Oxygen transfer parameters and oxygen uptake rates revisited

Area of Science:

• Environmental Engineering
• Biochemical Engineering
• Wastewater Treatment

Background:

• Bioreactor aeration system design relies on accurate oxygen mass transfer coefficients and saturation concentrations.
• Evaluating oxygen uptake rates (OURs) is crucial for understanding microbial activity in activated sludge processes.
• Traditional methods for OUR determination may require validation against mass balance approaches.

Purpose of the Study:

• To compare the log-deficit method (LDM) and non-linear regression method (NLRM) for estimating bioreactor aeration parameters.
• To evaluate differences in oxygen uptake rates (OURs) between the BOD bottle technique and mass balance calculations in activated sludge reactors.
• To investigate the influence of solids retention time (SRT) on the alpha-factor (α) in activated sludge systems.

Main Methods:

• Performed full- and bench-scale, non-steady state reaeration tests using sodium sulfite and cobalt chloride.
• Operated bench-scale completely-mixed activated sludge (CMAS) reactors.
• Compared oxygen mass transfer coefficients (KLa) and dissolved oxygen (DO) saturation concentrations (Cs) derived from LDM and NLRM.
• Assessed oxygen uptake rates (OURs) using the BOD bottle technique and mass balance calculations.

Main Results:

• No significant difference was found between LDM and NLRM estimates of KLa in tap water.
• Cs values were identical for LDM and NLRM in 70 out of 119 reaeration tests.
• Actual oxygen uptake rates (AOURs) and calculated oxygen uptake rates (COURS) agreed for 26 out of 51 datasets.
• The alpha-factor (α) demonstrated a positive correlation with increasing solids retention time (SRT).

Conclusions:

• LDM and NLRM are comparable methods for determining KLa and Cs in bioreactor aeration system design.
• The BOD bottle technique and mass balance calculations provide consistent OUR estimates under specific conditions.
• SRT is a significant factor influencing the alpha-factor in activated sludge processes, impacting oxygen transfer efficiency.