Study On Adsorption And Degradation Behavior Of Antihypertensive Drug Metoprolol In Water Environment

Metoprolol is the first β1-selective receptor blocker in the world and has been widely used in the treatment of hypertension and ischemic heart disease,arrhythmia and other cardiovascular disease in patients,since it was successfully developed in 1969.At the same time,it is one of the three kinds of β-blockers mostly used in the clinical application in China.As one of Pharmaceuticals and Personal Care Products,the emerging trace pollutants,it is potentially harmful to aquatic ecological environment due to the characteristics of large production and consumption,universality and persistence in the environment and high solubility in water.Until now,most of the studies on Metoprolol are focused on ecotoxicological properties,the adsorption on synthetic materials,and the reduction by various processes,while the research in the behaviors of adsorption degradation,natural light degradation is rarely reported.In this study,Metoprolol was used as the target pollutant and its adsorption,chlorine oxidation decomposition in the wastewater treatment plant as well as the natural degradation in the water were investigated with the following three aspects:degradation of Mtoprolol by natural light and the influence of environmental factors on degradation,adsorption behaviors of Metoprolol onto sediments and activated sludge and chlorination behaviors of Metoprolol in aqueous environment.The related research results are as follows:(1)Direct photodegradation of Metoprolol occurred when exposed to natural light and accorded with the first order kinetic model.The addition of HCO3-inhibited the photolysis while NO2-and NO3-promoted photodegradation.The photodegradation rate constants were exponentially fitted in the concentration range of 1-20 mg·L-1.(2)The adsorption processes of Metoprolol onto the sewage sludge,Pearl River sediment,and Central Lake sediment were a two-step processes: a rapid adsorption followed by a slow balance and the initial concentration of Metoprolol had little impact on equilibrium time which was about 4 hours.The kinetic results indicated that the adsorption process followed the pseudo-second-order model.Meanwhile,adsorption process included physical adsorption,and chemical adsorption and the latter was the dominant process.The control step in the adsorption reactions of Metoprolol absorbed by 3 different media was adsorption reaction.Thermodynamic study results showed that the adsorption isotherms of the three media showed good correlation.The adsorption of Metoprolol on Pearl River sediment,Central Lake sediment and activated sludge conformed to Linear model,Langmuir isotherm model,and Freundlich isotherm model,respectively.All of the adsorption reactions were spontaneousexothermic reaction.The pH and ionic strength of the solution have significant effects on the adsorption removal of Metoprolol which were promoted under acidic condition but inhibited by ionic strength.It was proved that the adsorption capacity of three kinds of media had a great relationship with the composition of components and increased with the content of organic matter.Inorganic minerals and humic acids were much bigger than complex sludge and sediments for adsorption,and the organic matter had the largest adsorption capacity.(3)Metoprolol can be removed by sodium hypochlorite.The decomposition reactions showed first-order reaction for both sodium hypochlorite and metoprolol.And the decomposition rate was significantly affected by concentration of metoprolol and available chlorine,temperature,pH as well as the presence of Br-,humic acid and surfactant respectively.It turned out that the results reaction rate constant increased with the rising concentration of available chlorine but decreased with the increasing initial concentration of Metoprolol.And high temperature accelerated the reaction rate which followed Van’t Hoff Rule.The activation energy Ea was 31.04 kJ·mol-1 under the experimental conditions.In the weak acid system,the oxidation reaction of Metoprolol was rapid,but occurred slowly in the neutral and weak alkaline condition.When the Br-was added to the solution,the reaction rate of Metoprolol was significantly promoted,and the reaction rate constant showed a positive correlation with Br-concentration.Although humic acid inhibited oxidation reaction at lower concentration,it could show a promotion action at higher concentration because of its high adsorption capacity.The presence of anionic surfactant sodium dodecylbenzenesulfonate(SDBS)could facilitate the decomposition of Metoprolol by sodium hypochlorite.At low concentration of SDBS,the acceleration was obvious.But with the concentration increased to a certain extent,the promoting effect was reduced and tended to be stable.The non-ionic surfactant Tween-80 had little effect on the reaction.It was also found that the decomposition of Metoprolol by sodium hypochlorite resulted in an intermediate product that was more difficult to be oxidized by sodium hypochlorite than Metoprolol,and the toxicity of the reaction system was unstable and the relative inhibitory effect on the luminous bacteria fluctuated significantly.But overall,the toxicity of the whole reaction system was reduced.