中国科学院海洋研究所机构知识库

近年来，我国近海有害藻华（harmful algal blooms，HABs）频发，对沿海生态系统、经济发展和人类生命安全造成了严重威胁，亟需研发安全、有效的防控措施。粘土矿物絮凝法是一种应用前景广阔的有害藻华防治方法，但天然粘土存在溶胶性质差、絮凝效率低等缺陷。故如何提升粘土矿物的除藻效率、降低粘土用量，已成为了该领域的研究热点。为此，我国科学家提出了旨在提高有害藻华治理效率的粘土表面改性理论与方法，得到了广泛的应用，改性粘土配方的多样化为有害藻华的治理提供了有力的保障。目前应用较多的无机改性剂大多为铝系化合物，主要是通过提升粘土的絮凝、沉降作用去除微藻，但其在高有机质水体中用量较高，且对微藻活性的抑制作用较弱。有机改性剂大多为季铵盐（Quaternary Ammonium Salt，QAC），由于其抗菌活性在很大程度上取决于烷基链的长度，故以往的改性剂大多为大分子季铵盐，偏向于通过产生生理胁迫来抑制、灭杀微藻，这使得此类大分子季铵盐可能存在一定的潜在毒性。其虽也具有一定的电中和能力，但海水中较强的离子强度会迫使其分子链卷曲，减弱其对粘土絮凝作用的增效性。近年的研究重点已转移到具有两亲性的高分子季铵盐上来，此类聚合物灭菌效果更强，多作为广谱灭菌剂使用。

本论文发现一种广泛应用于饮用水消毒等方面的高分子季铵盐聚二甲基二烯丙基氯化铵（Poly dimethyl diallyl ammonium chloride，PDMDAAC）在除藻方面有较好的应用前景，其是一种强阳离子表面活性剂，化学式为(C₈H₁₆NCl)n，具有无色无嗅、对pH值影响小、易溶于水和不发泡沫等优势。本论文以PDMDAAC为有机改性剂，研究了其对典型藻华生物的去除作用和安全性；研究了其对天然粘土除藻能力的增效作用与机制，研发了一种可高效除藻、对絮凝作用增效性强且安全环保的新型改性粘土。主要研究结果如下：

1、PDMDAAC改性粘土的研发制备  本文以近海广泛养殖的凡纳滨对虾（Penaeus vannamei）幼虾为受试生物，考察了PDMDAAC的安全性。结果表明，其安全浓度约为31.41 mg/L，远高于本文中达到高效除藻的实验用量。在与十六烷基三甲基溴化铵（HDTMA）、双烷基聚氧乙烯基三季铵盐（DPQAC）和烷基多糖苷（C6）的比对分析中发现，PDMDAAC的除藻能力最强。以PDMDAAC为改性剂，同五种天然粘土分别制备了改性粘土，发现PDMDAAC对天然粘土除藻能力的增效作用显著，其中改性印尼土的除藻能力最强。且在改性剂用量为1、2、5 mg/L时，去除率可达50、80和95%以上；故本论文确定高分子季铵盐改性粘土的制备条件为印尼土：PDMDAAC（质量比）= 200:1、2、5，分别记为MP1、MP2和MP5。

2、PDMDAAC改性粘土对不同种类藻华生物的去除作用  本文以东海原甲藻（Prorocentrum donghaiense）、强壮前沟藻（Heterosigma akashiwo）和赤潮异弯藻（Amphidinium carterae hulburt）为实验对象，分别考察了PDMDAAC改性粘土（MP）对三种藻华生物的去除作用。结果表明，改性剂用量为2 mg/mL的MP可在3 h内有效去除这三种藻华生物，去除率可达80%以上。分析发现，针对不同种类的藻华生物，其去除特点有所不同：MP可以与东海原甲藻形成粒径较大、生长性较强（Sg ≥ 16.69 μm/min）、强度（M ≥ 187.84）和分形维数均较高的絮体；MP与强壮前沟藻形成的絮体较小，但具有较强的沉降能力（30 min处颗粒密度可降低约70%）；MP对赤潮异弯藻的絮凝、沉降作用较弱（絮体粒径较小、分形维数较低），但MP可诱导较强的过氧化胁迫来抑制微藻活性，最终实现对该藻的有效去除。

3、PDMDAAC改性粘土的除藻机制研究  本文以东海原甲藻为典型藻华生物，分别从絮凝作用、生理生化以及细胞膜损伤等角度，研究了MP的除藻作用机制。（1）絮凝作用：经PDMDAAC改性后的粘土颗粒表面呈正电性，负载在MP表面的PDMDAAC可通过静电吸引和桥联作用与微藻结合，从而极大地提升改性粘土捕获和卷扫藻华生物细胞的能力，使得MP对微藻的絮凝、沉降作用较强，在短时间内即可实现水体澄清。（2）生理生化：MP可对藻细胞产生过氧化胁迫，使脂质过氧化程度显著升高（P < 0.05），抑制藻细胞活性。（3）细胞膜损伤：MP可显著干扰细胞膜通透性，使得胞内氨基酸外渗、Ca²⁺内流；破坏细胞膜的组分构成，造成微藻磷脂和总蛋白质含量以及膜蛋白占比显著降低（P < 0.05）；迫使微藻原生质体皱缩，引发细胞膜的机械性损伤，最终导致微藻裂解。

综上所述，本论文选用PDMDAAC对天然粘土进行改性处理，研发出可高效除藻且对环境友好的高分子季铵盐改性粘土，阐述了PDMDAAC的增效作用及其改性粘土的除藻机制。本论文将为为改性粘土技术的进一步发展提供参考。

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 pH, 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 ≥ 16.69 μm/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.