Photocatalytic Nitrate Reduction
Paul Westerhff - Kiril Hristovski, ASU
To successfully translate bench-scale research into proof-of concept demonstrations, we propose the following activities:
- Collect new data related to nitrate reduction efficiencies in synthetic and “real” IX brines. The data will be generated using suspended photocatalysts in batch and continuous flow reactors equipped with low-pressure mercury vapor lamps. These reactor systems are available at our lab. The commercially available Photo-Cat system (Figure 6) is equipped with ceramic membrane to recover the catalyst and it can be operated in either recycle or single pass treatment mode.
- Compare commercially available TiO2 photocatalysts to newer materials. Emphasis will be placed on water-splitting photocatalysts as a novel technology leading towards a zero-chemical addition objective. These activities will be synchronized with activities conducted under objective 2 of Task 1.
- Examine the feasibilityof using LED as a potentialr eplacement of mercury vapor lamps. Research focus on developing an engineered solution to replace the mercury lamps in the existing bench scale photoreactor located in our lab; and comparing the performance against a baseline data obtained with mercury vapor lamps.
- Estimate the operation costs associated with integrating a photocatalytic reduction system with an ion exchange technology.
- Demonstrate photocatalytic reduction using existing ion exchange technology from a local utility. Research will focus on developing a pilot scale proof-of-concept system, capable of nitrate reduction in ion exchange brines and other complex matrices.
To develop these novel photocatalysts, we propose the following three activities:
- Develop and test a suite of novel photocatalysts (e.g., tantalate or titanium based) that facilitate electron transfer in the absence of an organic electron donor. Research will focus on discovering new photocatalysts that, from the literature, hold promise for improving nitrate/surface interactions and utilizing water as the electron donor (e.g., water splitting such as NaTaO3:La/NiO; BiVO4/Ag; SrTiO3/Rh, etc.).
- Identify nitrate reduction intermediates which influence favorable pathways towards N-gas production (i.e., minimize ammonia production). This will be achieved by measuring the intermediates, and their absorption spectra with the intent of tailoring wavelengths to influence favorable reaction pathways.
- Examine the feasibility of adding sacrificial intermediates (e.g., nitrous oxides) to influence pathway progression towards N-gases instead of undesirable ammonia. Research will focus on understanding the role of these intermediaries in the different reaction pathways as an intermediate step in moving towards zero chemical addition objective.