Study On The Degradation Of Urea In Swimming Pool Water Using Ultraviolet Methods

Urea is a kind of organic matter in swimming pool water,that can be readily brought into swimming pools by swimmers via perspiration and urination processes.Although not toxic itself,urea can react with the free residual chlorine,which is used to disinfect swimming pool water to form trichloramine.Trichloramine is pungent and harmful to human body.Therefore,it is very important to explore a method that can effectively remove urea from swimming pool water.This study aimed to find a green and robust ultraviolet?UV?-based method for urea abatement from swimming pool water.This study compared the performances of seven UV methods on removing urea,including UV alone,UV/H₂O₂,UV/Na₂SO₃,UV/K₂S₂O₈,vacuum UV?VUV?alone,VUV/H₂O₂,and VUV/K₂S₂O₈.Among them,UV and UV/Na₂SO₃ showed little urea removal while UV/H₂O₂ removed only 12.8%of urea within 3 h experiments.VUV alone degraded 71.7%of urea,UV/K₂S₂O₈ and VUV/K₂S₂O₈ had better urea removal efficiencies.VUV alone had little total dissolved solid?TDS?increment,but additions of K₂S₂O₈ obviously increased TDS.Considering that the TDS limit of the water quality standard of swimming pool in China,the use of K₂S₂O₈ was relatively inapplicable in swimming pool water.Hence,this study focused on urea photodegradation by VUV alone.The results showed that cyanuric acid,humic acid,NO₃^-,and HCO₃^-inhibited urea photodegradation,and the inhibitation effect was increased with increasing of these componds.In contrast,the presence of Cl^-and SO₄^2-facilitated urea degradation,while free chlorine at doses<3 mg/L and pH from 6.8 to 8.5 did not affect urea degradation significantly.with the impacts of multiple water matrix,VUV alone degraded only 12.73%and 38.61%of urea dosed into a real tap water and a SPW.According to the products analyses,the mass balance of nitrogen was basically met during the urea photodegradation process,resulting in formation of NO₃^-and NH₄⁺as the key products.In comparison,the content of total organic carbon?TOC?kept decreasing,although the rate of TOC was slightly lower than that of urea degradation,suggesting that urea was mostly mineralized and partially converted to unknown organic compounds under VUV irradiation.This study demonstrates VUV as an efficient and green method for urea removal from SPW.