CN109626493B

CN109626493B - Application of surfactant modified goethite in removing microcystis aeruginosa

Info

Publication number: CN109626493B
Application number: CN201910008869.3A
Authority: CN
Inventors: 李瑞萍; 任慧君; 黄应平
Original assignee: China Three Gorges University CTGU
Current assignee: China Three Gorges University CTGU
Priority date: 2019-01-04
Filing date: 2019-01-04
Publication date: 2021-08-31
Anticipated expiration: 2039-01-04
Also published as: CN109626493A

Abstract

The invention provides an application of surfactant modified goethite in removing microcystis aeruginosa. The surfactant comprises hexadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide, hexadecyl dimethyl benzyl ammonium chloride or octadecyl trimethyl ammonium bromide. The preparation method specifically comprises the steps of dissolving a surfactant in water, adding goethite into the dissolved solution, stirring, centrifuging, removing supernate, freeze-drying and grinding to obtain the surfactant modified goethite. In the process of removing microcystis aeruginosa, the carbon chain with positive charges can trap and bond algae cells with negative charges, the alkyl chain penetrates through the cell membrane of the algae, the integrity of phospholipid bilayers is changed, the membrane is broken, the reaction is carried out with protein and nucleic acid in an algae body, and the bridge bond between cellulose molecules is loosened or the synthesis of the protein is inhibited. Under the action of light, goethite generates strong oxidizing free radicals to attack algae cells, so that organic matters in the algae cells seep out, and the growth of the algae cells is inhibited.

Description

Application of surfactant modified goethite in removing microcystis aeruginosa

Technical Field

The invention relates to surfactant modified goethite, which is applied to removal of microcystis aeruginosa and belongs to the technical field of water pollution control.

Background

At present, the frequency of the occurrence of cyanobacterial bloom is higher and higher in many countries, and the cyanobacterial bloom becomes a global environmental problem. The overgrowth of cyanobacteria poses a color, odor, and toxin hazard to humans, animals, and aquatic organisms, and the overgrowth must be controlled in situ. Microcystis aeruginosa is a well-known species of algae that causes cyanobacterial blooms in freshwater lakes and reservoirs worldwide. Some common treatment methods are chemical algaecides, clay flocculation, ultrasonic irradiation, large aquatic plants, biotechnology, ultraviolet irradiation, and the like.

Among them, clay minerals are widely noted as an effective, economical and environmentally friendly material and are used for cyanobacterial algal bloom control. After the traditional clay minerals are flocculated with algae cells, the flocculating constituent is resuspended due to the movement of water flow, and the algae removal effect is influenced. At present, modifying minerals by using surfactants becomes a great hot point of research, which not only can reduce the surface and interfacial tension between liquid, solid and gas and improve the adhesive force of minerals to achieve high-efficiency removal effect, but also active free radicals generated by semiconductor metal oxides under the irradiation of light can oxidize proteins, lipids and nucleic acids in algae cells and destroy cell membranes to cause the algae cells to break. WuTing and the like modify vermiculite and montmorillonite by Gemini surfactant, and the modified vermiculite is found to have the maximum removal rate in 24h when the concentration is 6.5mg/L by removing marine Scutellaria. The clay modified with Cetyl Trimethyl Ammonium Bromide (CTAB) such as bang not only aggregates cells but also lyses cells during flocculation.

A large amount of iron oxides exist in the nature, wherein goethite widely exists in soil, sediments and other environment media, and attracts a plurality of researchers for environment friendliness, large reserves, stable chemical properties and the like.

Disclosure of Invention

The invention adopts 4 surfactants to modify goethite, analyzes the algae removal performance of the modified material, and explores the algae removal performance of the material with the best performance under different physicochemical conditions. The specific contents are as follows:

the invention provides an application of surfactant modified goethite in removing microcystis aeruginosa. The method comprises the following steps: under the conditions of pH value of 7.5-9.5, 20-30 ℃ and illumination of 1000-.

The density of the microcystis aeruginosa is 1.0 multiplied by 10⁶-1.0×10⁷cells/mL, microcystis aeruginosa includes algal cells in log phase and death phase.

The addition amount of the surfactant modified goethite is 10mg/L-60 mg/L. The surfactant comprises any one of hexadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide, hexadecyl dimethyl benzyl ammonium chloride and octadecyl trimethyl ammonium bromide.

