Removal of pharmaceutical residues in aerobic granular sludge and activated sludge – a comparison study in full-scale
Approximately half of the micropollutants in municipal wastewater are removed in wastewater treatment plants (WWTPs) through adsorption or biological degradation. However, the knowledge about this removal is inadequate.
At the Österröd Wastewater Treatment Plant in Strömstad the first Nordic facility with aerobic granular sludge (AGS) is situated. The AGS run in parallel with a conventional activated sludge process. The two processes receive the same wastewater. The concentration of sludge is about three times higher in the AGS than in the activated sludge. This means that the residence time of the water can be kept much shorter in the granulation process. In addition, the microbial species richness is higher in the granules.
For most micropollutants measured, removal was slightly higher and faster for activated sludge than for the AGS. Even in lab tests, there were higher separation rates with biomass from activated sludge. An exception was diclofenac, which was better separated with granules.
The results from the project lead to the question of whether the microbial diversity is really important or whether other parameters determine the rate of decomposition, for example the proportion of active biomass. The granules consist of thick biofilm with high diffusion resistance, which makes it difficult to determine the proportion of active biomass. Activated sludge flocs are smaller and have a larger specific surface in relation to the volume and can therefore have a smaller proportion of inactive biomass. The activated sludge process had approx. 50% longer residence time. This made the contact time between wastewater and biomass longer, and it gave more time for the separation of micropollutants.
Britt-Marie Wilén, University of Chalmers