Microflow injection system based on a multicommutation technique for nitrite determination in wastewaters

Area of Science:

• Analytical Chemistry
• Environmental Science
• Microfluidics

Background:

• Accurate monitoring of nitrite levels is crucial for wastewater treatment plant (WWTP) efficiency.
• Traditional analytical methods can be cumbersome for on-line monitoring.
• Microfluidic systems offer miniaturization and potential for enhanced analytical performance.

Purpose of the Study:

• To design, fabricate, and evaluate a microfluidic system for micro flow injection analysis (micro-FIA).
• To implement the micro-FIA system for on-line nitrite determination using the Griess-Ilosvay reaction.
• To apply the developed system for analyzing real wastewater samples and validating a nitrification inhibition model.

Main Methods:

• Micromachining of silicon microchannels and Pyrex glass sealing.
• Integration of optical windows for LED-based absorbance measurements.
• Development of a Visual-Basic controlled system for reagent delivery and data acquisition.
• Application of multicommutation for optimized mixing and analysis.

Main Results:

• Two optimal commutation frequencies were identified, yielding different analytical ranges and sensitivities.
• A 150/450 ms commutation ratio provided a smaller linear range (0-50 ppm) but superior detection limit (0.17 ppm) and sensitivity (0.0091 AU ppm-1).
• The micro-FIA system successfully analyzed real wastewater samples with high nitrite concentrations (0-1500 ppm).

Conclusions:

• The developed micro-FIA system is effective for on-line nitrite monitoring in WWTPs.
• The system's performance, particularly sensitivity and detection limits, can be tuned by adjusting commutation parameters.
• The results validated the nitrite ion inhibition model in the nitrification process with high accuracy.