絮凝预处理对微囊藻机械过滤的影响

Effect of Pre-flocculation on the Performance of Mechanical Filter in Removal of Microcystis

蓝藻水华是水体富营养化破坏性灾变的表现之一,其治理一直是国内外的研究热点。受限于水华蓝藻广泛的尺寸分布,机械过滤作为水中悬浮颗粒的去除手段尚未在水华治理中推广。微囊藻是水华蓝藻中常见的优势种,絮凝可使其形成较大尺寸的絮体,有利于机械过滤设备将其去除。通过比较不同尺寸絮体的叶绿素a浓度,可以考察聚合硫酸铝、聚合硫酸铁、聚合氯化铝、聚合氯化铝铁对微囊藻机械截留效果的影响。结果表明,絮凝效果PFS>PAS>PAC>PAFC,200 mg/L PFS的絮体有92.26%可被250μm滤网截留,97.55%可被100μm滤网截留。pH值为7~10时絮体截留效果较好;搅拌转速250 r/min时PFS絮体粒径最大,滤网截留效果最好。通过PFS絮凝预处理,64μm滤网对微囊藻的截留效果由14.6%提高到95.1%,并大幅度削减藻水的营养物质。

Cyanobacterial bloom is one of the devastating results of eutrophication,of which the treatment is always a hot topic.Filtration is generally used in removing suspended particle from wastewater,however,its application in the algae bloom is limited by the size distribution characteristics of algae particles.In this study,the removal capacity of combined flocculation and filtration on Microcystis,one of the dominants in cyanobacterial bloom was evaluated.The removal efficiency by filters of the flocs,formed by poly aluminum sulfate(PAS),poly ferric sulfate(PFS),poly aluminum chloride(PAC)and poly aluminum ferric chloride(PAFC),was estimated by the chlorophyll a content of flocs in different size ranges.The results showed that flocculating efficiency order is PFS>PAS>PAC>PAFC when 92.26%of the algae flocculated by PFS could be detained by 250μm filter and 97.55%by 100μm filter.It was convenient to flocculate the algae at the pH value between 7 to 10.The agitator speed in 250 r/min was in favor of forming larger flocs to improve the removal efficiency of filter.With the pretreatment of PFS,the algae removal efficiency of the 64μm filter was improved from 14.6%to 95.1%at the water level of 28 cm,giving a large number of cuts in nutrient substance.