Biological nitrogen removal at low water temperatures — long term experience

摘要

Many earlier publication presented the lowest temperature of 10℃ as feasible for nitrification process. The article evaluates long-term experience with biological nitrogen removal at low temperatures (between 2 and 10℃), studied at four wastewater treatment plants operated with SBR-technology: Holbaek (Denmark), Nowy Targ (Poland), Nynashamn and Skaulo (Sweden). Influence if nitrogen loads and COD/N ratio on nitrification rate was studied. Despite of operation at low temperatures during 3-4 months of the year good relation between the nitrogen load and the specific nitrification rate has been obtained. Long-term studies regarding nitrification, temperature and SRT demonstrated that the actually needed (aerated) SRT were lower than the normally recommended values. In some cases the nitrification was maintained at a lower efficiency even during non-aerated phases due to remaining free oxygen in the reactor that is used for nitrification.