Study On Fast Oxidative Degradation Of Odor Compounds In Drinking Water By Hydroxyl Radicals

Taste and odor（T&O）problem caused by 2-MIB and GSM is a global problem facing by the drinking water treatment industry.Eutrophic lakes,reservoirs and other surface drinking water sources have made the T&O problem more serious.This is due to the low concentration of human olfactory threshold for them,and they are difficult to remove in traditional drinking water process.Additionally,the ship drinking water also faced with the T&O problem and some other health safety problems,especially for the ocean ships.Studies have shown that,for those ocean ships over five years old,less than 60%of their drinking water can reach the standard of drinking water.Due to China’s late start in the research on T&O problem of drinking water,it’s an important and urgent requirement for the drinking water industry to solve the T&O problem.In this study,a rapid detection method for odor substances in water was established,and a new hydroxyl radicals（·OH）method generated with strong ionization discharge（SID）and hydraulic cavitation jet was used for quickly and effectively oxidative degradation of the odor substances in drinking water.What’s more,the-OH method is green,safety and no byproducts.The major original conclusions are as follows:（1）O₂ was ionized and dissociated by high-energy electrons generated in the process of SID to produce high concentration of active oxygen species（AOS）such as O₂+,O（1D）,O（3p）,o2-,O₃,and so on.The concentration of them could reach 227 mg/L.Then the AOS was injected into the gas-liquid dissolver.Under the effect of hydraulic cavitation,a series of plasma chemical reaction could happen between AOS and H2O to generate ·OH and other active oxygen substances like HO₂-,H2O₂,·O₂-,·O₃-,·HO₃,O₂+·H2O.In the water treatment system,the total reactive oxidant（TRO）concentration can reach 16.5 mg/L,the maximum concentration of-OH could reach 67.4 μmol/L.By studying the influence of water quality on the dissolution and attenuation of TRO,it was shown that natural organic matter（NOM）and carbonate（CO₃2-/HCO₃-）could promote TRO attenuation.With the increase of water temperature,TRO decay rate was gradually faster.sulfate radical（SO42-）could inhibit TRO attenuation in water,and chloride（C1-）had little effects on TRO attenuation.（2）A headspace solid phase micro-extraction（HP-SPME）combined with gas chromatography-mass spectrometry（GC-MS）method was established for simultaneous determination of these two trace taste and odor compounds in water.The conditions of HP-SPME,such as the amount of salt,extraction time,extraction temperature,stirring speed and desorption time were optimized based on orthogonal analysis.The results showed that the quantitative detection limits for 2-MIB and GSM were 2.4 ng/L and 1.1 ng/L,respectively.The accuracy and recovery of the method were also verified.The results showed that the relative standard deviation（RSD）of 2-MIB and GSM were less than 6.1%and 5.8%respectively,and the average recoveries of the target compounds were 93.6～107.7%,Then based on this method,the target compounds in nature water bodys were analyzed.（3）2-MIB and GSM could be effectively degraded by advanced oxidation method of ·OH,and the removal efficiency improved with the increasing of the TRO dosages.Under the initial concentrations of 2-MIB and GSM（60～1000 ng/L）and the threshold dose of TRO（0.5-3.8 mg/L）,2-MIB and GSM in water pipes could be reduced to less than 10 ng/L within 6 s.It was also found that GSM was more easily degraded by ·OH than 2-MIB.The water quality studies on the oxidative degradation of 2-MIB and GSM showed that NOM and HCO₃-/CO₃2-were the most vital reasons for the inhibition of 2-MIB and GSM removal by-OH.On the contrary,SO42-could react with ·OH or other AOS to form the sulfate radicals（SO44-·）in the ·OH advanced oxidation system,so SO42-could promote the oxidative degradation of 2-MIB and GSM in water.With the increase of pH,the effects of oxidative degradation of 2-MIB and GSM gradually improved.C1-played little role in the oxidative degradation of 2-MIB and GSM.The study on the mechanism of oxidative degradation of 2-MIB and GSM by ·OH showed that both the bridge ring of 2-MIB and the double ring of GSM could be destroyed by ·OH.And then through broken bond and addition reaction,2-MIB and GSM were gradually oxidized to form small molecules of aldehyde,ketone,acid,and so on.Finally they were mineralized to CO₂ and H2O.In comparison with KMnO4,NaCIO,C1O₂ and H2O₂,they almost had no removal effects on 2-MIB and GSM.Additionally,H2O₂/UV and O₃ reacted more than 30 min to remove the odor compounds 2-MIB and GSM.（4）In view of the T&O problem in high algae water source,a pilot test was carried out to remove the odor compounds from high algae water by ·OH.The results of oxidative degradation of 2-MIB and GSM from raw water,coagulant sedimentation water and sand filter water showed that the ·OH method also had a good effect on oxidative degradation of 2-MIB and GSM in different pretreatment processes for drinking water,For the removal of the odor compounds,the addition of ·OH to the coagulation&sedimentation water and the sand filter water was better than the raw water.By using the“raw water-coagulation sedimentation-·OH peroxidation-sand filter-·OH oxidation-chlorination-water supply”water treatment process,the high algae water was treated.The coagulant sedimentation water containing 175 ng/L 2-MIB,188 ng/L GSM and 3.47×104 cells/mL algae was used.It was found that after addition of 0.9 mg/L TRO for preoxidation and 0.4 mg/L TRO for the second oxidation treatment,the odor compounds of 2-MIB and GSM were reduced to 4 ng/L and 1 ng/L respectively,and all algae cells in water could be killed.What’s more,the other physicochemical and microbial indexes of the treated water were better than the standards for drinking water quality.