The preparation method of the surfactant modified goethite comprises the following steps: dissolving a surfactant in water at 55-65 ℃, adding goethite into the dissolved solution, stirring, centrifuging, removing supernatant, drying in vacuum, and grinding to obtain the surfactant modified goethite.

The invention analyzes the removal effect of surfactant modified goethite on microcystis aeruginosa, and of the 4 surfactants, ODTMA modified goethite has the best removal effect on chlorophyll a. Through single-factor physicochemical condition experiments, the removal rate of chlorophyll a of ODTMA/goethite is the largest under the conditions that the reaction concentration is 50mg/L, the temperature is 35 ℃, the illumination is 2000Lx, and the reaction pH is weak acidity and neutrality. This is because during the process of removing microcystis aeruginosa by using ODTMA/goethite, the carbon chain with positive charges on one side can trap and bind with the algae cells with negative charges, and the alkyl chain penetrates the algae cell membrane to change the integrity of phospholipid bilayer, so that the membrane is broken, reacts with protein and nucleic acid in the algae body, and relaxes the bridge bond between cellulose molecules or inhibits the synthesis of protein. On the other hand, goethite generates strong oxidizing free radicals under the action of light to attack algae cells, so that organic matters in the algae cells are exuded, and the growth of the algae cells is inhibited.

Drawings

FIG. 1 shows the removal rate (a) of chlorophyll a by goethite and the Zeta potential (b) thereof under different surfactant modifications.

FIG. 2 is an XRD pattern of ODTMA/goethite samples.

FIG. 3 is an SEM of samples of natural goethite; (c) - (d) ODTMA/goethite

FIG. 4 shows the effect of physicochemical conditions on the removal of chlorophyll a by ODTMA/goethite (a) ODTMA/goethite addition; (b) the light intensity; (c) (ii) temperature; (d) the pH value.

FIG. 5 shows the effect of ODTMA/goethite on the removal rate of physiological indices (a) Chla-chlorophyll a and Caro-carotenoid; (b) PC-phycocyanin; APC-allophycocyanin and PE-phycoerythrin; (c) TSP-soluble protein; (d) MDA-malondialdehyde.

FIG. 6 is SEM pictures of algal cells (a) - (b) before ODTMA/goethite treatment; (c) after (d) ODTMA/goethite treatment.

FIG. 7 is an algal flow cytometer (a) before ODTMA/goethite treatment; (b) ODTMA/goethite treatment.

FIG. 8 is a graph showing the change in TOC in BG-11 medium after removing algae by ODTMA/goethite.

Detailed Description

The reagents and instruments used to implement the technical scheme of the invention are as follows:

the main experimental reagents are as follows: cetyltrimethylammonium chloride (CTAC, alatin reagent, AR); cetyltrimethylammonium bromide CTAB, alatin reagent, AR); hexadecyldimethylbenzyl ammonium chloride (HDTMA, alatin reagent, AR); octadecyl trimethyl ammonium bromide (ODTMA, Sigma Aldrich, AR); goethite (Sigma Aldrich, AR).

The main experimental apparatus: ultra-clean bench (SW-CJ-1F, Weifeng clarification facility Co., Wujiang); autoclave (SYQ-DSY-280B, Shanghai Shenan medical instruments factory); light incubator (PGX-250B, Ningbo Hai Shuichi Saver laboratory instruments); ultraviolet-visible spectrophotometer (UV-Vis DRS, Lambda25, usa); a pH meter (Delta 320, Mettler-Toledo, Shanghai Co., Ltd.); x-ray diffractometer (XRD, D/max2500, Rigaku, Japan); cold field scanning electron microscopy (SEM, JSM-7500F, JEOL, Japan); total organic carbon tester (TOC, Multi N/C2000, Germany).

Preparation and characterization of ODTMA/goethite

Preparation of ODTMA/goethite: 0.48g of ODTMA is weighed and dissolved in 100mL of 60 ℃ water, 0.11g of goethite is added into the dissolved solution, the solution is placed on a magnetic stirrer and stirred for 72 hours, centrifugation is carried out, supernatant liquid is discarded, vacuum drying and grinding are carried out. CTAC, CTAB, HDTMA modified goethite were prepared according to the same method.

Characterization of ODTMA/goethite: measuring the crystal form of ODTMA/goethite by using an X-ray diffractometer, wherein the scanning 2 theta range is 20-60 degrees; the morphology was determined using a cold field scanning electron microscope.

