EN-11 photo-degradation of bpa and cytotoxicity of photo-degradation by-products under UV and UV/H2O2
Ng, Yong Shin
Date of Issue2018
School of Civil and Environmental Engineering
Bisphenol A, with the chemical formula (CH3)2C(C6H4OH)2, is a synthetic organic compound belonging to the group of diphenylmethane derivatives and bisphenols with two hydroxyphenyl groups. It exists as a white to light brown flakes or powder and has a boiling point of 360 °C and melting point of 152-153°C at room temperature and pressure. It is used primarily in the production of polycarbonate plastics and epoxy resins. Low levels of the compound were detected in most of the drinking water samples. Bisphenol A concentrations in tap water ranged from 3.5 to 59.8 ng/L and samples collected from taps connected to PVC pipes and water filter devices were found to contain the highest levels. Bisphenol A is sparingly soluble in water but is soluble in organic solvents. Bisphenol A is exhibits estrogen-mimicking, hormone-like properties which could disrupt the development of fetuses in pregnant women. Investigations into the safety of the use of Bisphenol A were conducted, and the U.S. Food and Drug Administration ended its authorization of the use of BPA in baby bottles and infant formula packaging, based on market abandonment, not safety. When exposed to ultraviolet radiation, photodegradation of Bisphenol A occurs. Previous studies of photodegradation of Bisphenol A, have concluded that Bisphenol A readily absorbs ultraviolet radiation of wavelengths 200nm-300nm range. Photodegradation mechanism is mainly due to photolysis and advanced oxidation process. Photolysis of Bisphenol A obeys first law reaction kinetics, and is affected by pH. Photodegradation of Bisphenol A via Advanced Oxidation Process obeys first law reaction kinetics and is affected by concentration of the oxidising agent and pH. However, the order of reaction with respect to the factors have yet to be quantified by rate law. In addition, the effect on salts and humic acid and reaction pathway on the advanced oxidation process of Bisphenol A is not clearly understood. Hence there is a need for further research. This experiment first investigates the factors that affect both photolysis and Advanced Oxidation Process of Bisphenol A, using H2O2 as the oxidising agent. Using an optimal concentration of H2O2, the effect of salt and humic acid would be investigated. Photodegradation by-products would be identified and a reaction pathway would be formulated based on the concentration of the by-products against time. Results obtained show photodegradation of Bisphenol A observes first order kinetics for both photolysis and Advanced Oxidation Process. Ultraviolet wavelength ranges affect the rate of reaction, however there are no means to quantify it using rate law. Order of reaction with respect to Concentration of H2O2 is 1, however high concentrations of H2O2 could inhibit oxidation rate, resulting in a lower rate of reaction. Order of reaction with respect to [H+] and [OH-] are both 1, however the rate of reaction in acidic medium is higher than alkaline medium for Advanced Oxidation Process. A possible reason is due to how H2O2 readily oxidises in acidic medium, minimising the need of generation of OH free radicals to degrade Bisphenol A for Advanced Oxidation Process. Comparing photodegradation of Bisphenol A in ultrapure water, synthetic water and water with Natural Organic Matter, the effects of salts and humic acid on rate of reaction can be studied. From the experiment, the presence of salts increases the rate of reaction and the order of reaction with respect to salts is 1. In the presence of salts, the rate of reaction increases by 4 times. A likely reason is the presence of salts provides an alternative pathway with lower activation energy for the reaction, resulting in a higher rate of reaction. However, synthetic seawater comprises of a variety of salts. Further study would need to determine the effect of individual salt on Advanced Oxidation Process of Bisphenol A. Advanced Oxidation Process of Bisphenol A in water with Natural Order Matter follows first order kinetics. Compared with the initial rate of reaction of Bisphenol A in ultrapure water, the initial rate of photodegradation of Bisphenol A in water with Natural Order Matter is 7.5 times higher. k constant of Bisphenol A in water with Natural Order Matter is higher than k constant of Bisphenol A in synthetic water, indicating the alternative pathway provided by the humic acid could have a lower activation energy than the alternative pathway provided from salts. 5 by-products of Advanced Oxidation Process are identified and based on their ion counts against time graph, a reaction pathway is proposed. Bisphenol A would first photodegrade to form 4-[2-(4-Hydroxyphenyl)-2-propanyl]-1,2-benzenediol (C15H16O3), which then reacts with hydroxyl radical to form the intermediate compound 4-[2-(4-Hydroxyphenyl)-2-propanyl]-1,2-benzoquinone (C15H16O4). The intermediate compound would finally photodegrade to form 3-methylbenzoic acid (C8H8O2). Cytotoxicity tests of Bisphenol A and its photodegraded compound reveals cell viability did not decrease significantly when expose to increasing concentration of Bisphenol A and its photodegraded compound. The results obtained could be used to better removal of Bisphenol A and its photodegraded products. Reaction Kinetics obtained from this experiment can be used determine the most effective conditions for removal of Bisphenol A in water treatment and wastewater treatment.
Final Year Project (FYP)
Nanyang Technological University