Degradation Of Propranolol By UV-LED/chlorine Process: Efficiency And Mechanism

In recent years,water pollution caused by trace organic pollutants(TOrCs)has became a new environmental threat.Although most TOrCs were detected in water in the range of ng/L toμg/L,they are difficult to be removed by the traditional water and wastewater treatment,and then accumulated in the contaminated water over time.Long-term exposure to TOrCs may be harmful to the physiological properties and growth of living things.UV/chlorine is an advanced oxidation technology that degrades pollutant by producing reactive species,and is considered a potential water treatment technology to degrade trace organic pollutants.UV-LED is mercury-free,sturdy,ready-to-open,and able to provide UV light at any wavelength,that making it the most promising UV source.The application of UV-LED lamps in UV/chlorine system is more environmentally friendly,flexible and efficient comparing to traditional mercury.In our experiment,the UV-LED/chlorine technology was used to degrade a kind ofβ-blocker propranolol.The effects of chlorine dosage,pH value,humic acid,common anions and ammonium ions to this system were explored.Either UV-LED alone nor chlorine alone can not effectively degrade PRO,while UV-LED/chlorine has a significant synergistic effect on the degradation of PRO(about95%removal rate after 15 minutes of reaction),thanks to the ractive species(RCS,HO·,~1O2,etc.)formed by chlorine photolysis.When the molar ratio of PRO to chlorine is 1:4,removal rate of PRO achieves a high level(~95%).The pH value has little effection,and the degradation rate of PRO is only slightly higher under alkaline conditions.The degradation of PRO by UV-LED/chlorine follows pseudo-first-order kinetics.As for the other impact factors,we found that bicarbonate ions and chloride ions have no significant influence on the removal of PRO;while humic acid and ammonium ions inhibit the removal of PRO.When using different light sources combined with chlorine to degrade PRO,it is found that the removal efficiency of xenon lamp with a wavelength range of200-1000nm is the lowest(only 24.8%PRO is removed 15 minutes of reaction),high pressure mercury lamp(254nm)and UV-LED lamp(275nm)can both remove more than95%PRO,but PRO degrades faster under the UV254/chlorine system.In our paper,the mechanism of degradation of propranolol in water by UV-LED/chlorine was studied.We use T-butanol as a quench,proving HO·and Cl·were produced in the system;~1O2 was detected by Electron Paramagnetic Resonance Spectrometer(EPR).We evaluated the degradation products of PRO by LC-MS technology and found that PRO mainly undergoes substitution reaction to form five possible degradation products in UV-LED/chlorine system,and PRO is not completely mineralized.The TOC only slightly fluctuated during the reaction,within a range of 1%,which also proved that PRO haven’t been completely mineralized.At the same time,the acute toxicity was detected by the T3 bright photobacterium method,and we confirmed there were oxidation byproducts more toxic than PRO during UV-LED/chlorine process.At the end of our paper,the application for degradation of propranolol by UV-LED/chlorine process were initially explored.We took water from the Dongjiu Lake of Huazhong University of Science and Technology as natural water sample,and compared the degradation of PRO in natural water with that in ultrapure water.We found the background substance of natural water inhibited the degradation of PRO.Then the degradation of other TOrCs by UV-LED/chlorine process was also verified.Under the same conditions,The degradation rates of sulfamethoxazole,oxytetracycline hydrochloride,gatifloxacin,acetaminophen,chloramphenicol and carbamazepine were99.7%,99.0%,98.5%,47.7%,31.5%,15.1%respectively within 15 minutes respectively,indicating that UV-LED/chlorine process has wide applicability and some selectivity for pollutant degradation.