KONTROLL AV AKTIVTSLAMS SEDIMENTERINGSEGENSKAPER VID DRIFT FÖR KVÄVEREDUKTION - RESULTAT FRÅN FÖRSÖKSDRIFT / Control of activated sludge settling characteristics in a nitrogen removal plant - results from trials
Sludge bulking has been a problem ever since the activated sludge process was introduced for wastewater treatment. The problems were accentuated when low-loaded processes for nitrogen removal were introduced. Sludge bulking may appear in many forms and be caused by many different factors. Common in low-loaded processes are bulking caused by mass-appearance of filamentous bacteria. The knowledge about this kind of bulking has increased during the last decades and chemical methods for control have in most cases been replaced by alternative system design making biological control possible.
For the wastewater treatment plant in Mjölby it was theoretically shown that a high degree of nitrogen removal could be obtained in existing volumes if the sludge concentration was sufficiently high. However, a high sludge concentration was not possible to obtain due to shallow sedimentation basins and mass-appearance of filamentous bacteria. It was therefore decided to use a part of the biological process to examine the effect of a system, in which a combined kinetic and metabolic control method was used. The process was designed in a way that an anoxic selector was followed by three volumes, which could either be operated anoxic or aerobic, and one final aerobic volume. At low water temperature during the winter it was foreseen that only the selector could be operated in an anoxic mode, thus minimising the metabolic selection.