Calibration and validation of an activated sludge model for greenhouse gases no. 1 (ASMG1): prediction of temperature-dependent N2O emission dynamics

Abstract

An activated sludge model for greenhouse gases no. 1 was calibrated with data from a wastewater treatment plant (WWTP) without control systems and validated with data from three similar plants equipped with control systems. Special about the calibration/validation approach adopted in this paper is that the data are obtained from simulations with a mathematical model that is widely accepted to describe effluent quality and operating costs of actual WWTPs, the Benchmark Simulation Model No. 2 (BSM2). The calibration also aimed at fitting the model to typical observed nitrous oxide (N₂O) emission data, i.e., a yearly average of 0.5% of the influent total nitrogen load emitted as N₂O-N. Model validation was performed by challenging the model in configurations with different control strategies. The kinetic term describing the dissolved oxygen effect on the denitrification by ammonia-oxidizing bacteria (AOB) was modified into a Haldane term. Both original and Haldane-modified models passed calibration and validation. Even though their yearly averaged values were similar, the two models presented different dynamic N₂O emissions under cold temperature conditions and control. Therefore, data collected in such situations can potentially permit model discrimination. Observed seasonal trends in N₂O emissions are simulated well with both original and Haldane-modified models. A mechanistic explanation based on the temperature-dependent interaction between heterotrophic and autotrophic N₂O pathways was provided. Finally, while adding the AOB denitrification pathway to a model with only heterotrophic N₂O production showed little impact on effluent quality and operating cost criteria, it clearly affected N2O emission productions.

Greenhouse gases from wastewater treatment — A review of modelling tools

“…The authors confirmed the importance of using plant-wide modelling and stressed the need for setting up dedicated databases for reliable and feasible WWTP analysis at the plant-wide scale. During the last years, the interest in moving towards a wastewater treatment plant-wide control (including GHG) with the use of BSM was emphasized in literature (Guo et al, 2012;Guo and Vanrolleghem, 2014;Kim et al, 2015b) (Fig. 1).…”

“…The approaches for GHG modelling can be grouped (Corominas et al, 2012): i) empirical models based on the emission factors at the treatment unit scale (e.g., IPCC, 2006;LGOP, 2008); ii) simple comprehensive process-based models at the treatment unit scale (e.g., Monteith et al, 2005;Gori et al, 2011); iii) dynamic mechanistic models at the treatment unit (e.g., Mannina and Cosenza, 2015) or plant-wide scale (e.g., Guo and Vanrolleghem, 2014).…”

“…The authors demonstrated that simplified models compared with process-based models underestimate GHG emissions, mainly in terms of N 2 O. Thus, detailed process-based models are required to better understand and describe the processes involved in GHG emissions and their relationship to the other processes (Corominas et al, 2012;Guo and Vanrolleghem, 2014). Corominas et al (2012) also investigated the role of dynamic and steady-state simulations in predicting GHG emissions (Table 1).…”

“…Furthermore, GHG measurements contain a large amount of uncertainty (especially in terms of N 2 O), which contrasts with the use of fixed emission factors . Measurement uncertainties and lack of transposable data still hinder a correct and required GHG emission quantification process (Sweetapple et al, 2013;Guo and Vanrolleghem, 2014;Caniani et al, 2015;Kim et al, 2015b).…”

“…However, despite early efforts towards the integration of established activated sludge models (Henze et al, 2000) with GHG models (Batstone et al, 2002;Hiatt and Grady, 2008;Ni et al, 2013aNi et al, , 2013bMampaey et al, 2013;Guo and Vanrolleghem, 2014), few studies have discussed the benefits (in terms of reducing the GHG emissions coupled with the limitation of other pollutants from WWTPs) of applying GHG model at the plant-wide scale (Gori et al, 2011;Sweetapple et al, 2013;Flores-Alsina et al, 2014;Kim et al, 2015a).…”