Study On Removal Performance Of As(Ⅲ) In Water By Nanobubbles

At present,arsenic pollution has become one of the most serious environmental problems in the world,seriously threatening people’s health and life safety,and its prevention and control work has been paid more and more attention.Most of the water treatment methods have a significantly lower effect on As(Ⅲ)than As(Ⅴ).So far,As(Ⅲ)oxidation methods mainly include chemical oxidation,photochemical oxidation,photocatalytic oxidation(and microbial oxidation,but these methods have many problems in practical applications.Seeking a low-energy,high-efficiency,environmentally-friendly and sustainable As(Ⅲ)pre-oxidation technology is the key to ensuring the arsenic removal effect of drinking water.Nanobubbles(NBs)have attracted more and more attention due to their long residence time in water,high surface potential,large specific surface area,high mass transfer efficiency and the release of a large number of hydroxyl radicals,which provides a new idea for As(Ⅲ)pre-oxidation technology.This project aims to develop high-efficiency,environmentally-friendly and sustainable As(Ⅲ)pre-oxidation technology,and systematically study the environmental characteristics of NBs under different environmental conditions(As(Ⅲ)initial concentration,inlet pressure,pH,interference ion).The influence of arsenic removal conditions was optimized to explore the chemical properties of nanobubbles and their mechanism of action on As(Ⅲ)in water.The research results provide a theoretical basis for understanding the mechanism of action of NBs on As(Ⅲ).It has important theoretical and practical significance for the practical application of low energy consumption and green NBs technology in water treatment.This study draws the following conclusions:(1)A comparative experiment of As(Ⅲ)removal performance between conventional and nano-bubbles was carried out,Removal performance test results show that the removal effect of NBs on As(Ⅲ)is much better than that of ordinary large bubbles.(2)The effects of initial concentration,inlet pressure and pH on the removal of As(Ⅲ)by NBs were investigated by single factor experiments.The experimental results show that the initial concentration of As(Ⅲ)has a positive effect on the removal of As(Ⅲ).The inlet pressure also hasa positive effect on the removal of As(Ⅲ);the removal of As(Ⅲ)at pH 3 and 9 The rate is the fastest,and the removal rate of As(Ⅲ)is the lowest at pH 7.The removal of As(Ⅲ)by pure oxygen nanobubbles(ONBs)in each single factor test is superior to that of air nanobubbles(ANBs).(3)The response conditions were optimized by Response Surface Methodology(RSM).The optimized results were the best conditions for ANBs to remove As(Ⅲ)in water: pH=3,inlet pressure 0.22 MPa,As(Ⅲ)initial concentration 0.8 mg/L;The optimum conditions for the removal of As(Ⅲ)in water by OABs: pH=3,inlet pressure 0.175 MPa,As(Ⅲ)initial concentration 0.9mg/L.The significant influence factors for the R1 model are: As(Ⅲ)initial concentration>pH>inlet pressure,and R2 significant influence factors are: As(Ⅲ)initial concentration>inlet pressure>pH.(4)The mechanism of arsenic removal in nanobubbles was analyzed.The hydroxyl radicals in nanobubble aqueous solution were determined by high performance liquid chromatography(HPLC).Studies on the mechanism of arsenic removal show that hydroxyl radicals play an important role in the oxidation of As(Ⅲ).Hydroxyl radicals can interact with As(Ⅲ)to form an As(Ⅳ)intermediate which is then further oxidized to As(Ⅴ).