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

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Author

  • Kimberly Solon
  • Xavier Flores-Alsina
  • Christian Kazadi Mbamba
  • Eveline I P Volcke
  • Stephan Tait
  • Damien Batstone
  • Krist Gernaey
  • Ulf Jeppsson

Summary, in English

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.

Publishing year

2015

Language

English

Pages

235-245

Publication/Series

Water Research

Volume

70

Issue

March

Document type

Journal article

Publisher

Elsevier

Topic

  • Other Electrical Engineering, Electronic Engineering, Information Engineering

Keywords

  • Physico-chemical framework
  • Wastewater plant-wide modelling

Status

Published

ISBN/ISSN/Other

  • ISSN: 1879-2448