Surfactant modified goethite algae removal experiment

In the technical scheme of the invention, the pH value is controlled to be 7.5, the temperature is controlled to be 25 ℃, and the illumination is 2000 Lx. To 200mL of sterilized medium was added an equal amount of medium at logCells of algae in growth phase to make initial algae density 1.7X 10⁶cells/mL. Weighing a certain amount of surfactant modified goethite into the algae liquid, and placing the algae liquid into an illumination incubator for reaction for a certain time. Each experimental group was set up for 2 replicates using chlorophyll a removal as an evaluation criterion.

In the algae removal experiment of the goethite modified by the 4 surfactants, the dosage of the catalyst is 50 mg/L; in order to investigate the influence of the optimal surfactant modified goethite reaction concentration, 0mg/L, 10mg/L, 20mg/L, 30mg/L, 40mg/L, 50mg/L and 60mg/L are set; light intensity influence setting gradients of 0Lx (dark), 500Lx, 1000Lx, 1500Lx, 2000 Lx; temperature range examined: 15 ℃, 20 ℃, 25 ℃, 30 ℃ and 35 ℃, and the pH of the medium is in the range of 6.5, 7.5, 8.5, 9.5 and 10.5. And (3) putting the surfactant modified goethite in an incubator for experiment 1d in experiments of concentration, light intensity, temperature and pH.

ODTMA/goethite is adopted in the experiment of the influence of the surfactant modified goethite on the physiological indexes of the algae cells, and the experiment is carried out in an illumination incubator for 1 d. The contents of chlorophyll a, carotenoid, phycobiliprotein, soluble protein and malondialdehyde in the algae cells are measured, and the influences of the surfactant modified iron on the growth, physiological state, cell metabolism and cell membrane damage of the algae are respectively reflected.

In addition, the removal mechanism of the surfactant modified goethite on the algae cells is revealed by monitoring the change of Total Organic Carbon (TOC) of the culture medium in the algae removal process, the change of the appearance of the algae cells after the algae removal and the integrity of cell membranes.

Index analysis method

Measurement of physiological indexes of algae cell (including chlorophyll a, carotenoid, soluble protein, malondialdehyde), and measurement of surface structure and membrane integrity of algae cell.

Determination of chlorophyll a and carotenoid content: centrifuging 10mL of algae solution at 5000r/min for 5min, removing supernatant, adding equal volume of 95% ethanol into the precipitate, standing overnight at 4 deg.C, centrifuging at 5000r/min for 5min, and measuring 665, 649 and 470nm values of the supernatant with spectrophotometer. The calculation formula of the chlorophyll a and carotenoid content is as follows:

Chla(mg/L)＝13.7×A₆₆₅-5.76×A₆₄₉

Caro(mg/L)＝(1000×A₄₇₀-2.05×Chla)/245

and (3) measuring the content of phycobiliprotein: 5mL of algal solution was centrifuged at 10000r/min for 10min, the supernatant was removed, and 5mL of phosphate buffer (0.05mol/L, pH 7.0) was added. Sonicate for 120s (working time 3s, gap time 2s) on a sonicator overnight at 4 ℃ and centrifuge again for 10min at 12000 r/min. The supernatant was taken and measured spectrophotometrically at 650, 620 and 565 nm. The calculation formula of the content of Phycocyanin (PC), Allophycocyanin (APC) and Phycoerythrin (PE) is as follows:

PC＝(A₆₂₀-0.7×A₆₅₀)/7.38

APC＝(A₆₅₀-0.19×A₆₂₀)/5.65

PE＝(A₅₆₅-2.8×PC-1.34×APC)/1.27

determination of soluble protein and malondialdehyde content: taking 20mL of algae liquid, centrifuging at 5000r/min for 10min, collecting algae cells, adding 1mL of 0.05mol/L phosphate buffer (pH 7.8), crushing the cells by an ultrasonic cell crusher in an ice bath for 10min (working for 5s during the process and clearance for 20s), centrifuging at 12000r/min for 10min after microscopic examination of no intact cells, and obtaining a supernatant which is a crude enzyme liquid. The determination of the soluble protein content and the malondialdehyde content is carried out according to the specification of a protein content determination kit (product number: A045-2) and a malondialdehyde kit (product number: A003-1) of Nanjing institute of bioengineering.

