Biological Process

IFAS

Population Equivalents

35,000

Annual Energy Consumption

1.14 GWh

Canton of St. Gallen IFAS 3 lines

The biological treatment stage of the Bazenheid WWTP is operated using the IFAS (integrated fixed-film activated sludge) process. Nitrifiers can grow on the carriers or in the sludge, which makes control challenging. During the winter months, at lower temperatures, the ammonium and nitrite effluent limits were partially exceeded. Nitrous oxide emissions are significant, at a factor of 1.4% (relative to the nitrogen load in the influent).

DNA Analysis

DNA samples were analyzed to optimize nitrification in the IFAS system of the Bazenheid WWTP. 

ara ebnat

Baseline Measurement

Weekly DNA analyses were carried out on the sludge and on the carriers over a period of 4 weeks. The measurements show that nitrification occurs exclusively on the carriers. For winter operation, there is significant potential for nitrification in the sludge.

Proposal and Implementation of Measures 

Based on the results, the sludge age was increased. In addition, the return sludge flow rate was increased to achieve higher denitrification capacity. This is because the DNA analyses show significant growth of Bio-P bacteria, which leads to precipitation problems in digestion.

Effectiveness

After implementing the measures, the ammonia-oxidizing bacteria (AOB) in the sludge could be significantly increased. The Bazenheid WWTP had significantly fewer ammonium exceedances that winter, as well as in the following two winters.

Success Monitoring on Carrier Material

Measurements of the carrier material show that nitrite-oxidizing bacteria (NOB) continue to grow on the carriers despite the increased sludge age. In addition, comammox bacteria are now growing on the carriers, which is a major advantage: comammox carry out complete nitrification without producing climate-damaging nitrous oxide.

Baseline Measurement

Weekly DNA analyses were carried out on the sludge and on the carriers over a period of 4 weeks. The measurements show that nitrification occurs exclusively on the carriers. For winter operation, there is significant potential for nitrification in the sludge.

Proposal and Implementation of Measures 

Based on the results, the sludge age was increased. In addition, the return sludge flow rate was increased to achieve higher denitrification capacity. This is because the DNA analyses show significant growth of Bio-P bacteria, which leads to precipitation problems in digestion.

Effectiveness

After implementing the measures, the ammonia-oxidizing bacteria (AOB) in the sludge could be significantly increased. The Bazenheid WWTP had significantly fewer ammonium exceedances that winter, as well as in the following two winters.

Success Monitoring on Carrier Material

Measurements of the carrier material show that nitrite-oxidizing bacteria (NOB) continue to grow on the carriers despite the increased sludge age. In addition, comammox bacteria are now growing on the carriers, which is a major advantage: comammox carry out complete nitrification without producing climate-damaging nitrous oxide.