The effect of winter on the floc formation in activated sludge process

Theme 1. Environmental protection
Session Name 1.8 Modelling and control of water and wastewater treatment in the Arctic conditions
Presentation Type Poster
Author(s) Elisa Koivuranta (University of Oulu, Finland), Jani Tomperi (University of Oulu, Finland), Esko Juuso (University of Oulu, Finland)
Abstract text

The floc formation is a critical phase in the activated sludge process (ASP) in which microorganisms are used to degrade the organic matter in wastewater. Due to the biological nature of the floc formation, the ASP is highly sensitive to the temperature of wastewater. Especially, the arctic conditions are challenging. In this study, the effect of winter on the floc formation was investigated with an online optical monitoring device in a Finnish municipal wastewater treatment plant during a 16 months’ period. The results were correlated with the influent temperature and the quality of the treated wastewater. Additionally, mathematical variable selection methods were utilized to find the input variables for the predictive models of the treated wastewater quality. The results showed that floc formation has a clear, seasonal pattern, correlating the wastewater temperature. Cold winter conditions enhanced the growth of filamentous bacteria in wastewater, decreasing treatment efficiency. On the other hand, in summer, flocs were larger and rounder, and having fewer filaments and small particles. Treatment efficiency also increased in summer. In the municipal WWTP, the temperature of the influent wastewater is one of the significant factors in the treatment process operation. The variable selection showed that the quality of the treated wastewater has dependences on the wastewater temperature and the process parameters strongly related to the temperature as being included in the input variable subsets of the quality models.