低功率密度超声波强化絮凝沉降除藻技术研究

Algae-removal by Low Power Ultrasound Enhanced Flocculation

超声波强化絮凝沉降除藻技术能够提高絮凝沉降除藻效率,但以往研究采用的较高超声波功率限制了这一组合技术的应用。通过探究低功率密度超声波(0.5～1.0 W/L)对絮凝沉降技术去除微囊藻的增效作用,比较了增重剂种类及用量、超声波预处理的时间和距离、超声波预处理与絮凝沉降的间隔时长、日光照射时长等因素对除藻率的影响,并通过水池试验验证了低功率密度超声波的增效作用。结果显示:(1)超声波的处理距离对除藻率无显著影响,但增加超声波预处理时长则明显有利于提高除藻率,处理30 s时的除藻率显著高于仅处理10 s时的除藻率;(2)除藻率的日均变幅较大,当日光光照时长为3～9 h时,试验组的除藻率平均比对照组高17%,日光照射时长为0 h和12 h时,试验组与对照组的除藻率则无显著差异;(3)随着超声波预处理与絮凝沉降间隔时长的增加,除藻率会明显下降,仅当间隔时长不超过30 min时,试验组的除藻率才显著高于对照组;(4)水池原位试验中,试验组的除藻率高达70.47%,显著高于对照组的58.12%。研究表明,低功率密度超声波预处理能明显增加絮凝沉降除藻率,且应在日光开始减弱的下午作业。

Ultrasound enhanced flocculation is efficient for algae-control,but the high power density required for ultrasound treatment prevents wide application.In this study,low power density ultrasound(LPDU,0.5-1.0 W/L)enhanced flocculation was used to remove wild Microcystis aeruginosa.The treatment parameters were optimized,including the coagulation agent and dose,duration and distance of ultrasonic treatment,time interval between ultrasonic treatment and flocculation,and illumination duration.A pilot test was carried out in a pond to determine the algae removal efficiency achieved by LPDU enhanced flocculation.Five findings are reported:(1)The type and dosage of coagulation agents has a significant effect on algae-removal efficiency.The highest algae-removal efficiency was obtained by using 11-22 g/L of loess(mesh 40-80)or quartz sand(mesh 120-200).(2)Algae removal was not affected by the distance of ultrasonic treatment,but increased with treatment time,and the algae-removal efficiency with 30 s of ultrasonic treatment was significantly higher than with 10 s(P<0.05).(3)Algae-removal efficiency was closely related to sunlight duration;removal efficiency was 17%higher in the treatment group,compared to the control,when sunlight duration was 3-9 h(P<0.05),while no significant difference was observed between treatment group and control when the sunlight duration was 0 h or 12 h(P>0.05).(4)Algae-removal efficiency decreased with increased time between ultrasonic treatment and flocculation;removal efficiency was significantly higher when the interval did not exceed 30 min(P<0.05).(5)In the in situ pond experiment,the algae-removal efficiency with LPDU(70.47%)was significantly higher than the control(58.12%).These results show that LPDU treatment significantly improves algae-removal efficiency and that afternoon is the best time for removing Microcystis blooms using LPDU enhanced flocculation.