Estimation of nitrification capacity of rock media trickling filters in external nitrification BNR

In the external nitrification (EN) biological nutrient removal (BNR) activated sludge (AS) system, the nitrification process is removed from the BNR activated sludge system and performed ‘externally’ on an integrated nitrifying trickling filter (NTF). As such, optimum design and operation of the NTF is essential for reliable performance of the ENBNRAS system. Although information on the design and operation of NTFs is available in the literature, this experience is not directly applicable to the NTF in the ENBNRAS system. To address this deficiency, a full-scale ENBNRAS prototype was implemented at the Daspoort Wastewater Treatment Works (DWWTW) in Tshwane, South Africa. In this investigation an average apparent nitrification capacity of approximately 1.25 to 1.29 gN per m2 of media surface area per day [gN/(ms2·d)] ammonia removal was determined for 2 existing rock media TFs retrofitted as NTFs in the prototype ENBNRAS system (nominal surface area of 45 ms2/m3 for the rock media). This nitrification capacity corresponded to a removal efficiency of about 14 mgN/l (96%), or 149 kgN/d, of the influent ammonia load applied to the NTFs (average influent flow rate of 10 Ml/d). General concordance was found with corresponding nitrate and nitrite production and alkalinity usage measurements, which substantiated the observed removal performance. This paper details determination of the nitrification capacity of the 2 rock media NTFs used in the prototype ENBNRAS system.