| In the past few years,human activities have led to a significant increase in the frequency and extent of toxic algal blooms in offshore areas.This problem not only impedes the expansion of coastal industry,aquaculture,and tourism,but also poses a serious threat to marine ecological health and human life safety.The modified clay flocculation method is currently the sole emergency treatment for harmful algal blooms that has been extensively utilized in coastal waters of China.The conventional modified clay technique employs metal ions or inorganic polymer flocculants as modifiers to enhance natural clay’s efficiency of algae flocculation through interlayer intercalation or surface adsorption.With the advancement and progression of modified clay technology,surface modification methods have expanded from inorganic modification to organic modification and even biological modification.Based on the modified clay technology,researchers are exploring the possibility of using commonly used polyacrylamide polymer flocculants as surface modifiers for clays by combining their high-efficiency flocculation advantages with those of organic polymers.Initially,a copolymer of dimethyl diallyl ammonium chloride（DMDAAC）and acrylamide（AM）was synthesized to create the acrylamide/dimethyl diallyl ammonium chloride copolymer（PDA）.The PDA was optimized to address the issue of traditional polypropylene Amide flocculants curling up impacted by high salt ionic strength in seawater.Subsequently,this new surface modifier was utilized to produce acrylamide copolymer modified clay（PDAMC）,which exhibited remarkable algae removal performance.Additionally,the synergistic effect of synthetic PDA on clay flocculation algal blooms was examined.Finally,through analyzing the surface electrical properties of particles in the algae fluid before and after flocculation as well as observing floc growth changes during the process,an efficient mechanism for PDAMC flocculation and algae removal capabilities were determined.The paper presents the main research findings as follows:1.Synthesis and optimization of PDA for effective flocculation of harmful algal blooms.PDA was synthesized and refined via the technique of visible light-induced radical polymerization and demonstrated remarkable flocculation performance when exposed to seawater.The optimal preparation conditions for PDA were determined through the use of orthogonal experiments,along with the ideal ratio of cationic groups that have a significant impact on flocculation efficiency.The composition,structure,and morphology of PDA were characterized using Fourier transform infrared spectroscopy,nuclear magnetic resonance imaging,differential thermal analysis,and scanning electron microscopy.Results showed that PDA had high electropositive properties with apparent viscosity in seawater environments leading to good flocculation ability.Removal efficiency tests on Heterosigma akashiwo indicated that the removal rate exceeded 90%at a concentration level as low as 10 mg·L-1 compared to lower dosages with significant removal efficiencies observed when compared to PAM or PDA-Com.2.The study investigated the synergistic effect of PDA on clay flocculation of harmful algal blooms.PDAMC was prepared using a surface modification method with PDA as a modifier,and it was applied to remove typical algal blooms in seawater environments.The research analyzed the Zeta potential,apparent viscosity,and morphology characteristics in seawater of PDAMC with different modification ratios to screen out a modified clay formula that had high positive charge and efficient algae removal in seawater systems.The flocculation efficiency and kinetics of PDAMC on H.akashiwo were measured,and the effects of PDAMC and PACMC on other algal species were compared.The results showed that PDA adsorbed onto the surface of clay particles forming a cross-linked network structure.With an increase in modification ratio,the Zeta potential,particle size,and apparent viscosity increased first then decreased.After screening,50 mg·L-1PDAMC removed up to 90%H.akashiwo within one hour while having stronger flocculation effects on larger-sized algal organisms with lower organic matter content than PACMC under similar conditions but at nearly 90%less amount used for removal efficiency.3.Research on the algae removal mechanism of PDAMC.PDAMC with different modification ratios was added to the algae liquid of H.akashiwo,and the particle imaging velocimeter,scanning electron microscope,rotational viscometer and other analysis methods were used to analyze the Zeta potential of PDAMC on the particles in the algae liquid and the resulting zeta potential during the flocculation process.The influence of parameters such as floc particle size and floc fractal dimension,and the change of floc morphology were observed to analyze the flocculation mechanism of PDAMC on H.akashiwo cells.The results showed that according to the Zeta potential changes of the particles in the algae liquid,it was found that PDAMC can exert a strong charge neutralization effect,and combined with the particle size and fractal dimension of the flocs and the observation and analysis of SEM photos,it was found that PDAMC had a strong effect on H.akashiwo.During the flocculation process,the flocculation can be completed through the combined action of electric neutralization and cross-network capture,forming tightly wrapped flocs with good sedimentation performance,which greatly improves the removal efficiency of modified clay for harmful algal blooms.In this study,a remarkable polymer flocculant PDA was synthesized and optimized for high flocculation performance in seawater environments.The PDA was then applied to the surface of natural clay for modification,resulting in the development of a modified clay material with exceptional algae removal performance.This breakthrough further enhances the potential of modified clay flocculation as an effective method for removing algae and provides valuable insights into its widespread application and adoption. |
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