Grantee Research Project Results

Final Report: An Innovative Online Monitoring and Control System for Improved Biological Nutrient Removal

EPA Contract Number: 68D00234
Title: An Innovative Online Monitoring and Control System for Improved Biological Nutrient Removal
Investigators: Coleman, Thomas E.
Small Business: dTEC Systems LLC
EPA Contact:
Phase: I
Project Period: September 1, 2000 through March 1, 2001
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2000) RFA Text |  Recipients Lists
Research Category: SBIR - Water and Wastewater , Watersheds , Small Business Innovation Research (SBIR)

Description:

The objective of this Phase I research project is the development of an innovative online monitoring and process control system that will improve the reliability and performance of biological nutrient removal (BNR) systems which are designed to achieve low discharge concentrations of phosphorus and/or nitrogen from municipal wastewater treatment plants. The proposed monitoring system will utilize Raman spectroscopy in conjunction with an in situ membrane filter assembly to enable real time measurement of nitrate and nitrite in BNR system reactors without the need for reagent additions or complex calibration procedures.

The availability of new more powerful laser excitation sources, improved optics technologies, and solid state detectors have revolutionized Raman spectroscopy in recent years, creating the potential for measuring specific analytes in complex mixtures under real plant conditions with little or no sample preparation. The specific objectives and activities of this Phase I project included:

1. Determination of the practical detection limits and the optimal excitation source wavelength(s) for nitrate and nitrite using Raman spectroscopy;
   
2. Determination of the potential for interference from other chemical species commonly found in wastewater systems;
   
3. Development and demonstration of a prototype membrane filter cartridge assembly which would be installed in the BNR reactor; and
   
4. Identification of inexpensive laser sources for development of an instrument to enable widespread commercialization of the technology.
   

Summary/Accomplishments (Outputs/Outcomes):

The important findings which have been demonstrated in this Phase I research include;

1. The Raman spectral bands of nitrite and nitrate are distinct, and the main spectral features are well separated;
   
2. Raman spectroscopy can be applied to enable detection of nitrate and nitrite concentrations in water to less than 0.2 ppm as N;
   
3. The chemical species present in representative filtered activated sludge wastewater samples do not interfere with the quantitative detection of nitrate and nitrite in these samples down to the same detection limits as observed in pure water;
   
4. The optimal wavelength range for Raman spectral measurement of nitrate and nitrite was determined, and a relatively low cost laser system is currently available as a beta test unit in an appropriate excitation wavelength;
   
5. More powerful low cost laser systems with appropriate wavelengths are currently under development which are expected to be available for prototype testing within one to one and a half years;
   
6. A commercially available 0.45 mm pore size membrane material was successfully incorporated into an in situ filtration assembly, developed in this research, to provide the necessary sample pretreatment for on-line, real time measurement of nitrate and nitrite in BNR wastewater treatment plants.

While the objective of this research was the quantitative detection of nitrate and nitrite, the Phase I investigations have suggested that additional Raman shift bands may also be useful as diagnostic measurements for monitoring and control of wastewater treatment processes. The identification of the chemical species responsible for other bands of potential interest has been identified as a topic for future research.

Conclusions:

The results of these Phase I investigations demonstrate the ability of Raman spectroscopy to measure nitrate and nitrite in wastewater treatment systems down to detection limits significantly below the 1 ppm level identified as a technical objective in the Phase I proposal. The capability to measure both analytes at detection limits less than 0.2 ppm (as N) with this system has been demonstrated. It is anticipated that through further optimization it will be possible to achieve detection limits at concentrations below 0.1 ppm.

The initial commercialization strategy will focus on defining a market for this application by first developing an instrument with the best possible price/performance characteristics in terms of detection limits. The capabilities of such an instrument would far exceed the capabilities of existing monitoring technologies by simultaneously detecting nitrate and nitrite to 0.2 ppm or less without the use of reagents or need for site specific calibration. Dual beam, UV absorption nitrate/nitrite monitoring systems currently in use can not differentiate nitrate from nitrite, require site specific calibration, and are subject to a variety of interferences from organic compounds and other UV absorbing chemical species. Systems using NADH fluorescence measurement are currently being marketed for control of simultaneous nitrification and denitrification processes where very low dissolved oxygen levels must be maintained. However, the NADH monitoring method is currently costly and also requires site specific calibration and adjustments. Direct simultaneous measurements of nitrate and nitrite will be much more practical and effective for use as control system input variables for this type of process. The only required calibration of the Raman system could be done automatically using water as an internal reference standard. Unlike automated colorometric spectroscopy based analyzers, including those using flow injection analysis (FIA) methods, the Raman spectroscopy system requires no reagent additions.

One of the obstacles to the widespread application of Raman spectroscopy for monitoring analytes such as nitrate and nitrite has been the relatively high the cost of the necessary laser excitation source. However, as lower cost lasers become available in the near future, Raman spectroscopy will ultimately be very cost competitive with other analytical technologies while at the same time having superior performance capabilities. By demonstrating this superior performance in a prototype instrument, this application of Raman spectroscopy can be recognized not just as an alternative to the existing monitoring technologies, but as an enabling technology which can lead to significant improvements in the design and operation of BNR wastewater treatment systems.

While this Phase I research project has focused on the application of Raman spectroscopy to the monitoring and control of BNR wastewater treatment processes, it could readily be adapted to other applications such as drinking water treatment where nitrate removal is required. Through future research and development, additional applications of Raman spectroscopy for detection of other analytes of environmental interest are anticipated. Continued improvements in the laser and optic component technologies will soon make it feasible to develop a relatively low cost, rugged portable instrument for direct analysis of samples in remote locations without the need for sample preservation or transportation to a laboratory.

Supplemental Keywords:

Nitrification/denitrification, activated sludge, anoxic, secondary phosphorous release, nitrate, nitrite., RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Water, Waste, Chemical Engineering, Municipal, Environmental Chemistry, Wastewater, Monitoring/Modeling, Environmental Engineering, Environmental Monitoring, online monitoring, biological nutrient removal (BNR), monitoring, phosphorus, real-time monitoring, spectroscopy, wastewater treatment plants, nitrogen, wastewater treatment, biological nutrient removal (BNR)