Climate change impacts on activated sludge wastewater treatment: a case study from Norway

摘要

We present an investigation on climate change effects on a wastewater treatment system thatnreceive sewage collected in a combined sewer system in Oslo, Norway, during winter operation.nResults obtained, by contrasting meteorological data with sewage data, show that wastewaterntreatment plant (WWTP) influent flow rates are significantly increased during temporary snownmelting periods above a critical daily air mean temperature of approx. 21.58C degree (TCrit)nidentified in the area. In order to assess melting patterns, the number of days above and belownTCrit was assessed, and the annual number of melting periods was additionally evaluated usingnmeteorological data obtained in the last decade. A striking thing about the daily air temperaturenpattern is that, despite the progressively warmer winter temperatures in the last decade, annincreasing number of days with temperatures below 21.58C could be observed. The frequency ofnmelting periods is shown to increase in wintertime, and it is identified as an additional climatenchange related factor in the Oslo region. We demonstrate that these impacts can deteriorate thenWWTP operation through progressively increasing the relative frequencies of very high influentnflow rate and of the very low influent sewage temperature. Such climate change related effectsnon sewage treatment processes can be characterised as shock-conditions, i.e. significantnchanges in a system’s boundary conditions, occurring in a relatively short period of time.nIn the six year period examined, biological nitrogen removal and secondary clarification processesnare shown to be significantly affected by the climate factors. A striking thing about using thenstate-of-the-art mathematical models of wastewater treatment processes in decision supportnsystems is their inability of describing, and thus predicting the effects of such shock-loadingnevents, as they have not been studied so far. Adaptation and optimisation of process models,nalso for use in design, optimisation as well as in real-time automation and process controlnschemes, are thus critical to meet the challenges of climatic changes in the future.