Stress Effect Of Calcium Peroxide On Microcystis Aeruginosa And Its Application Effect On Raw Water Of East Lake In Wuhan

Recently,cyanobacteria bloom is one of the most serious threats to the global freshwater water body.The rapid growth rate and wide adaptability of cyanobacteria make it seriously threaten the water quality safety.At present,the disposal methods of cyanobacteria blooms include physical,chemical and biological methods.Therein,oxidation method is one of the principal chemical methods to control cyanobacteria blooms.Calcium peroxide,known as"solid hydrogen peroxide",can slowly release hydrogen peroxide in water bodies to control cyanobacteria density and reduce phosphorus content.Although calcium peroxide has many advantages to control cyanobacterial blooms,it is still poorly understand of mechanism of control and applied practice.In this study,Microcystis aeruginosa,the do minant species of cyanobacteria blooms,was used as experimental material.By setting up gradient doses of calcium peroxide,cell density,chlorophyll a,carotenoid contents,chlorophyll fluorescence changes,ROS and Catalase enzyme(CAT)activity changes in the culture medium were measured to monitor the oxidative damage effects of calcium peroxide to M.aeruginosa.Meanwhile,the changes of extracellular protein content,total nitrogen and total phosphorus were measured to monitor the changes of nutrients in the medium.The sedimentation effect of calcium peroxide on M.aeruginosa,the changes of p H and turbidity in the culture medium were measured to analyze its disposal effect on M.aeruginosa,providing theoretical basis to control cyanobacteria blooms.Moreover,we added calcium peroxide into raw water from East Lake in wuhan,and use a special device to monitor hydrogen peroxide content,the change of chlorophyll a and orthophosphate in different depth,and the change of phytoplankton community in different gradient doses of calcium peroxide.Thus,this study provides data support for practical application calcium peroxide to control cyanobacteria blooms,the main content of this study is as follows:1.Through adding different doses calcium peroxide,deter mination of hydrogen peroxide concentration in culture medium,the content of chlorophyll a and carotenoids,ROS and CAT activity and the change of chlorophyll fluorescence,we observe that 120 mg/L is the most appropriate dose of calcium peroxide to control cyanobacteria blooms.At this dose,hydrogen peroxide was sustained released in the culture medium for 48 h,which significantly increased ROS content in algal cells and the content of malondialdehyde.The Q_A～Q_B side electron transfer were blocked,which resulted in oxidative damage to Photosynthetic System II in M.aeruginosa.Meanwhile,the extracellular protein content and extracellular total nitrogen content were increasing and proved that calcium peroxide could destroy cells.2.In this study,we found that sedimentation rate of M.aeroginosa reached 54.07%in200 mg/L concentration of calcium peroxide.In 24 h after adding calcium peroxide,p H value rapidly increased to between 10 to11,and the turbidity was significantly reduced.And the reduction of total extracellular phosphorus content in the treated groups ranged from 79.36%to 86.88%.The polysaccharide content of algal cells increased and lead to the formation of colony cells.The alkaline phosphatase activity of M.aeruginosa increased.3.After added calcium oxide in raw water from East Lake in wuhan,the released hydrogen peroxide main exists in upper-middle-class(0～1 m),This result mean that hydrogen peroxide consume rate is higher in bottom class than upper-middle class.Meanwhile,we measured change of orthophosphate and chlorophyll a content in different depth.The result shown that added calcium peroxide can significantly reduce both values of orthophosphate and chlorophyll a and selectively caused death of cyanobacteria,eventually changed the structure of the phytoplankton community,effectively reduce the content of total nitrogen and phosphorus and increase the content of dissolved oxygen in the water bodies.Added Calcium peroxide releasing a large amount of hydrogen peroxide causes strong oxidative stress on Microcystis,and by combined phosphate significantly reduce phosphate content in water,promote the reoxygenation of water bodies.These results showed that added calcium peroxide is significant control cyanobacteria blooms,which has significant application for ecological restoration in waterbodies with cyanobacteria blooms.