(374f) Solar Photocatalytic Treatment of Atrazine-Contaminated Agricultural Water in the Rio Grande Basin

To develop a cost-effective and nearly maintenance-free solar treatment process for herbicides in agricultural water, we studied the photocatalytic decomposition of dissolved atrazine, an herbicide contaminant common in the Rio Grande Basin rivers and agricultural run-off water. Atrazine (C₈H₁₄ClN₅), widely used in corn, sorghum and wheat fields, is toxic to water-life (leopard frogs, etc) and can cause prostate cancer, cardiovascular damage etc. to human beings [1-3]. Without treatment, the atrazine-contaminated water is hazardous and detrimental to the water sustainability in the Rio Grande Basin.

The available atrazine treatment methods include active carbon adsorption, UVC decomposition and photocatalytic decomposition [4-10]. As photocatalytic decomposition has the potential to use visible light, it could be a nearly maintenance-free process for environmental remediation. In our lab, we demonstrated that atrazine decomposed under a 4W fluorescent light (Fig. 1) with Degussa P-25 and BA-PW25 (Ecodevice, Japan) TiO₂ photocatalysts suspended in a 2 L atrazine solution. The kinetic data of the photochemical decomposition of atrazine can be fitted with a first-order rate equation:

 dC/dt = - kC                                                 (1)

The photocatalysis results in a main product, hydroxyatrazine, that can further decompose to CO₂ and water.  Hydroxyatrazine is relatively harmless compared to atrazine. The optimum catalyst loading was found to be around 0.3% by weight (Fig. 2).

 

Fig. 1 Atrazine photocatalytic decomposition under 4 W fluorescent light in a 2 L batch reactor with BA-PW 25 as the photocatalyst.

 

Fig. 2. Optimum loading of BA-PW 25 photocatalyst in a suspension

Using a 395 nm optical filter, we also observed the activities of the photocatalysts, Fig. 3.

 

Fig. 3. Atrazine photodecomposition under 4 W fluorescent light with 395 nm filter in 2 L batch reactor.

In a sunny day, atrazine rapidly decomposes from 56 ppb to below 3 ppb in 30 minutes in a 2 L reactor with Degussa P-25 as the photocatalyst under sunlight, while another photocatalyst BA-PW 25 needs 6 hours (Fig. 4). The latter has the following kinetic equation with a R²= 0.997.

dC/dt = -0.448C                                              (2)

 

 Fig. 4. Atrazine photodecomposition in a 2 L batch reactor under solar light in a sunny day

Atrazine photodecomposition with immobilized photocatalyst will be reported in a separate paper.                                        

                                                      References

1. US EPA, Ambient Aquatic Life Water Quality Criteria for Atrazine-Revised Draft, EPA-822-R-03-03, 2003.  
2. V. Hequet, C. Gonzalez, P. L. Cloirec, Water Research (2001) 18, 4254-4260
3. Hayes, T., Haston, K., Tsui, M., Hoang, A., Haeffele C., and Vonk, A., Environmental Health Perspectives, V. 111 (4), Apr. 2003.
4. National Renewable Energy Laboratory (2001, October). Photochemical treatment of pollutants (CDS-SS25-B001). CO. www.nrel.gov/research/industrial_tech/pollution.html
5. Ye, X, Chen, D. H., Flaherty, D., Wang, B., Tadmor, R., Sternes, K., ?Photochemical Treatment of Herbicide/Pathogen Contaminated Agricultural Water in the Rio Grande Basin?, AIChE 2005 Annual Meeting at Cincinnati, OH, November 2005.
6. Fujishima, A., Hashimoto, K. & Wuatanabe, T. (1999). TiO₂ photocatalysis fundamentals and applications (p. 126 ? 156). Tokyo: Bkc, Inc.
7. Ye, X., Chen, D.H., and Li, K. "Oxidation of PCE with a UV LED Photoreactor", Chemical Engineering & Technology, 28, No. 1, 95-97 (2005).
8. Devahasdin, S., C. F., K. Li, and D. H. Chen ?TiO₂ Photocatalytic Oxidation Of Nitric Oxide: Transient Behavior And Reaction Kinetics?, Journal of Photochemistry and Photobiology A; Chemistry, 156, 161-170 (2003).
9. Chen, D. H., C. Huang, and K. Li, "Photocatalytic Oxidation of Butyraldehyde over Titania in Air: Byproduct Identification and Reaction Pathways,? Chem. Eng. Comm., 190, 373-392 (2003).
10. Chen, D. H., K. Li, S.Y.C. Liu, C. Huang, and S. Esariyaumpai "TiO2 Photocatalytic Oxidation of Butyraldehyde and PCE in the Air through Concentric Reactors," J. Adv. Oxid. Technol, 5, 227-232 (2002).