Study On The In-situ Removal Of Vaporized Organic Matter In Solar Distillation

In the past few years,a new seawater desalination technology--interface solar distillation has emerged.As its no additional energy requirement and simple operation,it has been regarded as an emerging technology that can be used for water supply in special conditions.This technology accelerates the evaporation of water by converting solar energy into heat and realizes the separation of water and impurities through the phase change of water.However,seawater or surface water generally contains complex organic matter.The phase change process of water can effectively separate inorganic salts,but the separation of organic matter is not satisfactory.Therefore,it is a very meaningful and necessary to remove the vaporized organic matter in the solar distillation.In response to this issue,this work studied the evaporation of organic matter in the actual water body in solar distillation;subsequently,the distillation membrane was modified to introduce the catalytic function,which could in-situ degrade the organic matter in the distillation membrane.The current research results are as follows:First,volatile substances such as phenol and non-volatile substances such as bovine serum albumin are used as model pollutants to investigate the vaporization of single substances in solar distillation.Volatile organic compounds such as phenol can be vaporized in large amounts from feed water,and the ratio of vaporization are all above 50%;non-volatile organic bovine serum albumin,humic acid,rhodamine B,and glucose solution can also be steamed in solar distillation,and the vaporization ratios are 16.2%,7.7%,13.0%,and 14.6%,respectively.Subsequently,the actual surface water and seawater were used as feedwater to study the evaporation of organic matter under complex water quality.Different surface water have different steaming ratios of organic matter.The steaming ratio of organic matter in the Baiyangdian water sample is the lowest.The TOC of raw water is10.58 mg/L,the TOC of collected condensate is 3.14 mg/L,and the vaporization ratio of organic matter is 29.7%.The water samples from Youjiang River had the highest steaming ratio of organic matter,with feed water TOC of 1.26 mg/L,condensed water TOC of 0.78 mg/L,and organic matter vaporization ratio of 61.9%.Combining three-dimensional fluorescence analysis to study the water quality changes before and after solar interface distillation,it is found that protein substances are easier to be steamed out,while humus is more difficult to be steamed out.Since the organic matter in water is easy to steam out,the persulfate activation function is introduced into the solar distillation membrane through the modification,so as to realize the in-situ degradation of the vaporized organic matter.First,the composite cobalt-manganese oxide is deposited on the carbon fiber membrane by dipping and calcining（C/Mn Co）.The solar energy absorption of C/Mn Co fiber membrane is 94.58%,and the distillation rate is 1.29 kg m^-2 h^-1.When the C/Mn Co fiber membrane solar distills 10 mg/L phenol solution,the phenol concentration in the distilled condensate is 10.20 mg/L（the phenol evaporation rate is 102%）.When PMS and PDS are added to the phenol solution,the phenol evaporation ra te decreases.They are 40.2%and 50.4%.By detecting the phenol concentration of raw water and condensed water at different times,it was found that the de gradation reaction of phenol occurred on the C/Mn Co fiber membrane.In distillation of Songhua River water by the C/Mn Co fiber membrane,without photocatalysis,the TOC evaporation rate was 56.6%.Adding PMS and PDS respectively,the TOC evaporation rate dropped to 15.0%and 21.8%.Combined with electron paramagnetic resonance detection,it is found that·OH plays a key role in both PMS and PDS the oxidation process.C/Mn Co fiber membrane activated persulfate can also effectively degrade organic matter steamed out from high salt water.Although persulfate oxidation can effectively degrade the organic matter vaporized in the solar distillation,it is necessary to continuously add oxidants,which is not convenient in actual use.For this reason,there is a need for a technology that does not need to add oxidizing agent continuously.Firstly,m-Ti O_2-xis coated on the Si O₂ fiber by sol-gel method and reduction method to form m-Ti O_2-x shell,and a black m-Ti O_2-x fiber membrane is obtained.The solar light absorption is 82.2%.The interface distillation rate is 1.08 kg m^-2 h^-1,and the light-vapor conversion efficiency is 73.3%.In the m-Ti O_2-x fiber membrane distillation system,without light illumination,the phenol concentration in the condensed water collected by the bulk heating distillation is 10.5 mg/L（the evaporation rate is 105%）;with light illumination,the phenol evaporation rate is4.5%.Taking the actual Songhua River water as the distillation object,without light illumination,the TOC evaporation rate in bulk heating distillation is 47.3%;with light illumination,the TOC evaporation rate in solar interfacial distillation is 20.1%.In this process,m-Ti O_2-x acts as both a photothermal material and a photocatalyst.The electrons of m-Ti O_2-x are excited by irradiation and transition to high energy levels,a small part of the excited electrons combine with O₂ molecules on the surface of m-Ti O_2-x to form superoxide radicals,and most of the electrons recombine with holes during the relaxation process,then radiate heat.At the same time,the m-Ti O_2-x fiber membrane has good mechanical properties and corrosion resistance.After 30 days of cyclic immersion,the catalytic performance does not decrease.This work first studied the vaporization of organic matter in solar distillation.Through the membrane modification,the persulfate activation and photocatalytic functions are introduced to realize the in-situ removal of the organic matter vaporized in the solar distillation.In the next research work,the steaming law of organic matter could be further researched for the application of the mathematical model.At the same time,the optimization of the catalytic activity of the distillation membrane should be realized.