| In recent years,the frequent outbreaks of red tide in the global offshore waters not only endanger the ecological environment of the outbreak waters,affect the development of coastal aquaculture,tourism,nuclear power and other marine-related industries,but also seriously threaten human health through the food chain,which is a global Marine ecological disaster.Modified clay(MC)not only has good flocculation and sedimentation effect on red tide microalgae,but also can purify water and improve the water environment.After nearly 30 years of development,an internationally leading modified clay technology system for red tide control has been formed.As MC is characterized by high efficiency of removing algae,low cost and green environment,it is considered to be the most promising method for red tide treatment,and the only method applied to on-site large-scale red tide emergency treatment at present.During the outbreak of red tide,algal organic matter(AOM)in water increased rapidly due to the proliferation and aggregation of a large number of red tide algal cells,which became a non-negligible factor affecting the efficiency of MC control of red tide.However,due to the unique complexity of seawater and MC management processes,there is a lack of specific studies on the effect of increasing AOM in water on MC management efficiency during red tide outbreaks.In order to find out the effect of AOM produced by red tide algae on MC flocculation process and algae-removing efficiency,this paper took Prorocentrum donghaiense as the model red tide organism,observed the flocculation characteristics of MC under different concentrations of AOM and the corresponding changes of AOM composition and content in the experimental system,and explored the regulatory effect of environmental factors on the influence of algal organic matter on the flocculation of modified clay.Based on the difference of MC’s algae-removing efficiency under different concentrations of AOM,the law and mechanism of AOM’s effect on the flocculation and algae-removing process of modified clay were preliminatively analyzed,and the types and methods of modified clay that can effectively resist the effect of algae-derived organic matter were explored.The results of this study provide experimental support for exploring the causes affecting the efficiency of MC control of red tide in water bodies with high organic matter and the methods to overcome them.The main results are as follows:(1)Revealed the characteristics of AOM affecting MC flocculation process.Particle image velocimetry was used to observe the differences of MC flocculation morphology and kinetics at different concentrations of AOM.The results showed that AOM could promote MC flocculation at low concentration and inhibit MC flocculation at high concentration.By comparing the changes of AOM concentration,molecular weight and hydrophilicity before and after MC flocculation,it was found that MC would preferentially bind hydrophobic macromolecular substances in AOM,and the amount of MC binding AOM increased with the increase of AOM concentration.(2)The effects of p H,sulfate ions,salinity and other environmental factors on MC flocculation in the presence of AOM were investigated.By comparing the differences of different environmental factors on MC flocculation under the influence of AOM,it was found that p H further affected the flocculation effect mainly by changing the hydrolytic morphology of aluminum in MC.The particle size and growth rate of flocs generated by MC first increased and then decreased with the increase of p H,while the strength and regeneration of flocs showed a monotonically decreasing trend with the increase of p H.Both sulfate ion and salinity further affect the flocculation process of MC by affecting the potential and changing the thickness of the double electric layer.The flocculation process of MC first increases and then weakens with the increase of sulfate ion concentration,while the flocculation process of MC will be inhibited with the increase of salinity.(3)The mechanism of AOM affecting the efficiency of MC removal was analyzed.Through the correlation analysis of flocculation characteristic parameters,AOM concentration and algaecal removal efficiency,it was found that the size,growth rate,strength and regeneration of flocs were significantly negatively correlated with the concentration of AOM,and positively correlated with algaecal removal efficiency,indicating that AOM affected the algaecal removal efficiency mainly by affecting the flocculation process of MC.When the concentration of AOM is less than 2.85mg/L,AOM can promote the flocculation process of MC,and the effect of MC removal is better.When the concentration of AOM was higher than 5.08mg/L,AOM had a strong inhibitory effect on MC flocculation,and the removal efficiency of MC was low,and the dosage of MC was increased.On this basis,the adaptability of different kinds of MC to resist the influence of AOM was compared.The results showed that oxidized MC could reduce the concentration of AOM in water,weaken the inhibition effect of AOM on the flocculation process of MC,and the algae removal efficiency was relatively high.At the same time,it was found that the adding mode of MC also had an impact on the removal efficiency of MC under the presence of AOM.When the same dosage was taken,the secondary adding mode and the adding mode every 5 minutes would improve the flocculation removal process of MC. |
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