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

Xavier Flores-Alsina, Christian Kazadi Mbamba, Kimberly Solon, Eveline Volcke, Stephan Tait, Damien Batstone, Krist V. Gernaey, Ulf Jeppsson

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The objective of this study is to show the influence of ionic strength (as activity corrections) andion pairing on (plant-wide) modelling of anaerobic digestion processes in wastewater treatment plants(WWTPs). Using the Benchmark Simulation Model No. 2 (BSM2) as a case study, this paper presents the effects that an improved physico-chemical description will have on the predicted effluent quality (EQI) and operational cost (OCI) indices. 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. Also, a speciation sub-routine based on a multi-dimensional Newton-Raphson iteration method accounts for the formation of some of the ion pairs playing an important role in wastewater treatment processes. Results at high ionic strength demonstrate that corrections to account for non-ideal conditions lead to significant differences in predicted process performance. In addition, the paper describes: 1) how the anaerobic digester performance is affected; 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.
Original languageEnglish
Title of host publicationProceedings of the 2014 IWA World Water Congress & Exhibition
Number of pages9
Publication date2014
Publication statusPublished - 2014
Event2014 IWA World Water Congress & Exhibition - Lisbon, Portugal
Duration: 21 Sept 201426 Sept 2014


Conference2014 IWA World Water Congress & Exhibition


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