Removal Of Microcystis Aeruginosa By Tea And Its Influencing Factors

Cyanobacteria are the Earth’s oldest oxygen evolving organisms,and they have important impacts on forming our modern-day biosphere.Conversely,biospheric environmental perturbations,including eutrophication and climatic changes,strongly affect cyanobacterial growth and algal bloom in freshwater and marine ecosystems.Harmful cyanobacterial algal blooms(Cyano HABs)always cause toxicity,food web altering,hypoxia generating.Cyano HABs happen world-wide due to eutrophication and climatic changes,and they cause a serious threat to our freshwater resources.There are five ways that can be used to control Cyano HABs,including:mechanical,biological,chemical,genetic and environmental control.The objective of this paper is to explore whether it is possible to use allelopathic to remove Microcystis aeruginosa.In this paper,M.aeruginosa,which is the main dominant species of the algae bloom in cyanobacteria,was used as experimental materials.Chlorophyll a(Chl a)content was investigated as the biological indicators to screen out efficient algaecide in terrestrial plants.Four methods were applied to find out the most suitable one for algae removal by tea.Then the damage effects by tea on M.aeruginosa were analyzed through the oxidation and anti-oxidation of algal cells.Total antioxidant capacity(T-AOC),the content of carotenoid and malondialdehyde(MDA)were taken as the experiment indicators.In the end,the tea’influence on the growth of M.aeruginosa under single environmental factor and complex environment factors were studied.These were supposed to provide more comprehensive scientific basis on using tea to control alga.At the same time,tea polyphenols content was measured in culture medium to analyze and forecast the effects of using tea to remove of M.aeruginosa.The main results of this study are as follows:(1)Screening out efficient algaecide in terrestrial plants:Phyllostachys sulphurea promoted the growth of M.aeruginosa at 1 g/L and 5 g/L.The effects of tea and Ajuga nipponensis Makino on the growth of M.aeruginosa were not obvious at 1 g/L,but were obvious at 5g/L.They are the best inhibitory effect in the 28 kinds of terrestrial plants,as they showed high removal rate and lasting effect.The other 25 terrestrial plant had no obvious effect or promote the growth of M.aeruginosa when the concentration wasl g/L,although they have effect in 5 g/L in prophase,later showed obvious promotion,so they were not suitable algaecide materials.(2)Finding out the most suitable method of algae removal by tea:four methods were brewing dry tea,brewing fresh tea,extracting the tea by ultrasonic,and extracting the tea by tradition.The effects were not obvious and TP were not detected when brewing fresh tea at the concentration of 0.5～2 g/L.They had a certain inhibitory effect,but showed no removal effect;their TP contents were low,when the concentration was 4～6 g/L.The content of TP when extracted the tea by ultrasonic was lower than extracted the tea by tradition.The content of TP in the extract by tradition was higher than brewing dry tea at the 2nd day,but from the 4th day the content of TP was lower than brewing dry tea.The best concentration was 2g/L for extracted the tea by ultrasonic;was lg/L for extracting the tea by tradition;and was 0.5g/L for brewing dry tea.Brewing dry tea was the best way,because it had some advantages,such as high removal rate,low use dosage,easy to operate,etc.(3)The contents of algae,protein,Chl a and carotenoid in the 0.5～1g/L treatment group were decreased with time in the same treatment group,and decreased with the increase of the tea concentration.The level of T-AOC of M.aeruginosa increased on the 2nd day,but began to decline on the 4th day;the strength increased with the increase of tea concentration.MDA content increased with the increase of tea concentration and time.Therefore,the tea can break the cell membrane structure and antioxidant defense system of algal cells and destroy algal cells.When the concentration was in the range of 2～6g/L,the content of T-AOC was higher,the content of MDA was lower,and the content of Chl a and carotenoid was lower compared with the 0.5～1g/L treatment group.It can be seen that high-concentration experimental group had stronger antioxidant capacity,and low removal rate.(4)Temperature,light and flow rate affect the growth of M.aeruginosa and removal effect of tea on M.aeruginosa.The optimum conditions for the growth of M.aeruginosa were as follows:30℃,2500～45001x,5 cm/s,in respectively single-factor experiments.In the temperature range of 25～30℃,the tea could effectively remove M.aeruginosa,15～20℃were not conducive to the removal of M.aeruginosa.In a short time,stronger intensity of light was favorable,but the impact of light was stable with the increase of time.In the short time,higher flow rate was conducive to the removal of algae,but the effect of flow rate was stable with the increase of time;the removal effect was significantly higher than the static state.Higher temperature and flow rate,stronger intensity of light could accelerate the decomposition of tea TP,but different flow rates had little effect on the decomposition of TP.(5)The results of orthogonal experiment showed that the importances of four factors affecting the removal rate of algal cells decrease as follows:tea concentration>flow rate>temperature>light.The importances of factors affecting the removal rate of Chi a in algal cells decrease as follows:tea concentration>flow rate>light>temperature.The factors affecting the TP coutent in the medium decrease as follows:tea concentration>temperature>flow rate>light.Combining the results of orthogonal experiment and the actual situation,the optimum conditions for removing the M.aeruginosa were suggested as followes:light intensity was 2500 lx,the concentration of tea was 1 g/L,the flow rate was 5cm/s and the temperature was 25 ℃.