Long-term evaluation of a spectral sensor for nitrite and nitrate

Area of Science:

• Environmental Engineering
• Analytical Chemistry
• Water Quality Monitoring

Background:

• Accurate measurement of nitrite and nitrate is crucial for wastewater treatment plant (WWTP) process control and effluent quality management.
• Existing monitoring methods may require frequent maintenance or are not suitable for continuous in-situ measurements.

Purpose of the Study:

• To investigate the performance of a spectral in-situ UV sensor for measuring nitrite and nitrate concentrations in WWTP effluent.
• To assess the sensor's accuracy, precision, and long-term stability under operational conditions with minimal maintenance.

Main Methods:

• A spectral in-situ UV sensor was deployed at the EAWAG pilot-scale plant for 1.5 years.
• Sensor calibration was based on data from another WWTP.
• Minimal maintenance was performed, including manual cleaning once a month.

Main Results:

• The sensor demonstrated constant accuracy over the 1.5-year operational period.
• Accurate prediction of nitrite and nitrate concentrations with a 95% prediction interval of 0.32 mg N/l for nitrite (at 1.15 mg N/l) and 1.08 mg N/l for nitrate (at 5.55 mg N/l).
• The UV sensor showed good performance for low nitrite concentrations and very accurate results for higher concentrations (up to 10 mg N/l).

Conclusions:

• The spectral in-situ UV sensor is a reliable tool for monitoring nitrite and nitrate in WWTP effluent.
• The sensor's consistent accuracy and low maintenance requirements make it suitable for continuous monitoring.
• The findings support the use of this sensor for alarm systems and advanced control strategies in WWTPs.