Determination of dissolved oxygen: mixing BiBOr₉Fabric addition to 200mL of 2.0X 10⁶In cells/mL of the algae solution, probes of a dissolved oxygen meter were inserted into the algae solution of the control group and the treated group every 3d to measure the dissolved oxygen content, and the average value was taken 3 times.

Detection of active species: four Erlenmeyer flasks were taken and 200mL of 2.0X 10 was added to each Erlenmeyer flask⁶cells/mL algae solution and BiBOr₉Fabric. Benzoquinone (BQ 1mM), isopropanol (IPA 1mM) and ethylenediaminetetraacetic acid (EDTA 1mM) were added to three of the flasks, respectively, and reacted for 18d, and samples were taken every 3d to determine chlorophyll-a values.

And (3) observing the surface structure of the algae cells: 100mL of blank algae solution after reaction and algae solution treated by adding BiOBr/fabric are centrifuged at 4000r/min for 10min, supernatant is discarded, 1mL of 2% glutaraldehyde is added to the collected algae cells to fix the algae cells for 2h, and then the algae cells are washed with 1mL of 0.1mol/L phosphate buffer (pH 6.8) for 3 times, 10min each time. The sample was then dried by dehydration with 1mL of 50%, 70%, 90% ethanol gradient for 15min, 100% ethanol for 2 times, each for 30 min. When the sample is measured, the sample is adhered to a sample table by using double-sided glue, and the sample is subjected to gold film plating by using an ion sputtering instrument and then is observed and photographed under a Hitachi scanning electron microscope.

Algae cell membrane integrity test: propidium iodide is a nuclear staining reagent that stains DNA. It is an analogue of ethidium bromide that releases red fluorescence after intercalation into double-stranded DNA. PI can not penetrate the whole cell membrane, but the cell membrane of dead cells and cells in the late apoptosis presents a damaged state, PI molecules can penetrate, and the cell nucleus is stained red. And (3) centrifuging 1mL of the treated BiOBr/fabric and the normally grown and propagated microcystis aeruginosa liquid at 4000r/min for 5min, discarding the supernatant, adding ultrapure water for cleaning for 2 times, centrifuging, discarding the supernatant, adding 1mL of ultrapure water, and uniformly mixing. An additional 61L of PI solution (1mg/mL) was added to give a final concentration of 65.2 mg/L. Staining in the dark for 15min, detection by up-flow cytometry using a FL2 detector, and data analysis using BD facsuie Software.

Determination of TOC: 5mg of ODTMA/goethite is added into 100mL of algae solution, 2mL of algae solution is taken every day and filtered by a 0.22 μm filter membrane, and the content of total organic carbon in a sample is measured by a total organic carbon measuring instrument by supernatant.

Comparison of activities of different cationic surfactants for removing algae from goethite

The influence of the encapsulation modification of goethite by using 4 kinds of cationic surfactants HDTMA, CTAC, CTAB and ODTMA on the removal result of microcystis aeruginosa chlorophyll a is shown in figure 1 (a). As can be seen from fig. 1(a), the algae removal efficiency of the goethite modified by the surfactant is significantly improved, wherein the activity of the goethite modified by ODTMA is improved most, and the removal rate of the chlorophyll a is sequentially from high to low: ODTMA/goethite (90.81%) > CTAB/goethite (84.23%) > CTAC/goethite (81.20%) > HDTMA/goethite (79.12%) > goethite (57.24%). FIG. 1(b) shows the Zeta potential changes of 4 kinds of modified goethite and unmodified goethite, and it can be seen from FIG. 1(b) that the Zeta potentials of the modified goethite are all shifted to the positive charge direction, wherein the Zeta potentials of ODTMA/goethite are between 50.12mV and 65.01mV, and the Zeta potentials of HDTMA/goethite, CTAB/goethite and CTAC/goethite are between 25.21mV and 45.32mV, which are lower than the potential of ODTMA/goethite. This is because ODTMA has a longer carbon chain than the other three, and the larger the Zeta potential value after modification of goethite, the stronger the adsorption capacity. In addition, the longer the carbon chain, the more favorable the quaternary ammonium group and the goethite surface are for effective coating modification, and the stronger the capability of the quaternary ammonium group and the goethite surface for combining with the alga cell membrane phospholipid bilayer is, so that the quaternary ammonium group and the goethite phospholipid bilayer are more easily adsorbed on the alga cell membrane, the function of the cell membrane is damaged, and the chlorophyll a is reduced.

