Study On The Inhibition Of Phenol Entering The Desalinated Water By Activating Peroxide During Photothermal Distillation

Recently,the new technology of photothermal distillation has been applied to seawater desalination based on air-water interfacial solar heating.This new technology is considered one of the effective methods to solve the problem of freshwater shortage in remote scattered islands with tight power supply due to its high photothermal conversion rate,simple process,and direct utilization of solar energy.However,the "high-temperature,high-salt and intense-light" environment formed in the photothermal distillation process causes volatile pollutants(such as phenol)in seawater to volatilize into condensed freshwater,causing quality safety risks of the freshwater.In this paper,the condition of "high-temperature,high-salt and intense-light" was used to activate peroxide to inhibit phenol from entering into condensed freshwater,and the key influencing factors and mechanism of phenol reduction were explored.Molybdenum disulfide(MoS2)was used as the photothermal material.It was assembled with glass fiber membrane(FB),polytetrafluoroethylene sheet(PTFE)and expanded polyethylene(EPE)foam to form an integrated distillation module(denoted as MFPE).Under the optimal operating conditions,the seawater evaporation rate was 1.28 kg/m2·h(with correspondingly photothermal conversion efficiency of 86.98%),which is 5 times that of direct solar evaporation of seawater.Under the same conditions,the removal efficiency of the phenol by the four kinds of peroxides were in the following order:hydrogen peroxide(H2O2)<peroxydisulfate(PDS)<peroxyacetic acid(PAA)<peroxymonosulfate(PMS).The distillation rate(RD)of phenol reached 0%when the dosage of PMS was 0.1 mmol/L,indicating the complete inhibition of phenol from entering into the condensed freshwater.Increasing salinity,peroxide dosage,and sunlight intensity were all beneficial to activate H2O2,PMS and PAA to reduce phenol into condensed freshwater.However,the reduction efficiencies of phenol entering into condensed freshwater were decreased with the increased initial concentration of phenol and the concentration of humic acid.In the process of photothermal distillation,the factors including temperature,salinity and light can activate peroxide.The main factor for activating H2O2,PMS,PDS,and PAA were heat,Cl-,heat/light,and Cl-/heat,respectively.Although both PMS and PAA could effectively degrade phenol and reduced its entry into condensed freshwater,halogenated by-products were formed during the oxidation process.Under 1 sunlight intensity,the concentrations of total organic chlorine(TOCl)in the condensed freshwater collected after addition of 1 mmol/L of PMS and PAA were 1.59 mg/L and 22.77 mg/L,respectively.It was found that the main halogenated by-products in desalinated water were halogenated phenol,halogenated p-hydroxybenzoic acid by the UPLC/MS detection.Finally,the possible conversion pathway of halogenated by-products was proposed.