Optical monitoring of activated sludge flocs in bulking and non-bulking conditions

Abstract

This study introduces a novel optical monitoring method to image and characterize activated sludge flocs and to study the dependency of sludge settling properties on the floc structure. The novel method can easily analyse thousands of particles in a short timeframe using the developed image analysis program. The main advantage of this method is its applicability for in situ use because the only required pre-treatment is sample dilution. This study tested real process samples from activated sludge plants treating wastewater from a pulp mill. The sludge samples were collected in bulking and non-bulking situations, and the image analysis results were compared to the settling speed of the samples. The structure of the activated sludge flocs was clearly different in bulking sludge situations as characterized by more fragile and elongated flocs. Additionally, excessive amounts of filamentous bacteria hold the flocs apart, hindering sludge settling. These results show that this method is suitable for studying and optimizing activated sludge processes.

Keywords:

• floc structure
• image analysis
• bulking sludge
• filamentous bacteria
• settling properties

Acknowledgements

This research has been carried out in the Measurement, Monitoring and Environmental Efficiency Assessment (MMEA) research program of CLEEN Ltd. - Cluster for Energy and Environment. The authors would also like to acknowledge Tekes (the Finnish Funding Agency for Technology) for the financial support and Metso Inc. for providing the floc imaging setup.