Dynamic α-factor models for fine-bubble- and surface aeration – impact of settleability and implications on N2O emission

Yuge Qiu, Vince Bakos, Nyle Stewart-Campbell, Benedek Plosz

Research output: Contribution to journalArticlepeer-review


In water resource recovery facilities (WRRF), aeration efficiency and N2O greenhouse gas emission are affected by the variability of the α-factor. Dynamic calibration of α using sensor data represents a significant knowledge gap this contribution aims to address. To assess factors influencing oxygen and N2O gas mass-transfer, a continuous flow laboratory-scale reactor system was operated to encourage the proliferation of filamentous bacteria. Gas mass-transfer was assessed using fine-bubble and surface aeration. Significant impacts of solid settling velocity on the α-factor – relative to that by MLSS concentration – is obtained. The feasibility of using solid settling velocity and concentration, as α-factor predictors, is tested. The theoretical approach of using relative diffusivity to dissolved oxygen – as an effective predictor of N2O liquid–gas mass-transfer stripping – is experimentally validated, for the first time. Plant-wide WRRF simulations show that surface aeration is inferior to fine-bubble aeration in terms of greenhouse gas emission and treated water quality.

Original languageEnglish
Article number150650
Number of pages9
JournalChemical Engineering Journal
Early online date26 Mar 2024
Publication statusPublished - 15 May 2024

Data Availability Statement

Data will be made available on request.


  • Alpha-factor modelling
  • Filamentous bulking
  • Gas mass transfer in activated sludge reactors
  • Laboratory-scale experiments
  • WRRF simulations

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Chemistry(all)
  • Industrial and Manufacturing Engineering
  • Environmental Chemistry


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