A comparison between floc morphology and the effluent clarity at a full-scale activated sludge plant using optical monitoring

Abstract

A charge-coupled device camera was used for the optical monitoring of activated sludge flocs and filaments, and the image analysis results were compared with the effluent clarity at a full-scale activated sludge plant during a three-month period. The study included a maintenance stoppage at the wastewater treatment plant, which was followed by a settling problem. Thus, the study presents the development of floc morphology from poor flocculation to good flocculation. In this case, the evolution of flocs was a slow process, and the optimum floc morphology was achieved before the purification results improved. To diagnose the cause of the settling problems using optical monitoring, four major factors were found to be relevant: the mean area of the flocs, the amount of small particles, the amount of filament and the shape parameters of the flocs. In this case, the settling problem was caused by dispersed growth based on the image analysis results. In conclusion, the method used has the potential for usefulness in the development of monitoring applications to predict plant performance and also to diagnose the causes of the settling problems.

Keywords:

• image analysis
• settling properties
• deflocculation
• biological flocs
• separation problem

Acknowledgements

This research was carried out as part of the Measurement, Monitoring and Environmental Efficiency Assessment (MMEA) research programme of CLEEN Ltd. – Cluster for Energy and Environment. The authors thank Metso Inc. for providing the floc imaging setup and Mrs Ulla-Maija Romo for the laboratory work.