Study On The Degradation Of Typical PPCPs In Water Via Sulfite Activated By Cu(Ⅱ)

In recent years,pharmaceuticals and personal care products（PPCPs）,as emerging organic pollutants,have been frequently detected in the environment.Due to the characteristics of strong toxicity,persistence and bioenrichment,most PPCPs pose long-term potential risks to the safety of drinking water and aquatic organisms.The traditional biological process is difficult to effectively remove PPCPs,and the advanced oxidation technology based on hydroxyl radical（HO·）has some problems,such as high operating cost,secondary pollution,poor p H applicability,and difficult to achieve good dehalogenation of halogenated organic matter.Therefore,it is of great significance to develop safe,efficient,environmentally friendly and economically feasible processes to remove various types of PPCPs from water bodies.Based on this,this study selects Cu（Ⅱ）as catalyst with good catalytic performance in p H neutral environment,and forms Cu（Ⅱ）/sulfite system with low price and environmental protection sulfite.Two different types of PPCPs,sulfadiazine（SCP）,a sulfonamide antibiotic commonly used in livestock and poultry farming,and sodium panthenate（DTZ）,a iodine contrast agent commonly used in medical industry,were selected as target pollutants.According to their different physical structures and chemical properties,their degradation efficiency was explored under aerobic and anoxic conditions,the reaction mechanism was revealed,and the optimal working conditions were determined.Finally,the degradation capacity of the process in actual water was investigated,and the main research conclusions were as follows:（1）Under the conditions of temperature 25±1℃,SCP concentration of 1.0 mg/L,p H=8,Cu²⁺concentration of 150μmol/L,Na₂SO₃ concentration of 500μmol/L,the Cu（Ⅱ）/sulfite aerobic system had a good degradation effect on SCP.The degradation rate was 83.2%after 60min reaction.Based on methanol and tert-butanol inhibitors and the detection of Cu（III）,it can be seen that the Cu（Ⅱ）/sulfite aerobic system is a mixture of free radicals and non-free radicals,the active substances of which are·OH,SO₄·-and Cu（III）.Oxygen is a key factor in the further conversion of SO₃·^-to SO₄·^-and·OH,and is indispensable in free radical chain reactions.（2）Single factor experiments showed that the degradation rate of SCP increased with the increase of Cu（Ⅱ）dosage,and the optimal Cu（Ⅱ）concentration was 150μmol/L based on economic and environmental factors.With the increase of sulfite dosage,the degradation rate of SCP increased first and then decreased,and the optimal sulfite concentration was 200μmol/L.When the initial p H value increased from 4 to 8,the degradation rate of SCP gradually increased,and when the p H value continued to rise to 10,the degradation rate of SCP decreased.The optimal initial p H value was determined to be 8.Under the optimal working condition,the degradation rate of SCP by Cu（Ⅱ）/sulfite aerobic system was 92.0%.The degradation rate of SCP by Cu（Ⅱ）/sulfite aerobic system was slightly increased by Cl^-,and the process of SCP reaction was accelerated.HCO₃^-can inhibit the degradation rate of SCP by Cu（Ⅱ）/sulfite aerobic system,because HCO₃^-and CO₃^2-can trap the active species·OH and SO₄·^-.In addition,HCO₃^-has strong complexation ability with Cu²⁺,which may occupy the active site with more copper ions,leading to the reduction of Cu SO₃ complex.The formation of active oxidizing species was inhibited,thus reducing the degradation rate of SCP.SCP is degraded in three main ways:SO₂ removal recombination,N-S bond cleavage,hydroxylation,and then degradation into smaller small molecules or CO₂ and water through a series of oxidation processes.（3）The degradation rate of DTZ in the Cu（Ⅱ）/sulfite system was lower under aerobic conditions,and the degradation rate of DTZ was better under anoxic conditions.50 m M methanol and 50 m M tert-butanol had little effect on the degradation of DTZ in Cu（Ⅱ）/sulfite anoxic system,indicating that SO₄·-and·OH were not the main active species in the system.When 0.5 m M new copper reagent was added to the system,it was found that the solution quickly turned yellow in the early stage of the reaction process,indicating that Cu（I）-Neocuproine complex was produced,and the degradation rate of DTZ decreased to 12.2%.According to the above experimental results,the main active species of DTZ degradation in Cu（Ⅱ）/sulfite anoxic system is Cu（I）.（4）The single-factor experiment showed that the degradation rate of DTZ increased with the increase of Cu（Ⅱ）dosage.Considering the economic and environmental factors,the optimal Cu（Ⅱ）concentration was determined to be 150μmol/L.With the increase of sulfite concentration,the degradation rate of DTZ firstly increased and then decreased,and the optimal sulfite concentration was determined to be 1000μmol/L.As the initial p H value increased from3 to 7,the degradation rate of DTZ also increased,but when the p H value continued to rise to9,the degradation rate of DTZ gradually decreased,and the optimal initial p H value was determined to be 7.The degradation rate of DTZ in Cu（Ⅱ）/sulfite anoxic system is 92.2%under optimal working condition.Water quality background ion Cl^-has no effect on the degradation of DTZ in Cu（Ⅱ）/sulfite anoxic system,but HCO₃^-can significantly inhibit the degradation of DTZ in Cu（Ⅱ）/sulfite anoxic system,because Cu⁺/Cu²⁺and HCO₃^-/CO₃^2-can form complexes and inhibit the formation of Cu SO₃ complexes.At the same time,HCO₃^-will lead to the increase of p H value of the reaction system,and also inhibit the formation of Cu SO₃ complex,resulting in the reduction of Cu（Ⅰ）production,and thus the reduction of DTZ removal rate.（5）The main degradation mode of DTZ in Cu（Ⅱ）/sulfite anoxic system is reduction and deiodization,and the resulting products are further hydroxylated.After deiodization,the structural stability of the products is reduced,and a series of reactions such as deiodization,decarboxylation and side chain breaking will occur to produce products with lower molecular weight.（6）The degradation efficiency of DTZ in actual water by Cu（Ⅱ）/sulfite anoxic system（53.0%）was better than that of SCP in actual water by Cu（Ⅱ）/sulfite aerobic system（33.0%）,because the main active species of pollutants degraded by the aerobic system were·OH and SO₄·^-,and the selective oxidation ability was poor.It will be consumed by dissolved organic matter（DOC）in the actual water body,while Cu（I）is the main active species to degrade pollutants in the anoxic system,which has a high selectivity,and the interference of DOC to it is relatively small.The above experimental results show that the resistance of Cu（Ⅱ）/sulfite anoxic system to water background interference is better than that of Cu（Ⅱ）/sulfite aerobic system.