Study On Effect And Mechanism Of Tanfloc Modified Diatomite Flocculating Algae Removal

A large amount of nutrients such as nitrogen and phosphorus were continuously discharged into the water body,causing the nutrient salt of the water body to be out of balance,leading to increasing eutrophication problems.The frequency,intensity,scope and duration of harmful algal bloom outbreaks in my country and the world continued to increase.The deterioration of water quality affected the safety of drinking water supply and threatens human health.In China,research on the treatment of harmful algal blooms with modified clay began in the early 1990s,and it was considered a safe,efficient and most promising method for algae removal.In this paper,a water treatment agent whose main component is plant tannin was used to modify diatomaceous earth and to flocculate and remove harmful algal blooms.The influences of factors such as the growth period of the algae,the dosage,p H value of water,compound ratio,quieting time,and the coagulation and mixing time were on the effect of the modified diatomite flocculation.Explore the best experimental conditions through orthogonal experiments,and analyze the feasibility of practical application based on the flocculation effect on the algae cells cultured in the actual water body and the influence of the nitrogen and phosphorus nutrient concentration in the water body;The mechanism of flocculation and algae removal was explained through the changes of surface morphology and crystal structure before and after the modification of diatomite,the morphology of algae cell flocs and the analysis of Zeta potential.The main conclusions drawn are as follows:（1）Unmodified diatomite had poor flocculation and algae removal ability.When the dosage and the removal rate of algae cells were 30 mg/L and 11.51%,Tanfloc had a good effect on removing algae cells in water.When the dosage was 10 mg/L,the removal rate of algae cell density reached 93.5%,but the flocs were relatively loose.（2）The flocculation and algae removal ability of diatomite modified by Tanfloc were significantly improved.When the dosage was 64 mg/L and m _Tanfloc:m_diatomite=1:15,the flocculation and algae removal effect was the best,and it had the best effect on algae cell density,turbidity,and turbidity.The removal rates of chl-a reached 97.1%,89.8%,and 99.1%respectively,and the formed flocs were tightly bonded and had good settling performance.（3）EOM could be divided into soluble extracellular organic matter（d EOM）dissolved in the culture medium and bound extracellular organic matter（b EOM）adhered to the cell surface.The concentration of d EOM had almost no effect on the flocculation and algae removal effect of modified diatomaceous earth.But b EOM had a certain hindering effect on it.（4）A small amount of EOM could promote the flocculation and algae removal of modified diatomite to a certain extent,and as the concentration of EOM in the water body increases,its hindering effect on flocculation also increased.Stirring time and static settling time had little effect on the flocculation and algae removal effect of Tanfloc modified diatomite.Modified diatomite can effectively flocculate and remove algae cells in water in a short time.（5）Orthogonal experiments’results showed that when the dosage,the compound ratio and the settling time were 128 mg/L,1:12 and 15 min,the flocculation and algae removal effect were better and the treatment cost was lower.It had a good effect on algae density,turbidity and chl-a.The removal rate of the patients reached 98.33%,94.34%,98.10%,respectively.Tanfloc modified diatomaceous earth also had an efficient flocculation removal ability for algae cells cultured in raw water.When the dosage was 172mg/L,the removal rate of turbidity,algae cell density and chl-a reached 89.81%,98.65%and 100%,respectively.It could be seen that Tanfloc modified diatomaceous earth could be used in actual water treatment.（6）As the proportion of Tanfloc in the modified diatomaceous earth increased,the surface potential of the diatomaceous earth changed from negative to positive,colliding with the negatively charged algae cells under the action of compressing the electric double layer and neutralizing the electric properties,and aggregates and settles.Analysis of the composition and structure of the diatomite before and after modification.On the surface,Tanfloc only attached to the surface of the diatomite and changed its crystal structure.It did not insert into the diatomite and did not change the distance between the diatomite layers.The morphological analysis of the algae flocs showed that Tanfloc’s bridging net trapping function binds the flocs together to obtain algae flocs with diatomaceous earth as condensation nuclei,which sped up the settling speed.The main mechanisms of Tanfloc modified diatomite flocculation and algae removal were electrical neutralization,adsorption bridging and net trapping and sweeping.（7）The effect of Tanfloc modified diatomite flocculation and algae removal on nutrients in the water body showed that after using it to remove algae,the changes in the concentration of DTN and DTP in the water body are basically the same as the blank control group.It showed that this method had basically no effect on the concentration of N and P nutrients in the water body when removing harmful algal blooms by flocculation.After the algae cells were flocculated and settled to the bottom of the water by the modified diatomaceous earth,there was no resuspension for a long time.It showed that the addition of modified diatomite could control the density of algae cells and the concentration of chlorophyll a in water for a long time.