Grantee Research Project Results
Final Report: A Low-Cost UV Raman Instrument Measuring Nitrate and Nitrite for Improved Operation and Control of Nitrification/Denitrification Treatment Processes
EPA Contract Number: EPD05033Title: A Low-Cost UV Raman Instrument Measuring Nitrate and Nitrite for Improved Operation and Control of Nitrification/Denitrification Treatment Processes
Investigators: Hug, William F.
Small Business: Photon Systems, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2005 through August 31, 2005
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2005) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Watersheds , SBIR - Water and Wastewater
Description:
This research project was directed toward the development of an online monitoring and process control system to improve the reliability and performance of wastewater treatment systems designed to remove nitrogen through simultaneous nitrification and denitrification (SNdN). A key component technology of this innovative process control system is an analytical instrument, based on ultraviolet resonance Raman (UVRR) spectroscopy, that will enable real-time, in situ measurement of nitrate and nitrite in biological nutrient removal system reactors, without the need for reagent additions or complex calibration procedures.
The important commercial applications of this new technology include:
- In situ monitoring and control of small, decentralized, membrane bioreactor (MBR) satellite wastewater treatment systems, producing reclaimed water for local reuse.
- Retrofitting existing wastewater treatment plant process control systems to improve energy efficiency and treatment efficiency.
- Cost-effective and energy efficient treatment of high nitrogen-containing side streams in wastewater treatment plants, such as digester supernatant and centrate or filtrate.
Summary/Accomplishments (Outputs/Outcomes):
The major goals of the project were accomplished. Photon Systems, Inc., demonstrated the proof of concept of a miniature, low-cost UV Raman instrument capable of measuring nitrites and nitrates in municipal wastewater treatment facilities. Compared to prior technology, the new instrument developed by Photon Systems has about 800-1,000 times less power consumption, 30-40 times lower cost, 10-15 times reduction in size and weight, and is 10 times faster. With approximately 10,000 times less laser energy, this instrument detected the Raman water emission band at 1,640 wave numbers, corresponding to a limit of detection of nitrates and nitrites between 2 and 10 ppm. Moreover, Photon Systems has not finished optimizing the optics, electronics, and software. The instrument has its own Internet protocol address, so it can be deployed in arrays of instruments controlled and operated over an intranet or Internet. The specific features of the technology improvement are illustrated in Table 1.
Table 1. Prior and New Technology for Raman Identification of NO2 and NO3
Prior Technology | New Technology | |
---|---|---|
Power consumption (watts) | 15,000 | 15 |
Size (cubic feet) | 6 | 0.5 |
Weight (pounds) | 200 | 15 |
Cost (U.S. dollars) | 450,000 | 15,000 |
The instrument uses new laser and optical detection technology to make a vast improvement in the laser power output and input needed to make Raman measurements of nitrites and nitrates. Photon Systems will continue to evolve the optical geometry and electronics to improve signal-to-noise and reduce the limits of detection for nitrates and nitrites. The exact limits of detection are not yet established.
Background
Raman spectroscopy is the measurement of the wavelength and intensity of scattered light from molecules. It is a noncontact, noninvasive method of measurement that requires no sample preparation or handling. The Raman-scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations. The probability that an incident photon will undergo Raman scattering is very low. Because of this, it was experimentally difficult to observe when the phenomenon was discovered in 1928 and, therefore, of little practical significance. However, in recent years, Raman spectroscopy has been revolutionized by new technological developments, including the availability of laser systems covering a wide range of wavelengths. The use of lasers has resulted in enormous increases in Raman signal detection capabilities, making possible important applications in analytical chemistry and in biochemical research involving the structure and function of proteins. Advances in optics, electronics, and photon detection technologies also have contributed to the emergence of Raman spectroscopy as a powerful analytical tool.
Raman intensity is proportional to the fourth power of the excitation light frequency. As an example, the Raman intensity obtained using a 224 nm deep UV laser light source will be approximately 150 times that obtained using a 785 nm red diode laser light source. A resonance Raman effect occurs when the excitation source wavelength is within an electronic absorption band of the target chemical species and results in an increase in the Raman scattering cross section of up to 100-million fold as compared to normal scattering. Therefore, for chemical species that have electronic absorption bands in the UV region, UVRR spectroscopy may be an ideal analytical method. By selecting an appropriate excitation frequency, resonance Raman can be a very sensitive and highly specific detection method for target chemicals and will be free from most interferences—including fluorescence—that might be present in environmental samples and their backgrounds. Because the water molecule does not provide interference, measurement in aqueous samples can be made with little or no sample preparation and without the need for any reagent additions.
The potential for using UVRR to measure nitrate and nitrite in wastewater treatment systems has been previously demonstrated by members of Photon Systems’ project team. Other potential applications that have been demonstrated for environmental monitoring using UVRR include biotoxins, such as the amino acid neurotoxin domoic acid, which is associated with red tides and contaminated seafood. To date, the major obstacles to the commercial development of UVRR instruments targeting these and similar applications for real-time and/or remote environmental monitoring have been the relatively high cost and complexity of the instrument components. The technological innovations that Photon Systems demonstrated in this research project enable a dramatic reduction in the size, weight, power consumption, complexity, and cost of special purpose UVRR analytical instruments not only for nitrite/nitrate monitoring, but also for a wide range of wastewater contamination monitoring. The particular commercial instrument application targeted in this research is the monitoring of nitrate and nitrite for enhanced control of nitrogen removal and energy savings in wastewater treatment systems.
