The Research Of Flocculation To Cyanobacteria And Its Mechanism By PDM Modified Illite

Nutrients such as nitrogen and phosphorus are discharged into lakes and reservoirs in large quantities,causing eutrophication of water bodies and rapid propagation of algae such as cyanobacteria.So the water is getting worse and affecting the safety of drinking water supply and threatening human health.Clay flocculation is a safe and efficient method of algae removal that is considered to be more promising.In this paper,Microcystis flos-aquae as the research object,polydimethyldiallylammonium chloride?PDM?was used to modify illite flocculation and algae removal.The effects of particle size,dosage,compounding ratio,initial pH value,algae growth period,extracellular secretion?EOM?,stirring time,static settling time as well as other fathors on algae removal was investigated.Through orthogonal experimental analysis of factors such as growth period,dosage,compounding ratio and static settling time to get the experimental conditions were optimized,and compared with the removal effect of algae in actual water,analyz the feasibility of practical application.The characterization of PDM modified illite algae removal mechanism was revealed by the feature of before and after illite modification,algal floc morphology and zeta potential analysis.The main conclusions are as follows:?1?The algae removal effect of illite alone shows that the removal rate of algae to algae was only about 5%.The illite was modified by high temperature,ultrasonic wave,hydrochloric acid,sodium hydroxide,ferrous sulfate and PDM,respectively.The results showed that the treatment effect of PDM modified illite was the best,and the removal rates of turbidity,algae density and chlorophyll a?Chl-a?were 93.96%,96.84%and 98.27%,respectively.So PDM was used as a modifier to modify illite.?2?The effect of PDM alone on the removal of algae was studied.The results showed that when the dosage of PDM was 2.6 mg/L,the removal rates of turbidity,algae density and Chl-a were89.91%,93.89%and 95.45%,respectively,and the adaptability to the pH of the water was also good.However,the obtained flocs was loose and easy to float.?3?The effect of different factors on the algae removal effect of PDM modified illite shows that the PDM modified illite particle size was 80 mesh,the dosage was 25mg/L,the composite ratio was1:15,the initial pH value of algal solution was 7⁸,the algae growth period was logarithmic,the removal rates of turbidity,algae density,Chl-a,UV₂₅₄,and DOC were 95.96%,99.34%,100%,84.21%,and 50.32%,respectively.The obtained flocs were large,dense and had strong anti-disturbance ability.When the optimal removal effect was achieved,the dosage of PDM-modified illite was 25 mg/L and 12 mg/L when EOM was not removed and removed,EOM will reduce the effective dosage of flocculant.EOM can play a bridging role at low concentration?DOC<20 mL?to facilitate flocculation.At high concentrations?DOC>60 mL?,the electronegativity of EOM was too strong to hinder flocculation.On the basis of this,when the stirring time was 15 min and the shaking time was 40 min,the turbidity,algae density and Chl-a removal rate were 95.98%,98.77%and 99.87%,respectively.?4?The results of orthogonal experiment showed that algae growth period,dosage,compounding ratio and static settling time had little effect on algae removal,and PDM modified illite had good stability in algae removal.The optimal algae removal process conditions were logarithmic phase,dosage 25mg/L,composite ratio 1:15,and static sinking for 40min.At this time,the turbidity,algae density,Chl-a,and UV₂₅₄ removal rates were 96.06%,99.75%,100%,and86.03%,respectively.When PDM modified illite treatment of algae in actual water,and the removal rate of the four was 92.70%,94.17%,98.50%,and 81.67%,respectively when the dosage of 45 mg/L.Therefore,PDM modified illite also has good application value in the treatment of actual algae polluted water.?5?Mechanism analysis of flocculation and algae removal by PDM modified illite.Characterization analysis before and after illite modification showed that PDM modified illite changed the surface structure of illite and increased its specific surface area.Morphological analysis of algae flocs showed that the PDM modified illite condensed the flocs into a mass and became spherical;the bridging of PDM and the net trapping of illite bonded the flocs together to obtain algae with illite as the core of condensation.The flocs have an increased particle size and enhanced water disturbance stability.Zeta potential results showed that under the condition of pH value of<8,PDM changed the zeta potential of illite to be positive,and neutralized with negatively charged algae cells,causing the algae cells to destabilize and collide with each other,and aggregate sedimentation.The main mechanism of PDM modified illite flocculation and algae removal is electrical neutralization,bridging and net trapping.