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

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 proliferation of filamentous bacteria. Besides the impact of sludge settleability, gas mass-transfer was assessed using fine-bubble and surface aeration. Significant impacts of solid settling on the α-factor – relative to that by MLSS concentration – is obtained. The feasibility of surrogating viscosity measurements with hindered settling velocity is demonstrated. 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 indicate the incompatibility of surface aeration with sustainable development of urban water systems in terms of greenhouse gas emission and treated water quality.