The most common, well-accepted, and economical approach to nitrogen removal is biological nitrification and denitrification. Nitrogen enters wastewater treatment plants in the form of organic and ammonium nitrogen. During nitrification, the nitrogen is oxidized by autotrophic bacteria to nitrate nitrogen. During biological denitrification, biological reactors are operated without oxygen addition, so that the bacteria use nitrate as an electron acceptor for their respiration. Various designs are used, and one of the common approaches employs an anoxic tank (i.e., respiration using nitrate in the absence of oxygen) ahead of aeration, where recycled nitrate is contacted with influent wastewater to promote its reduction to nitrogen gas.
In recent years, a great deal of interest has been focused on treatment plant designs and control strategies that achieve simultaneous nitrification and denitrification in one reactor. To reliably achieve SNdN, the dissolved oxygen levels must be tightly controlled at very low levels. Advantages that can be attributed to SNdN, as compared to more conventional nitrogen removal processes, include:
- Reduced tankage requirements (lower capital costs and smaller footprint)
- Internal recycle is not required (lower capital costs and simpler operation)
- Reduced energy consumption due to improved oxygen-transfer driving force.
The major challenge involved in the design and operation of a system to reliably achieve SNdN is the development of an instrumentation and control system that can maintain the required low levels of dissolved oxygen, even as influent loading and other operating conditions vary. If too little oxygen is present, then nitrification will be inhibited and the effluent ammonia will increase. If the dissolved oxygen levels are too high, then denitrification will be inhibited, resulting in reduced energy efficiency and increased effluent nitrate nitrogen. Various methods have been employed to control dissolved oxygen levels within the range needed to achieve SNdN; however, each of these has significant limitations. The control method that Photon Systems demonstrated will dramatically improve reliability and cost-effectiveness of SNdN treatment processes by reducing energy consumption as well as the potential for both ammonia bleed through and excess effluent nitrate.
Conclusions:
According to the U.S. Environmental Protection Agency, 25 percent of all U.S. households and 33 percent of new development are served by onsite and decentralized treatment systems. In some areas of the country, onsite system failure rates are high, resulting in water quality and public health concerns. However, for many communities, it can be cost-prohibitive to transport wastewater to a centralized municipal treatment facility. Furthermore, as water supplies become scarcer and costs increase, many communities are looking for wastewater treatment solutions that enable recycling and reuse. The high cost of piping reclaimed wastewater through miles of distribution lines from a centralized wastewater reclamation plant back to where it is needed also stands in the way of implementing cost-effective reuse strategies. A technology that is receiving increasing interest for wastewater treatment and reuse for small communities and decentralized systems is the MBR treatment process. To comply with reclaimed water reuse standards, it is necessary to meet strict effluent limits for nitrogen. To be cost-effective, small, decentralized wastewater reclamation systems must be capable of reliable performance and easy to operate. Improved instrumentation and automated control systems are essential to achieving these objectives and for decentralized MBR systems to gain wide acceptance. The instrumentation and control system that Photon Systems proposes based on UVRR for monitoring of nitrate and nitrite will be ideally suited to achieving reliable SNdN and energy savings, with minimal operator attention using MBRs.
Another significant commercial opportunity for Photon Systems’ proposed monitoring and control system is its application to the retrofitting of existing treatment plants for improved nitrogen removal efficiency and reductions in energy requirements. The energy savings that will be possible using this more robust instrumentation system will be very substantial. Photon Systems’ system also could be used with MBRs for treatment of high-nitrogen side streams in larger treatment plants. The treatment of these side streams would be of particular interest for the implementation of operation and control strategies aimed at achieving the nitrite shunt metabolic pathway using Photon Systems’ nitrate/nitrite monitoring system.
Follow-on research and commercialization efforts will include development of other special purpose low-cost UVRR instruments for detection of compounds of interest in water supplies, such as algal biotoxins, disinfection byproducts, and other toxic materials that could be accidentally or deliberately introduced.
Supplemental Keywords:
water, wastewater, ultraviolet resonance Raman spectroscopy, UVRR, Raman scattering, in situ monitoring, membrane bioreactor, nitrites, nitrates, wastewater treatment systems, laser and optical detection, wavelength, environmental monitoring, biotoxins, nitrification, denitrification, simultaneous nitrification and denitrification, SNdN, disinfection byproducts, EPA, small business, SBIR,, RFA, Scientific Discipline, Water, TREATMENT/CONTROL, Waste, Ecosystem Protection/Environmental Exposure & Risk, Chemical Engineering, Wastewater, Municipal, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, Water Pollution Control, wastewater treatment, monitoring, dentrification, online monitoring, wastewater treatment plants, spectroscopy, nitrification, municipal wastewater, in situ monitoring, phosphorus, ultraviolet resonance Raman spectroscopy, nitrogenThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.