Therefore, among the four quaternary ammonium salt cationic surfactants, the ODTMA modified goethite has the best algae removal effect, and the magnitude of the Zeta potential after modification is in direct proportion to the algae removal performance. Therefore, in subsequent researches, the ODTMA modified goethite is selected to deeply research the removal effect of microcystis aeruginosa and various physicochemical factors influencing the algae removal effect.

Characterization of ODTMA/goethite

XRD

ODTMA/goethite crystal purity was characterized by XRD. As shown in fig. 2, the diffraction peaks appearing at 17.77 °, 21.24 °, and 53.63 ° 2 θ all correspond to the diffraction peaks of natural goethite, and the peak shapes are relatively sharp, which indicates that the degree of crystallinity of ODTMA/goethite is good and the purity is high. Additional diffraction peaks also appeared on the XRD patterns of ODTMA/goethite due to ODTMA encapsulation.

SEM

The morphology of ODTMA/goethite is shown in fig. 3, and fig. 3(a) and 3(b) are SEM images of natural goethite, from which it is found that the natural goethite is aggregated by a large number of acicular nanorods. FIGS. 3(c) and 3(d) are SEM images of ODTMA/goethite, from which it is found that the surface of the nanorods seems to have a film coating, i.e., the ionic surfactant is mainly coated on the surface and edges of goethite, unlike natural goethite.

Research on ODTMA/goethite algae removal effect under different physicochemical conditions

The effect of ODTMA/goethite of different concentrations on microcystis aeruginosa chlorophyll a is shown in FIG. 4 (a). From the figure, ODTMA/goethite is found to be capable of effectively inhibiting the growth of microcystis aeruginosa, and the algae removal performance is in direct proportion to the adding amount within a certain range. When the concentration of ODTMA/goethite is less than 50mg/L, the algae removal performance is proportional to the concentration. When the concentration of ODTMA/goethite exceeds 50mg/L, the algae removal performance tends to be balanced. After the ODTMA is used for modifying the goethite, adsorption sites on the surface of the goethite are increased, when the concentration of the ODTMA/goethite is less than 50mg/L, the interaction between the ODTMA/goethite and algae cells can be improved by increasing the using amount of the ODTMA/goethite when the number of the algae cells is constant, so that the removal efficiency is increased, and when the using amount of the ODTMA/goethite is continuously increased, the interaction between the algae cells and the ODTMA/goethite tends to be saturated, so that the inhibition effect tends to be stable. Therefore, ODTMA/goethite of 50mg/L was selected as the optimum concentration for the reaction.

The effect of light intensity on ODTMA/goethite algaecide performance is shown in FIG. 4 (b). In the absence of illumination, the algae removal rate is 42.18%, and with the increase of illumination, the algae removal rate is increased from 67.04% to 92.04%. The goethite has photocatalytic activity, can excite active species under the irradiation of light, has a large specific surface area, is adsorbed with algae cells in a dark state, and settles the algae cells by utilizing the self gravity. After the light intensity is increased, the active species generated by goethite attacks the algae cell membranes adsorbing the algae cells, so that the cell membranes are damaged to influence the growth and the propagation.

ODTMA/goethite all had high removal efficiency at different temperatures, and as shown in FIG. 4(c), the algae removal rate increased from 88.23% to 100% with increasing temperature in the range of 20 ℃ to 35 ℃ under investigation. The reasons are, on the one hand, the solubilization of the ODTMA surfactant, the thermal motion that is exacerbated by the temperature increase, so that there is more space in the micelle to accommodate the algal cells, and, on the other hand, the overall reaction process of ODTMA/goethite algae removal is endothermic. The increase in temperature accelerates the frequency of movement of ODTMA/goethite and microcystis aeruginosa, which adhere to the surface of the material as they approach ODTMA/goethite, thereby increasing the algae removal rate. The algae removal rate of 94.08% at 15 ℃ is caused by that the algae removal rate is increased because the microcystis aeruginosa is not suitable for self-growth at the low temperature of 15 ℃.

