facultative Pond Effluents

Rock filters used to treat effluents from waste stabilization ponds do not remove ammonia as they are anoxic. A pilot-scale aerated rock filter was investigated, in parallel with an unaerated control, over an 18-month period to determine whether aeration provided conditions within the rock filter for nitrification to occur. Facultative pond effluent containing ~10 mg NH4-N/L was applied to the filters at a hydraulic loading rate of 0.15 m3/m3 day during the first 8 months and at 0.3 m3/m3 day thereafter. The results show that the ammonia and nitrate concentrations in the effluent from the aerated filter were <3 and ~5 mg N/L, respectively, whereas the ammonia concentration in the effluent from the control filter was ~7 mg N/L. Fecal coliforms were reduced in the aerated filter to a geometric mean count of 65 per 100 mL; in contrast the effluent from the control filter contained 103-104 fecal coliforms per 100 mL. Aerated rock filters are thus a useful land-saving alternative to aerobic maturation ponds.