| Iodine is widely distributed in nature,and the phenol group is also a basic component of natural organic substances?such as humic acid?.When disinfecting water bodies,oxidants can oxidize iodine ions to hypoiodic acid and react with phenolic substances to form Iodophenol by-products.During the chlorination?or chloramine?reaction of source water and wastewater,iodized phenolic by-products have been detected more and more frequently.Iodized aromatic by-products are generally more toxic than iodo-aliphatic by-products such as iodoform and iodoacetic acid.Exploring methods to control the formation of Iodophenol by-products is important.Ammonia nitrogen?NH3-N?is widely present in source water and domestic wastewater.When chlorine is used to disinfect water bodies,the turning point chlorination is divided into three stages: the first stage molar ratio of HOCl / NH3-N is less than 1: 1.The active chlorine in the system is mainly monochloramine.The molar ratio of HOCl / NH3-N in the second stage is greater than 1: 1 and less than 2: 1.The total chlorine in the system is mainly composed of monochloramine,dichloramine and trichloramine.In the third stage,the molar ratio of HOCl / NH3-N is greater than 2: 1.The active chlorine in the system is mainly free chlorine.During the breakpoint chlorination process,the amount of iodophenol by-products increased with the increase in the molar ratio of HOCl / NH3-N in stage one;during stage two,as the total chlorine gradually decreases,the generated iodophenolic by-products also decrease;in the third stage of the breakpoint chlorination,the concentration of iodophenol by-products increased first with the increase of the HOCl / NH3-N molar ratio,and then cut back with the increase of free chlorine concentration.The total chlorine concentration was the lowest at the breakpoint,and the amount of iodophenol by-products was the lowest at the breakpoint.At a high HOCl / NH3-N molar ratio,due to the presence of a high concentration of free chlorine,the iodine ions in the system are oxidized to IO3-,which can avoid the accumulation of HOI in water,leading to the formation of iodophenol by-products reduced in water.In addition,high concentrations of free chlorine can also convert a portion of the iodophenols to other chlorinated and iodinated aromatic products,leading to a reduction in the concentration of the iodophenol by-products detected.In the system with low HOCl / NH3-N molar ratio?mainly monochloramine disinfection?,the iodine phenol by-products in the water body gradually formed and then remained stable.In the system with high HOCl / NH3-N molar ratio?mainly free chlorine disinfection?,the concentration of iodophenol by-products in the water body increased first and then decreased.This also indicates that free chlorine can further convert the generated iodophenol by-products into other chlorinated aliphatic by-products.The pre-oxidation of potassium ferrate can greatly reduce the formation of byproducts of iodophenols during the subsequent breakpoint chlorination process.On the one hand,potassium ferrate can directly degrade precursor substances?phenolic compounds?of by-products of iodophenols;on the other hand,potassium ferrate can rapidly oxidize most of the iodine ions in water to non-toxic and harmless IO3-to avoid the accumulation of HOI in water and the production of iodized phenolic disinfection byproducts.After pre-oxidation of ferrate under raw water conditions,phenol and BPS were degraded by 100% and 83% respectively;and after potassium ferrate pre-oxidation treatment,more than 70% of the iodide ions in phenol and BPS systems were oxidized to Iodate,more than 90% of the iodide ion in the p-NP system is oxidized to iodate.The pre-oxidation treatment of potassium ferrate is an effective measure to control the formation of by-products of iodophenols in the subsequent disinfection process. |
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