Optimization of the biodegradation of 17-a-ethynylestradiol (EE2) using response surface methodology

• Main Author: Yuk, Sokunsreiroat
• Format: text
• Language: English
• Published: Animo Repository 2012
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/4391
• Institution: De La Salle University

17-a-Ethynylestradiol (EE2) is a synthetic estrogen which is mainly used in oral contraceptives. EE2 degrades very slowly in the environment, and gives a negative effect on the aquatic life. Thus, increase of the EE2 concentration in the environment requires the development of an efficient and effective method of treatment to degrade the pollutant in the water. This research used biofilms to degrade EE2 using medium containing organic carbon and without organic carbon added with tween 80 as solubility enhancer. The fluidized bed biofilm reactor used was in the form of modified Imhoff cones. The biofilm, which was grown on modified cement balls, was acclimatized first to EE2 before the actual batch experimental runs. Through manipulation of four independent control factors, such as initial pH, initial EE2 concentration, initial nitrogen content, and biomass volume, and the application of the method of Response Surface Methodology with the % degradation and the EE2 degradation efficiency as responses for choosing the best parameter for each control factor, the biodegradation of EE2 effectiveness was investigated. The % degradation is the percentage of EE2 removal, and the EE2 degradation efficiency is the mg of EE2 removal per hour in 1000mL of biofilm solution. At the optimum conditions, the verification run was performed to determine the presence of possible metabolites as intermediates in the biodegradation of EE2 using HPLC. The data obtained on EE2 concentrations were fitted to different relevant reaction models to determine the kinetics of the EE2 biodegradation. The result of the response surface methodology on the runs with the medium using glucose showed that the optimum condition which yielded the highest EE2 per cent biodegradation of 89.45 % are: initial pH of 8, initial EE2 concentration of 10 ppm, initial NH4Cl content of of 0.817 g/L, and 5% biofilm volume in 1000 mL solution (50ml biofilm/1000mL solution). On the other hand, the optimum conditions for the runs using medium without glucose are the same as those with glucose, except for initial pH of 8.5, and 82.07% highest EE2 degradation. Furthermore, the optimum v De La Salle University conditions of EE2 biodegradation for biofilm degradation efficiency were found to be 7.5 of initial pH, 10 ppm of initial EE2 concentration, 0.989 g/L of nitrogen content, and 5% of biofilm volume in 1000mL for medium containing glucose. For medium without glucose, the optimum condition were initial pH of 7.5, initial EE2 concentration of 20ppm, nitrogen content of 0.84 g/L, and 5% biofilm volume in 1000mL. At the optimum conditions, the verification runs were performed to determine the presence of intermediates. By using HPLC to measure EE2 concentrations, the results showed that there were some peaks that appeared besides the peak of EE2. Those peaks indicated the intermediates of EE2. The percent of EE2 degradation was found to be 84.025% for medium containing glucose and 91.723% for medium without glucose. Both the monod model and the first order rate of reaction suit well for EE2 biodegradation. The monod model parameters were found to be as follows: average concentration of biomass X of 2.372 g/L, growth yield coefficient Yx/s of 0.75 mg cell/mg EE2, maximum specific growth rate µmax of 0.148*10-2 hr -1, and half saturation coefficient Ks of 115.004 mg EE2/L for EE2 biodegradation in medium with glucose. For the medium without glucose, the constants were: average concentration of biomass X of 2.444 g/L, growth yield coefficient Yx/s of 0.563 mg cell/mg EE2, maximum specific growth rate µmax of 0.138*10-2 hr -1, and half saturation coefficient Ks of 115 mg EE2/L. The first order rate constants were found to be 0.041 for medium with glucose and 0.048 for medium without glucose. In this study, a possible microbial strain responsible for the EE2 degradation is Oligella ureolytica.