The pH of the solution is one of the most important parameters in the adsorption process, as it affects the physicochemical properties of the catalyst surface and the surface binding sites. The performance of ODTMA/goethite in removing microcystis aeruginosa under different pH environments is examined, and the result is shown in FIG. 4 (d). In the pH range examined (6.5-10.5), ODTMA/goethite exhibited algae removal rates of 71.01% -93.12%, with the maximum algae removal rate of 93.21% at pH 6.5 and slightly decreasing with increasing alkalinity at pH 7.5-10.5.

Zeta potential measurement results show that ODTMA/goethite has positive charges on the surface in the pH range of 2-10 and is stable in the range of 55mV-65mV, and when the pH value is less than 6, a large amount of protons exist in the solution, and a large amount of positive charges can be generated on the surface of the goethite. Indicating that strong electrostatic attraction exists between ODTMA/goethite and algae cells, and therefore high removal effect can be achieved at a lower pH value. When the pH of the solution is greater than 7, a large number of hydroxide ions are present in the solution, which reduces the number of positively charged sites on the surface of ODTMA/goethite and increases the number of negatively charged sites on the surface of the adsorbent, so that the amount of negatively charged algal cells adsorbed on the surface of ODTMA/goethite is reduced. The removal efficiency of chlorophyll a of algae cells gradually decreases with the increase of hydroxide ions in the solution, indicating that high pH is not favorable for adsorption of algae cells because of the competitive relationship between the excess hydroxide ions in the solution and the active adsorption sites for adsorbing algae cells.

Influence of ODTMA/goethite on physiological indexes of algae cells

Chlorophyll a and carotenoid are indispensable indexes for determining the photosynthetic rate, and play important roles in capturing and transferring energy in the process of photosynthesis. Chlorophyll a and carotenoid are the most important photosynthetic pigments in microcystis aeruginosa, and the content of chlorophyll a and carotenoid can also prove the primary productivity of the water body. The effect of ODTMA/goethite on chlorophyll a and carotenoids is shown in FIG. 5 (a). The removal rate of chlorophyll a and carotenoid is gradually increased along with the reaction, and after 24 hours of reaction, the removal rate of chlorophyll a and carotenoid is respectively 90.33% and 81.34%. Mainly because the synthesis of chlorophyll a and carotenoid is hindered and the cell reproduction is inhibited when the concentration of the surfactant ODTMA/goethite is higher.

The photosynthesis is the basis of the survival of algae, phycobiliprotein needs to utilize and absorb light energy to promote the synthesis of biochemical components in algae cells, and the change of the biochemical components reflects the physiological state of algae indirectly. FIG. 5(b) is a graph showing the effect of ODTMA/goethite on the removal rate of phycobiliprotein, which is proportional to the time for either phycocyanin, allophycocyanin or phycoerythrin during the reaction, and after 24 hours of reaction, the removal rates were 62.47%, 67.68% and 40.14%, respectively. This is because ODTMA/goethite stimulates the PS II reaction center, inhibits the primary reaction of photosynthesis, blocks the transmission of photoelectrons from primary to secondary electron acceptors, causes reduced carbon fixation and assimilation, slows down the synthesis of biochemical components, and thus inhibits the photosynthesis of algal cells.

The soluble protein is not only an important component of biomacromolecule in the algae cell, but also a catalyst of biochemical reaction, participates in various metabolic activities, and is an important indicator of the metabolic condition of the algae cell. As shown in FIG. 5(c), the effect of ODTMA/goethite on the removal rate of soluble proteins was observed, and the removal rate of ODTMA/goethite on soluble proteins was gradually increased with the lapse of time. The removal rate reaches 30.22 percent after 24 hours of reaction. The results of this study were consistent with the trend of changes in soluble proteins in toxic effects of CTAC and ODTMA on Scenedesmus tetrastigma and Chlorella pyrenoidosa studied in Hedgersia et al. The protein is used as an organic component of the algal cell body, has obvious influence on the enzyme activity, is a substance guarantee for the normal physiological function of the algal cell, and the reduction of the content of the protein adversely affects the normal function of chlorophyll so as to affect the content of MDA.

