Treatment of Endosulfan in water matrix using UV and zero-valent iron

• Main Authors: Alfonso, Ana Patricia D., Chua, Stephanie Nicole S., Pangilinan, Christian David C.
• Format: text
• Language: English
• Published: Animo Repository 2008
• Subjects: Endosulfan > Environmental aspects; Endosulfan > Toxicology; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/7268
• Institution: De La Salle University

Endosulfan has been used worldwide as an insecticide and acaricide, and is currently in restricted used in the Philippines as a pesticide in pineapple and banana plantations. Because of its persistence in the environment and the hazards it poses to the environment and the ecosystem, this organochlorine pesticide is currently classified as Category 1b Highly Hazardous by the US-EPA and has been identified as a Persistent Toxic Substance by UNEP. An immediate response is therefore considered necessary regarding this growing concern on the elimination and reduction of POPs like endosulfan in the environment. The project investigates the effectiveness of using the physical process of UV irradiation and the chemical process if zero-valent iron (ZVI) oxidation in the degradation of endosulfan in water matrix. Parametric evaluation was made to monitor the efficiency of the processes and toxicity testing was done on the effluent to check that it is not toxic and it can be released back into the environment. Preliminary experiments were done to determine the initial concentration, purity and composition of the endosulfan sample taken from the stockpile of Planters Products Incorporated. In addition, preliminary test runs were done to determine the effect of adding surfactant to endosulfan in water. Results show that the sample was 46.45% (w/v) pure and that it contains 80,690 ppm of Endosulfan I (a - endosulfan) and 39,800 ppm of Endosulfan II (B-endosulfan). Also, it was found that the sample contains not only endosulfan but other compounds as well, such as an organic solvent that is miscible in water. Hence, the addition of surfactant is no longer necessary. Parallel degradation tests were done for ZVI treatment, UV irradiation treatment and combined ZVI and UV irradiation treatment. Five (5)-mL samples of 10 ppm endosulfan in water was prepared and placed in 15-mL screw capped glass vials for all three degradation tests. The vials containing the sample were then placed in a rocking shaker for continuous agitation. For the UV irradiation treatment, a 254-nm UV lamp was used and the rocking shaker was placed inside an aluminum casing to eliminate further effect of light on the sample. The test with UV was done on solutions at natural pH. On the other hand, for the ZVI treatment and combined UV-ZVI treatment, the pH of the samples was adjusted to 2 prior to the test. Also, 0.125 g of zero valent iron powder was added to the samples. For the combined UV-ZVI treatment, the same set-up as that used in the UV treatment was used. Whereas, for ZVI treatment, the lamp was turned off. The samples were taken at pre-determined time intervals and underwent liquid-liquid extraction in preparation for the chemical analysis. Toxicity analyses were also conducted using activated sludge and redox dye Tetrazolium to determine if the samples are toxic. Gas chromatography with Electron Capture Detector (GC-ECD) was used to monitor the concentration of the endosulfan sample used in the degradation tests. Results show that the UV treatment and the combined UV-ZVI treatment has decreased the concentration of endosulfan in the solution the greatest with about a 86% decrease in concentration as compared to the results of the ZVI treatment where a-endosulfan decreased by 64.73% and B-endosulfan decreased by 81.86% in the span of two hours. High Performance Liquid Chromatography was used to determine the chloride ion content of the sample. Also, the pH of the samples was monitored. For the ZVI and combined UV-ZVI treated solutions, decholorination took place and an increase in the pH levels were observed. This may be due to the generation of hydroxyl ions during the corrosion of iron. For the ZVI treatment, it is better to purge the system with an inert gas so as to remove the dissolved oxygen in the solution as this competes with the redox reaction between the target compound and the iron. The purged solution were able to reach a decrease in concentration of 64.73% for a-endosulfan and 81.86% by B-endosulfan as compared to the solutions that were not purged that only showed a decrease in concentration of 28.43% for a-endosulfan and 27.17 for B-endosulfan. The GC-MS results o the treated samples could help determine the mechanism as to which the treatment works. Results show that the mechanism of the UV treatment is by free radical reaction. Although the concentration of endosulfan in the solution decreased, it just transformed endosulfan ether as shown in the GC-MS results thus the treated solutions presented itself as still being toxic as based from the toxicity analysis that was done. The mechanism for the ZVI treatment is by reductive dechlorination rather than free radical reaction as seen in the UV treatment. Dechlorination took place and based from the GC-MS result of the treated ZVI solution, endosulfan ether diol was not found thus the treated solutions were no longer toxic as presented through the toxicity analysis that was done. The combined UV-ZVI treatment, a high decrease in endosulfan concentration was achieved and dechlorination occurred. The treatment proved to be effective in degrading endosulfan giving a resulting solution that is no longer toxic as seen from the results of the toxicity analysis.