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A Novel Bioreactor for High Density Cultivation of Diverse Microbial Communities

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Simultaneous nitrification-denitrification achieved by an innovative internal-loop airlift MBR: comparative study.

Y Z Li¹, Y L He, D G Ohandja

¹Institute of Environmental Science and Engineering, Nanyang Technological University, 18 Nanyang Drive, Singapore 637723, Singapore. lyzxjtu@hotmail.com

Bioresource Technology

|November 17, 2007

Summary

This study on membrane bioreactors (MBR) found that airlift reactors (ALR) enhance total nitrogen removal. Higher solids (MLSS) improved nitrogen reduction by creating better conditions for simultaneous nitrification and denitrification (SND).

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Area of Science:

Environmental Engineering
Water Treatment Technologies
Bioreactor Design

Background:

Single-stage continuous aerated submerged membrane bioreactors (MBR) are crucial for wastewater treatment.
Optimizing nitrogen removal in MBRs is essential for environmental protection.
Understanding the mechanisms of nitrogen removal, like simultaneous nitrification and denitrification (SND), is key to improving efficiency.

Purpose of the Study:

To assess and compare the performance of different MBR configurations for nitrogen removal.
To investigate the impact of operating modes and biomass systems on nitrogen removal efficiency.
To elucidate the role of micro- and macroenvironmental factors in SND within MBRs.

Main Methods:

Comparison of MBR performance using internal-loop airlift reactor (ALR) and continuous stirred-tank reactor (CSTR) configurations.
Analysis of nitrogen removal efficiency, focusing on nitrification and denitrification processes.
Investigation of the influence of dissolved oxygen (DO) gradients and mixed liquor suspended solid (MLSS) concentrations on SND.

Main Results:

High nitrification rates were achieved across all tested MBRs.
Denitrification was identified as the rate-limiting step for total nitrogen (T-N) removal.
The ALR configuration demonstrated superior T-N removal compared to CSTR.
SND was confirmed as the primary nitrogen removal mechanism, significantly influenced by hybrid biomass and DO gradients.
Elevated MLSS concentrations (>12.6 g/L) improved T-N removal by enhancing anoxic microenvironments, leading to nitrite accumulation and higher nitrogen reduction.

Conclusions:

Airlift MBRs are more effective for total nitrogen removal than CSTRs.
Optimizing MLSS concentration and managing DO gradients are critical for enhancing SND and nitrogen removal in MBRs.
Hybrid biomass systems can improve the efficiency of SND in MBRs.