A design model for nitrification on structured cross flow plastic media trickling filters

An empirical model has been developed to predict the effluent ammoniacal nitrogen concentration from structured cross flow plastic media trickling filters operated over the range of BOD loadings 0.12-0.38 kg/m 3 /day and ammoniacal nitrogen loadings of 0.06-0.23 kg/m 3 /day. The model gives good predictions based on 24-h average effluent concentrations over a range of filter depths, organic and hydraulic loading rates. When incorporated with suitable hydraulic models, effluent ammoniacal concentration can be predicted through the diurnal range. The data gathering for the model included depth profiles on three filters. These have shown that at all but the very highest BOD loadings, nitrification commences from the very top of the filter in the presence of soluble BOD loadings previously thought to preclude the development of nitrifying biomass. Several reasons have been proposed to explain this, with the key argument being that the efficient oxygen transfer afforded by the media design is sufficient to satisfy heterotroph and autotroph oxygen demand simultaneously.