Effects of ionic strength and ion pairing on (plant-wide) modelling of anaerobic digestion

Solon, Kimberly and Flores-Alsina, Xavier and Kazadi Mbamba, Christian and Volcke, Eveline I. P. and Tait, Stephan and Batstone, Damien and Gernaey, Krist V. and Jeppsson, Ulf (2015) Effects of ionic strength and ion pairing on (plant-wide) modelling of anaerobic digestion. Water Research, 70. pp. 235-245. ISSN 0043-1354


Plant-wide models of wastewater treatment (such as the Benchmark Simulation Model No. 2 or BSM2) are gaining popularity for use in holistic virtual studies of treatment plant control and operations. The objective of this study is to show the influence of ionic strength (as activity corrections) and ion pairing on modelling of anaerobic digestion processes in such plant-wide models of wastewater treatment. Using the BSM2 as a case study with a number of model variants and cationic load scenarios, this paper presents the effects of an improved physico-chemical description on model predictions and overall plant performance indicators, namely effluent quality index (EQI) and operational cost index (OCI). The acid-base equilibria implemented in the Anaerobic Digestion Model No. 1 (ADM1) are modified to account for non-ideal aqueous-phase chemistry. The model corrects for ionic strength via the Davies approach to consider chemical activities instead of molar concentrations. A speciation sub-routine based on a multi-dimensional Newton–Raphson (NR) iteration method is developed to address algebraic interdependencies. The model also includes ion pairs that play an important role in wastewater treatment. The paper describes: 1) how the anaerobic digester performance is affected by physico-chemical corrections; 2) the effect on pH and the anaerobic digestion products (CO2, CH4 and H2); and, 3) how these variations are propagated from the sludge treatment to the water line. Results at high ionic strength demonstrate that corrections to account for non-ideal conditions lead to significant differences in predicted process performance (up to 18% for effluent quality and 7% for operational cost) but that for pH prediction, activity corrections are more important than ion pairing effects. Both are likely to be required when precipitation is to be modelled.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Files associated with this item cannot be displayed due to copyright restrictions.
Faculty/School / Institute/Centre: Current - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying
Date Deposited: 12 May 2019 23:56
Last Modified: 30 May 2019 02:23
Uncontrolled Keywords: ADM1, BSM2, non-ideality, physico-chemical framework, wastewater plant-wide modelling
Fields of Research : 09 Engineering > 0907 Environmental Engineering > 090703 Environmental Technologies
Identification Number or DOI: 10.1016/j.watres.2014.11.035
URI: http://eprints.usq.edu.au/id/eprint/36222

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