A dynamic modelling approach to evaluate GHG emissions from wastewater treatment plants

Xavier Flores-Alsina, Magnus Arnell, Youri Amerlinck, Lluis Corominas, Krist Gernaey, Lisha Guo, Erik Lindblom, Ingmar Nopens, Jose Poro, Andy Shaw, Peter A. Vanrolleghem, Ulf Jeppsson

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The widened scope for wastewater treatment plants (WWTP) to consider not only water quality and cost, but also
greenhouse gas (GHG) emissions and climate change calls for new tools to evaluate operational strategies/treatment
technologies. The IWA Benchmark Simulation Model no. 2 (BSM2) has been widely used within the scientific
community for the unbiased comparison of control strategies in wastewater treatment facilities. In this paper, the
default set of BSM models is extended with a set of comprehensive dynamic approaches that estimate the most
significant on-site (secondary treatment, sludge processing) and off-site (net energy use, embedded chemicals, sludge
disposal) sources of GHG emissions. The case study presented here calculates and discusses the changes in the
effluent quality (EQI) and operational cost (OCI) indices and the formation of carbon dioxide (CO2), methane (CH4)
and nitrous oxide (N2O) when modifying the percentage of total suspended solids (TSS) removal efficiency in the
primary clarifier (PRIM). Simulations show that high PRIM efficiency decreases the quantity of TSS entering the
activate sludge (AS) section leading to lower operational cost due to better energy recovery (and subsequent reduced
GHG emissions) in the sludge line, but increases the overall N2O emissions due to the low C/N ratio as a trade-off.
Overloading of the bioreactors as a result of poor PRIM performance: i) increases the biogenic CO2 emissions from
BOD oxidation and biomass decay in the AS section; ii) increases off-site CO2 emissions due to higher energy
demand during the nitrification stage; and, iii) reduces energy recovery from settled organics. The reported results
emphasize the importance of a plant-wide approach and the need to consider the interactions between the different
treatment units when evaluating the global warming potential (GWP) of a WWTP. Finally, the paper demonstrates
the potential of using the proposed approach as a general model-based tool for determining the most sustainable
WWTP operational strategies, which is essential in a water sector where climate change, energy and sustainability
are key challenges to be tackled.

Original languageEnglish
Title of host publicationProceedings of the World Congress on Water, Climate and Energy
Number of pages8
Publication date2012
Publication statusPublished - 2012
EventIWA World Congress on Water, Climate and Energy 2012 - Dublin, Ireland
Duration: 13 May 201218 May 2012


ConferenceIWA World Congress on Water, Climate and Energy 2012


  • Activated sludge modelling
  • Benchmarking
  • Global warming
  • Model-based evaluation
  • Multi-criteria decision making
  • Process control
  • Sustainability

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