| Water quality is closely related to human health.The sewage must be strictly disinfected when it is discharged.The existing disinfection still have many problems in the application,such as the health risks of chlorine by-products,the high cost of ozone operation and maintenance,and the disinfection effect of ultraviolet is greatly affected by water quality.Therefore,under the situation that sewage discharge continues to rise and the pressure of ecological environment in China has not been fundamentally alleviated,it is urgent to develop efficient disinfection technology.The underwater pulsed arc discharge with low voltage and high current was proposed by the paper’s research group,which has the advantages of environmental friendliness and significant disinfection effect.It is expected to be applied in the field of sewage disinfection.Aiming at the problems that the reactor volume is small and the disinfection mechanism in pilot-scale reactor is unknown in the existing research,the physicochemical effcts and the disinfection effects of underwater pulsed arc discharge in pilot-scale reactor with 1000 liters are systematically studied in this paper,which is of great significance for the practical application of this technology.In the pilot-scale reactor,due to the expansion of the treatment range,the attenuation effect of distance on the physicochemical effects needs to be considered.Among the three physicochemical effcts of pressure wave,pulsed ultraviolet and active species produced by the discharge,the pressure wave plays a leading role in disinfection.Because it has high intensity,long attenuation distance and low effective amplitude.In order to study the propagation and attenuation of pressure wave in the pilot-scale reactor,the pressure wave propagation 3D numerical model based on transient pressure acoustics was proposed.It is found that the reflection of the reactor causes the maximum pressure amplitude to appear in the reflected wave.Using this phenomenon,increasing the initial pressure wave frequency and reducing the reactor diameter can significantly increase the maximum pressure amplitude.When the initial pressure wave frequency increased to 1.67 times,the maximum pressure amplitude increased by 2.31 times.And when the reactor diameter decreased to0.50 times,the maximum pressure amplitude increased by 3.12 times.Through experiments,it is also found that discharge voltage,gap distance and water velocity are the main factors affecting the propagation of pressure wave.Next,the distribution laws of physicochemical effects in the pilot-scale reactor were studied.Pressure wave and pulsed ultraviolet are large volume effects.The generated H2O2and O3 have low concentration and short diffusion distance,whihc disinfeciton effect alone is limited.Combined with the disinfecrtion effects of different positions,it is found that there is a critical value of the pressure wave stress effect,which is between 0.85×105 Pa and1.08×105 Pa.The synergistic disinfeciton mechanism of underwater pulsed arc discharge in the pilot-scale reactor was analyzed.Within the range of UVC action,the pressure wave stress effect,combined effect and pulsed ultraviolet effect are used for disinfecion.When the UVC decayed to zero,the pressure wave stress effect and the combined effect are used for disinfection.And when the maximum pressure amplitude is less than the critical value of the stress effect,the disinfeciotn effect is the combined effect.This mechanism further elaborates the dominant role of pressure wave in the pilot-scale disinfection.Finally,the pilot-scale disinfecion rules were studied.In this study,the pilot-scale disinfection system achieved the treatment of static water with the volume from 300 L to1000 L and the treatment of flowing water with the flow rate from 66 L/min to 107 L/min.When the static water of 106 CFU/L is completely disinfected,the D value is 0.25 J/（m L·1log）.This energy efficiency is at an upstream level in underwater pulsed disinfeciton system.It is found that the reduction of the treatment volume and the increase of the number of discharge electrode pairs can increase the injection energy density,which is contributed to the improvement of the disinfection efficiency.When the initial cell concentration is105～107 CFU/L and the injected energy density is 1.50 J/m L,the bacterial concentration decreases by 3.46～6.07 logs.It is shown that the increase of the initial bacterial concentration will weaken the discharge effect and reduce the disinfection efficiency.And the increase in flow rate not only reduces the injection energy density,but also weakens the effect of the discharge,resulting in a significant decrease in the disinfection efficiency:when the initial cell concentration of E.coli is 106 CFU/L and the injection energy density is 0.68J/m L,the bacterial concentration decreases by 0.21～0.27 logs. |
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