超声波处理对微囊藻群体光合活性和沉降过程的影响

关注微囊藻群体在超声处理下光合活性变化及超声解除后的浮力恢复情况,可以为超声波控藻技术提供理论依据和数据支撑,具有重要的实践意义.本研究采用处理后水柱中叶绿素a浓度的垂向分布比例和叶绿素荧光变化情况分析微囊藻群体在超声波处理下的光合活性变化和沉降过程.结果表明,适量的超声处理(35 kHz、0.0353 W/cm~3)能在避免破裂藻细胞的同时,显著抑制其光合活性;60 s的处理造成了45.5%的光合活性被抑制.然而,在适宜生长条件下,所有实验组藻细胞中受抑制的光合活性均在24 h内恢复至对照组的80%左右.此外,在上述超声条件下,5 s的超声处理能使水柱中叶绿素a浓度在短时间内(0.5 h)的去除率达79.5%.然而,当处理时间小于30 s时,大于90%的沉降藻细胞可在超声解除后的72 h内恢复浮力上浮;而当处理时间延长至60 s以后,藻细胞基本丧失了上浮能力.通过分析发现,超声处理后微囊藻群体的粒径分布对藻细胞沉降及上浮过程起决定性作用,并且还发现微囊藻群体在超声处理时首先表现为藻细胞失去浮力下沉和光合系统受损,进而发生大群体振散.

Effects of ultrasound on photosynthetic activity and sinking process of Microcystis colonies

Studies on damages in photosynthetic activities of Microcystis colonies and effect on their sinking process induced by ultrasound merited are of important practical value, which could provide powerful support for the promotion of ultrasound application in dealing with cyanobaterial blooms. Therefore, these processes have been assessed according to changes of chlorophyll-a (Chl.a) fluorescence and the vertical distribution of the Chl.a content in water column, respectively. Results showed that appropriate ultrasound parameters (35 kHz, 0.0353 W/cm³) did not disrupted algal cells, but significantly inhibited their photosynthetic activities. For example, the photosynthetic activities of Microcystis colonies treated for 60 s had been inhibited by 45.5%. However, the inhibited photosynthetic activities of all treated algae were recovered approximately to 80% of the control within 24 h of culture after treatment. The maximal removal rate of Chl.a from raw water (79.5%) was obtained at 5 s of sonication when cultivation time was up to 0.5 h. More than 90% of algal cells that had been treated for 30 s and then sank to the bottom, resuspended or refloated after 72 h of the culture. However, algal cells treated for 60 s did not refloat during the experiment period (96 h). Changes of colony size played a key role in the sedimentation character during ultrasonication and the recovery process of buoyancy after exposure. Furthermore, when Microcystis colonies were exposed to ultrasound, gas vesicles and photosynthesis pigment were damaged firstly, which followed by the declumping of cyanobacteria markedly.