In order to study the effect of oxidative stress on the oxidative damage of Microcystis aeruginosa, membrane lipid peroxidation was evaluated. The degradation product MDA has been used as a biomarker to evaluate oxidative damage in cells. The effect of ODTMA/goethite on algal cell membrane damage is shown in FIG. 5(d), with the MDA content increasing significantly with the reaction time. After reaction for 18h, the MDA content increased from the initial 5.20nmol.mg/TSP to a maximum of 7.28nmol.mg/TSP, and then began to decrease until the MDA content became 6.11nmol.mg/TSP at reaction 1 d. The algal cell membrane is composed of unsaturated phospholipids and is susceptible to active oxygen. At the 18 th reaction hour, the MDA content of the algae cells is remarkably increased, which shows that ODTMA/goethite induces the abnormal lipid peroxidation reaction of the microcystis aeruginosa, and oxidizing species generated by the ODTMA/goethite in the reaction process cause severe oxidative stress on the microcystis aeruginosa and damage to polyunsaturated fatty acids of cell membranes.

Mechanism for removing algae cells by ODTMA/goethite

Observation of cell surface Structure

FIGS. 6(a) and 6(b) show normal growing and propagating Microcystis aeruginosa cells, and FIGS. 6(c) and 6(d) show ODTMA/goethite treated Microcystis aeruginosa cells, from which it can be seen that the normal surface of the algae cells is full, uniform and smooth, and the treated surface of the algae cells is deposited on the cell membrane due to the direct physical interaction between ODTMA/goethite nanoparticles and the algae cells, so that the membrane is deformed, ODTMA at low concentration can cause the propagation of the algae cells to be damaged, ODTMA at medium concentration can induce the permeabilization of the cell membrane of the algae, and the cell membrane of the algae can be directly damaged at high concentration. Some cells are damaged seriously, and are sunken inwards and even cracked, so that the permeability of cell membranes is changed, and metabolism is influenced.

From fig. 6(c) and 6(d), it can be seen that ODTMA/goethite granules are attached to the algal cells, since the positively charged carbon chains can trap and bind negatively charged algal cells and other particles, resulting in the destruction of the surface structure of algal cells, and there are some irregularly shaped substances around the partially deformed algal cells that cause them to stick together, presumably extracellular secretions of algal cells or intracellular substances released by cell rupture.

Apoptotic status of algal cells

In recent years, flow cytometry has been widely used to assess the effects on algal cell viability and membrane integrity during oxidation. With the help of the nucleic acid stain, the flow cytometer can rapidly carry out quantitative and sensitive measurement on each cyanobacterial cell. The effect of ODTMA/goethite on the integrity of algal cell membranes is shown in FIG. 7. FIG. 7(a) shows normal growth and reproduction of Microcystis aeruginosa, and FIG. 7(b) shows Microcystis aeruginosa cells treated with ODTMA/goethite. Since the cell membrane of normal algae cells is not destroyed, PI molecules cannot enter the cells, 98.03% of the algae cells are in a negative state, and in fig. 7(b), 52.47% of red areas are in a positive state of PI, 47.46% are in a negative state of PI, indicating that 52.47% of the algae cells die or the cell membrane is destroyed.

TOC Change

When the cell wall and the cell membrane of the algae cell are damaged, organic matters in the algae cell are released to an external BG-11 culture medium, so that the change of the TOC content in BG-11 is measured in order to further study the damage condition of the cell wall and the cell membrane of the algae cell. The change in TOC during ODTMA/goethite algae removal is shown in FIG. 8. From the graph, it can be found that the TOC value of the algal cells not subjected to the ODTMA/goethite treatment did not change much with time because of normal growth, while the TOC value of the algal solution added to the ODTMA/goethite treatment increased with the increase of the reaction time. This is because the oxidative species generated by ODTMA/goethite under the action of light damages the cell wall and the cell membrane of the algae cell, so that cytoplasm leaks, and the TOC value in BG-11 culture medium is increased, thereby preventing the growth and survival of the microcystis aeruginosa.

Claims

1. The application of the surfactant modified goethite in removing microcystis aeruginosa is characterized by comprising the following steps: under the conditions that the pH value is 7.5-9.5, the temperature is 20-30 ℃ and the illumination is 1000-; the preparation method of the surfactant modified goethite comprises the following steps: dissolving a surfactant in water at 55-65 ℃, adding goethite into the dissolved solution, stirring, centrifuging, removing supernatant, drying in vacuum, and grinding to obtain surfactant modified goethite; the surfactant comprises any one of hexadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide, hexadecyl dimethyl benzyl ammonium chloride and octadecyl trimethyl ammonium bromide.

2. The use of claim 1, wherein the microcystis aeruginosa has a density of 1.0 x 10⁶-1.0×10⁷cells/mL, microcystis aeruginosa includes algal cells in log phase and death phase.