Experimental Study On The Treatment Of Micropolluted Water By Ultrasonic Enhanced Ozone Oxidation Combined Process In Pastoral Area

Gannan alpine pasture area is always low temperature,by the production and lifestyle constraints and the slow development of the regional economy and other factors,resulting in pastoralists drinking water sources mostly from the nearby surface runoff and shallow groundwater,the formation of direct drinking or by simple precipitation treatment of water habits.With the joint influence of animal husbandry activities,natural environmental changes and climate change,organic pollutants and microbial pollution often appear in the water bodies of pastoral areas,resulting in different degrees of water quality exceeds the standard,posing a potential threat to the drinking water safety of pastoralists.In order to improve and guarantee the water safety of pastoralists,this paper proposes a green process of ultrasound-enhanced ozone oxidation,in which ultrasound cavitation is added on the basis of ozone oxidation to enhance the removal efficiency of pollutants,so as to achieve the joint removal of organic pollutants and microorganisms from water sources in Gannan pastoral area.The following conclusions were reached:（1）Individual ozone oxidation operation parameters optimization.The effect of ozone oxidation alone on the removal of organic pollutants in simulated pasture water was investigated using the control variable method by varying the ozone concentration,reaction time and ozone flow rate,etc.It was found that under the working conditions of ozone concentration of 6 mg/L,ozone gas volume of 2.0 L/min and reaction time of 30 min,the effect of ozone oxidation alone on the removal of COD_Mn,UV₂₅₄ and chromaticity in water was optimal,with 23.5%.The direct oxidation of ozone is the main mechanism of organic pollutant degradation in water,and its selective oxidation is the main reason for the insufficient removal rate of COD_Mn;in addition,the temperature shows a negative correlation with the ability of ozone oxidation alone,and the low temperature environment is more suitable for the operation of ozone oxidation alone.（2）Optimization of operating parameters of separate ultrasonic cavitation oxidation.The effect of ultrasonic frequency,ultrasonic power and reaction time on the efficiency of separate ultrasonic cavitation oxidation in degrading organic pollutants in water was investigated,and the optimal ultrasonic operating conditions for a given interval were 40 k Hz and 175 W/L.The removal rates of COD_Mn,UV₂₅₄ and chromaticity were 2.82%,6.98%and 0%,respectively,within a reaction time of 30 min,and the removal efficiency of pollutants The efficiency of pollutant removal increased with the prolongation of reaction time;the increase of ultrasonic frequency and power enhanced the effect of cavitation oxidation to some extent,but did not bring about a significant increase of pollutant degradation efficiency,which may be related to the low concentration of strong oxidation radicals including·OH produced by ultrasonic cavitation alone;in addition,the removal efficiency of organic pollutants by ultrasonic cavitation alone was much lower than that by ozone oxidation alone.（3）Optimization of operating parameters of ultrasonic-enhanced ozone oxidation.The optimal ozone conditions were controlled,the ultrasonic conditions were changed,and the effects of ultrasonic frequency,ultrasonic power,reaction temperature and temperature control/non-temperature control on the removal effect of organic pollutants were investigated.34.13%and 73.95%,which accelerated the degradation rate of chromaticity;the degradation efficiency of the ultrasound-enhanced ozone oxidation process for organic pollutants was higher than the sum of ultrasound process alone and ozone oxidation process alone,and the combination of the two had obvious synergistic effects.In addition,although the increase of reaction temperature reduced the removal efficiency of pollutants by the combined process to a certain extent,the intervention of ultrasound reduced the influence of reaction temperature on ozone oxidation efficiency,making it easier and applicable to different ambient temperatures,and the non-temperature-controlled conditions had less influence on the removal efficiency of pollutants by the combined process.Combined with the analysis of three-dimensional fluorescence spectra of organic matter,the simulated pasture water is dominated by humus-like organic matter,and the degradation efficiency of the total fluorescence region reached 96.67%under the combined process,and the intervention of ultrasonic waves has a significant effect on the removal rate of fulvic acid-like organic matter（region III）,which is related to the further oxidation of organic pollutants by strong oxidation radicals.（4）The experimental study on the inactivation effect of the combined process on E.coli flora showed that the combined process of ultrasonic and ozone could accelerate the inactivation effect of E.coli,which was mainly attributed to the effective dispersion of E.coli flora by ultrasonic waves,which increased the utilization rate of ozone and the contact chance with bacteria,and ozone was the main disinfection factor in the inactivation process of E.coli flora.（5）Preliminary investigation of the strengthening mechanism of ultrasound.Ultrasound enhanced the mass transfer and utilization of ozone,which increased the apparent mass transfer coefficient and utilization of ozone by 51.22%and 33.5%,respectively,compared to the optimal reaction conditions created by ozone alone.In addition,the ultrasound intervention reduces the influence of temperature on the apparent mass transfer coefficient of ozone,making it more easily applicable to different ambient temperatures.The combined premixed coagulation process achieved 89.63%,83.33%,53.57%,84.09%and 100%of the total removal of turbidity,color,COD_Mn,UV₂₅₄ and E.coli in the simulated pasture water.It met the Sanitary Standard for Drinking Water（GB5749-2022）.