Development of a standardized method for examination of vacuum degassing of activated sludge for improvement of settling properties

Paper in proceeding, 2013

Vacuum degassing of activated sludge was tested at eight different Swedish wastewater treatment plants with laboratory-scale equipment in batch mode in order to evaluate its efficiency on improvement of sludge compaction and settling properties. The results show that the efficiency of the degassing technique is mainly dependent on the initial sludge volume index (SVI) of the target sludge which was found to be related to its process configuration. Plants with complete activated sludge based nitrogen removal processes were observed to have high SVIs (>300 ml/g) and were strongly affected by vacuum degassing in terms of reduction of SVI up to 30%. Nitrogen removal plants also including biological phosphorus removal showed better compaction and settling properties with relatively lower SVIs and were affected to a lesser extent by degassing with SVI reduction of 10-20%. Wastewater treatment plants without complete biological nitrogen removal, missing either nitrification or denitrification (or both) processes in the activated sludge had the lowest SVIs observed with almost no effect of vacuum degassing.