Potentials and limits of a pre-denitrification/nitrification biofilter configuration for advanced municipal wastewater treatment Available to Purchase

Pre-denitrification in biofilters is limited by the amount of easily degradable organic substrate, resulting in relatively high requirements for external carbon. The combination of pre-DN, N and post-DN filters is much more advisable for most municipal wastewaters, because the recycle rate can be reduced and external carbon can be saved. For minimum use of external carbon, 100–150% recycle rate should not be exceeded. Then, approximately 50–60% of the total NO₃-N can be depleted in the pre-DN stage. On average, 10 g total (t) COD/g NO₃-N were required in the pre-DN stage for denitrification in the pilot and full-scale plant and 0.4–0.5 kg NO₃-N/(m³_DN d) can be reached without external carbon. As only 40–70% of the COD load is eliminated in the pre-DN, the remaining COD load is removed in the nitrification stage. 1 kg COD/(m³ d) suppresses nitrification rates by approximately 0.1 kg NH₄-N/(m³ d). For nitrification rates, >0.5 kg NH₄N/(m³ d) at 12°C not more than 2 kg COD/(m³_N d) may be eliminated in the nitrification.