Influence of activated sludge dissolved oxygen concentration on a membrane bioreactor performance with intermittent aeration

Abstract

This study measured the effect of low activated sludge dissolved oxygen (DO) concentration on a membrane bioreactor (MBR) treating real urban wastewater with respect to organic matter and nitrogen removal efficiency and transmembrane pressure evolution. For this purpose, a full-scale experimental pre-denitrification MBR system was operated at a constant permeate flow rate of Q = 0.45 m³h⁻¹ with intermittent aeration. The experimental installation worked at high hydraulic retention time, variable sludge retention time and with activated sludge temperatures of between 22.0 to 31.3 °C. Mean DO concentrations in the activated sludge were gradually decreased from 1.25 mgO₂L⁻¹ to less than 0.20 mgO₂L⁻¹. Variations in DO set points did not affect the main operational parameters of the MBR system and no clear relation was shown between DO concentration decrease and membrane fouling. At DO concentrations lower than 0.2 mgO₂L⁻¹, a deterioration in MBR effluent quality was observed, mainly with respect to chemical oxygen demand, biochemical oxygen demand at five days and NH₄⁺, however, the opposite effect was observed for NO₃^-. These results indicate that employing low DO set points is a promising strategy for application in MBR systems.

Keywords:

• MBR
• wastewater treatment
• intermittent aeration cycle
• low dissolved oxygen concentration
• biological nutrient removal

Additional information

Funding

This research (NET 324936/1) was funded by the Andalusian Government (Andalusian Water Agency) with European Union funds (FEDER) and it was conducted with the collaboration of EMASAGRA.