Research On The Development And Algae Removal Mechanism Of Polymer Quaternary Salt Modified Clay

In recent years,the frequent occurrence of harmful algal blooms（HABs）in China’s coastal waters has posed a serious threat to coastal ecosystems,economic development and the safety of human life,and there is an urgent need to develop safe and effective prevention and control measures.The clay mineral flocculation method is a promising method for the control of HABs,but the natural clays have poor solute properties and low flocculation efficiency.How to improve the efficiency of clay minerals and reduce the doseage of clay has become a hot research topic in this field.Therefore,scientists in China have proposed theories and methods of clay surface modification aimed at improving the efficiency of HABs treatment,which have been widely applied,the diversification of modified clay formulations has provided a powerful guarantee for the treatment of harmful algal blooms.Currently,most of the inorganic modifiers are aluminium compounds,which are mainly used to remove microalgae by enhancing the flocculation and sedimentation of clays,but their dosage is high in high organic matter water bodies and their inhibitory effect on microalgal activity is weak.Most of the organic modifiers are quaternary ammonium salts（QAC）.As their antibacterial activity depends largely on the length of the alkyl chain,most of the previous modifiers are large-molecule quaternary ammonium salts,which tend to inhibit and kill microalgae by producing physiological stress,which makes such large-molecule quaternary ammonium salts may have some potential toxicity.Although they also have some electro-neutralized ability,the stronger ionic strength in seawater systems can cause their molecular chains to curl,weakening their role in flocculation.In recent years,the focus of research has shifted to amphiphilic polymer quaternary ammonium salts,such polymers are more sterilized and mostly used as a broad spectrum sterilant.This thesis found that a widely used in the disinfection of drinking water and other aspects of polymer quaternary ammonium salt poly dimethyl diallyl ammonium chloride（Poly dimethyl diallyl ammonium chloride,PDMDAAC）in addition to algae has good prospects for application,it is a strong cationic surfactant,the chemical formula is(C₈H₁₆NCl)n,has It has no color and odor,has little effect on p H,is easily soluble in water and does not foam.This thesis investigates the removal and safety of typical algal bloom organisms using PDMDAAC as an organic modified regent;its synergistic effect and mechanism on the algae removal ability of natural clay was studied,and a new modified clay was developed which can remove algae efficiently,has strong synergistic effect on flocculation and is safe and environmentally friendly.The main findings are as follows:1.The invention of PDMDAAC-modified clay.The safety of PDMDAAC was investigated using juvenile Penaeus vannamei,which are widely cultured offshore,as test organisms.The results showed that its 96 h-LC₅₀ was approximately 314.05 mg/L,which was much higher than the experimental dosage in the organic modified clay study in this paper,ensuring the safety of the use of PDMDAAC-modified clay.Compared with hexadecyl trimethyl ammonium Bromide（HDTMA）,dialkyl polyoxyvinyl triquaternary ammonium salt（DPQAC）and alkyl polysaccharide（C6）,PDMDAAC has the strongest algae removal capacity and is an environmentally friendly and efficient algae removal material.PDMDAAC was used as a modifier to produce organically modified clays with five natural clays.It was found that PDMDAAC had a significant synergistic effect on the algae removal ability of the natural clays,with the modified Indonesian clay having the strongest algae removal ability.The removal rate was over 50,80 and 95%at the dosage of 1,2 and 5 mg/L of modifier;therefore,the preparation condition of polymer quaternary ammonium salt modified clay（later referred to as MP）was determined as Indonesian clay:PDMDAAC（mass ratio）=200:1,2 and 5,which were recorded as MP1,MP2 and MP5 respectively.2.Removal effect of PDMDAAC modified clay on different species of algal blooms In this paper,the removal effect of PDMDAAC modified clay（MP）on three species of algal blooms was investigated separately,using Prorocentrum donghaiense,Amphidinium carterae and Heterosigma akashiwo as experimental objects.The results showed that MP at a dosage of 2 mg/mL could effectively remove the three microalgae within 3 h,and the removal rate could reach over 80%.The analysis showed that the removal characteristics of the different species of algal blooms were different:MP could form flocs with large particle size,high growth（Sg≥16.69μm/min）,high strength（M≥187.84）and fractal dimension with P.donghaiense,which could settle quickly;MP formed smaller flocs with A.carterae,but still had a strong settling ability(particle However,MP can induce strong peroxidative damage to H.akashiwo to inhibit the microalgal activity and finally achieve the effective removal of the algae.3.The mechanism of algae removal by PDMDAAC modified clay was studied from the perspectives of flocculation,physiological and biochemical effects,and cell biology,using the East China Sea Prochlorococcus as a typical algal bloom organism.（1）Flocculation:The surface of the clay particles modified by PDMDAAC is positively charged,and the PDMDAAC loaded on the surface of MP can bind to microalgae through electrostatic attraction and bridging,thus greatly enhancing the ability of the modified clay to capture and sweep the algal cells,which makes MP have a strong flocculation and sedimentation effect on microalgae and can achieve water clarification within a short time.（2）Physiological and biochemical effects:MP can induce peroxidative stress in algal cells,causing a significant increase in lipid peroxidation（P<0.05）and inhibiting algal cell activity.（3）Effects on cell membranes:MP significantly interfered with cell membrane permeability,causing extravasation of intracellular amino acids and inward flow of Ca²⁺;disrupted the composition of cell membranes,resulting in a significant decrease in the phospholipid and total protein content of microalgae and the proportion of membrane proteins（P<0.05）;forced microalgae protoplasts to crumple,triggering mechanical damage to cell membranes and eventually causing microalgae lysis.In summary,this thesis selects PDMDAAC to modify the natural clay to develop a polymer quaternary ammonium salt modified clay that can efficiently remove algae and is friendly to the environment.The synergistic effect of polymer quaternary ammonium salt and its algae removal mechanism of the modified clay were discussed.This thesis will inform the further development of modified clay technology.